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Concrete Casting News from the Hill and Griffith Company

The Influence of Form Release Agent Application to the Quality of Concrete Surfaces

Posted by Hill and Griffith Company on Sep 19, 2019 11:00:54 AM

ACI 318-19 was published in response to new engineering practices and industry changes.

Excerpt from a technical paper by A. Klovas and M. Daukšys 2013 IOP Conf. Ser.: Mater. Sci. Eng. 47 012061.

Introduction

High quality surface finishes are a feature of self-compacting concrete (SCC), but by careful attention to mix design and job site workmanship, nice surfaces with the conventional concrete mixture could be achieved. The appearance of an element mainly depends on: the type of cement and addition used; the mix composition; the quality of the concrete mold and release agent; and the placing procedure. If compared self-compacting concrete with the conventional–the color is generally more uniform. Also, it is easier to avoid defects due to leakage spots at the location of mold joints. Blowholes, honeycombing and other blemishes can be found in all types of concrete but with more fluid concrete mixture it is possible to improve the surface finish. International Council for Building Research has provided guidelines how the concrete may be defined referring the surface quality:

  • ROUGH class – no special requirements for finishing
  • ORDINARY – surface finishing has a minor factor
  • ELABORATE – definite requirements for visual appearance
  • SPECIAL – highest standards for appearance
Concrete Form Release Agents Help Form Removal
photo credit: Bob Sawyer

Formworks are also very important factors for concrete surface quality. Scientist, J. Sousa Coutinho, has researched using two different formworks: controlled permeability (CP) and five-layer wood-based formworks. The results have shown that by using CP formworks, the pore diameter (nm) of concrete surface has decreased up to 50%, porosity – up to 45%, surface hardness (MPa) increased up to 70%, and blow-hole ratio has decreased up to 90 % compared with those concrete surfaces using five-layer wood-based formworks.
 
A number of studies determine how to achieve better consolidation resulting in fewer surface blemishes [7-15]. To minimize the size and number of bug holes and all other effects, the following practices should be followed:
  • Vibration period should be of sufficient duration
  • Vibrator insertions should be properly spaced and overlapped and the vibrator removed slowly
  • Each concrete layer should be consolidated from the bottom upward
  • Vibration periods should be increased on withdrawal when using impermeable forms that permit air trapped at the form surface to escape through joints as between
  • Inward sloping forms and other complex design details should be avoided
  • Vibrator should penetrate into the previous layer;

The main outcome of this research is to evaluate the usage of different form release agent applications on the formwork. In addition, this paper presents a technique which provides:

  1. A method how to evaluate the concrete surface quality using image analysis process;
  2. An evaluation of concrete surfaces quality by the following documents: CIB report no. 24 [4] and GOST 13015.0-83.
  3. A combined method how to evaluate and divide concrete surfaces into special categories provided by CIB report no. 24 GOST 13015.0-83 and “ImageJ” in respect to the area of blemishes.

Read More


 

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ACI Releases New Building Code Requirements for Structural Concrete

Posted by Hill and Griffith Company on Sep 12, 2019 4:58:19 PM

ACI 318-19 was published in response to new engineering practices and industry changes.

Article excerpt by Jack Moehle published in the Concrete Contractor August/September 2019 issue.

The American Concrete Institute (ACI) published ACI 318-19: “Building Code Requirements for Structural Concrete in July 2019, in response to new engineering practices and industry changes.

ACI 318 presents requirements for design and construction of structural concrete that are necessary to ensure public health and safety. The document is intended for engineers and building officials, but because it addresses materials advancements and applications, it is expected to have an impact on jobsite procedures. It is anticipated the final code requirements of 318-19 will be referenced in the 2021 International Building Code (IBC).

318_19_cover_highres2.5d39ca6a430aa

New Engineering Practices Translate to Changes in the Field

  • ACI was prompted to make updates in the code due to:
    • new technology (computers used for design and analysis by engineers and architects)
    • increased construction of tall buildings
    • the need for seismic resistance
  • New requirements include:
    • minimum reinforcement on interior column-to-slab connections
    • longer bar lengths for thicker, two-way slabs
    • additional transverse reinforcement
  • Updates include
    • expansion of permissible applications of high-strength reinforcement
    • new requirements for material properties of high-strength steels
    • several changes to strut-and-tie method (STM) for design of discontinuity regions
    • clarity on Anchorage-zone reinforcement

New Materials Addressed

  • IBC shotcrete provisions were included
  • Post-installed concrete screw anchors are now recognized

Alternate Cements and Aggregates

  • Now includes provisions for alternate cements and aggregates
  • No details are readily available for these materials because not enough industry testing is available

Read More


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Selecting and Using Concrete Release Agents - Excerpt

Posted by Hill and Griffith Company on Sep 6, 2019 5:35:38 PM

Enhance the quality and economy of precast products by using the right release agent

Article excerpt by John A. Koski published in the Concrete Construction March 1994 issue.

