Mouldy smell coming from underneath bathtub

lobster01

I've recently bought and moved into a flat and I've noticed the bathroom sometimes has a mouldy/mildewy smell which has gotten worse recently (possibly due to the heat?). I've finally narrowed down the source of the smell and it seems to be coming from underneath the bathtub. Does anyone know possible causes, maybe a leak in the bath? The tub has a mirrored panel with a big gap on the bottom and I can feel/see wood behind the panel. The panel isn't removable otherwise I'd take a better look. I'm a FTB so a newbie at property maintenance - I'm not even sure what kind of tradesman I would need to fix this. Any help appreciated

Ebe_Scrooge

It's difficult to be sure, but the most likely explanation is that the sealant around where the top of the bath meets the wall has deteriorated, and has split or got holes in it. This will allow water to dribble down the walls and underneath the bath every time it gets splashed.

Simple to fix. Remove all the old sealant and replace it with fresh silicone sealant. Make sure you use one specifically designed for bathrooms, these will have a mould inhibitor in them. It won't cost much for a tube from Screwfix or B&Q or similar. It's not difficult to do. Make sure you remove all traces of the old sealant - peel off the worst of it, then use a very sharp chisel to gently scrape away the last bits. Preparation is everything - make sure you remove every last bit of the old stuff and make sure everything is perfectly clean. Give the top of the bath and the wall a good clean with meths to remove any grease, then use two parallel strips of masking tape to mark where the new sealant is going to go. Apply the sealant between the two strips of tape to get a nice neat edge, carefully remove the tape, leave it overnight to cure, job done.

It's best to fill the bath with water before you apply the new sealant, otherwise it'll sink slightly when you first fill it and pull the sealant away.

I'd be surprised if the side panel isn't removable, if you look carefully there will more than likely be some hidden screws somewhere. If you can remove it you can have a proper look and make sure it's not something more awkward like a leaking tap joint or waste pipe. You can also check the condition of the floor underneath. But if all else fails, it's cheap and easy enough to just replace the sealant, then hopefully the floor underneath will gradually dry out over the next couple of weeks.

lobster01

I took a look at the sealant and there were a lot of gaps at the shower end, so this is likely to be the issue. I've taped it all up for now and will get some sealant ASAP.

I was able to partially take off the bath panel and nothing looked mouldy, although I didn't have great visibility so will take off the entire panel sometime and check for leaks.

Thanks for the advice!

GDB2222

Leave the bath panel off completely for a while, until it is fully dried out.

Replacing the sealant is harder than you might expect. You might be better off getting someone really good in.

missile

Another issue, is the bath and wall need to be dry for sealant to stick. This can take several days / weeks - a real issue if you shower daily?

Ectophile

A little tip I got from someone who does bathrooms for a living...


Before applying the new sealant, fill the bath with water to a normal level. Cold water will do. Don't drain the water until the sealant has dried.


That's because a full bath always tends to pull away from the wall a little bit, under the weight of all the water.

frozen_wastes

If you can smell mould, then there definitely is mould and probably a lot of it.

I had a musty smell in my bedroom everytime I lifted the carpet. I couldn't quite figure about where it came from as both the carpet, underlay and floor smelt and looked fine. One day though I put my nose to the wall, and the insidious smell of mould was unmistakable.

One the other side of my wall was the shower. I regrouted and resealed it, only to realise that neither the grout or sealant was the trouble - what I had before was fine.

There was nothing for it but to cut open the plasterboard from the bedroom side and take a closer look.

The plasterboard against the tiles near the bottom was damp and stained brownish from what I could see, but at the bottom was 45cm of plywood - this is where the plasterboard was sandwiched between the tiles and the plywood. The back of the plywood was fine, but the top of the plywood edge had bits of black mould.

So the thing about mould is that you often need to get rid of the material that it's growing on. Mould killer spray is no good on any porous surface as the active ingredient does not soak into the surface (great for tiles and plastic, but not wood and plasterboard - surface mould can be killed but the roots are embedded in the substrate and it will come back!).

In my case I removed the tiles (hammer and chisel job) and revealed a very mouldy plasterboard beneath. I cut away the plasterboard and revealed an even blacker plywood underneath - it was soaking.

By this time the air was filled with must and spores - I anticipated this and had my dustmask on. Don't do this job without breathing protection!

I cut up and removed all the bad plasterboard and plywood. There's still a residual smell of mould, and luckily the leak didn't reach the floor. Now I need to get some pros in to reinstate the bottom row of tiles or reconstruct my shower enclosure.

My advice to you is that you need to do an an inspection job with anticipation of a demolition job soon after. The sealant won't fix the mould that's already present. There is trapped moisture somewhere behind your bath and it won't dry out in a hurry. Get the panel removed completely and have a good look at the wall behind the bath.

Top tip: The camera and torch on your phone is an excellent utility for looking into awkward spaces by the way.