How to seal between floorboard and bare wall over suspended timber floor

[Red2k]

We recently had a Ikea wardrobe fitted in an alcove next to a fireplace, with the gaps around it sealed so it had a built-in look. To make it as flush as possible, the skirting board at the back was taken out. A few weeks later while painting the room we noticed damp on the chimney breast next to the wardrobe, so took apart the infill between chimney breast and wardrobe to inspect the side wall of the chimney breast.

Looks like taking out the skirting at the back has left a gap between where the plaster ends and the carpet starts, leading to cold air coming up from the suspended timber floor and causing damp in the area that had been boxed in. The resulting damp has been so bad that the carpet fibers are coming off their backing in that boxed up area!

So I'm thinking I will have to pull out the wardrobe and seal the gap between the floorboard and the plaster, so the room is relatively air tight at that end. What is the best material to do this with? The carpeted area has building paper under the underlay stopping drafts, but this extends only to the gripper rods. What's the best way to seal this?

1) Caulk or Silicone sealant - only good if gap is up to quarter of an inch?
2) Expanding foam - any particular ones?
3) Plaster all the way to floorboards - will crack with movement?

Ideally would prefer to avoid anything that gives off noxious fumes as its in the bedroom.

Many thanks!

 

[foxhole]

Air under floor boards prevents damp it’s not a source .Doubt lack of skirting has anything to do with damp , on chimney breast usually lack of ventilation on capped chimney or leaks at roof/stack, poor flashing etc.

 

[chris1982]

is it on the ground floor or higher up?

 

[Red2k]

I should have been clearer in my description. The damp is only at the bottom of the chimney breast (on the ground floor) and only on one side of the chimney (I will get a photo up shortly). Its in a building with 4 more floors above. My thinking is that cold air coming up from below is meeting hot and humid air from inside the room, causing condensation in an unventilated enclosed space. The fix could be to ventilate the area continuously (which would mean an untidy finish) or seal the gap so that the temperature difference of any air coming up through the floorboard is not as stark. I have checked the ventilation bricks on the outside and they are not blocked.

I am secretly hoping that is correct and easy to fix and not a case of rising damp! If that was the case, I would have expected it to be on both sides?

 

[Red2k]

The right hand side is the wall of the chimney breast. It is covered in lining paper over plaster and painted. The lining paper was damp and hence came off in places when I was getting the wardrobe infill out.

 

[chris1982]

To test for condensation you could tape a piece of cling film tightly over the area that gets damp. If it is condensation, there should be water forming on top of it.
But I (DIYer)'d guess -given a similar problem I had in a previous house- that it is not, but that the wardrobe reduces the airflow that allowed the plaster that is wet (from the ground, the chimney, or hygroscopic salts that migrated from the chimney's soot) to dry out quickly and without you noticing it.

 

[Red2k]

So I have now pulled out the wardrobe and the carpet below is ruined with the damp. Pulled up the carpet and the underlay ...and the builder's paper between the underlay and floorboard was soaking wet in one spot...lifted that it pieces and so is the floorboard in that place

So looks like there is a water issue there, which might have been there for a while and just aggravated when the area was boxed in killing any ventilation. The skirting board and carpet seal probably kept it outside the room and hidden below the carpet.

Now need to figure out and fix whatever is making the floorboard wet... and potentially replace the floorboards. Who do I need to call for this? Builder or damp specialists?

 

[sircerebus666]

You need to lift those floorboards and have a mooch under them , can we see what's on the other side of that wall?

Any water pipes under the floorboards?

You are aware that this issue and your other issue on your chimney breast are more than likely going to be linked

 

[Red2k]

A

You need to lift those floorboards and have a mooch under them , can we see what's on the other side of that wall?

Any water pipes under the floorboards?

You are aware that this issue and your other issue on your chimney breast are more than likely going to be linked

Agree, its probably related. The other issue seems to be due to hygroscopic salts so might have been aggravated due to this issue rather than being directly related.

This corner of the flat is the furthest from the kitchen or bathroom, so could be radiator pipes under there. The other side of the wall is another flat and lifting up floorboards is pushing my DIY abilities. So I will need to call someone out at this point...question is if that is a plumber, builder or damp specialist?

 

[sircerebus666]

A


Agree, its probably related. The other issue seems to be due to hygroscopic salts so might have been aggravated due to this issue rather than being directly related.

This corner of the flat is the furthest from the kitchen or bathroom, so could be radiator pipes under there. The other side of the wall is another flat and lifting up floorboards is pushing my DIY abilities. So I will need to call someone out at this point...question is if that is a plumber, builder or damp specialist?

Could be water pipes feeding that flat , could be a leak from the chimney , could even be a leak in the other flat which has come through to yours

You need to have a chat with your neighbour and check their flat , remind me is your flat ground floor? First floor?

 

[JohnD]

The other issue seems to be due to hygroscopic salts

I bet you've got a leak.

 

[Red2k]

Could be water pipes feeding that flat , could be a leak from the chimney , could even be a leak in the other flat which has come through to yours

You need to have a chat with your neighbour and check their flat , remind me is your flat ground floor? First floor?

Its a ground floor flat and I've had a look on the other side of the wall facing the outside (and not the common wall) and there is an air brick there well above the ground and no blockages.

Could be water pipes feeding that flat , could be a leak from the chimney , could even be a leak in the other flat which has come through to yours

You need to have a chat with your neighbor and check their flat , remind me is your flat ground floor? First floor?

 

[tel765]

OP,
Can you post pics showing the outside of the wall at ground level?
And pics showing the whole wall with the chimney breast?
Strip the wallpaper off and pic the wall behind.
Is this (bedroom) wall the full length of your party wall from one elevation to another elevation or does your party wall continue in other rooms?

Is there a cellar below?
The skirting boards appear to have been fixed in recent years suggesting that previous damp work may have been done.
Walk your property and notice all air bricks.

You would do well to empty that room of furniture and completely lift all carpeting to expose bare boards.
Its most probable that floor boards have to be lifted and joists examined for rot.
Plaster hacked off, and skirtings removed.
Photo will show if the fireplace is blocked up but chimney flue will have to be swept & smoke tested after consulting with the flats above.

 

[sircerebus666]

Let me get this straight , is the chimney breast wall backing on to another flat?

Is so you must have a chat with your neighbours , either you or your neighbour has a leak , you need to get yourself a plumber , lift your floorboards and examine under your suspended floor

Fyi soaking wet floorboards is more than a condensation issue

 

[tel765]

With respect for your excellent posts but you dont need a plumber - simply getting a handyman in to cut and lift the boards will do for now.
The idea is to merely find out whats happening under the floor - and Plumbers in London can cost up to £100 to £150 per hour.
so only call in the cavalry when you know that you need them.