Almost every precaster has had a double-tee or an architectural precast panel crack as it was being removed from a form. In some cases, an ineffective or improperly applied release agent may have been the culprit. At other times, the wrong type of release agent may have been used. Knowing how to properly use form release agents and which agent should be used for a particular application can go a long way toward preventing costly mistakes. In addition, following proper procedures and using the right agent can enhance the quality and economy of a finished precast piece.

Less is better with Precast Concrete From Release 3

BASICS OF USE

  • Make sure the release agent you are using is compatible with the form or mold it is being used on. For example, some release agents can cause an adverse chemical reaction when used on foam or rubber forms.
  • Don’t purchase a release agent based on price alone. When examining prices of comparable release agents, compare them based on their cost per square foot of coverage, not by the cost of a 5-gallon pail or 55-gallon drum.
  • Protect form release agents from temperature extremes. Release agents that have frozen and then become liquid again may have had their form release properties altered or destroyed. Extremely high temperatures also can damage the properties of release agents. 
  • Thoroughly mix or agitate release agents that require mixing or agitating. This ensures proper dispersion and continuity of the chemical components within the release agent. Always follow manufacturer recommendations when considering mixing or agitating. Some release agents don’t need to be, or shouldn’t be, mixed or agitated.
  • Make sure workers wear respirators, goggles, face shields, gloves, and other protective clothing as required by the manufacturer and government agencies. Make sure workers are properly trained in all aspects of the application process. This includes not only safety concerns, but also how to properly apply the release agent being used. The application technique workers use, however, may not be appropriate for the new product and can cause it to perform unsatisfactorily or not at all.
  • Before applying the release agent, remove any buildups of concrete, rust, scale, or dirt that may be on the forms.
  • Repair any holes, fractures, or other defects in the forms. Just prior to applying a release agent, make sure that the surfaces of the forms are clean and free of water, dust, dirt, or residues that could be transferred to the surface of the concrete or affect the ability of the release agent to function properly.
  • Make sure that forms are coated uniformly with no gaps, sags, runs, or beads. To avoid these problems, never apply a too-heavy coat. Sags, drips, and runs should be removed as recommended by the manufacturer.
  • Make sure spray equipment is working properly. 
  • Do not over-apply a release agent, especially when using a release agent that is chemically reactive.
  • On new wooden forms, thoroughly saturate the forms according to manufacturer directions before placing concrete.
  • It is best not to wait an excessive amount of time after applying the release agent and before placing concrete as dust and other airborne contaminants can form a light coating over the release agent
  • If the concrete is to be painted, plastered, or have other coatings applied, be sure to use a release agent that won’t prevent the coating from bonding with the concrete.
  • Don’t allow release agents to contact reinforcing steel. Doing so can prevent the concrete from bonding to the reinforcement.

Read More


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Hill and Griffith Customer Service

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Please Release Me - Appropriate Use of Concrete Release Agents

Posted by Hill and Griffith Company on Aug 29, 2019 9:24:55 AM

The use of an appropriate release agent, correctly applied, is critical to creating a good, consistent surface quality

by Elaine Toogood

Originally published in the Winter 2018 Issue of Concrete Quarterly.

Applying a release agent to the face of the formwork is like greasing a cake tin. Without it, the formwork cannot easily be removed or released from the hardened concrete.
According to the Concrete Society publication Visual concrete – Planning & Assessment, there are essentially two types of release agent: barrier and reactive. These are further divided into eight categories, though developments in this field mean that some products do not easily fall within these categories.

Not all release agents are suitable for creating visual concrete and selection will be based on many factors, including compatibility with form-facing material, concrete specification and expected site conditions. A good release agent will also help maximize the number of times that a form can be used.

Concrete Form Release Agent

4 Pancras Square by Eric Parry Architects, where the post-tensioned slabs are exposed as soffits. The concrete contractor specified a concrete mold oil release agent for use with the plastic-faced ply lining of the formwork system.

Photo credit: Rory Gardiner

Barrier release agents work by creating a layer between the form face and the concrete. Oils with surfactants are general-purpose release agents for many different types of formwork, including steel, and are often used in the precast industry. None of the other barrier types such as neat oils, mold cream emulsions, water-soluble emulsions and barrier paints are recommended for high-quality finishes. Although barrier paints may be part of a preparatory treatment for timber and plywood before it is first used to extend the life of the formwork.

