Gyproc under chipboard flooring - water damage

[Tomatoes]

I had a substantial leak in my 1st floor flat. I am doing the remedial work myself under insurance. After lifting some flooring I have discovered 2 layers of 12mm plasterboard under the chipboard which is saturated and has spread quite far including under partitions. Its turning into a nightmare! I was expecting to just replace the worst effected chipboard which wasn't that substantial.

All the partitions are built on this floor obviously. It's easy enough to cut it all out but it really has to come out from under the partitions as I can't see it drying out or having the same properties any more, it just crumbles. Just the chipboard and it would have been OK.

Will it be possible to remove it all from under the partition without taking that down?

No way I'm putting plasterboard back in. It was probably for a combination of sound and fire proofing. Will 2 layers of 22mm chipboard be OK?

 

[Deleted member 174758]

No way I'm putting plasterboard back in. It was probably for a combination of sound and fire proofing. Will 2 layers of 22mm chipboard be OK?

I doubt that you have any choice - two layers of PB are primarily a fire safety measure, but also add to sound proofing and heat insulation, so if that comes out, then that must go back. I would have thought your insurers would insist on it

As to two layers of 22mm chipboard - you'd be replacing a fire compartment wall by a flamable compartment wall which in the event of a fire downstairs would accelerate the progress of fire through the building, potentially killing or injuring occupants of your flat as well as speeding up the progress of the fire. So I am pretty sure you ARE under a legal obligation to replace the plasterboard, although yoj might be able to replace with something like cement fibreboard (more expensive, but waterproof). What do your deeds tell you?

 

[Tomatoes]

I doubt that you have any choice - two layers of PB are primarily a fire safety measure, but also add to sound proofing and heat insulation, so if that comes out, then that must go back. I would have thought your insurers would insist on it

As to two layers of 22mm chipboard - you'd be replacing a fire compartment wall by a flamable compartment wall which in the event of a fire downstairs would accelerate the progress of fire through the building, potentially killing or injuring occupants of your flat as well as speeding up the progress of the fire. So I am pretty sure you ARE under a legal obligation to replace the plasterboard, although yoj might be able to replace with something like cement fibreboard (more expensive, but waterproof). What do your deeds tell you?

The insurers have not specified anything. I had a large firm to quote for the job before I decided to do it myself and all they were expecting was chipboard...

 

[Deleted member 174758]

That can't be right. Did they lift the floor and find the PB? The whole point of installing fireproof boarding beneath floors is safety.

 

[Tomatoes]

That can't be right. Did they lift the floor and find the PB? The whole point of installing fireproof boarding beneath floors is safety.

They didn't lift up any of the floor to quote. I agree a cement board would be best.

I don't know if it will be possible to remove it all from under the partitions and then be able to get 3 layers back underneath? Even in smallish sections at a time. It might be a demolition job which is more than I can take on myself

 

[Deleted member 174758]

I've installed cement board on a few conversions - very heavy, dusty to cut, but very waterproof. A downside, though, is the price.

Beneath the partition walls it may be necessary to chop it out a bit at a time and slide in strips of PB. The sheets abutting the bases of the walls can be supported on something like 2 x 2in (44 x 44mm) CLS screwed to the sides of the joists. Remember that to meet fire regs all the joints and gaps to masonry walls should be caulked with fire mastic (messy stuff to use). Just finished doing a job on a school where I had to restore a fire compartment integrity following a wall being tanked and that was the messiest bit of the job

 

[Tomatoes]

I've installed cement board on a few conversions - very heavy, dusty to cut, but very waterproof. A downside, though, is the price.

Beneath the partition walls it may be necessary to chop it out a bit at a time and slide in strips of PB. The sheets abutting the bases of the walls can be supported on something like 2 x 2in (44 x 44mm) CLS screwed to the sides of the joists. Remember that to meet fire regs all the joints and gaps to masonry walls should be caulked with fire mastic (messy stuff to use). Just finished doing a job on a school where I had to restore a fire compartment integrity following a wall being tanked and that was the messiest bit of the job

PB would be easier to use and I can do other things to try to stop anything like this happening again.

Doesn't the PB need to have as few joints as possible to retain its fire rating? I can't see how I'll be able to slide it under the partition, mostly the last layer of chipboard. Won't it be too tight?

 

[Deleted member 174758]

PB would be easier to use and I can do other things to try to stop anything like this happening again.

If the flooring is chipboard use a P5 grade tongue and groove type (moisture resistant) and glue the joints with D4 adhesive.

Doesn't the PB need to have as few joints as possible to retain its fire rating?

