Joint Fill Advisory
Displaced Fine Particulates
Technical Note: DFP – Displaced Fine Particulates
Since the introduction of coal fly ash into many of the new concrete mix designs, fine particulates are troweled into the surface where they have the probability of being displaced from the concrete. This is especially evident when any adhesive type material is applied to the surface. This includes duct tape, joint fillers and SPF (stain preventive films). Coal fly ash has a glass like surface that does not adhere well into concrete. It has become evident that a bond breaker type material or Ivory bar soap type product be applied to the surface area on both sides of the joint prior to installing the specified joint filler material. This precaution will prevent the coal fly ash/fine particulates from being displaced, when the joints are shaved for leveling. This condition is often mistaken as being a “stain” or residue along side the shaved joints. This is not residue or staining. It appears to look more like an etching of the surface; however, it is very fine particulates such as coal fly ash, which have been pulled or displaced from the concrete surface paste.
There are many projects where the use of coal fly ash is part of the concrete mix. Several of the large box stores use coal fly ash as part of their standard concrete mix design. Installing contractors should always ask the general contractor or owner if coal fly ash is in the mix. Precautions should be taken to prevent any condition mentioned above that may not be an acceptable result for a finished project.
VersaFlex, Inc. recommends that some type of precautionary method(s) be taken to prevent this condition.
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