Most of the reactive types of release agents are suitable for visual concrete and are categorized as chemical release agents, surface retardants and other specialist release agents, including those based on vegetable oil (VERA). They allow the formwork to be struck by creating a very thin layer of unhardened concrete or “soap” on the surface that must be brushed away when the formwork is struck. Chemical release agents are a popular choice but can lead to dusting if over-applied. Although recommended for high-quality finishes, they may not be appropriate for concrete containing silica fume or high amounts of admixtures. VERA fall under the category of other specialist release agents and are recommended for visual concrete, with the added advantage of being non-toxic and biodegradable, and reportedly with a low incidence of blowholes and blemishes.

Design professionals do not need to specify the release agent that is to be used, but rather provide a performance specification. This directs the contractor to select one appropriate for creating high-quality visual concrete surfaces, that has little or no detrimental impact on the appearance of the concrete and that suits the choice of formwork facing and concrete used. Consultation with the manufacturer and form-facing material supplier will be necessary to select the best product and method of application for the specific project. Biodegradable and non-toxic products may also be identified for health and safety reasons.

The selected product or products should then be tested with a full-scale mock-up panel or in a non-critical location of the structure to review the results and trial the method of covering the formwork before final selection. Release agents should be applied in accordance with manufacturers’ guidance – they are often sprayed or applied with a soft brush – to create a thin, uniform and complete coating. Once satisfactory results have been established, the standard of workmanship must be rigorously maintained to ensure consistency. Incorrect application, whether too much or too little, can lead to abrupt color or tone changes in the concrete surface. The surface of the formwork should be cleaned and a coating of release agent applied before every use.

Read More.


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Hill and Griffith Customer Service

We're known for our hands on approach. Let us visit your plant and recommend concrete release agents, packerhead concrete form releases, concrete form seasoning, potable water concrete form release, non-petroleum concrete form release, biodegradable concrete form release, rust inhibitors and concrete dissolver products that suit your needs.

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Wood Form Concrete Release Agents

Posted by Hill and Griffith Company on Aug 22, 2019 1:04:51 PM

(This week's post comes from a HOMEGUIDES' article, "How to Keep Concrete From Sticking to Wood." It has a unique perspective from the homebuilder's point of view. You can read the full article here.)

How to Keep Concrete From Sticking to Wood

Concrete-Form-Release-For-Wood.jpgConstruction professionals routinely use plywood panels as shaping forms when pouring concrete for new home foundations. If the wood forms were treated properly with a form release agent, you can easily pull them away after the concrete dries. A do-it-yourselfer can pour concrete between 2-by-4 forms when installing a new sidewalk or patio, but for best results, pretreat the wood in the same way the pros do.

(Caption: Hill and Griffith recommends Grifcote Bio Gold concrete form release for wood. A non-petroleum, non-staining concrete form release that is both VOC compliant and biodegradable.)

Oil-Based Release Agents

At one time, construction professionals would create their own oil-based form release agents using materials such as diesel fuel, home heating oil and mineral oil to keep poured concrete from sticking to wood. Today's homebuilders often select stick-resistant plywood or OSB panels pretreated at the lumber mill with proprietary chemical blends that may include parafin, mineral oil and linseed oil. Some concrete contractors extend the stick-resistant life of the plywood by using a refresher coating of a commercial release agent or a solvent-thinned linseed oil.

Water-Based Barrier Agents

Water-based release agents can also keep concrete from sticking to wood forms, and unlike oil-based formulas, they do so without releasing high levels of volatile organic compounds into the air. VOC-releasing chemicals are highly regulated in some regions because they contribute to atmospheric smog. Commercial water-based release agents are produced from plant-based materials and are less likely to discolor the concrete's surface. Ordinary vegetable oils can serve the same purpose if applied in two or three successive coats.

Reactive Release Agents

Chemically active release agents react with the alkalinity of the concrete to prevent the concrete from sticking to wood molds and forms. Commercial products of this type are formulated with a fatty acid and a soapy surfactant that react chemically with the concrete to help create a clean, unstained concrete surface with a smooth edge. At the same time, they create their own thin chemical membrane that blocks the concrete from infiltrating the wood's pores.


Hill and Griffith Customer Service

We're known for our hands on approach. Let us visit your plant and recommend concrete release agents, packerhead concrete form releases, concrete form seasoning, potable water concrete form release, non-petroleum concrete form release, biodegradable concrete form release, rust inhibitors and concrete dissolver products that suit your needs.

