DIY Doctor

Damp and Rotting Floorboard Problem Under Floor

Postby Richy88 » Sun Apr 05, 2020 11:41 am

Hi people, I have had a damp problem in a corner of my house for as long as I have lived here.
Last year I cut some of the floorboards out and investigated. Everything was sodden underneath, it was raining at the time and I could see water slowly running down the brickwork that forms the foundation (such as it is). Some of the timbers were rotten so I got some new ones in and replaced the damp course which was ruined, some of the timbers had actually been touching the brickwork. Outside there was a small area of concrete that had a back fall towards the house so I broke that out hoping that was the main culprit. I cut a piece of 18mm ply for the hole with a view to investigating later to see If the problem was solved.
I took that ply up today to find that it was still very damp under the floor (new ply covered in mould and new screws badly rusted after a few months) I thought the air brick on the outside must be blocked, couldn't tell so I cut it out. It was an air brick inserted into a gap in a 9" wall with nowhere for the air to go, words fail me.
Does anyone know of an air brick solution for a 9" wall (no cavity) that is telescopic, as the ground level outside is the same as the floor level inside.
Also I am considering painting just the outside of the brickwork with auqaproof to stop the water seeping through, what are your thoughts on that? Some people swear by the stuff but some people think it causes more problems than it solves.
Thanks for reading this, sorry it's so long winded, thats what happens when you’re forced to take several weeks off.
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Richy88
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Postby stoneyboy » Sun Apr 05, 2020 10:18 pm

Hi richy88,
Suggest you start by sorting out ventilation of the underfloor area - plastic telescopic air ducts are available.
The wet area under the floor will take ages to dry but you should ensure that the ground level outside is 150mm lower than the floor level inside unless you are going to tank the outside. The easiest solution would be to dig a channel along the outer wall.
Regards S.
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Postby Richy88 » Mon Apr 06, 2020 8:05 am

Thanks for the reply Stoneboy. I’m guessing I can’t just build a plastic duct into the wall and will need to use concrete lintels?
Definitely going to have to tank the outside of the wall, no way I can drop the ground level. Would aqua proof do for that and would it need to extend above ground level?
Richy88
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Postby stoneyboy » Mon Apr 06, 2020 9:41 pm

Hi richy88,
Use terracotta air bricks outside - no need for lintel.
You could use plastic duct but you need to bear in mind the duct acting as a water channel.
You could use aquaproof above ground level but this will not stop damp entering below ground level. This is why I suggest you form a narrow channel along the outer wall.
Regards S.
stoneyboy
Rank: Project Manager
Posts: 3853
Joined: Wed Dec 10, 2008 6:44 pm


Postby Richy88 » Wed Apr 08, 2020 9:32 am

I understood what you meant about digging a channel to tank the outside of the wall, but should the tanking extend above ground level at all, as well as below it?
Think I might have to get a bricklayer in to fit the vents, it feels like something I could make a real mess of.
Richy88
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Postby stoneyboy » Wed Apr 08, 2020 8:42 pm

Hi richy88,
Rain will splash up a wall when it hits the ground. Since you have solid walls it's better to keep the 150mm of wall above ground level, as dry as possible.
Regards S.
stoneyboy
Rank: Project Manager
Posts: 3853
Joined: Wed Dec 10, 2008 6:44 pm



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