FAQ for Concrete Mix Problems: If you have a question or answer you'd like to see listed here, please contact us.
- Problem: Lots of pinholes in concrete or GFRC facecoat using Polyplex in the mix design.
- Solution: Typically this is the result of mold release, and if spraying GFRC Facecoat; gun pressure settings, spray technique and slump. If Polyplex has been stored in direct sunlight or at high temperatures with the lid off, the de-foamer can evaporate out of the Polyplex, which will result in the air content of the concrete/GFRC mix to rise dramatically. Nine out of ten times, mix temperature ends up getting too hot (above 74 F) causing a rapid loss in slump and pinholes in the concrete surface. Keeping mixes below 74 F, using COLD water and/or ice in the mix to control temperature will help solve this issue. Also, keep the lid on the Polyplex container during mixing, and out of direct sun or hot areas.
- Problem: When filling pinhole and voids in the concrete using a slurry, the slurry seems to just come off when dry.
- Solution: Cement Slurry should be mixed so that it is thick like peanut butter, and whenever possible a small amount of plasticizer (such as Riteks SP7000), and Polyplex (about 1 part Polyplex to 5 parts water) should be added to water, and then that water used to mix the slurry until the peanut butter texture. The concrete should be damp prior to applying slurry to it, so it doesn't absorb the moisture from the slurry instantly. Usually too much water will result in slurry that is weak, and will come off when dry.
- Problem: Lots of pinholes in concrete using a wet-cast recipe.
- Solution: Completely removing all air pockets and pinholes in a cast concrete piece is near impossible for most applications. To minimize the air pockets, ensure the concrete mixes for 4-5 minutes, or longer, once the correct amount of water is achieved to make the concrete mix like an oatmeal consistency. If the concrete doesn't mix for a while after seeing that consistency, the sand/gravel in the mix may not get fully hydrated by the water, and can trap air. Hydrating the aggregates will help remove air during mixing. And of course, proper vibration of the forms will release and drive air up to the top of the form.
- Problem: Pinholes in concrete countertops that show up weeks or months after the concrete piece is sealed and installed.
- Solution: Often times pinholes and voids in the concrete will be just under the surface of a pre-cast concrete piece. They may have a paper-thin coating of cement over them, and normal use of the concrete surface will eventually break that thin cement layer and expose the void underneath. Polishing the concrete surface with diamond pads will expose any lurking voids, but even in cases where polishing the concrete is not desired, a simple quick sanding with 200 grit sandpaper on a palm sander will usually open all hidden voids and pinholes so they can be filled with a cement slurry. Most topical concrete countertop hybrid sealers also bond best to a surface that is honed to a 200 grit, so they can get a good grip to the concrete.