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General: Screed drying time

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  1.  
    • CommentAuthorRex
    • CommentTimeOct 21st 2016
     
    What ho one and all,

    Chatting with a neighbour today who is having an extension to the kitchen built. Looking good at the moment and they are very happy with the builder; they seem to think he is the bees knees.

    About two weeks ago, they had the oversite concrete pumped. In less than two weeks time, Celetox insulation will go down, then the UFH and around 50mm of liquid screed. Apart from the fact that there will not be much Celetox thickness, they have been told that the screed will have an accelerator, and will be ready in three weeks for the Karndean flooring to be installed.

    They have been told, drying time is inch per week so three weeks is sufficient for 50mm. Sounds very optimistic to me, particularly as vinyl tiles are hardly conducive to drying. I expressed my opinion, but as I am not a professional builder, what do I know?

    Gentlemen, any thoughts?

    Toodle pip

    Rex
    • CommentAuthorcjard
    • CommentTimeOct 21st 2016 edited
     
    1 day per millimetre up to 40mm, plus 2 days per remaining millimetre. It can be force dried by an underfloor heating system after it has been down for 1, maybe 2 weeks

    Bit of trivia; my screed had been down for 10 months before I considered laying my karndean. Two weeks prior, I turned the underfloor heating on to 22 degrees(slab temp) and you could clearly see the shadow of the pipes appear as the warmth drove residual moisture out of the screed. A day later the shadow was gone..

    Few tips, put. A bit of cling film on the screed for a day/night and see if condensation forms on its underside. If it does on that it will on the vinyl glue too. Get the builder to cast a few more nuggets of screed 50mm thick and the size of a brick. These can be keft in the same environment as the screed and then weighed, baked in an oven for 4 hours and weighed again to assess moisture content. Don't bake all the bricks at once.

    As part of my floor prep I also hired a Numatic sanding machine and spent a day scrubbing the laitence off with a 40 grit pad, I used f ball's P121 stopgap primer and f46 glue and it's still stuck.. but it has only been a month!

    As to whether you pipe up, I can't see it going well with the tradesman. Maybe suggest they do some light reading and retain some funds in case all their planks peel off in 6 months time if the builder insists on this accelerated schedule. The additive I'm aware of for liquid screeds allows them to go thinner, rather than dry out faster. End of the day, a huge amount of water is needed to make it liquid (it ends up a bit like sandstone) and only so much is needed for the crystallization process that sets it. THe rest has to evaporate
    • CommentAuthortony
    • CommentTimeOct 22nd 2016
     
    What about the concrete?

    I reckon an inch a month including the concrete, pumped screeds can be faster if they are polymer but same for cement/water based ones.
    • CommentAuthorRex
    • CommentTimeOct 22nd 2016
     
    If the screed is not fully dry and they put the Karndean down, what is a likely outcome?
    • CommentAuthorjamesingram
    • CommentTimeOct 22nd 2016 edited
     
    If it's a liquid screed it may be very different from a traditional sand cement hand laid screed.
    I'd investigate the supplier and get product details.
    I've heard of products like flowscreed that self level , are thinner (75mm would be norm for ufh) and dry much quicker. Not used them myself
    Good tips cjard
    • CommentAuthorEd Davies
    • CommentTimeOct 22nd 2016
     
    I know nothing but Google finds this to back up Jamesingram:

    http://www.screedscientist.com/screeding-under-floor-heating/optimum-drying-time-for-ufh-screeds/

    “Fast drying floor screeds like FlexiDry are some of the most popular screed options now commonly in use for under floor heating systems. These screeds provide very low drying periods of up to just 3 days for complete drying, as compared to the 110 days for traditional screeds. These screeds do not require the usual 7-day curing and allows light foot traffic from 12 hours after installation.”
    • CommentAuthorcjard
    • CommentTimeOct 23rd 2016 edited
     
    If the screed is not dry and they put a moisture impervious floor covering down, then the moisture may well cause the glue to fail, and the karndean will cease to be well adhered to the floor. Whether this makes a difference in practice only time will tell. The screed will be very flat and the karndean could sit on top of it without coming to much harm. If it starts curling or is subject to a lot of traffic, furniture movements etc, then it'll start lifting up

    I have some karndean samples that have been left in the sun. They've warped to the point that they wouldn't sit flat. I'd imagine that being glued to the substrate helps karndean dissipate acquired heat to reduce this, plus being bonded it will be encouraged to stay flat.

    Calcium sulphate screeds are quite hard wearing in relation to normal foot traffic, so despite the pressure from clients to get everything finished in quick order, it'd be worth leaving it as long as pissible before laying

    You might find some tips on the internet that recommend force drying by activating the UFH at e.g. 25 degrees and upping it 5 degrees a day til you reach 55, then back down. Personally I think this is mental, and asking for the slab to break due to expansion stresses but clearly some companies have very pushy clients
    • CommentAuthorRex
    • CommentTimeOct 24th 2016
     
    Thanks for all the comments and thoughts. This is nothing to do with me, so I figure it best, not to offer any advice, leave it to the experts and if it goes wrong, ................!

    But in searching the web, I did find some links to fast setting liquid screeds, 25 to 30 days. May be the builders know something that I don't. But in my humble opinion, there is no substitute for time for drying things out.
  9.  
    We've just had this stuff put down - http://www.tarmac.com/solutions/readymix/topflow-screed-c-belitex/

    Seems good and judging by absence of condensation apart from first day, no longer putting out much water vapour.

    We're advised that it will take our microconcrete coating in 30 days by the installer (25 days according to the manufacturer, apparently), but will probably give it rather longer to be on the safe side.

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