Underfloor Heating Screed NIGHTMARE

[The Legend; Phil Hobson RIP]

Again it's all been said,

 

[Ajax123]

All,
Thanks for all the quick replies, great stuff!
I no particular order...
My local tile warehouse recommended sx-1 for first screed, then also over wires. He now says he didnt, so somewhere there has been some confusion. Never the less, i just need to get some confidence its either no problem at all, or its definately something to worry about.
Yes, I used a knotched trowel / comb with flexible adheisive on insulation boards. They seem to have stuck well no problem.
I think the hollow sound is because of the boards, and not a full solid base like concrete for example. It just 'sounds' a bit fragile, maybe i am worrying too much. Just wondered if anyone recognises what i'm explaining when screeding over boards.
The screed seems to have bonded to the boards ok, and as Dave says I think the hammer test(!) is becuase its a shock point load crushing the foam, allowing screed to break.
No heating under appliances or kitchen units, just open area.
As built in I could set appliances, dishwasher and washing machine, on a wooden base to spread their load under the cabinets.
If latex Plan is a close match, no fibres, and seems ok then maybe sx-1 is too.
Tremco technical support have told me that all their screeds meet the BS of 27deg surface temp, but would normally recommed the sx-100. They havnt tested any of them it seems, just developed them to meet certain properties, if they can do this without testing.

It will sound "hollow" and is not a suitable substrate to carry out a hammer test on as Dave says it will crush the insulation and cause deflection cracks. Tremco are not saying it is not suitable (I assume) it is just that they would normally recomend the one with fibres. I am not sure the presence of fibres would make a substantial difference but if they have not done any testing then they will no doubt over specify.

I think I agree with Dave that for complete peace of mind on your part as this is always likley to play on your mind and spoil your enjoyment of the floor I think an uncoupling membrane would be a good idea. That way the tile face is protected from the lateral stresses created if the laeveller does begin to crack later. Have you sorted a tiler yet. It may be that one of the members on here would be grateful for the work.

The 27oC surface temperature is a red herring in this case. That is trhe maximum surface temperature advised when using resillient flooring such as vynil and is to take account of the fact that the adhesives used to stick them down begin to break down at that point.

Putting your washing machine on a timber support could be more trouble than it is worth because if it gets wet it will start to mould and swell and rot. If you want to spread the load a peice of hardiebacker type board might be better.

 

[Rob_1]

Thanks for the replies.
I will be looking for a tiler yes, if anyone is in coventry and could give some advise and maybe interested in the job let me know.
I've never come across uncoupling membrame before. I will do some research, is it a membrame (off a roll / or painted on) that goes on before tile adheisive?
I will look at hardiebacker to put under appliances then too.
I have turned the UFH on, set on its timer to come on and off a couple of times every day. I will see what happens with the screed over a week to see if any movement appears. I'd like to think that if it was going to move / fail it would do so over that time anyway.

 

[Rob_1]

Just an update on the floor screed. I have had the UFH on and off since yesterday. The floor now has shown hairline cracks all over it, seem to be in lines where joints of the insulation boards are below, but some run do run diagonally. They seem to have got a touch worse after cooling, though that could just be me seeing more of them the more i look! It does also seem to be de-laminating it from the insulation in places too.
I looked at the ditra product, it looks great. I spoke to them, but they advised it was only as good as the surface it was laid onto, makes sense.
So, i think i'm going to make the decision and have a busy weekend taking the screed and UFH wires back up.
I have tried a patch, it seems to come up and leave insulation surface resonably intact. What are the views on keeping the insulation down and re-laying wires and correct(!) screed over the top? Obviously all primed propoerly?
Thanks for any more advice.

 

[Ajax123]

Just an update on the floor screed. I have had the UFH on and off since yesterday. The floor now has shown hairline cracks all over it, seem to be in lines where joints of the insulation boards are below, but some run do run diagonally. They seem to have got a touch worse after cooling, though that could just be me seeing more of them the more i look! It does also seem to be de-laminating it from the insulation in places too.
I looked at the ditra product, it looks great. I spoke to them, but they advised it was only as good as the surface it was laid onto, makes sense.
So, i think i'm going to make the decision and have a busy weekend taking the screed and UFH wires back up.
I have tried a patch, it seems to come up and leave insulation surface resonably intact. What are the views on keeping the insulation down and re-laying wires and correct(!) screed over the top? Obviously all primed propoerly?
Thanks for any more advice.

Sadly despite trying to think of an alternative I think I have to agree. Bite the bullet, take it up and start again. You do need to make certain the insulation is stuck down solid. If you are getting cracks along the joints this suggest they were either not sealed (taped) or there is movement at the edges. Have you got any pics?