Engineered wood flooring underlay

29 Jul 2006
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United Kingdom
What underlay would you recommend to go under an 21mm oak engineered wood floor as a vapour barrier and with some acoustic qualities. Floor to be floated over an anhydrite screed with wet underfloor heating.
Regards JD
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In this case fully bonding with flexible adhesive would be best - to avoid air-gaps. Most manufacturers of 21mm engineered board recommend that too.
For more information see here
Thanks "woodyoulike"for your comment however the glueing down of the wood floor does contradict much of the research carried out so far ESPECIALLY on anhydrite screeds which is what we`ve got. I have a leaning towards Heatflow from Duralay but because of its extremely high cost am researching further first. Am also not sure if it acts as a vapour barrier as well.
From the research and test results on "our" Duoplank (by TNO):
"If you install a wood-engineered floor on a under floor heated sub floor, there are some conditions you should respect:

- Tubes should be located minimal 3cm below the surface of the screed.
- The screed must dry naturally to below 1,8% moisture content (anhydrite: 0,3%). Do not turn the under-floor heating on before the correct moisture level is achieved

- A PU-based adhesive, such as Sika T54, Mapei P990 or similar, should be used, and will act as both adhesive and moisture barrier, and thermal conductor."

As for price comparison: Heathflow per sq m £ 5.73 ex VAT, Mapei P990 (tub of 15 kg, usage 1 kg per sq m) £ 5.73 ex VAT
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I`m afraid I find your reference to "our" Duoplank slightly confusing. The implication is that you actually manufacture the product?
(The reason for the stability and durability of DuoPlank® is its unique structure. A 15mm water resistant plywood lower layer together with a 5.9 mm solid hardwood layer ensures a stable durable product. DuoPlank®)
As to research I can quote numerous international manufacturers ( See Nybron-Europes market leader-i.e. Karhs-see and other advisers who have no problem with "floating" floors over a screed containing underfloor heating and as a cabinet maker of some years experience I am well aware of the "living" problems of wood. My flooring has been directly sourced from a major European MANUFACTURER ( not chinese) selling internationally and consists of 15mm Russian ply (10 cross bonded layers) with a 6mm Oak (North European so slow grown) wear layer.
Whilst I recognise that it is very acceptable to "glue" direct to the screed and indeed have been in discussion with both Mapei and Ardex technical I have come to the conclusion that with advice from for example Uponor the underfloor heating supplier that as the problem of movement and my own concern regarding acoustics needs to be addressed a vapour barrier and low tog rated (thermal conductivity) underlay is my preference. I would finally add that 40 years in the building trade has taught me that I should take ALL the advice and knowlege that is available on a subject BUT finish with my own council especially if I am unable to locate a local "expert".

There`s a trick in every trade except stone masonery and thats ALL chiseling!!!
Can understand your confusion about "our" ;) The Duoplank manufacturer is based in our home town, so "close to home" which kind of makes us say our. And it is "engineered" the same way as your boards, with 11 layers of ply. TNO is a large Dutch organisation renowned for its rigorous testing for all types of products for all types of industries, even for NASA (and these tests don't come cheap!)

My quoted report was just to show you that there is sufficient data on problem free glueing of the boards on anhydrite underfloor - as long as you make sure it's dry enough - not to implement you can ONLY glue down wood-engineered boards when there is UFH concerned. If you want to install it floating using heathflow, fine with us. Price wise it hardly makes a difference as I also showed you.

We have excellent experiences with both methods, only most manufacturers still recommend fully bonding of the boards when there is UFH involved and I'm sure you know that not following recommendation of the manufacturer can render your guarantee on the product useless. You don't need 40 years of building trade experience to know this, it's common sense.

You can of course do as you wish, however pure logic should tell you that 21 mm wood plus loose-lay plus underlay is going to reduce your heat output.

You should tell whoever is calculating the system so that they can adjust pipe spacing to take this into account

Would be interested to know what your research has turned up that speaks against glueing on anhydride screeds.

the glueing down of the wood floor does contradict much of the research carried out so far ESPECIALLY on anhydrite screeds which is what we`ve got
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The thread to which this reply applies is now a couple of years old - but I am now seeking a solution to my problem of engineered wood on an anhydrite screed.

I have a large area to lay 150 m2) - so I have to get it right! My screed is anhydrite with water-fed underfloor heating fed from an air source heat pump - which means that there are more pipes but at a lower temperature. I have one 'L' - shaped room and one company has stated that engineered wood should always be bonded where 'L' shapes are encountered.

I'd like to include some sound-deadening and a dpm has been advise. The screed will need priming, followed by a dpm then sound insulation. Obviously I want good heat transfer - so what's the right / best solution?

Ideas / experiences welcome.

Thanks, Tallboyrip
Not sure about DPM on anhydrite with UFH to be honest.

Think your best solution would be Elastilon Lock - both sides of the underlayment have a self-adhesive layer, bonding the underlayment to the underfloor (preventing air-gaps) and the wood-engineered floor to the underlayment - giving you sound-insulation and a fully bonded floor.
Thanks for the reply WoodYouLike. That looks like a good idea. Do you know if it available in the UK? (I see it is an American or Canadian product.)

However, since it will be put down by our builders (who will have no doubt, been walking over our building site) I have visions of it picking up a lot of debris before the wood is in place - a is often the difficulty with all double-sided products!
It is an original Dutch product :D and available in the UK

As for installation of any wooden floor with any method: should be the last task!
I am puzzled by various questions/matters in this post.

Since you are having a new flooor poured, why would you want the DPM over the screed rather than under it ?

Having said that, the screed will be poured onto a plastic sheet anyway. Although the purpose is to stop the screed running away when it is in its liquid state, it will perform the function of a DPM afterwards, although you would have to ask for it to be left long enough to join into the walls or whatever. Might be best though to ask for a DPM thickness sheet to be used, otherwise might be thinner.

If you want the best heat transfer, then glue to the screed and forget the intermediate layers. The few mm of "sound-deadening_ will be completely ineffective except for lightening your wallet.

If you want to check this out, go to the building forum and search on sound insulation/noise problems and similar and see what people have to do to reduce noise, especially foot-fall impact noise.
You are right mointainwalker, there is a dpm under the screed and this is taken up the wall a bit and into it. The technical consultant from the flooring manufacturer (Tarkett) has told me that their engineered flooring should always have a moisture barrier between the floor & the screed - to make sure that any residual moisture in the screed doesn't get into the floor. A retired floor installer I know has told me the same. He advises to take the moisture barrier up a couple of inches as well.

I wouldn't want to compromise the heat transfer by excessive sound deadening - there are normally only two of us in the house. I'll do as you suggest and look at the Building Forum.
The technical consultant from the flooring manufacturer (Tarkett) has told me that their engineered flooring should always have a moisture barrier between the floor & the screed

That's puzzling. The Tarkett web-site says that their laminate wood EPOQUE can either float or be glued but does tell you to talk to the supplier. Haven't heard anything about that on this forum either and the standard advice is always to glue engineered-wood for most efficient heat-transfer.

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