DeHusband and DeFriend worked all day long Thursday adding more concrete (quikrete) to a concrete floor (about 4 inches onto a 2 inch base). Now, 48 hours later, it’s dry and you can walk on it. Problem is, the top is “powdery” and no matter how much I sweep, it just scrapes off more of the top layer.
What happened? And, how do we fix this? We don’t want to have to chip out 27 eighty pound bags of mix.
I can only assume that the concrete was mixed one or two bags at a time and no effort was made to finish the top surface with a float first and a trowel second. Sheeesh what a lot of work and poor finish as a result.
You might be able to salvage the job by applying a mix of sand and cement as a top coat, using a latex bonding liquid in the mix and on the top surface.
The size/area of the original 2" slab wasn’t mentioned, but at 4’’ thick, 27 bag of sakcrete wouldn’t cover much area. DeH & deF need to be sure they know what to do and how to do it prior to embarking on another irreversible project. Ask the experts at the big box next time…beforehand.
Don’t feel too bad. A contractor poured about 5 or 6 hundred square feet floor with embedded conduits and reinforcing mesh Thursday. He added a liquid for I know not what and added 1 1/2 the proper amount. As the concrete hardened it also cracked into thousands of pieces. Being still ‘green’ or not thoroughly hardened the crew was able to get it up and out on Friday.
DeFriend said he knew what to do because he learned from his dad who worked in construction. The room/porch is 50 square feet. There is still about 1/2 inch before it’s up to grade. They used a float but they don’t think they used it right. Plus it rained the first night and, even though it was under a roof, it still got pretty wet. Does that make any difference?
Someone does make a sealer for those kind of situations, but I’ve no idea if it works well or not.
There are a lot of epoxies for floors out there. I think they turn out better than just bare cement. Clean easily, impervious to water, and a heck of a lot cheaper than tile, carpet,linoeleum, or Pergo while still looking pretty nice.
Freshly (‘poured’) placed concerte MUST be protected from rain untill set.
This is most likely the cause of the dusting.
Taking all day indicates they mixed it one or two bags at a time and put it in place. By the time all of it was mixed and in place the first portion was already set too much to be floated and/or trowelled.
I would consider to mix enough sand/cement mix and possibly some very small gravel to make enough mix to bring the level up the additional 1/2". Use the latex bonding agent menitioned in prior post. Clean the top of the existing surface with a hose and when barely damp apply the latex per instruction on container.