Guys, this is not really a tiling question but a friend has the following problem and I wondered if any of the screeding experts eg ajax? had a view on it.
This is her situation:
Hi, I'm looking for some advice on our engineered wood floor which we've recently had laid by our builder.

We've had a ground floor extension built with a block and beam floor. On top of this they've laid Celotex insulation boards, a wet underfloor heating system and then sand and cement screed, approx 70-80mm thick. 9 days after laying the screed (the weekend before xmas), the builder insisted it was dry enough to lay the engineered walnut floor we had purchased. This was laid throughout the downstairs and over the UFH. It was then left for 3-4 weeks while they completed other jobs, with plastic sheeting protecting the wood.

This Friday the manifold for the underfloor heating was connected and the floor heated for the first time. They left it on full whack for 24 hours, at which point we uncovered the floor to find it wet and rippled all over; it has also lifted in places. We think this is due to the screed not being left to dry for long enough. Our builder denies this, saying the drying time is shorter for a block and beam floor. We had no heating downstairs when the screed went down and it was freezing outside most nights.

Has anyone experienced this problem at all? Is there anything that can be done to improve the appearance of the wood or are we going to have to ask him to replace that part of the floor? We are concerned that the unaffected part of the floor may get damaged where they key in the planks, not being professional floorers. Are we within our rights to ask him to get a pro in?

for tiling the drying time is usually 1mm per day this will ensure there will be no further movement and it will have dried out thoroughly

the floor should have been conditioned before the floor covering put down

builder at fault imho

Far too early, Alan will have a fit when he reads this. As David says 1mm per day, the screed should have been covered to maximise strength and prevent cracking. The builder will be putting his hand in his pocket I think.

as the lads above said, 1mm per day drying time but this is a guideline and other considerations have to be included ie the time of year? and site/premises conditions..

to turn the heating of full belt is stupid to begin with and neglagent. screeds need natural drying time and gradual heat introduction. extreme changes of temerature may result in permanent damage...as the others have said, ajax will be on so he's the expert so i'm sure he'll have the remedy.

AAAAAAAARRRRRRRGGGGHHHHHHHHH!!!!!!!!!!!

Just replied to this on the flooring forum I think. Here is my reply to that one. I will add here that the drying time does vary according to the conditions and given the conditions we have had recently I don't realistically think that any screeds have been drying naturally for a while.....

Sand Cement Screed dries at a rate of approximately 1mm per day given good drying environment. This time of year it would take longer. Typically I would expect somewhere around 90 to 100days. There are a few very specialised screeds which dry in 9 days but unless you have used one of those there is no possibility whatever that it was dry. The floor coverings should not have been placed untill after the underfloor heating had been comissioned, heated and cooled in a controlled regime. This helps to condition the screed and drive off some of the water. It has to be done carefully with cement based screeds because of the issues with shrinkage and curling. Underfloor heating in sand cement screed should not be comissioned for at least 28 days following the installation of the screed. Heating it up with the wood on top has acted likel a steam chamber and the wood has warped and curled as a result.

As for the screed drying faster on block and beam....I wish I had one of those really funny laghing emoticons cos I am not supposed to swear on here........

Anyway, in actual fact if the floor makeup is incorrect then it is likely that building over block and beam would actually cause its own issues. There must be a damp proof membrane over the top of the block and beam so that the warm floor above it is prevented from causing moisture migration upwards from the damper air in the vented space under the floor.

As I said AAAAAAAAAARRRRRRRGGGGGHHHHH!!!!!!

Oh by the way - Curing - Sand cement screed should be covered for a minimum of 7 days following installation in order to maintain the moisture content in order to maximise cement hydration during it's plastic phase so it goes properly hard........Grrrrr! Builder needs to be sorting this out cos it sounds like he has been negligent.

This might be of use

Ajax 123 you are the man, but mentioned already. Commissioning the floor is important, floor should be fired up prior to any covering being laid. After laying tiles/ laminate etc. Temp should be increased no more than 5 deg in any 24hrs. Until optimum temp reached, then hold for 2 days, then bring down again no more than 5 deg in any 24hrs. In most situations it is advisable to leave for 2 weeks after covering ufh before commissioning.

Can't add much more to that Phil ........... apart from perhaps

AAAAAAAARRRRRRGGGGHHHHH!!!

Thanks guys, Ajax looks like you may have answered her question in your flooring forum but thanks again from me. appreciated.........

The wood should also be allowed to climatize to the temprature in the room it is going to be laid

Originally Posted by Ajax123

Can't add much more to that Phil ........... apart from perhaps

AAAAAAAARRRRRRGGGGHHHHH!!!

??????

Alan is adding the aaaaaarrrrggggghhhh to carry on venting his frustration at the original post Phil, not your input mate.

Originally Posted by Phil Hobson

??????

Sorry Phil. Diamond is right - the arrrrghhh was indeed just carrying on from my frustration at the original post......apologies if you thought i was getting at your post.....I wasn't

Thanks Ajax, sorry if I took your post wrong, from what I have read from your replies you are the man. I thought my info re: commissioning ufh was wrong, I hope not. I bow to your expertise. Your posts are spot on. Regards, Phil.

Completely off the point but came across a product recently called maxit 4040 which is a levelling compound that dries in 10 minutes, wow you have to be quick and have someone to wash your tools off!

Hi All,

I hope someone can help me answer this?

My builders are paranoid about tiling on the screed for the underfloor heating as they have never done it before and they keep getting conflicting information on dryig times from 2mm/day to 0.5mm/day

They put down a portland cement based screed down a couple of months ago around 80mm deep and there has been no heating on at all in the house whilst it has been really cold (as there still installing the boiler).

They put a damp meter on the screed and the moisture content is just above 5%. What % content will it be safe to start the warm up of the floor and then do the tiling?

Many thanks in advance.

Hello and welcome..

A screed consisting of Portland cement needs 21 days to cure and dry,, after this period you can then turn on the screed heating and commission the heating .

The screed should be heated slowly at a rate of 5dgs cel per day till a max operating temp as recommended by the in-screed heating suppliers.

The heating is then to be maintained at this temp for a further 3 days before allowing to cool down to room temperature.

You should then have a relative humidity of max RH75%

I would advise the use of an uncoupling membrane on heated screeds.

Hi Dave,

Thanks for getting back so quickly. This sounds like it could be just what we are after. One question though and I hope it's not a daft one.

How does using an uncoulpled membrane affect the heat transfer to the room from the underfloor heating. Doesnt it act like an insulator as it's plastic?

Thanks again

Not at all, infact in can help with heat distribution IMO..

Originally Posted by tectonicfloors

The floor should have been conditioned before the floor covering put down. The wood should also be allowed to climates to the temperature in the room it is going to be laid. Thanks for sharing.

What wood ?