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Mystery Damp Issue Around Fire Place and Surrounding Walls

Postby jollyjohnny » Sun Jun 21, 2015 4:13 pm

HI everybody, can you help me please, it's a real mystery what's going on with our 'damp' problem that thus far, it's left 6 tradesmen and a building engineer with ice packs on their heads.

It started off with there being no DPM installed when the fireplaces and hearths were replaced by the previous owners. The concrete bed on one was crumbling which led to further investigation to discover both beds were wet through and damp was being drawn to the breast, walls and in one, the floorboards. We've dug them out, hacked off the plaster and let it dry naturally.

However, on one the floorboards won't dry. We've removed all nails and put a DPM along the joist and it's continually wet, I've been underneath to see if the boards are in contact with anything that would allow moisture to travel - nothing is in direct contact - they've been left for 5 weeks, boards to the side have been removed to help airflow, the damp doesn't travel, it's static.

Applying heat, they change colour as if to be drying, only for when the heat is turned off, an hour later they're sodden again - but there is no water source, nothing acting as a wick and to cap it all, it's only the boards in front of the hearth that was. Nobody thus far can explain it, we've checked airflows, they're OK, we are well and truly confused and running out of ideas. I know I could chop them and put moisture board in (which will eventually happen) but before we do, I'd like a solution and cure, not a short term fix. I've attached a few photos of the job and any sensible help and advice is more than welcome.
Since this was took, the boards to both sides have been lifted and a DPM was slid under the length of the joist - if anything, the DPM made it worse...
This was before it was all dug out showing the level of damp and how the concrete bed simply crumbled.
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Postby welsh brickie » Mon Jun 22, 2015 7:21 pm

by the pictures, I would say there is not enough airflow getting around the base of the breasting, the floor needs to be clear from any obstruction to allow air to circulate.
Also with that much moisture, there has to be a cracked drain or pipe causing that amount of damp, so I would have that checked
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Postby Perry525 » Fri Jun 26, 2015 2:45 pm

All wood is hygroscopic, it absorbes water vapour from the air.
I note that all the floor boards are concave, indicating that they are colder and wetter underneath and drier on top. I suspect that the wood is also colder than the room in general. This is causing the water vapour in the room to condense into the ends of the boards. The molecules of water are very tiny, so small that they can easily move inside the grain of the wood.
Check the boards with a damp meter, this will confirm their water content.
Check the room with a hygrometer, preferably one with a memory that will indicate the high and low room humidity over 24 hours.
It is hard to imagine that the wood can be below dew point at some point during 24 hours, at this time of year, but it has been quite cold overnight recently (not at all like summer)
You need to find the water source, perhaps damp walls, whatever.
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