Underfloor system, flooring problems, advice please...

H

HashHarry

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I have a wet underfloor heating system installed between joists in a 1930's house. The heating system itself works.

The issue is with the subfloor....

The builder installed insulation between the joists, then clipped the pipes to the insulation as seems to be the standard approach. He then filled the gap from the top of the insulation to the top of the joists with dry screed and installed water resistant chipboard over this to complete the floor. So far normal.

He then had flooring contractor come in to lay Karndean and flooring contractor tacked 4mm ply to chipboard and glued the Karndean onto the ply.

The problems after about 3/4 weeks was some tiles came loose and when they pulled up the loose tiles they discovered water stains , they could not find the reason for the water (undefloor system pressure steady) so they re glued new tiles and all seemed well for a while and now after a year we had the whole floor (Karndean & Ply layer only) pulled up after more tiles came loose, ridges appeared where the ply joins were indicating ply expanding or moving. On removing floor we now see water stains (dry to touch) in various places around the floor on the chipboard.

Questions I need help with please ...

1. Anyone else had this problem? or anyone have any ideas about where the water between chipboard and ply had come from?

a. Is it the chipboard or ply drying out with the underfloor heating driving the process but as it's sealed in by the Karndean nowhere to go?

b. Think heating went on immediately to test it after they laid floor, could it be the high temp adhesive not given time to cure/set?

2. I am wondering if the dry screed is the source, builder says he left it 2 days after putting the mix between the joists before covering with chipboard. Would that be enough time for excess moisture to dissapate before covering it? What would be the normal time before covering dry screedin this manner?

3. Should I tell them to pull up the chipboard to check before recovering with new floor? It will cost but prefer we dry it out if the dry screed is the source of the issue before starting again.

Thanks.
 
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It is somewhat amusing when you bandy about terms without explaining what you mean by them.

So what is your definition of dry mix in YOUR context?

Tony
 
That is not my understanding of the usual use of that term by builders. Which is a mix with some moisture, which looks dry, but still has enough water to enable the cement to cure.

If yours was really dry with no moisture to cure the cement then it will have remained as a dry powder with lesser heat transfer capability.

I still expect that it was NOT completely dry and DID contain moisture to cure the cement and is now hard! Is it now hard?

I then expect that it was covered up after two days and contained more moisture than required to cure and that it is the excess moisture that has caused your problem.

Depending on thickness cement needs a lot of time to fully dry out usually several weeks not days. But of course that depends on the actual quantity of water it contained when laid.

Tony
 
Did not know about "biscuit mix" name for it ... as you will have guessed I'm not a builder!

I'll see if I can load some photos of the water stains

Any ideas in the meanwhile?
 
Agile said:
That is not my understanding of the usual use of that term by builders. Which is a mix with some moisture, which looks dry, but still has enough water to enable the cement to cure.

If yours was really dry with no moisture to cure the cement then it will have remained as a dry powder with lesser heat transfer capability.

I still expect that it was NOT completely dry and DID contain moisture to cure the cement and is now hard! Is it now hard?

I then expect that it was covered up after two days and contained more moisture than required to cure and that it is the excess moisture that has caused your problem.

Depending on thickness cement needs a lot of time to fully dry out usually several weeks not days. But of course that depends on the actual quantity of water it contained when laid.

Tony
Click to expand...


Thanks...we will need to lift the chipboard to see if its hard. Do you think given the time since original installl it is not now necessary to lift the chipboard as any moisture likely to have passed through?
 
For my interest in your situation it would be good to lift up a corner or drill a small hole to test the mix.

But I am pretty sure that what I have suggested is going to be correct and it will be hard now.

After so long I would expect all or most of the moisture will have dried out.

But I would still expose all the chipboard and leave it open for a few weeks.

Tony
 
A simple test to see how much moisture is still in the chipboard is to place a sheet of glass about 600 x 600 or larger on top of the chipboard over night and see if there is condensation on the underside in the morning.

Also a probe type of timber dampness meter would give an indication. They are not terribly accurate though.

Tony
 
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