Concrete screed crumble

[Steve A]

Hi, i laid a new concrete floor and laid the screed on Thursday, i went back today and found the screed to be like crumble towards the end we laid last. It was delivered quite dry and by the time we had finished seemed even worse but it trowelled up o.k. so i thought it would go off.
Is there anything i could spray on it at this stage to harden it off or is it a case of taking it up again (i hope not). regards Steve.

[bighen]

Sounds like a bad batch.
You should always grab a hand full and squeeze into a ball. If it holds its form when you pass it from one hand to the other its fine. If it breaks up, crumbles etc you need to get onto the batcher and complain to the rep. They will come out at their expense and remove the tipped product.
There's nothing i know of that you can spray to harden it. The curing process has already begun, and if its crumbling it will never bond together.
As it is already laid you could get onto the rep who will take a sample for analysis in their labs.
Let me khow how you get on.

[Dave]

How thick is it..?

[Steve A]

I think it just may have been too dry as the last bit i laid was the worst. It was about 50mm thick which i know is a little thin but i primed the surface with sbr and cement. I have seen floor hardener for concrete floors but i think they are applied whilst the screed is still wet? regards Steve

[RockCeramics]

It looks like your gonna have to replace the screed from what you have said
Also the minnimal depth for screed is 65mm ,so it might all have weakened at some point anyway, can you replace and go to the correct level ?
How long of a drying period you leave the concrete to set as well every
xmm depth = 1day

[whitebeam]

Monolithic: to a clean, green concrete base @ 25mm thick min
Bonded: to a clean, wet, grouted sub-floor @40mm min
Unbonded: to a sheeted sub-floor @ 50mm min
Unbonded with heating cables: 65mm min

[Rob Z]

Hi Steve We do a lot of mudwork and I agree with the rest that there is nothing that can be done now other that to tear it out.

One thing that we do to help deal with the premature drying out that you are describing is that we spray the mud with garden sprayer once it's floated and then cover it with roofing paper or plastic to hold the moisture in and enhance the cure.

[whitebeam]

The only thing you might try is sbr with water 1-5 and pour onto the screed, when it soaks in do again and until it feels enough has been taken in. Try to break the finished surface so you have opened the screed trowelled surface

[jay]

hi is the finish just dusty or can you scrape right through,,,,,,,,,,,,,

[Steve A]

It can be scraped through in a few places. I was wondering if it was worth trying one of those dustproofing/hardening liquids and spraying it on? regards Steve

[Steve A]

I think i will try sbr as it seems to stick everything together so its worth a try i think. regards Steve

[whitebeam]

It may be to late for the hardening liquids which should be applied at the mixing stage, dustproofing is ok a dusty surface but your screed will be weak all the way through. Try the sbr method

[jay]

hi sounds not to good if it was mine i would remove the loose stuff and re render or patch render with render (nothing seems to take to dust or weak subs) sorry

[lucius]

All screeds were 2 inches thick (50mm) years ago, no problems.
Lucius.

[jay]

prob pay to check floor is not drummie if you lay it to dry sometimes it wont take