Laying Engineered wood on wet ufh

[meadowhog]

I have a nice dry cement sand screed which I want to fit an engineered click wood floor to. The screed as expected has slight undulations of 2-3mm and in some areas I have used self levelling compound to bring it all fairly level. I doubt that using SLC over the whole floor will get it any better than it is.

I have ordered the flooring but Im now not sure which way to fix it down. I am leaning towards glue but the floor supplier has recommended underlay as I could have debonding and lifting especially with ufh. My issue with underlay is in some areas there will be no direct contact with the screed which effects heat transfer and will have hollows.

I would like to know what the ideal final screed finish should be before laying and what system to use.

I can find below, which should do the job, but can anyone recommend either:
GLUE: Laybond L16; Rewmar Polymer; SikkensT5; Sika T54 and Mapei P990

Underlay: Tuplex; Quicktherm; Accubond and X Protack

 

[mointainwalker]

I contacted Laybond about their L16 and a technical representative was very circumspect and kept pushing their flexible glue ( L19 ?) which is much more expensive.

After some lengthy conversation he said that , although their web-site says L16 is ok for wet UFH, he felt there was a risk that the bond could be too strong/rigid and the engineered-wood could be torn apart during full heat-up/close-down cycles.

Underlay/air gaps will certainly diminish the efficiency of your system.

 

[meadowhog]

Thanks L19 is the way with Laybond.

After speaking to the suppliers again, they admitted they have learnt something. After digging around in their technical data they find that the Timbertech they were advising me to go with is not suitable for ufh and that glue should be used. I questioned it because it had high insulation properties. Their technical man then said they dont sell glue but recommended F.Ball, which Ive heard of and held in good regard.

So back to gluing. I'm sure the underlays are good but I dont see how they can work unless the floor is perfectly flat. Anhydrite screeds should be OK but not sand/cement even with latex.

Now to find the best glue that will also act as levelling agent for the small amount uneveness on the screed.

 

[aires69uk]

What is the difference between L16 and L19?

 

[tall_tone]

Laybond L16 is a solvent based rigid adhesive. Laybond L19 is an MS Polymer Silaine adhesive which has flexibility.

The L19 will in general stick to non-porous surfaces, has no nasty products in it and will allow the wood some movement particularly with UFH

L16 is based on Acetone which is a highly flammable solvent and has flammable and hazard labels all over the tin.

 

[aires69uk]

Laybond L16 is a solvent based rigid adhesive. Laybond L19 is an MS Polymer Silaine adhesive which has flexibility.

The L19 will in general stick to non-porous surfaces, has no nasty products in it and will allow the wood some movement particularly with UFH

L16 is based on Acetone which is a highly flammable solvent and has flammable and hazard labels all over the tin.

I have been led to believe that L16 itself is flexible, is this not the case?

 

[tall_tone]

Link to their front page to read for yourself
http://www.bostik.co.uk/construction/group/Professional-Flooring/1/Wood-Flooring-Adhesives/6

To quote their description "Heavy duty rigid adhesive for surface bonding wood flooring"

 

[mointainwalker]

Who led you to believe that , aires ? It isn't.

he said that , although their web-site says L16 is ok for wet UFH, he felt there was a risk that the bond could be too strong/rigid

 

[tall_tone]

Hi Mountainwalker
Aires only picked this topic up a few days ago. The original conversations were over a year ago.

But you are right "Flexible" adhesives have only been around for 10 years or slightly more, under floor heating has been around considerably longer.

If installed correctly and never run over 26 degrees "Rigid" adhesive is no problem with UFH

 

[mointainwalker]

Morning TT

Yes I noticed but since he doesn't have UFH it doesn't really matter to him anyway.

However since there is all this weirdness with doing a humidity test on a screed of unknown thickness after just four days and then no DPM, I think that will be the least of his problems.