Curing Concrete Slab

[Metung]

I am about to have a house slab put down - 180 sq.m. I intend polishing the whole slab before I start the framing. The literature I have read on concrete polishing suggests that the curing of the slab is critical to avoid any cracking. I had intended curing it for 28 days under plastic sheeting but read where this can cause local discolouration of the concrete - not sure to what depth and maybe the polishing would get rid of it. Another suggestion was a layer of damp sand on top of the concrete but I probably won't be around for the 28 days to keep it damp. I then had the bright idea of damp sand covered with tarpaulins - the idea being that the sand keeps the tarps off the concrete and the tarps stop the sand from drying out. Can anybody see any problems with this approach? Thanks all.

[dai sensei]

Damps sand covered by tarp or plastic works fine.

Make sure you work the finish as much as you can as this reseals early cracks (helicopter type steel finish).

[johnc]

As above, the fact that you are doing this in winter also helps and I would suggest leave out the driers.

[Gaza]

As you are polishing the slab, pior to doing your framing, you will need to be very carefuul with protecting it once it has been polished.
On major jobs that cover the slab with thin (7mm) ply to stop any damage. You will also need to be careful not to cause any mechinal damage ie drop hammer.

The process that you are doing does this envolve grinding the slab then fine polshing and sealing at a latter stage.

[Island Nomad]

Make sure your concrete mix is nice and dry ie. very low slump, as too much water weakons your cement and causes surface crazing.

Curing properly is the go to stop your slab drying out too quickly. The sand sounds like a good idea, make sure it is washed and very clean as it could stain.

[Metung]

Thanks all for some very useful advice.

Gaza, I like the idea of the ply. I was going to try and get old carpet and use that but I think the ply is a much better idea, with maybe carpet on top if I can get some easily. As I will be covering the external frame (2 stories) with ply I will have it coming out the proverbial so supply won't be a problem. I am going to use the "HTC Superfloor" system from Sweden to polish the concrete. It provides the machine and the grinding wheels. It is my aim to grind the floor to such an extent that it doesn't require sealing, although you do apply an impregnator at the start of the process that seals the pores of the concrete and supposedly makes it stronger.

I have specified 32MPa concrete and F81 mesh in the hope that crazing/cracking will be minimalat least and preferably non-existant..

The clean sand is also great advice - I could have ruined the whole thing.

Thanks again and any further advice would be most welcome. As the project progresses I am sure that I will be seeking a lot more.

[Stylesy]

Have seen a few polished concrete slabs that look great, but also seen a couple of shockers. Another tip (and this is from looking at the bad ones) is to ensure that all your plumbing, gas pipes & connections, etc are in the absolute perfect position upon laying the slab. I've seen repair jobs done post grinding where pipes have had to be moved, and you can never match the original slab - sticks out like the proverbial dog's :eek: .

I'd also still go with a sealer coat on top for a couple of reasons - provides that final shine coat and also eliminates any cement dust problems in the future. Keep in mind that cement keeps it's properties whenever it's returned to it's original form (powder) which is never good to have under foot - dermatitis, etc.