Wooden floor finish where damp exists

[deross]

I have severely rotten sprung wooden floors because of damp under my house. To tackle this we've decided to:

Increase ventilation by cleaning old air vents and adding additional ones
Remove strategic underfloor bricks in central passageway wall to encourage air flow in 'dead air' corners
Fit PVC sheeting to all subfloors
Lay new SA Pine wood in worst area and monitor over the winter months before sanding and treating

My question is how best to treat the floors to make them least susceptible to rotting again? Some advise sealing the underside of the boards with several layers of thick varnish, others say seal surface only with an oil product. I've found whatever one person suggests, another will say that it's the worst thing I could do.

Right now I'm thinking 3 layers of water resistant polyurethane to the surface of floorboards and monitor to ensure that ventilation under the floor is working. I don't want to spend unnecessary money, but I do want the solution to be once and for all. I've been through this once before and followed the incorrect advice that time.

Any further advice about the laying/securing of the PVC sheeting?

Any advice would be most welcome.

Many thanks

 

[mac391]

The only thing that sounds like a good idea here is to add more airbricks for ventilation.

When you say, remove strategic bricks, have you just taken the odd one out or removed a whole section and is it a structural or dwarf wall ?

I wouldn't attach pvc to anything it will just make the timber sweat and matters much worse!!

You need to remove all rotten floor boards, wallplate and joists. Replace joists with either "pressure treated" or "treated timber" or treat them yourself with preservative.
Wrap the ends of new joists with 4" dpc, you can use clout nails to fix it before fitting.

New pine flooring should be treated both sides with wood preserver only. Do Not use polyurethane, varnish or any oil based products !!

Done this way, there is no need to monitor so long as ventilation is working well.

 

[JohnD]

I see you are in South Africa. Conditions are not the same as we have here. Do you have concrete oversite or raft? does it have a DPM? is it damp? what sort of wood-eating insects do you get?

 

[mac391]

Well spotted johnD !!! how did i miss that lol..

 

[deross]

Thanks guys for your input.

Now I find myself completely out of my depth. I'm a non-DIY female who does not understand everything that you've said (very little, in fact), but I'll discuss it with the man who is going to add the ventilation and lay the new floor (he won't be doing the treatment of the floor so has left that decision to me) and get clarity.

No-one has mentioned using wood preserver before, just the finishes I mentioned. Would that allow a decent finish - these floors will not be covered over with carpets and need to look good?

As far as the PVC sheeting goes, I believe that he will lay this on the ground surface about 18 inches to 2 foot below the floorboards - is that how you understood it? I'm concerned now about your warnings against doing this as it seemed like a sensible thing to do.

I'll be back with answers to your questions..........

 

[mac391]

Hi deross

I misunderstood about laying the pvc (visqueen it's called here) on the actual sub-floor. I thought you were going to pin it to the underside of the floorboards but laying it under the boards on the floor is fine.

If you use a water based preserver you can cover it with varnish or oil but personally i would just treat the underneath of the boards and not the top. I know you've had conflicting advice on this butcommon sense tells you if moisture is rising then treat the surface it effects !!

Good luck

 

[JohnD]

the joists under the floor are even more prone to rot than the floorboards

if rot is found, then as well as curing the damp and ventilation problem, we cut out and replace all rotten items, and treat the new and existing with wood preserver. The spirit-based ones penetrate far better than the water-based ones. You can paint, oil or stain over Cuprinol Clear, perhaps there is an equivalent product over there.

if you look under the floorboards, do you see concrete, or bare earth, or what? does it smell or feel damp?

if the void is well-ventilated, from all sides so there is a crossflow, you should be able to feel a draught if you put your hand down there.

verify there is no plumbing or rainwater leak making it damp.