Fittin engineered wood flooring over concrete

Have chosen engineered wood flooring to fit over my UFH. As I understand it I have 3 (or maybe 4) choices of how to fit, and am interested in views on benefits/drawbacks of each.

1) Glue direct to concrete screed.

2) Fix (nail) to battens fitted into concrete.

3) Fix (nail) to joists, fitted periodically within concrete screed (perhaps every metre).

4) Leave floating (on top of underlay).

In some ways, 4 seems like the best on the basis that

- it's easier

- as and when there's any shrinkage I can simply push the boards together again. However, I worry a bit about how bouncy it might be.

By the way, should I avoid engineered flooring using pine underneath the "veneer", and prefer plywood - I've seen reports that plywood is a better material to be using as there's less shrinkage (the main reason for using engineered).

Thanks, Piers

Reply to
Piers Finlayson
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I floated mine, and it seemed a good approach. But then mine was designed solely for floated installation, so I didn't have much choice anyway.

Benefits:

1) You'll lay on a foam underlay which a) may (should ideally) contain a DPM layer which is belt and braces; b) allow a bit for any imperfections in the flatness of the concrete.

2) Is easier;

3) Can be lifted for repair (unlikely but at least you have the option), assuming dry fit click-lok type

4) If your subfloor is not insulated, lob 12mm marmox down first and screw that to the screed with stainless screws. For a very small loss of height,

12mm makes a huge improvement when you have a freezing cold slab underneath.

As for the foam, I used Tredaire (sp?) Boardwalk. Pretty decent stuff.

Cheers

Tim

Reply to
Tim Watts

You seem to be overlooking the fact that this flooring will have UFH under it - although the OP doesn't say whether it's wet or electric.

Either way, the foam slab needs to go *under* the heating system so that the heat can rise but not go into the ground.

If the floor doesn't need to float - which most engineered wood floors I've come across *do* - gluing it to the screed with a suitable adhesive for use over UFH would be the best bet.

Reply to
Roger Mills

4 is the most common way, and its unlikely to bounce unless the floor is very uneven. 2 is the way to go if the floor is very unlevel and needs flattening. If the boards are glued together, they won't pull apart.

Ply or MDF are the most common because the substrate is seasonally stable.

Reply to
John Rumm

This is what I have had done, as I don't like bouncy wooden floors - I'm

16 stone, so floating floors tend to depress quite a bit when I walk on them, I suspect the effect is less noticeable to lighter people. Before gluing the boards, my concrete floor was painted with a thick coating of epoxy sealant, mitigation against any current or future problem with the DPM, but since you have UFH this is probably not necessary.

Underlay will surely insulate you from the UFH - unless perhaps there is underlay specifically designed for this usage.

Yes, ply will be much more stable in the long term.

Reply to
pcb1962

Thanks all. As the screed hasn't gone down yet, I'll make sure it gets done very well (level) and probably leave floating, at least initially, ensuring there's no bouncing.

Another question. At one end of the room I'll be having a wood burning stove. (More for aethetics than to usefully heat.) I will be setting a stone hearth directly onto the concrete on which to sit this stove. What's the best way to terminate the wood floor against this hearth? I don't really want to leave a gap and then beading, cos I think it looks crap. But, presumably I can't just butt up against the hearth because then the floor might expand and warp. Is allowing the woodd floor to slide under the front of the hearth sensible?

Thanks, Piers

Reply to
Piers Finlayson

L-shaped infill strip that drops in the gap and has a thin bevelled piece the covers the gap and overlaps the wood by about 10mm. Glue lightly to the hearth edge so the wood and slide underneath it and maintain the expansion gap.

Reply to
Tim Watts

What I did was simply leave a small gap. If its engineering the expansion is low - so probably a couple of mm is enough to stop it bowing upwards. Or you can use a cork edge strip. Or you can glue beading to the hearth for a sliding fit over the floor Or use a flexible mastic caulk..

Reply to
The Natural Philosopher

If the hearth's tall enough to allow it I'd say yes - put a small lip in the leading edge and let the wood floor slide under it. As TNP says, it's likely only a matter of a couple of mm.

cheers

Jules

Reply to
Jules Richardson

It's typically 5-10mm depending on the dimensions of the room, based on the data sheet I followed (Kahrs). For most average to smaller rooms, 5mm all round is a sensible number.

Reply to
Tim Watts

The instructions for these types of flooring always annoy me - specifying fixed gaps without taking any account of the actual room dimensions! How difficult would it be to say "leave n mm gap for each metre of room length"?

Reply to
John Rumm

When I was talking to different contractors about getting a tongue-in-groove wood floor installed over chipboard, some of them claimed it was necessary to leave up to 10mm gap at the walls. This made no sense to me, since the floor was to be glued down. In the event, the installer I chose laid the wood so it butted snugly up against the walls. That was a couple of years ago, and there is no sign of any problem - no apparent movement. This doesn't surprise me, since I know the adhesive used is very strong.

Reply to
Gib Bogle

I got away with less than 5mm over a 15 meter wide room (Kahrs)

The material itself makes a reasonable amount of compression before it buckles.

Its worst in summer, when air is not heated and humidity is as high as outside: In winter with UFH the floor gets very dry indeed. If laying about now leave 5mm gap and relieve in summer ONLY if you experience issues.

Reply to
The Natural Philosopher

Also it expands more across the board than along it, sligthly.

BUT the joints will also allow some movement laterally.

I'd allow 1mm per meter myself give or take.

Its not possible to say how humid your room might get in summer, either.

Reply to
The Natural Philosopher

Yes. I laid floating and all that happened with no gap was the floor got a bit hollow - buckled up SLIGHTLY - at one point. Standing on it made it go back down. Glue would have held it no problems

Its the same principle as long welded rails with no expansion joints: Provided its laid with heavy concrete sleepers that wont allow buckling, it just goes into compression when it expands, so to speak.

Reply to
The Natural Philosopher

Hmm, maybe it's more for the engineered stuff. Ours are all 3/4"-high oak (1-1/2" wide strips) and the longest span (but that's along the grain, not across) is somewhere around 50 feet - my gut feeling is that the expansion really isn't much at all, though. (maybe I should measure it, but of course that's a long term project :-)

If the hearth is tall enough I think it'd be possible to take 7mm (say) out of it for the gap, anyway. (Do the boards, when delivered, come with a guarantee that they've have been stored such that they're close to their smallest size? Otherwise I don't see how anyone can engineer the expansion gaps to the right size - it'd be a bugger to lay it with a 5mm gap all around, only to find that the gap opens to 10mm because the boards were delivered at their biggest size!)

cheers

Jules

Reply to
Jules Richardson

No - it's entirely dependent on temperature and humidity.

I think that quoted gaps are "worst case". I've not noticed much variation with mine where I can still see the cut edge by a door (sans architrave).

I guarantee if they were fitted wedged tight in, then you'd have a problem (as TMH IIRC can attest to - I recall he had to fix one such case for someone).

However, if you leave 5mm all round, unless the room is massive, you'd be pretty safe.

Reply to
Tim Watts

It's a big room - 11m long (in the direction I'm worrying about here), so I do need to leave a gap.

Reply to
Piers Finlayson

Even a tiny small stove will kick out over a kW of heat. In a normal sized, insulated room, that is more than enough...

One assumes that the stone will be bedded on some mortar? Arrange the thickness of that to allow the flooring to slip under the stone.

Reply to
Dave Liquorice

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