Excerpt from the instructional book, The Construction of Tilt-Up, published by the Tilt-Up Concrete Association.
Bond breaker is one of the most critical materials used on a Tilt-Up project. As the name suggests, the bond breaker will facilitate separation between the wall panel and the casting slab.
Bond breakers generally fall into one of two major categories: chemically active or non-chemically active. They can be either water-based or solvent-based. Solvent-based bond breakers do not meet U.S. Federal EPA Clean Air Standards and, therefore, require the end user to pay an exceedance fee.
Chemically active bond breakers contain carboxylic acids which chemically react with calcium hydroxide (lime water) in fresh concrete to form metallic soaps, which prevent wall panel sticking. Non-chemically active bond breakers contain organic resins or wax which form a barrier on the casting/floor slab surface to prevent wall panel sticking.
Chemically active bond breakers have the advantage of being easily removed from floor and wall panel surfaces once the wall panels have been raised, allowing for the application of exterior patching materials, exterior coatings and flooring products. Non-chemically active bond breakers are generally more difficult to remove, and often interfere with adhesion of exterior patching materials, exterior coatings and flooring products.
When the forming is complete and the casting beds are ready for the insertion of reinforcing steel and inserts, it’s time to apply the bond breaker. Before placing anything on the slab, the bond breaking com - pound must be sprayed on the slab surface. The compatibility of the slab curing compound and the bond breaker, if separate items, must be verified before beginning construction. The use of a single bond breaker from the same manufacturer should be used, and dissimilar products should not be used.
A quality, hard steel-troweled slab finish is a prerequisite for any applied treatments and good panel surface. Slabs that are poorly finished, poorly cured or have low strength will exhibit higher permeability, thus increasing absorption of the bond breaker and reducing its effectiveness. All casting slabs should be cured according to ACI 302.1R, ACI 308 and ACI 360R.
Apply the bond breaker in strict accordance with the manufacturer’s recommendations. Bond breaker application rates, application procedures and user instructions vary widely among manufacturers. Although the chemical makeup of bond breakers varies among manufacturers, most bond breakers are reliable and perform properly if used correctly. Make sure the product is within its shelf life, has not frozen and is thoroughly mixed (applies primarily to water-based bond breakers) prior to use. Be sure the surface is clean and free of any sawdust, dirt or other substance that would impede the action of the bond breaker or stain the panel. Most manufacturers recommend that the bond breaker be applied in a minimum of two coats after all wood reveal strips, chamfer strips and blockouts are installed, but before installation of reinforcement and embedments. These coats are sprayed at right angles to each other to ensure complete coverage of the casting slab. Apply the bond breaker inside the forms to the outside face and the perimeter of the formwork. It is well worth the effort to apply additional bond breaker around the outside of the formwork nearby. This ensures easy cleanup of any concrete that was spilled during the placing process.
Although bond breaker manufacturer recommendations vary, in general, the casting/ floor slab should have a uniform film of bond breaker and should exhibit a slightly darkened uniform appearance prior to insertion of reinforcing steel and panel inserts. Avoid puddling the material, as this will cause discoloration and retardation of the panel surface. When in doubt as to the presence of an adequate bond breaker, consult the manufacturer.
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