Residue on Concrete Surface

Cool. It scratched off easy enough with my fingernail. I figured I could hit it with a wire brush and vacuum accordingly, but I knew someone with concrete expertise could tell me for sure.

A good stiff wire brush and a shop vac is allways a good idea before laying tile

Hello DAG, My brother helped me with a large concrete and tiled shower room, he was a certified mason, brick, tile, stone, & concrete. I had to lay down a waterproof membrane at least 6 inches high above my concrete pour, which was to be behind concrete board, as a backsplash. Your pan will leak water without some sort of membrane, if you did not install a liner before your pour, you will have to seal the concrete with sealant. To clean any residue simply use a large sponge and a bucket of water. Use towels or a heater to dry your cement pan. Hopefully your cement is hard enough to tile. Good luck

I have a membrane between two pours. The first pour was flawless... Of course it's underneath the one that's not so one can see my good concrete! The top layer is still really hard. It will will be fine for tile. I was just worried about my thin set sticking like it's supposed to. Thanks for your input!

Hello DAG, I deal with top coatings (decorative toppings) we allways reccommend to cook off that chalky residue before applying any coatings. This project is requiring adhesives that may somewhat change your prep. You do want to make sure if you go with wire brush and clean up you remove all the residue. If you want another avenue we reccommend a mild solution of muratic acid 2 parts acid to 10 parts water scrub and wash down well. I was not sure if you had the ability (ventilation and drainage) to use this process. And of course when working with acid allways use precautions..good luck...adhesives stick better to clean dry surfaces...thats for sure!

Thanks for the advice. I'm going to try a brush first. If that doesn't get it I'll try the muratic acid route. I try not to do too much with harsh chemicals as I have small children who are pretty sensitive to fumes. I do have good ventilation in the bathroom and since it's a shower I have water and a drain for wash down.

Very good...one thing after the brush and clean do a simple water test on the surface...all you do is put a few drops of water on different areas on the surface if they dry quickly thats good...if they dry slowly look in the drops and you may see some lingering residue..that also may be bad adhesion and recleaning may be nessary...I am not trying to make this a long drawn out deal but prep is paramount when applying any type of coating or adhesives..good luck