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We are pleased to provide samples in quantities large enough to allow you to "try before you buy."
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Choosing and Using a Form Release Agent

Posted by Hill and Griffith Company on Aug 15, 2019 3:16:52 PM

Excerpt from the article by M.K. Hurd in the October 1996 issue of Concrete Construction

Concrete Form Release Agents Help Form Removal

Most form materials require the application of a release agent to prevent adhesion of concrete to the face of the form. Many form oils and other release agents adequately prevent sticking, but using the correct type of agent for the form material can also help to minimize concrete color variations, staining, bugholes, and poor surface durability. Article discusses the two basic types of release agents (barrier and chemically active), how to select a release agent for different form materials, and release-agent application methods. It also describes the newer types of water-based release agents, which are formulated to meet environmental regulations limiting volatile organic compounds (VOCs).

Photo caption: Forms will strip cleanly and easily if you use the correct form release agent and apply it properly. - Photo by Bob Sawyer

With the wide range of release agents available today, how do you choose the best one for your forms?

Types of Release Agents Historically, form release agents have been grouped in the following categories :
• Petroleum oils
• Emulsions—either water- or oil-based
• Nonreactive coatings with volatile solvents
• Chemically active agents
• Waxes

Though products in these categories are still available, new products and new formulations are being introduced to meet environmental regulations limiting volatile organic compounds (VOCs). Also, manufacturers may combine release-agent types, such as a chemically reactive product and an emulsion, to produce a product that has the advantages of both. Many newer form release agents, therefore, do not fit neatly into the above categories. Because environmental restrictions have caused changes in the commercially available agents, and because of the great variety of chemical formulations, manufacturers now simply classify release agents in terms of how they act instead of what’s in them. The two basic categories are barrier agents and chemically active agents. Read More.

Precautions in Selecting A Release Agent

A release agent may be incompatible with concrete that contains a number of admixtures. Compatibility problems have been reported when chemically active agents were used with concretes containing microsilica, high-range water reducers, and unusually high amounts of admixtures. Be sure to discuss possible compatibility problems with the admixture and release-agent suppliers. Read More.

Application Methods

Use enough release agent to prevent adhesion, but don’t apply too much. When overapplied, the material runs to low points in the form face where it can retard cement hydration or produce staining. Most manufacturers recommend a thin, uniform coating. With some products, the thinner the better; sometimes as little as 1 ⁄2 mil (0.0005 inch) is recommended on nonabsorbent form surfaces. Read More.

Precautions to Take During Release Agent Application

•Keep release agents off construction joints and reinforcing steel. To avoid spilling release agent on rebar, apply it before placing the steel.

• Never use release agents containing wax or silicone if the concrete surface is to be painted.

• Follow manufacturer recommendations for when to apply release agent. Some agents must dry or cure before concrete is deposited, while others can be applied only minutes ahead of concrete placement. Generally, the shorter the time between applying release agent and placing concrete, the better. Too long a wait can result in the agent drying out, running down the form face, or being washed away by the rain. (Note: Some agents are rainproof.)

• If there is any ponding or puddling of release agent, be sure to wipe away the excess material.

• After coating form faces, protect them from contamination and weather.

SELECTING A RELEASE AGENT FOR DIFFERENT FORM MATERIALS

Read the complete article in Concrete Construction Magazine


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Hill and Griffith Customer Service

We're known for our hands on approach. Let us visit your plant and recommend concrete release agents, packerhead concrete form releases, concrete form seasoning, potable water concrete form release, non-petroleum concrete form release, biodegradable concrete form release, rust inhibitors and concrete dissolver products that suit your needs.

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Prefabricating Individual Components Within the Concrete Manufacturing Process

Posted by Hill and Griffith Company on Aug 8, 2019 6:39:04 PM

Excerpt from the article by Thomas Friedrich in the March 2019 issue of Concrete Plant International 

Screen Shot 2019-08-08 at 3.25.32 PM-1

Multifunctional construction components produced with traditional prefabrication methods need themselves to be divided up again into prefabricated modules, which are then pieced together as end products. Production work in a factory consists of assembling and connecting individual components to create an end product. The greater the number of components being installed in a concrete construction component, the greater the need to connect individual components together in advance so that they can be inserted as a unit on a ready and waiting formwork table. This defines prefabrication of components either pieced together locally in a production facility or supplied as finished components as in the automobile industry. Classic processes in a precast production facility are changing as there is an increasing demand for assembly activities. Concrete acts as a glue holding all components together. This division of labor enables product quality to be enhanced while, at the same time, accelerating production processes. Pipelines can be fastened to the reinforcement, for example. Specially created meshes can be employed in an optimum way for this purpose. Other components needing to be inserted can also be fastened to the reinforcement during installation.

