Slurry Won’t Stick

Question:
My slurry won’t stick to my concrete countertops, and it flakes off when I polish it. What can I do to make it stick?

Answer:
Homemade slurry, or grout, is usually a mix of cement, pigment and water. It may also include a fine filler (such as cenospheres), metakaolin or other pozzolan, superplasticizer and even an accelerator. However, adding an acrylic polymer is the key to getting the grout to stick.

Just like cementitious overlays and microtoppings, grout depends on the polymer additive to provide bond strength. Without polymer, you are depending on the cement bond alone. Since grout applied to a concrete countertop is often honed off within a day of application, the cement bond has not strengthened to the point that it can withstand the rigors of polishing. Polymer solves that.

Almost any polymer additive made for concrete can work, but you need to use the right amount. If you don’t use enough, you’ll get flaking. Add too much polymer, and the grout will be gummy when polishing it off.

To get the right consistency for your grout, dilute the polymer with water until it looks like whole milk. It’s better to err on the less-dilute side, but you don’t want it to be so thick that it’s like white glue. Whole-milk consistency is just right.