Ideally yes, but realistically you aren't going to be able to slide a sheet beneath the wall, if only because the sole plate fixings will get in the way. That's where the (intumescent) fire mastic is used to deal with small gaps, if any

I can't see how I'll be able to slide it under the partition, mostly the last layer of chipboard. Won't it be too tight?

I'd say that's a job where you need a long pry bar (say 36 to 48in, or longer - I'd use an even longer Burke bar for this sort of job, but at £120 to £160 a pop for a 60 to 72in bar that's maybe asking a lot) to lift the wall up a couple of mlimetres whilst you chop the old stuff out and put new stuff in. It's a 2 man job. You may need to fix somd 2 x 2in (44 x 44mm) stuff to the sides of joists to act as supports (but they will carry your board ends subsequently as well)

 

[Tomatoes]

PB would be easier to use and I can do other things to try to stop anything like this happening again.

Doesn't the PB need to have as few joints as possible to retain its fire rating? I can't see how I'll be able to slide it under the partition, mostly the last layer of chipboard. Won't it be too tight?

If the flooring is chipboard use a P5 grade tongue and groove type (moisture resistant) and glue the joints with D4 adhesive.

Ideally yes, but realistically you aren't going to be able to slide a sheet beneath the wall, if only because the sole plate fixings will get in the way. That's where the (intumescent) fire mastic is used to deal with small gaps, if any

I'd say that's a job where you need a long pry bar (say 36 to 48in, or longer - I'd use an even longer Burke bar for this sort of job, but at £120 to £160 a pop for a 60 to 72in bar that's maybe asking a lot) to lift the wall up a couple of mlimetres whilst you chop the old stuff out and put new stuff in. It's a 2 man job. You may need to fix somd 2 x 2in (44 x 44mm) stuff to the sides of joists to act as supports (but they will carry your board ends subsequently as well)

OK can you come and help?!
I think I'm going to start the claim again and get someone in to do it.

Thanks for your advice

 

[Deleted member 174758]

If it weren't for the plasterboard it would be a straight forward job. That plasterboard really makes it a lot more work. I was assuming worst case scenario where most of a 10ft wall was adfected, but just how bad is the plasterboard beneath the walls? If it can be dried out or it's only a couple of feet which is affected the job is still DIY doable IMHO

 

[Tomatoes]

If it weren't for the plasterboard it would be a straight forward job. That plasterboard really makes it a lot more work. But just how bad is the plasterboard beneath the walls? If it can be dried out or it's only a few feet which is affected the job is still DIY doable IMHO

The plaster board I have removed just breaks off in handfuls so I assume it is the same under the walls, I can see and feel where the damage ends. I have thought about what I could get away with leaving but I can't see the plasterboard ever recovering to what it was before and would take ages to dry out especially once the floor is back on top. It would be a disservice to the structure of the future of the flat? But then again I'm sure there are areas in these flats where some of this plasterboard is compromised in the same way and nobody knows

 

[Deleted member 174758]

Cut back to the edge of the wall, dry out the edges with a fan heater. Plasterboard is friable at the best of times and any gaps can be filled with intumescent fire stopping. If it really is bad you may need to reaplace it, but if it is only a 3 to 4 foot bad section you could repair it. At least it is worth trying before you get into a big financial outlay.

The main function of the PB (as a fire break) is to slow the progress of smoke and fire between different fire cells (in your building each flat is a fire cell). It does its' work long after anyone in the building has either been evacuated or perished. Intumescent stopping expands when the temperature exceeds 125 degrees C and is generally rated as non-slumping up to about a gap of 30 to 35mm (different manufacturers quote different figures). That's wjy we caulk gaps

 

[Tomatoes]

Cut back to the edge of the wall, dry out the edges with a fan heater. Plasterboard is friable at the best of times and any gaps can be filled with intumescent fire stopping. If it really is bad you may need to reaplace it, but if it is only a 3 to 4 foot bad section you could repair it. At least it is worth trying before you get into a big financial outlay.

The main function of the PB (as a fire break) is to slow the progress of smoke and fire between different fire cells (in your building each flat is a fire cell). It does its' work long after anyone in the building has either been evacuated or perished. Intumescent stopping expands when the temperature exceeds 125 degrees C and is generally rated as non-slumping up to about a gap of 30 to 35mm (different manufacturers quote different figures). That's wjy we caulk gaps

If I take the bath out and remove the flooring under that there would be maybe 2ft x 6ft areas strips on either side of the bathroom that are still saturated. The partion with the door in I could manage to work with. Would leaving those 2 relatively small areas be OK?