Photo caption: Multifunctional concrete floors: load-bearing elements with fully integrated technical building services

The trend toward multifunctional construction components and the consequences in manufacturing

In the future, there is a growing likelihood of companies producing more than just a "concrete bed." The industry is redefining increased complexity in the shape of numerous floor components.

This requires skilled labor to achieve at a construction site.

  • For example, laying empty electrical conduits during the shell construction stage can't happen concurrently with laying pipelines.
  • Different tradesmen work on the shell during different times. 
  • This strategy requires specialized firms to organize and coordinate the work and teams

The solution for flat-shaped construction components requires manufacturing processes with large-sized framework tables. Construction happens rapidly on these tables to make the most of the large expense of building stationary units on a track or tilting table.

Prefabricated reinforcing elements

An assembly unit for reinforcement generally consists of several components, such as single bars for the span reinforcement, which is supplemented with lattice girders and stirrup cages. A steel bar mesh is employed to this end that serves as a load-bearing unit for other reinforcement elements and installed components. Read more.

Screen Shot 2019-08-08 at 3.25.41 PM-1

Photo caption: Prefabricated meshes including pipelines for room air conditioning (cooling and heating above the concrete floor).

Supplementary elements in a composite construction method (hybrid construction method)

A composite construction method is often envisaged in order to create large web plate openings. This is because secondary moments occasioned by shear load can only be absorbed with a steel structure. Read more.

Pipelines for heating and cooling with a concrete slab (modified building component activation according to the Ceiltec® principle)

Building component activation for cost-effective heating and cooling via a concrete floor is increasingly gaining in importance. Its lower temperature level is making its contribution to this trend, along with the use of renewable energy. Prefabrication is particularly useful in creating the right pipeline arrangement for the air-conditioning planned. Read more.

Entirely prefabricated load-bearing ribs as semi-finished components

Instead of prefabricated reinforcement cages for load-bearing ribs of prefabricated slabs, the rib itself can be prefabricated as a reinforced concrete construction component and then installed with starter bars on the lower slab. Read more.

Preparation on formwork tables

Some installed components are inserted directly into the underside of the floor with multifunctional floor elements. Appropriate construction components, which can be fastened directly to the formwork base are needed for this purpose. Read more.

Process in successful manufacturing

The complexity of multifunctional elements requires different processes in manufacturing. Concrete, as a material, also makes its contribution as a load-bearing element and in keeping individual construction components together. Concrete in its hardened state offers a flexible environment for installing all components. Read more.

Results with the finished product

The result with this elaborate formwork plus all its inserted components and reinforced elements is reflected in the finished product once the concrete has hardened. The appearance of the outer concrete mantle is that of a sophisticated work of art despite the high density of components, which then disappear in the concrete. Read more.

Screen Shot 2019-08-08 at 4.32.31 PM

Photo caption: Finished floor elements for large span widths on a stationary system.


Hill and Griffith Customer Service

We're known for our hands on approach. Let us visit your plant and recommend concrete release agents, packerhead concrete form releases, concrete form seasoning, potable water concrete form release, non-petroleum concrete form release, biodegradable concrete form release, rust inhibitors and concrete dissolver products that suit your needs.

Hill and Griffith Samples

Product Samples

We are pleased to provide samples in quantities large enough to allow you to "try before you buy."
Contact Us »

 

Hill and Griffith Customer Service

Technical Services & Support

On-site casting defect investigations, product testing, machine start-ups and much more. Also, lab facilities are available to provide testing upon request.
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Bulletins and Technical Papers for Concrete Casting Products

 

Tags: Concrete Form Release Agents, Biodegradable Concrete Form Release, Concrete Release Agents, Concrete Forms, Concrete Form Seasoning, Concrete Casting Supplies, Concrete Voids, Concrete Form Release, Concrete Plant International

Eliminate Surface Concrete Casting Bug Holes

Posted by Hill and Griffith Company on Aug 2, 2019 8:24:46 AM

 

(From Smooth On Concrete Casting Products. This is one of the best Q&A for concrete casting defects we have seen. Enjoy!

 

Concrete-Voids-1_copy.jpgHOW CAN I ELIMINATE SURFACE CONCRETE CASTING VOIDS?

