Am I in deep poo poo? Mould underside of chipboard in bathroom

[Joe Fixit]

Hi, renovating bathroom due to discovering leak in the bath. Thought I had cut out all the damp damaged flooring. But thought I would be thorough and use a endoscope to see what's on the underside and other side of the partition walls.

Wish I hadn't now!!!

If it still feels sturdy (hard scraped and did the screwdriver push test), is there any chance I can just clean it and see if it's good? Of course, I will still need to figure a way to do that. Theres a couple of areas around 300mmx100mm

 

[mattylad]

No, that needs removing and replacing.
While doing that you need to identify why/how it went mouldy.

 

[Joe Fixit]

No, that needs removing and replacing.
While doing that you need to identify why/how it went mouldy.

So it went mouldy as a result of a slow leak from the bath tub. Soaked thought he subfloor, hence I cut out all the damaged area and was hoping I could just lay new subfloor until I spotted this on the underside of the subfloor thats on the other side of the joists (next room).

I've tried a mkmo screwdriver test going from underneath and still seems sturdy. Is it worth spraying it with bleach solution first to see if it's just surface?

Really trying not to have to remove the whole boards as it would likely mean either taking up the whole floor of the hallway and bedroom next door (photo). Ceiling under is a horrible drippy artex which will be a pain to repair one bit. (Guessing would need to redo whole ceiling)

 

[Joe Fixit]

No, that needs removing and replacing.
While doing that you need to identify why/how it went mouldy.

So it went mouldy as a result of a slow leak from the bath tub. Soaked thought he subfloor, hence I cut out all the damaged area and was hoping I could just lay new subfloor until I spotted this on the underside of the subfloor thats on the other side of the joists (next room).

I've tried a small screwdriver test going from underneath and still seems sturdy. Is it worth spraying it with bleach solution first

 

[Joe Fixit]

So took some normal (not close up) photos of the area. Any thoughts on this please?

There seems to be two school of thoughts on this.

One says once chipboards wet, remove it. Better safe than sorry. The other says, worth spraying bleach solution to see if it's just on the surface. If it clears, it's ok as it's on between floors and unlikely to be direct exposed and disturbed

 

[freddiemercurystwin]

What floor finish are you putting down? But really you already knew the answer to your original question before you even posted it.

 

[Joe Fixit]

What floor finish are you putting down? But really you already knew the answer to your original question before you even posted it.

Within the bathroom (the area I've cut down) I'm putting ply and then backer - then porcelain tiles outside bathtub and looking at maybe just tanking under the bathtub area

 

[Ivor Windybottom]

I'd avoid bleach in the vicinity of those copper pipes, you might set some horrible chemical reaction going there. The alkalinity of concrete dissolves copper, bleach is very alkaline.

If the strength of the chipboard is still OK then it's probably OK to leave it as-is. Don't worry about the mould, it will basically go dormant if you don't kill it - it will just go to sleep waiting for the rain that (hopefully) never arrives.

Only you can judge really, but don't let the severity of the job of replacing it cloud your judgement. Decide whether it needs replacing without thinking about whether you want to do it!

 

[Joe Fixit]

I'd avoid bleach in the vicinity of those copper pipes, you might set some horrible chemical reaction going there. The alkalinity of concrete dissolves copper, bleach is very alkaline.

If the strength of the chipboard is still OK then it's probably OK to leave it as-is. Don't worry about the mould, it will basically go dormant if you don't kill it - it will just go to sleep waiting for the rain that (hopefully) never arrives.

Only you can judge really, but don't let the severity of the job of replacing it cloud your judgement. Decide whether it needs replacing without thinking about whether you want to do it!

Yes, I'm at a crossroad and torn between the two. I think I will at first cut out more of the floor joist so I can really fit my arm through and give it a good clean and test. Might even be able to dry it and then apply zinnser mould primer or something

 

[mattylad]

For the sake of a couple of sheets of chipboard, I cannot believe that your even asking this?

 

[Joe Fixit]

For the sake of a couple of sheets of chipboard, I cannot believe that your even asking this?

If it was just losing and replacing a couple of sheets of chipboard. I'd done it by now. But to get to it, I would need to lift up the flooring on the other room. Will likely damage at least one to two boards (which I don't have a direct replacement) and then cut out 18mm ply to get to the chipboard whilst dodging pipes which I can't see exactly where it goes (view I blocked by joists and battens from the otherwise)

 

[mattylad]

cut it to free it up, use a multitool etc.

Add support blocks if you lose access to a joist doing so.

Either way I would not put that back down, that stuff spreads.

 

[catlad]

Chip board and bathrooms don't belong together.

 

[mattylad]

Quite right, better to replace it all with T&G floorboards.