Concrete drying / curing times

[julesg007]

Hi all,

Would like some advice about a new concrete slab I've just laid.

The slab has been laid internally in a small conservatory and this room gets really warm almost too warm (practically south facing), size is approx 2.4m * 1.25m * 0.1m (8ft * 4ft * 4in) and laid over a 1000 gauge plastic sheet DPM. The concrete was a bagged pre measured typed mixed by hand. It was tampped, levelled and smoothed.

The slab has now set up / harded nicely although I know it hasn't dried or cured completely and that this process does take some time.

I want to lay travertine tiles over insulation boards and was wondering approx how long should I leave it before starting - the powered adhesive I am going to use recommends that I should leave it at least 7 weeks.

Looking forward to the help and advice.

Thanks

Jules

 

[stuart45]

An inch a month, or 1mm a day is a rough guide but it does vary slightly with site conditions. Wasn't it expensive using pre-mixed bags?

 

[JohnD]

it cures while it is damp - two weeks of staying damp gives pretty good strength. Putting polythene over it or frequently spraying with water for these first two weeks will help it strengthen and harden. Once it has dried out, you will not be able to restart the curing process (underground concrete, which never dries out, is especially hard and strong)

After that, it will dry out fairly slowly because it is thick, as Stuart says. It will shrink very very slightly as it dries. You might notice a hairline gap opening up where it touches the walls

Putting a loose-weave rug or mat over it will help you while it dries - walking on concrete raises dust and erodes the surface (especially when it is new and not fully hard)

Efflorescence (dissolved salts) may rise to the surface at it reaches dryness, these can push off tiles or other coverings if fixed too early.

 

[julesg007]

Hi,

Thank you for the advice.

I know using the pre mixed bags wasn't the cheapest option but it was the most convenient for me, if I was doing anything bigger I'd have a ready mixed load delivered.

So, if I understand correctly as the slab is about 4ins thick it will take about 4 months to dry - I do know that is different to curing or hardening.

Having to be getting on with things I have already been carrying on with the work in the room and the surface is holding up fine, although that said I am working in soft soled shoes and not doing anything with heavy tools.

I am accutely aware of doing things too quickly can lead to problems further down the line but the other half won't be too pleased to hear that I have to leave things for so long before being able to tile the floor.

As the room the slab as been laid is internal and does get pretty warm and is completely watertight and I need to be cracking on with things do I really have to wait 4 months? If not what sort of period do you think would be OK? As stated earlier the powered adhesive recommends a minimum period of 7 weeks or is that a bit too soon?

Thanks again for the help.

Jules

 

[fastneattrowel]

Wondering how they manage on building sites after they laid concrete and screed,wait 6 months before they tile the floors