Hello Cheng. If the crack across the slab has not become larger in the past few years and the concrete has not moved, then it most likely will not settle anymore. The crack needs to be filled and repaired first. We recommend a product that uses a combination of sand and polyurea. A 1/2″ crack is large, so it will require much more product to fix. Here is an example of a product we recommend. After it has cured, you will want to grind the entire crack repaired area to make the transition more flush. After that is completed you can apply the Ardex K301 where necessary.

Great site, I was wondering what you would recommend, I have a couple dips in my garage 1/2-1/4 inch ..a crack that runs across my garage with the side o the crack higher than the other side of the crack(seems like it has settle like this for long time now)

will the ardex k301 level everything out and prevent it from cracking down the road. or is there more issues like the base issue below the concrete slab?

Thanks

Hello Tom. Yes, they are different. That is why we state in bold italics in the article above to not use self-leveling underlayments. They are not intended as a wear surface and they will not accept a coating properly. They don’t have the same compressive strength as well. If you just have one small low spot, we would recommend using a 100% solids epoxy instead. It will fill and feather small spots even better.

Hi Glen. Yes, you are fine. Ardex is just recommending that their product be treated with a sealer for best results. Just make sure that you allow enough time for it to cure and the moisture to evaporate out. It will need light grinding or heavy sanding once cured. You can’t etch polymer-modified cement.

However, I have noticed that the Ardex website states, “ARDEX CD should be sealed with a waterborne, breathable concrete sealer to prevent dusting and to help resist damage from standing water, salt and oil, as well as staining and marking.” Am I okay with the 100% solids epoxy?