'force drying' new screed floor

[Mike]

a mate of mine has a company laying wet ufh and screeds etc. he just rung and said a customer of his (he's just laid wet ufh and wet screed gyvlon i think) want s the floor tiled in around 4 weeks. i asked if the floor will be cured by then he said it's possible to 'force dry' the floor by putting the ufh on low then increase the temp next day and again day after so on. i didn't think this sounds right, surely the screed could crack ? i know there's a few pro's on here who deal directly with the screed. cheers

 

[nybor62]

you can force dry gyvlon , but the screed must be down for about a week 1st, raise the temperature bit by bit about 4-5 c every 3-4 days, from i think the ambient temperature

 

[Ajax123]

Turn on the heating at ambient (approx 20 degrees C) after minimum 7 days. Leave at this temperature for 3 days. Then increase the temperature by maximum 5 degrees C per day up to a maximum of 55 degrees C. Leave at this temperature for 7 days then reduce by 5 degrees per day down to its normal operating temperature and leave at this temperature for as long as you like but normally for 3 or 4 days. Then switch off for three days before moisture testing to determine if it is dry. The effect of force drying with the heating must be accompanied by good ventillation i.e. plenty of draught from open windows and doors. Alternatively Dehumdifiers can be used but they need to be man enough for the job as heating the screed will drive ou moisture quite quickly. All temperatures are flow temperatures and not surface temperatures.

If you are down to 85% RH you can use a gypsum based tile adhesive. If it is below 75% RH then you could use a cement based adhesive if you must but my recomendation is always for Gypsum on Gypsum. Another alternaitive would be to use an uncoupling membrane which can be placed at 2% moisture BUt I am always nervous about this and would prefer to get it down to 1.5% and use Gyspum to stick it down.

If there is a deficiency with the installation then it is possible that it may crack but if the installation is good then there is no reason to expect it to do so. Bear in mind these screeds work in a completely different way to cement based screed in that the early strength gain is rapid and any shrinkage will occur within the first three days

 

[Ajax123]

4 weeks will depend on the depth - keep the screed as thin as possible - with wet UFH normally 50mm - any more will delay the drying time. Also there MUSt be a DPM under the screed to stop any substrate moisture coming up from underneath as a result of heating.

 

[Mike]

he also said you mustn't get the floor wet after it's dried, i.e. when priming, this can't be right surely? and i think i read a post from ajax saying that water wo'nt damage the screed

 

[Mike]

just the man ajax. my mate has already laid it, nowt to do with me, i'm just tiling it, hopefully! he usually does 50mm. i'm tiling one of his floors at the moment

 

[Ajax123]

he also said you mustn't get the floor wet after it's dried, i.e. when priming, this can't be right surely? and i think i read a post from ajax saying that water wo'nt damage the screed

Water will not damage the screed but obviously large quantities of water will retard the drying so it is not desirable to spill buckets of water on the screed. However priming with a water based primer is not a problem provided it is allowed to dry after application. Typically with an acrylic this would take 4 hours give or take a bit. With a water dispersible epoxy you should leave it for around 16 hours before overlaying as it needs time to set. The issue with water in the screed is more to do with the way it encourages a chemical reaction with cement adhesive. This is the "enemy" as the chemical reaction leads to ettringite formation which causes the tiles to delaminate. However if Gypsum adhesive is used this is not a problem. If un coupling is not required then it is also possible to use one of a couple of reaction resistant adhesives such as Benfer Gyps and H40 Ideal. The Gypsum based adhesives are reasonably priced so as I say I would personally be looking towards them in the first instance. If you use a cement based I would generally recomend a water dispersible epoxy primer as there is less risk of the reaction occurring.

 

[Ajax123]

I guess based on the fact you are in Holyhead this will be Gyvlon from Hogans at Bangor.

 

[Mike]

no, my mate is a director of treadwarm based in chester . another mate of mine works for hogans tho, just about cos they're really struggling. got administrators running it.

 

[Ajax123]

no, my mate is a director of treadwarm based in chester . another mate of mine works for hogans tho, just about cos they're really struggling. got administrators running it.

I know Treadwarm very well. I did their initial training for laying the screeds. Wasn't aware Hogans had the admins in though. Nightmare!!

 

[Mike]

yeah, my mate's wife was laid off from the office at hogans and the remaining lads are on a short week. you may know my mate at treadwarm, alan, he has the concrete pump too (tw pumphire)

 

[Ajax123]

I know Andy at Treadwarm. When did Hogans go then?

 

[Mike]

andy's my mate alan's business partner, i've met him a few times at their office, they're doing well at the moment and have just moved to new premises. as for hogans, they're still trading but the administrators are in charge. i dunno if the whole company is like that, they have different branches, roadworkers, quarries concrete lorries etc. i didnt know they did gyvlon tho, i just thought it was readymix

 

[Ajax123]

they bin doing Gyvlon out of Bangor for about two years now. Shame they are struggling cos I have always thought they are a nice little outfit. Some nice guys working there but I guess just another casualty of the recession. Hopefully the administrators will be able to turn it round and they will carry on without too many changes.

 

[Mike]

hogans have been around for donkeys years. i remember them as a kid they were laying a tarmac car park near me and the boss hit one of the lads for slacking! i think he was mr. hogan himself . going back to the original topic i will be able to prime the floor with latex providing i let it dry? and can i use normal adhesive (provided it's for ufh) on it?