Repair damp floating floor in kitchen

12 Nov 2016
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United Kingdom
Two slow leaks have led to a saturated chipboard subfloor in our kitchen extension, as well as destroying the engineered wood floor. We noticed water leaking out through the walls at the DPC.

Construction of the floor is
Concrete slab
Thin blue membrane, visqueen
Thick black membrane, DPM? Turned up at the edges, and taken right up wall on the sink side
50mm celotex, foil covered
22mm chipboard, glued tg joints
Thin polystyrene ball plastic sandwich layer
Engineered floor.
The floor extends under the kitchen cabinets. Kitchen is galley layout.

The walls are
Plastic membrane
Wood studs, fibreglass between.

The plasterboard had been set down into the concrete and although the membrane is between the two, damp had wicked up the board. It has not fallen apart and appears to be OK. I believe a gap ought to be left between the concrete and the plasterboard to prevent such wicking.

So far I have removed the floor down to DPC in accessible areas and from under one side's cabinets, the wet side. I have left the insulation and chipboard under the drier side, with the cut being approximately where the kickboard will sit. I have folded back the DPC and visqueen where accessible to allow the slab to dry, allow it doesn't seem wet and there is no condensation underneath where it remains in place.
The chipboard is sodden, and between the DPC and insulation there is a small amount of water trapped. I'm running a dehumidifier 24/7.

I have also cut a gap in the plasterboard approx 100mm from the floor, but cannot access all the plasterboard due to the cabinets, and because the DPC is taken up the wall on the sink side of the kitchen. I hope not to remove the cabinets. I have removed their bases to help take the flooring out.

My questions are,
1. Can I leave the insulation and chipboard in situ under the cabinets on one side? This would result in a butt joint between the old and new chipboard floor, which concerns me. It means the floating floor would but be continuous.

2. Should I cut the DPC which is running up the wall on the sink side to countertop level, to allow me to cut my plasterboard gap? Is it serving a purpose or required? To what length would you go to create this gap in inaccessible areas?

3. The horizontal foot piece of the studwork has been damp. I think it cannot be removed without redoing the walls which I'd like to avoid. Is there a treatment I can apply to stabilise and prevent further rot?

4. Can I safely reuse the insulation where it is in reasonable condition?
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Why not post photos and a brief few sentences of what the issue is?
Thanks for the reply. Here are some pictures.

Gap i have cut in the plasterboard which was set into concrete slab. Is a continuous gap essential around the extension? It will be covered by the skirting. I feel some drafts coming through, any thoughts on sealing the gap prior to flooring?

Insulation and chipboard under cabinets. Should this be removed to allow a continuous span of flooring across the extension or can I butt new floorng against it and fill any gaps. Removal would also allow me to cut the plasterboard gap, although it will still be difficult as it's under cabinets.


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So, you have a solid floor with a membrane on top,
and insulation on top of the membrane, (the membrane flops up the walls?)
with chipboard on top of the insulation?

Water is trapped between the DPC (or do you mean the DPM /membrane?) & the insulation? IOW's the moisture is sitting on the floor between the membrane and the insulation?
What do you mean by water leaking through the walls?

Are the walls dot and dabbed?
Neither plasterboard nor plaster should have contact with the slab. A 30mm to 50mm gap is adequate.
When was the slab poured or is there a screed on top of the slab?

The sodden (& perhaps crumbling) chipboard under the cabinets can be removed and the engineered flooring can run just behind the plinths.
Doubtful that you could adequately cut and clean out the p/b behind the cabs, so just leave it.

Sand & cement can be used to fill any gaps.
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Water seeped out the exterior walls at the DPC, which is approximately at the interior slab level. It may have seeped through overlapped joints in the DPM which were not taped. We think the upturned DPM formed a pool which filled with water and then leaked out at the end which did not have this upturn.

Not sure when the slab was poured, or how thick it is, there's no exposed edge and it predates us. The plasterboard is screwed to the studwork.

What would you do with the bottom timbers of the studwork? Treat with a preservative/stabiliser?

Would you replace with more chipboard or t&g plywood?

We'll probably go for a click vinyl tile rather than engineered wood which is not great in a kitchen.
Have you stopped the water coming in ?

Btw - We've got marine ply on top of the chipboard with Karndean in our kitchen ... highly recommended
Yes the leak is stopped, although a cupful of water leaked out of the front of the washing machine today.
Realistically the proper way would be to remove the cabinets so that you have an fully accessible floor. Leaving damp chipboard and insulation under the cabinets will likely result in moisture being held and future problems building up.

Any membranes should be left in position if they are undamaged.

Depending on how long the leak went undetected, the sole plate may be OK if it allowed to dry out fully.

Don't reuse any material which has been saturated
Yes I know, but we're happy with the cabinets and countertops and probably not going to be in the house that long so loathe to take then out.

I'm resolved to get the insulation and board out so no water is trapped as you suggest though. It will be a pain to get the new floor in with the cabinets in place though.
Why would it "be a pain to get the new floor in with the cabinets in place"? I suggested how to run the Eng floor to just behind the plinths on Sat.
You've still not explained where you think the water originally came from?
Sorry, I mean pain to get the subfloor in place under cabinets.

Leaks at the washing machine connection and stopcock gland.
I'm being thick here but how are you planning to get the insulation and chipboard out and leave the base units in place?
Perseverance and a good deal of cursing.

A combination of removing the floor of the unit and or raising the units on either side to take the weight off the legs. This allows me to cut the chipboard joint and pull it out. Then I replace the legs on wood blocks.

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