Surface voids (small holes, also known as bug holes or pitting) found on the surface of concrete castings have affected anyone who has ever cast concrete. A significant number of concrete casting voids must be post finished or discarded, resulting in wasted product, time and labor. Understanding the causes of surface voids and what can be done to minimize them is the first step to a more efficient and productive casting operation.

The following information has been compiled through our (Smooth On Concrete Casting Products) experience with professionals who cast concrete for a living. Some of the tricks found here are results of many years of research and development. Although one may not find all the answers here, many of the common problems encountered when casting concrete will be addressed.

Question: What are surface voids?
Answer:
Surface voids are the cavities or little holes that appear on the surface of concrete castings. Surface voids (commonly known as pitting) are referred to as "bug holes" or "fish eyes". These voids may produce an unacceptable appearance on the surface of the finished casting.

Question: How are surface voids caused?
Answer:
Surface voids are generally attributed to the following three factors: release agent, water or air (sometimes a combination of the three).

Concrete-Voids-2_copy.jpgQuestion: How does a release agent affect the surface of a concrete casting?
Answer:
Release agents act as a "lubricant" between the mold and the concrete itself. The proper application of a release agent will yield castings without surface voids. However, when a release agent is over applied, it may "pool" or "puddle" on the lower extremities of the mold. As the concrete is poured into the mold these pools prevent the concrete from filling in all the detail. When the casting is removed from the mold voids will be apparent in the areas where pooling occurred. Vibration magnifies this problem by forcing additional release agent into the lower extremities of the mold. Voids caused by too much release agent are recognizable as small spherical voids on the surface
of the finished casting. These voids usually measure about 1/8" (.31 cm).

Question: How does water cause surface voids?
Answer:
Similar to release agents, water is also trapped against the mold's working surface resulting in voids. As the concrete cures and the residual water evaporates, a cavity is left behind on the surface of the casting. Vibration also tends to force water from the cementious material, however most voids caused by water are a result of a high water to cement ratio. Similar to release agents, water is also trapped against the mold's working surface resulting in voids. As the concrete cures and the residual water evaporates, a cavity is left behind on the surface of the casting. Vibration also tends to force water from the cementious material, however most voids caused by water are a result of a high water to cement ratio.

Question: How does air cause surface voids on my finished concrete casting?
Answer:
In most circumstances, air voids have an irregular shape and tend to be much larger (1/2" or 1.27 cm.) than those caused by water or release agents. The air voids are caused by air trapped between the mold surface and the concrete. They generally appear in low slump concrete and can be found underneath irregular (non-spherical) shaped pieces of crushed aggregate.
This is a result of having too little mortar to fill the spaces around the aggregate. Voids caused by air may also be found in castings that have severe undercuts.


HOW TO ELIMINATE VOIDS IN A CONCRETE CASTING:

While many variables must be considered in the elimination of surface voids or bug holes in concrete castings, there are a number of precautions that can remedy this unsightly problem.

Careful preparation and methodical practices can eliminate even the worst of surface voids. The following section describes procedures and materials that will produce finished castings that even the most discerning eye will accept.

Question: Will adding more mortar to the concrete assist in reducing surface voids?
Answer:
Yes. Increasing the amount of mortar in the cementious material will help make the material more fluid. A mixture that has a higher mortar content will assist in encapsulation of the aggregate. By encapsulating the aggregate, mortar also provides a chimney or venting system that will allow air and water bubbles to escape from the mixture. During vibration these bubbles will rise through the mortar and escape through the opening of your mold. A higher mortar content in your mixture also allows larger pieces of aggregate to easily move during vibration and thereby release any air that may have been trapped.

Question: What will happen to my casting if I use a larger aggregate?
Answer:
Using a larger aggregate may cause more surface voids because air is entrapped under the irregular shapes of this material. There is also a larger volume of voids between larger aggregate pieces than smaller pieces. It is therefore recommended that a smaller aggregate be used or that a smaller aggregate be mixed with the larger particles. The smaller aggregate will act as a "roller system" to assist in turning the larger pieces of aggregate during vibration. It is recommended to use aggregate that passes through a number 50, 100 or 200 sieve.

Question: Does the type of cement I use in my mixture make a difference?
Answer:
Cement acts as a lubricant during vibration and allows larger pieces of aggregate to move around freely. Therefore it is recommended that a very fine cement be used to achieve a more fluid consistency. Fly ash, which is finer than cement particles, will increase the lubricity of the cement even further.

