Damp Timber Joists within concrete floor - HELP

C

christian777

New Member
Lifted up the old laminate and found moisture underneath, mostly where the nails where within the floorboards.

Having got a damp proofing company round, they detected moisture within the floorboards and suggested the joists where the issue because they were in-between concrete and it was evident from the rusty nails. It looks like previously the potential suspended floor joists where filled with concrete now it looks like as per the picture (there not blocks)

Recommendation was to remove joists, fill with concrete, then self level and finally cover with liquid DPM

Question was - I was planning to remove some of the rotten joists and leave the ones which are intact, although prob do have moisture. Do I go with removing the joists or can I just put self leveling over the top? If the answer is remove them, what's the best and quickest way to do this? My main comcern is if i dont remove them will it comprimise the famp proofing in the future?20240929_170510.jpg
 
Hi there,
You've got a big task on there! Never known this too have been done before but not surprised there's damp/moisture in the floor joists from it. If a DPM had been laid first under the joists and then the concrete poured I'm sure that would have prevented a lot of what you're facing now.
What's the dimension of the floor area you're trying to tackle and how many joist's are involved?
Have the damp proofing company put forward any suggestions on how to remove the joists from the concrete at all?
I'm not trade just another old DIYer and being honest I don't see any easy means of removing the joists out of the concrete, they'll be held fast especially as they will have expanded due to being damp. Don't think leaving the joists in place is advisable even if some aren't as damp, they're likely to cause problems in the future if you apply a DPM over the lot and then you're back to where you are now all over again.
Only option I see is to rip the whole floor up, concrete and timber, and start afresh. Can't see an easy means of getting the joist's out but I'm not trade and others who are may have other idea's and better advise.
 
I would try a stock axe. They probably have different names in different parts of the country, but basically a pick axe with a tip about 50mm wide on each end aligned at 90deg to each other. Idel for rough work like this as you're relying on weigth rather than sharpness to do the cutting
 
Thanks for responses having ripped up all the floorboards. The joists seem pretty OK. I think most of the moisture came from the concrete when Initially pouring it in. I think I should be OK with a dehumidifier for couple days and another layer of dpm
 
I would get yourself a basic cheap damp meter/tester, (around a tenner on ebay) they'll give you some idea of what the actual moisture content of the joists are. At the moment the timber is open to the air circulating and the top surface will start to dry but could still be very moist deeper in the joists. There's only about 5cm on top of each joist that's exposed to the air, likely 50cm that is enclosed in concrete that can't breathe. At the moment you have no idea if the concrete is in direct contact with the ground below or not, likewise with joist's, If you apply a DPM over them and the concrete you'll lock in whatever damp/moisture is currently there and could end up with bigger problems further down the line. An mini inspection camera passed through a drilled hole would give you a better idea of what beneath the floor if you can get hold of one.
 
Thanks for the idea. I cleaned up the rotten joists and drilled a hole in one which was OK. Pic on the right u can see concrete and the other joist it had rubble. Also there only 5cm deep. Bit strange. Not feeling much moisture so I'm thinking the damp company had me worried for no reason. I think I should crack on?
 

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Ah right! So looks like they're arent really floor joists then, thats handy. Would think thayd laid 2in x 2in battens on top of the concrete so it's easy to fix wooden floor boards down on top.
I'd have them all up if they're all the same and clean up properly just in case there's any rot started and fill the channels with concrete. Very strange but I could see why it was done for relaying a timber floor down.
The damp company would have seen what we all saw and presume they're full joists they'd have had no idea what was beneath.
 
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