Engineered floor on concrete base

[Redeye]

I've just bought some engineered oak flooring which I'm planning on putting in our kitchen and dining room on top of a concrete floor. Having just taken up the previous laminate/chipboard/DP/polystyrene floating floor combo which was down in the dining room i discovered a smallish area of mould on the chipboard near the back door. I think this is probably due to condensation rather than water ingress, although I have to admit I'm a bit confused about that bit.

Anyway, I've opted for the engineered rather than the solid wood option to hopefully help avoid/reduce potential warping problems but I still appear to have 2 potential options for laying this floor :

1. DP membrane and insulating layer (it gets mighty cold in our house in the winter), then glue the T&G boards together as a floating floor.
2. DP membrane and insulating layer, then screw battens down to the concrete floor and secret nail the boards on top. The main thing that puts me off this is the increase in the floor height as I guess I'll need battens at least 15mm thick?.

Does anyone have any experience of either of these methods, or advice either way?

 

[Andrew Bodenham]

Redeye,

Did something similar in my house recently.

As you have a concrete floor this presumably has a DPM incorporated in it, so it should be relatively dry. However, I agree that an additional layer of DPM will help to ensure that your wood floor stays dry and flat. As for insulation, it's difficult to get any meaningful insulating effect without a significant thickness of material. Maybe you have to compromise on that.
Some systems recommend gluing the flooring direct to the concrete, which I'm sure works well if you have a flat slab and can be sure about dryness. I wasn't convinced that would work in my case. In the end I used a combined 3mm foam/DPM underlay, followed by 12mm plywood screwed down, with my 10mm overlay oak strips on top, glued to the ply with PU and pinned through the tongues too. End result is very solid. Overall thickness of 22mm is just about OK for adjoining areas.

If your existing floor is pretty flat I'd be inclined to lay the woodwork as a floating floor, glued on all joints. Some sort of underlay would be needed to deaden the noise though, and this would give some insulation effect too.

Suspect your damp patch could be due to wind-blown rain getting under your door. It wouldn't need much to create good conditions for mould growth.

 

[Becka]

andrew, would that method work for a concrete floor without dpm? (I know it's lacking as in one area where the slab doesn't quite reach a rebuilt wall i can reach round the side of it (also what would you recommend to fill that gap?) and a plumber had to dig through it once and just found mud). I have no noticable damp other than the occassional musty smell when i move furniture thats been sat in the same place too long. I suspect any damp i get evaporates fairly harmlessly thru the hessian back carpet i currently have but i would really really like a wood floor as carpet+cats has not turned out to be a very good mix. I had a wood floor specialist round who got rather nervy about the whole thing and refused to even quote till i had one of the dreaded damp specialists round so i'm a bit stuck at the moment.

 

[Redeye]

Thanks Andrew.

I don't think there is a DPC in my house - building is from around 1790's, converted sometime 1920ish so it's unlikely. We have lots of condensation problems which look like damp problems which is why I'm more concerned about trying to reduce condensation near the wood which might cause mould problems.

After removing the old flooring the concrete base was a little bit damp but it's dried out very quickly. Condensation/dampness seems to be worst around the back door, although I sealed a big gap under there recently so I may already have solved that problem by accident.

 

[Big Dave]

Hi There
My advise, would be to lay a 300 micro meter thick sheet of visqueen on the floor over lapped 200mm and taped with a waterproof tape, directly over the concrete subfloor and lapping up the sides (to be trapped behind skirting boards if applicable), I would then use a floating system on a 2-3mm polyfoam insulation layer.
This way any latent moisture will remain in the fabric of the building and not find its way into the wood flooring.

Whilst on the subject of concrete floors the subfloor should have no more than a 3mm deviation under a 3m straight edge in any direction, if your floor doesn't meet that then you need to look at screeding with self levelling screed.

My reasons for avoiding the batten idea is that a 15mm engineered floor is not a structural flooring system and if the floor were to fail in anyway this method of installation may invalidate any warranty.

Just a few points on finishing detail, if the floor is part of a larger scope of works which include the removal or replacement of skirting boards I would do the floor before the skirting, leaving a much more proffessional appearence.
If however the skirting boards are to remain and a beading is to be used, please paint the beading to match the skirting and not to match the floor! Otherwise your floor looks like a baking tray! In addition for an older property I always find a quadrant moulding looks better than a scotia, its also usually half the price.

Hope this helps
Dave

 

[dze]

Just one tip, have the flooring stacked nice and flat in the room its going in for as long as possible before you lay it, this will let it aclimatise to the room temp and humidity thus making sure any movement or shrinkage happens before it goes down.

 

[Big Dave]

The only problem with allowing an engineered floor to acclimatise is that at this time of year humidity is at its highest therefore the boards will expand artificially more than the usual amount. Most engineered boards instructions point out that the boards should be kept in there packaging until installation.

Provided you allow sufficient expansion gap ALL around the perimeter then as the boards expand this gap will close and then as the floor contracts the gaps will open up again all out of sight under the moulding/skirting.

If the boards are allowed to 'acclimatise' then it is highly likely the boards will contract leaving unforseen gaps around the perimeter, also the fit of the boards may be afffected to such an extent that the floor is difficult to put together and may have slight gaps.

The process of acclimatisation is only suitable if the moisture content of a floor is higher than around 9% as most floors will stabalise between these amounts. Most proffessionally manufactured flooring is around 6% or less due to kiln and pressure drying methods. Reclaimed flooring on the other hand would benefit from acclimatisation.

If in any doubt follow the instructions supplied to the letter, the manufacturer has a lot more experience of his product than any of us.