Question: What precautions should I take if my concrete has a low water-cement ratio?
Answer:
If the concrete you are casting has a low water-cement ratio, more mixing time will ensure that water and air bubbles are forced away from the aggregate and thereby eliminate the voids on the casting surface. Low water-cement ratio concrete also requires an increased vibration period.

Question: I've heard that adding plasticizers to my concrete mixture will help eliminate surface voids. Is this true?
Answer:
Yes. The addition of plasticizers are used effectively in creating large slump increases. The benefit of using a plasticizer is that these large increases can be attained without effecting the water-cement ratio. The result of increasing the slump will assist air, water and aggregate to move more freely throughout the mixture. Although plasticizers will permit a large increase in slump, the concrete will begin to set much quicker. This means that there is a much smaller time period for the concrete to be vibrated. In order to eliminate surface voids from appearing we recommend using a release agent in tandem with plasticizers. The release agent will allow the concrete to move freely and force voids away from the surface of the casting

Question: What type of mold or form material should I use?
Answer:
Form or mold surfaces be as smooth as possible to decrease the surface tension between the concrete and the mold. Rubber molds are being used more and more for just this reason. The proper release used on a rubber mold will give the best possible surface.

Question: I'm vibrating the concrete, but still have bug holes in the casting?
Answer:
This occurs because air and water bubbles are the lightest elements of the concrete and will naturally flow to the most fluid portion of the mix. It just happens that this area is next to vibrator. So if you are using an external vibrator, the form or mold should be hammered. Hammering allows the mortar to flow toward the area being hit, consequently pushing air and water bubbles to the opening of your mold. This technique is recommended for molds with deep undercuts, where air and water bubbles tend to be predominate.

Question: How beneficial are release agents?
Answer:
Not only do release agents assist in eliminating surface voids, they also prolong the life of your mold. However, choosing the correct release agent and proper application are extremely critical. Various release agents will provide different surface finishes of your concrete casting. We recommend a chemically active release agent.

The amount of release that is applied to the mold or form will greatly effect the surface of your casting. Excess release agent tends to consolidate into spheres that cause bug holes. Too much release agent can be evidenced by voids on the lower portions of your casting. Applying release agent in a thin coat will eliminate these voids.



HELPFUL HINTS TO VOID FREE CASTING:
As any professional caster will tell you casting concrete is not an exact science. There are many variables and therefore no way to ensure void free castings. Voids can be minimized, however, and the following hints are offered to improve your chances for success.

Hint # 1
Extend the mix time to help break up any residual air or water bubbles. This will promote a more uniform and workable consistency.

Hint # 2
Make sure to that release agents are applied in thin films. This will eliminated any pooling or puddling in the lower portions of your mold.

Hint # 3
Lower the viscosity of cement by adding sand or fly ash. This allows large aggregate to move more freely and reduces the amount of air entrapment.

Hint # 4
Use aggregate that is more uniform in shape. Irregular shaped pieces of aggregate tend to make the concrete less fluid.

Hint # 5
Techniques used during vibration can eliminate most surface voids. Vibrating both the outside and inside of your mold will draw most air and water bubbles away from the surface of the concrete. Hammering the mold can eliminate any residual voids.

Disclaimer
This FAQ article is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Safety Data Sheets (SDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.


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Tags: Concrete Form Release Agents, Biodegradable Concrete Form Release, Concrete Release Agents, Concrete Forms, Concrete Form Seasoning, Concrete Casting Supplies, Concrete Voids, Concrete Form Release, Bug Holes

Precast Concrete Form Release Agent Q&A from ACI

Posted by Hill and Griffith Company on Jul 25, 2019 8:00:00 AM

Technical Questions - Precast Concrete Form Release Agent 

American Concrete Institute

Q. I need to select a precast concrete form release agent for a new project requiring an architectural finish. Can you provide information on different types of form release agents and recommendations for using them? Does ACI have a publication on form release agents I could use as a reference?

A. Form release agents ease formwork removal, extending the useful life of a form and improving the smoothness and texture of concrete surfaces. Two main types are available: barrier and chemically active.

Barrier-type agents (examples include diesel oil, wax, and silicone) create a barrier between the form and the concrete. These are not recommended for architectural concrete, because they can cause stains, surface air voids, and problems with form removal in very cold or very hot weather; they also may prevent subsequent adhesion of coatings to the hardened concrete. While diesel oil was once commonly used, it’s now prohibited because the associated volatile organic content (VOC) emissions contribute to smog. (Note: In the United States, form release agents have to meet federal VOC limits of 450 g/L [3.8 lb/gal.] and may have to meet more restrictive limits of 250 g/L [2.2 lb/gal.] in some states.)

