Moisture in floorboards around screw heads?

CaptainJack88 · 23 Jul 2019

We recently have part of our garage decked out and converted into a room.

On top of the concrete floor was laid 50mm solid foil backed insulation followed by T&G floorboards with bitumen in between each layer.

There must have been some slightly deflections in the original floor, as in places when you walk over the flooring now, there is slight movement leading to a noise that sounds like when you walk over a plastic floor with wet feet.

Holes were then drilled through the floorboards into the concrete, and concrete screws inserted to just tighten the floor enough to remove the noise.

We've noticed though that these screws now have a very slight damp area around the head of the screw. Does anyone know what this could be from? Condensation build up on the cold head near the wood (it has been recently skimmed)? Moisture/condensation draw from the concrete?

Any suggestions on what to do here? We were going to lay a 6mm subfloor on top of the floorboards with LVT on it, but obviously don't want to trap any moisture in the wood.

John D v2.0 · 23 Jul 2019

No one has replied so I'll have a go...

If there was no dpm in the original well , veventilated flooring then covering it could result in the original floor becoming pretty much saturated due to no more evaporation. This does mean that any imperfections in the new dpm would cause a big problem like this.
Condensation you could check by checking the humidity, but it doesn't sound likely.

^woody^ · 23 Jul 2019

Damp from the screw holes in to the floor slab. This will rot the chipboard, so you need to deal with it not cover it.

CaptainJack88 · 23 Jul 2019

^woody^ said:
Damp from the screw holes in to the floor slab. This will rot the chipboard, so you need to deal with it not cover it.

Yup.. Only thing I can think of is to remove the screws and seal the hole with some form of waterproof filler. Not sure how that's going to get round holding the board down though, or any moisture issues below the insulation..

John D v2.0 · 23 Jul 2019

It's fine to trap moisture below the dpm as everything below it is supposed to be not damaged by water. Just make sure the dpm is continuous so that water can't soak through around it. If your dpc is not sufficient then it may have been relying on drying out as quickly as it gets wet, this is often described as the new floor forcing the water up the walls.

CaptainJack88 · 23 Jul 2019

Can anyone offer a solution that doesn't involve ripping the floor up? I can't see how I'd have broken the DPM under the concrete. I've got 50mm insulation and 25mm floorboards, should be 150mm concrete and I only had a 100mm drill bit and didn't go in all the way

big-all · 23 Jul 2019

try placing a rubber mat over some screw heads a bit off carpet over some more this will give some thermal insulation and may give you an idea off how bad it will continue to be
also cover an area with plastic i expect this will be by far the worst as no thermal insulation and no evaporation
also keep in mind the very hot weather may skew the results

^woody^ · 23 Jul 2019

Have you had a proper conversion, inspected by building control and all that?

CaptainJack88 · 23 Jul 2019

^woody^ said:
Have you had a proper conversion, inspected by building control and all that?

Yup, previous owners had already done it and Bovis had signed it off as was missing when we bought the house

^woody^ · 23 Jul 2019

Evostance said:
Bovis had signed it off

CaptainJack88 · 23 Jul 2019

^woody^ said:

Yeah exactly haha. I've already redone the walls properly because they fell down..

^woody^ · 23 Jul 2019

To start with you need to lift a board and see whats going on. There may be interstitial condensation going on, or there may be damp coming up through the slab, or both.

Standard detailing would be to lay a polythene DPM on the slab first, then the insulation and then the flooring.The boards should not need to be screwed down, but will just rest on the insualtion and wont move as long as the joints are glued.

CaptainJack88 · 23 Jul 2019

^woody^ said:
To start with you need to lift a board and see whats going on. There may be interstitial condensation going on, or there may be damp coming up through the slab, or both.

Standard detailing would be to lay a polythene DPM on the slab first, then the insulation and then the flooring.The boards should not need to be screwed down, but will just rest on the insualtion and wont move as long as the joints are glued.

The boards aren't moving about the room, there just seems to be a bit of play in them horizontally as I guess something isn't perfectly flat under it. As you walk on them, the compression of the floor makes them creak/crunch

CaptainJack88 · 24 Jul 2019

There was "damp" around the screw heads again this morning, however after removing one of the screws, I think its quite clear that this is condensation. The dust on the screw was bone dry, however the screw was very cold and the top of the screw head was slightly damp.

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Moisture in floorboards around screw heads?

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