Q. We have a problem with tilt-up wall panels sticking to the floor slab. Is there a test that can be performed to check the porosity of the floor surface? I think there may be a problem with the finish on the slab as a result of hot weather conditions. If the slab is sprayed with a bond breaker prior to the concrete pour, can the porosity still affect the wall panels?
A. The hot weather could be resulting in excessive surface drying of the casting slab prior to application of the bond breaker. The bond breaker is a membrane-forming material that relies on moisture in the slab surface to adequately disperse the agent. If the bond breaker is absorbed into the casting slab surface there will be ‘pin holes' or discontinuities in the film. This allows the fresh concrete a chance to bond to the casting slab. Try damping the casting slab to satisfy the surface absorption prior to applying the bond breaker. Also note that the water puddling test on the top of the bond breaker is not a good indicator of a sufficient film. (Answer from Bob Neal.)