Chemically active form release agents (certain types of fatty acids) react with calcium ions in the cement paste to produce a soap that prevents concrete from bonding to the formwork. Based on the reactivity, they are divided into buffered (partially) reactive and fully reactive. Buffered agents produce an improved soap film that helps remove entrapped air and may promote better flow of a thin skin of cement paste at the surface of the form. Fully reactive agents can provide a good basic soap film that, depending on the brand, works well in most cases. Because chemically active form release agents produce fewer bugholes, stains, and surface irregularities than barrier type of form release agents, they are commonly used for architectural concrete.

For more information on this topic refer to ACI 347R “Guide to Formwork for Concrete”, ACI 303R “303R-12 Guide to Cast-in-Place Architectural Concrete Practice”, and ACI 533R “Guide for Precast Concrete Wall Panels”.


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Article Review: Concrete Formed Surface Classifications & Specifications

Posted by Hill and Griffith Company on Jul 18, 2019 1:06:30 PM

Details on classifications & specifications for surface finishes

An excerpt from the July/August 2019 issue of Precast Inc., by Eric Carleton, P.E., NPCA's director of codes and standards.

Evaluating_and_Diagnosing_Concrete_Formed_Surface_Imperfections

Less is better when spraying concrete form release agents on concrete forms.

In 1975, the International Council for Building Research established a general classification of formed surfaces which is referenced in the most recent edition of ACI 301.2R, "Identification and Control of Visible Effects of Consolidation on Formed Concrete Surfaces."

Those classifications are:

  1. Rough - No special requirements for finishing
  2. Ordinary - surface finishing has a minor factor
  3. Elaborate - definite requirements for visual appearance
  4. Special - highest standards for appearance [considered architectural]

Within ACI 347R-14, "Guide to Formwork for Concrete," there is a similar class system to differentiate concrete surface evaluation based on application:

  1. Class D - minimum quality requirement for surfaces where roughness is not objectionable, usually applied where surfaces will be permanently concealed.
  2. Class C - general standard for permanently exposed surfaces where other finishes are not specified
  3. Class B - intended for coarse-textured, concrete form surfaces intended to receive plaster, stucco or wainscoting
  4. Class A - suggested for surfaces prominently exposed to public view where appearance is of special importance

ACI 301-16, "Specifications for Structural Concrete," provides more detailed information.

5.3.3.3(a) Surface finish-1.0 (SF-1.0):

  • No formwork facing material is specified
  • Patch voids larger than 1-1/2-inch wide or 1/2-inch deep
  • Remove projections larger than 1 inch
  • Tie holes need not be patched
  • Surface tolerance Class D as specified in ACI 117-10, "Specification for Tolerances for Concrete Construction and Materials and Commentary."
  • Mockup not required

5.3.3.3(b) Surface finish-2.0 (SF-2.0):

  • Patch voids larger than 3/4-inch wide or 1/2-inch deep
  • Remove projections larger than 1/4 inch
  • Patch Tie holes
  • Surface tolerance Class B as specified in ACI 117
  • Unless otherwise specified, provide mockup of concrete surface appearance and texture

5.3.3.3(c) Surface finish-3.0 (SF-3.0):

  • Patch voids larger than 3/4-inch wide or 1/2-inch deep
  • Remove projections larger than 1/8 inch
  • Patch Tie holes
  • Surface tolerance Class A as specified in ACI 117
  • Provide mockup of concrete surface appearance and texture

5.3.3.5 Unspecified as - cast-finishes - if a surface finish is not specified, provide the following finishes:

  • SF-1.0 on concrete surfaces not exposed to view
  • SF-2.0 on concrete surfaces exposed to view

For the full article, please visit the Precast.org site.


Hill and Griffith Customer Service

We're known for our hands on approach. Let us visit your plant and recommend concrete release agents, packerhead concrete form releases, concrete form seasoning, potable water concrete form release, non-petroleum concrete form release, biodegradable concrete form release, rust inhibitors and concrete dissolver products that suit your needs.

Hill and Griffith Samples

Product Samples

We are pleased to provide samples in quantities large enough to allow you to "try before you buy."
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Hill and Griffith Customer Service

Technical Services & Support

On-site casting defect investigations, product testing, machine start-ups and much more. Also, lab facilities are available to provide testing upon request.
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 Bulletins and Technical Papers for Concrete Casting Products

Tags: Concrete Casting Products, Concrete Release Agents, Concrete Casting Supplies, Precast Concrete, Gricote, Precast Inc Magazine

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