Damp walls behind tiles

[Smarty Pants]

Hi all,

First time posting on here so be gentle with me!

I have just started a DIY renovation of my bathroom in preparation for selling the house. the bathroom is relatively small, about 2.5m x 2.5m, is on the ground floor in a modern extension on the back of a Victorian house. My first job was to remove the ceramic wall tiles (it was completely tiled floor to ceiling on all four walls). I found that some of the tiles were coming away worryingly easily, and that the plaster to the back (external) wall was soaking wet - so wet in fact that I could dig it out with my fingers like mud. This wall doesn't have the bath along it so there is no internal water source, so I guess the source must be external. I think the wall is single skin brick.

Having checked the exterior of the back wall, the bottom 2 or 3 courses are painted with black bitumen that is old and peeling off. From reading through these forums it seems that most people don't believe in rising damp any more so I guess there is a problem with rain splash from the patio (which goes right up to the wall) penetrating. What (I think) is making the problem worse is that the patio is pretty much level with the internal floor level. Another possibility is rain dripping down along the exterior wall from a window sill, but as the damp is worst at the bottom I guess not.

So - I want to know what to do next! I'm hoping that with the tiles removed, the plaster will start to slowly dry out (I guess the ceramic tiles were sealing in the damp). I am encouraging this with gentle heating but from what I read a dehumidifier is more effective so I might try one of those. Do I have to hack off the plaster to get the wall properly dry through the brick? Should I repaint the bitumen to the outside to prevent more damp entering the wall, or will that just trap in the damp and make things worse? And once the damp is rectified could I re-tile this wall (this could hide the problem for selling purposes...but of course that would be unethical if it will cause future problems) or just paint so that the wall can breath better? Is there anything else I can treat the inside of the wall with to help the problem but still allowing the wall to breath?

Any help much appreciated!

 

[Burnerman]

Bizarre that a 'modern' extension is just a single brick leaf.......anyway, surely there is a DPC in the lower brick course somewhere? That's essential to prevent rising damp and without it you'll have continuous problems. It might be possible to render the outside brickwork (which stops at DPC level with a slope to cast water clear.) You also need to avoid rainwater splash where at all possible.
Can you tell us what the floor is like? There could be some treatments from the Permagard range of products which could help.
John

 

[Smarty Pants]

Hi John,

Thanks for getting back to me. I think you may be right, I checked the thickness of the back wall and it's about 25cm so I guess it must be more than single brick. When I say 'modern' - I actually have no idea when the extension was built, other than obviously after the rest of the house (1899).

I have checked and there is no sign of a DPC membrane sticking out of the mortar between courses. I'm not entirely surprised as all of the work done on my house before I bought it seems to be bodged. There are no signs of drill holes for a chemical DPC either. Do you think a chemical DPC would help, and are the DIY kits any good? I keep on reading that 'rising damp is a myth' and the chemical treatments are a waste of money.

The rendering sounds sensible but also sounds like a a big / expensive job, and if the lack of DPC is the issue then it might not be the cure I guess anyway?

The floor in the extension is solid concrete (that's caused a number of issues with damp to other parts of the house...as it's blocking off air flow beneath the timber floor in the original parts of the house...) with ceramic floor tiles in the bathroom.

I just Googled Permagard, it certainly looks like some of their stuff could help...any products in particular, given the above info?

Cheers,

Adrian

 

[Burnerman]

For sure, if you don't have a DPC then I've no idea how successful the outcome will be.
Rising damp is certainly not a myth - if it was, then properties wouldn't have one. Its vital that there is a DPC around every internal and external wall, and that includes any sleeper walls that support suspended floors.
Injected DPC's certainly have their place - these days a cream is injected into pre drilled holes in the wall, and then the cream is injected. Theoretically the cream spreads through all porous surfaces and gives a barrier to rising wet. In ideal circumstances - i.e no breaks in the cream application - its about as good as it gets. personally I have only used it in random rubble stone construction and it seemed to work well there.
I have used two Permagard products - both on floors. One was the DPC paint (effectively a vinyl membrane, it seemed to me.) This was to prevent rising vapour more than anything and it worked perfectly. The other was an epoxy membrane (more expensive by a mile) and this was to prevent visible damp. Again, it was a success.
So - in your difficult situation, I'd suggest injecting a DPC, treating the internal walls with a tanking membrane (another Permagard product if I remember) and then a floor treatment. As for the outside, avoiding rain splash is essential, and probably a render on the outside. Guttering where applicable must be working to prevent any water coursing down the wall.
When the concrete floor was laid, provision should have been made for the underfloor ventilation, in the form of ducting etc.
So - I'm sorry for sounding like an angel of doom here but that wall must be in one hell of a state and significant works are needed to make it inhabitable - or rebuilt!
Lets see if anyone else comes along with some comments, but there's some food for thought.
Regards
John

 

[Smarty Pants]

Thanks for all the useful advice John. I will definitely go for an injection DPC and an internal tanking product. Is it necessary to remove the internal plaster and replace with a different non-gypsum type? I assume the tanking membrane goes underneath any new plaster? There are no visible signs of salt crystals.

I'll also take a look at the guttering, although I don't think that is to blame as the wall seems bone-dry at the top. Keeping the area clear of debris and repainting the bitumen / masonry paint should help the rain splash once the wall is dry (not easy once it's raining). I'll make some enquiries about the render although ideally I am trying to avoid getting the pros in due to cost.

Cheers, Adrian

 

[Smarty Pants]

One other thing...do you think it's possible for condensation to enter into the wall through the grout between the ceramic tiles? It is a cold exterior back wall in a warm, humid bathroom so condensation would be obvious...but I had assumed it would not have been able to get into the wall through the tilework.

 

[Burnerman]

I think the internal plaster should go.....if its been drenched then its no use anyway. My own thoughts would be to thoroughly tank the inside of the wall and then fix up some timber laths that you could get some insulation in between (30mm minimum thickness) and then plasterboard on top of that if you're happy that things aren't still damp.
I can't see so much dampness coming through tile or tile grout (on a wall anyway - different if it was the floor of a wet room.)
How about running our thoughts by a builder?
John

 

[theprinceofdarkness]

Tanking the inside is problematic. If you batten the wall, put insulation then a VCl then plaster board. Any water vapour that gets through this lot will soak into the wall and will then evaporate out through it. If you tank the inside of the wall and water vapour that gets through/past your VCL, will end up as drops of water on the tanking and run down to the floor as they cannot evaporate away. That Permaguard looks interesting I'll be phoning them tomorrow, about applying it to non dry surfaces. Like you , it'll take 6 months to dry your wall out (1" per month).
One thing I am curious about,what is in the loft above the bathroom? because Ii was wondering if its water dripping from your roof that's the real problem. There are 10,000,000 Victorian houses in this country with solid 9" walls and the vast majority of them don't suffer with this problem.
Frank

 

[Smarty Pants]

Hi Frank,

Re: the loft - the bathroom is in a single storey extension, above it there is a tiled pitched roof with a small loft cavity which is well insulated. I had assumed the damp wasn't coming in from the roof, as the wall is wet at the bottom only and completely dry elsewhere. I have had problems in the past in the original part of the house with water coming in from the roof, and the damp manifested itself as wet patches on the walls.

Adrian

 

[theprinceofdarkness]

That's good, looks like rain penetration from the outside then. Its just that I have never seen condensation or rising damp at such a high level. We'll have to see if Permaguard lives up to its hype as I have tried Thompsons (does what it says on the tin?) and B&Q silicone.
Frank

 

[Smarty Pants]

The damp only goes up to about 2 ft from ground level - is that unusually high?