Damp and efflorescence inside bathroom

TrixA

We're having a problem with damp in the downstairs bathroom of our new house (Victorian end terrace). The room is at the back of the house beyond the kitchen, with external walls on three sides and a solid cement floor.

The paint on the inside of the external facing walls is bubbling off in patches and there is a white crusty deposit forming underneath - online research suggests this is likely something called efflorescence which is supposedly due to penetrating damp. We tried stripping the affected section back to the plaster and repainting but the problem immediately reoccurred.

The bathroom also has some issues with condensation which we are attempting to rectify, but from what I've read it seems like this particular problem is not likely to be related to condensation, is that right?

We've looked at getting an independent damp expert round to help diagnose the problem, but have been quoted £600+ so not keen to go down that route until any obvious possibilities have been eliminated.

Any thoughts?

WestonDave

I'd be willing to bet that its a single skin brick construction (a lot of these back bathrooms were) and that is why you are getting both penetrating damp and condensation (which is due to the cold wall surface).


If it is single skin construction you can try to treat the symptoms but in reality its going to keep recurring. I'd be tempted to dry line the walls (insulation then plasterboard over) so that you have both a warmer room and a barrier to the moisture. There is a product called Marmox which is a solid insulation board which can be plastered straight over. Its more expensive than traditional dry lining but because it avoids the need to plasterboard over the top you cut down the lost space.

TrixA

WestonDave wrote: »

I'd be willing to bet that its a single skin brick construction (a lot of these back bathrooms were) and that is why you are getting both penetrating damp and condensation (which is due to the cold wall surface).

If it is single skin construction you can try to treat the symptoms but in reality its going to keep recurring. I'd be tempted to dry line the walls (insulation then plasterboard over) so that you have both a warmer room and a barrier to the moisture. There is a product called Marmox which is a solid insulation board which can be plastered straight over. Its more expensive than traditional dry lining but because it avoids the need to plasterboard over the top you cut down the lost space.

Thanks for your advice, it's really helpful. I don't know if the wall is single skin (does that mean only one brick thick?) but you're right that it gets really cold and that's what seems to be causing the condensation. Can you give me an idea of how big a job what you'd describing would be i.e. how many days would the bathroom be out of action for? Would it mean totally redoing the whole bathroom?

dampdaveski

Trix,
there's only one person I know of that charges £600 for a survey and if it's who I think it is, he'll tell you that all damproofers are w##kers, strip the plaster, redo it in lime mortar and paint the walls with a traditional breathable paint! you might get the paint to stick but you'll still end up with what you have now, and that is a bloody fridge!
As WestonDave has said, if you can insulate the walls either using the product he has mentioned or a closed cell polyurethane based thermal board (plasterboard with insulation bonded to the back).

To do a good job you would need to remove the bathroom suite so you can get all the walls done. Don't forget to install a decent extractor fan too.
Subject to your builder and the size of the room you might lose your bathroom for up to a week, though i'm sure they would be able to keep the toilet in place

you do need to make sure that the external pointing is sound and that there are no roof or gutter leaks, this should be your first job.
If you do need to repoint externally I would suggest that you use a hydraulic lime mortar. If it takes a lot of driving rain then you should also consider an external sealer such as Safeguards Stormdry

good luck
DD

TrixA

Thanks for all the info. We had two people quote for a survey and they were both £600+, we are in london so I guess that's why. There was a third company that was cheaper but I wasn't satisfied they were truly independent.

In 3-5 years we're planning to extend the house further and move the bathroom in the process so I was hoping to find a solution that wouldn't involve overhauling the whole bathroom.

SG27

Try academy remedial surveyors. Cost £225 a couple of years ago and they were good. I'm sure they cover London. Try googling them.

WestonDave

Without seeing the bathroom its hard to advise on partial solutions. If you were talking long term then obviously dismantling it all, insulating it and then putting it back is the answer. In your case I can understand you wanting a less intrusive solution. It depends a bit on the nature of the bath etc that you have in the room. One thing to look at is whether you could add say 10mm of Marmox and a layer of cheap tiles over the current wall surface within the rims etc of the bath whilst in situ. Different bath shapes have differing rim depths - one we had in a previous house had a 2cm rim on it which would easily cope with what I'm suggesting - the one we've inherited here is much less so wouldn't work. That solution would block out the efflorescence and give some insulation. Another alternative is to use the waterproof panels that are sold for showers - these are fairly thin so wouldn't give much insulation but would still cover over the mess. It would only be a short term solution as they'd probably rot from the back but for a couple of years would probably avoid you having to paint it every month!.

TrixA

When you walk into the bathroom the bath is on your left, washbasin straight ahead and toilet on the right. It's a small room and the bath takes up the full depth, with only a small rim surrounding it - the bath surround touches the wall on three sides. The area surrounding the bath is fully tiled and there don't seem to be any problems there. The problem with damp/efflorescence relates to the rear-facing section of wall to the right of the basin, and the right hand wall next to the toilet.