To de-tank or not?

[Gow87]

I've got the pleasure of living in an old Georgian terraced house - nothing grand, likely a row of old workers cottages no dpc, not even slate.

Over the years it's been gutted, cement floor installed, walls have had injected dpc, cement tanking half way and then gypsum over everything - all done in the 80s when seemingly we didn't know better.

Having talked to neighbours (all houses have had the same treatment), they've all got the same random damp spots appearing in nooks and crannies and we've had some particularly bad bits with one starting halfway up the wall. Trying to figure that one out led to be realizing the cement render stopped half way and water was creeping up to wherever it could get out. All of the skirting was also a little moldy in this area. Everywhere else, there was a tiny bit here and there.

Not deterred, we've decided to play guinea pig - I've hacked off all the cement and plaster and got back to brick on that wall but the brick has taken a beating as its old soft reds. The plan was to then finish that wall in lime or some modern equivalent that breathes and leave the rest of the seemingly damp free walls as they are. But I've just chased in some new wiring on a wall that's had the same treatment and the bricks behind feel damp. The odd chunk of cement has come off and from prior experience - that's probably just going to be where all the moisture now tries to get out.

I'm already financially strained by all this and our living room is bare floors and no furniture at the moment. It's a bit tortous.

So I've got two options:

1: re-tank the bit that fell off patch with a bit of gypsum and hope that the wall continues to remain damp free.

2: break out the hammer and bolster and remove all plaster and cement around the entire room and then re do with lime or lime-ish. (This sounds like hell).

Can any of you help me make up my mind? Pros and cons? Lived experience?

 

[malcolm]

I had a similar experience that might be worth a read. Seems fixed now after 2 years of drying out. https://www.periodproperty.co.uk/forum/threads/interior-damp-project.17860/

Tanking is nonsense - the idea that you can keep a wall dry by covering it with waterproof stuff boggles belief. If there is water getting in then it's only going to keep getting in until the water gets past the tanking and then you have damp coming out halfway up the wall. Fortunately there is rarely too much water getting in and breathable walls are plenty enough to let it out without causing problems. Breathable outside is best but inside is good too.

 

[larry]

We had the issue but on the other side of the wall. Knocking off the cement render was a fair bit of work but a good DIY project. Now have NHL based render on top and much happier.

If you can learn to plaster it's easy enough to mix your own NHL based plaster. The 'magic sponge' trick here (https://projectdingle.co.uk/the-magic-sponge-the-secret-to-internal-lime-plastering/) helped me a lot!! I found 'Breathaplasta' smooth for the top coat quite forgiving as a novice, and also a long plastering edge quite helpful. Cheaper to mix your own NHL + Plastering sand for the base coat though.

We've also added wood fibre insulation which has made a huge difference. And a much warmer room. Of course adds to costs. But it's easy to install.

 

[Gow87]

I had a similar experience that might be worth a read. Seems fixed now after 2 years of drying out. https://www.periodproperty.co.uk/forum/threads/interior-damp-project.17860/

Tanking is nonsense - the idea that you can keep a wall dry by covering it with waterproof stuff boggles belief. If there is water getting in then it's only going to keep getting in until the water gets past the tanking and then you have damp coming out halfway up the wall. Fortunately there is rarely too much water getting in and breathable walls are plenty enough to let it out without causing problems. Breathable outside is best but inside is good too.

Cheers - that certainly seems like a similar situation! So I see you did the inverse of tanking! How did you manage to blend the plasters? Isn't the lime finish rougher looking than the gypsum?

 

[Gow87]

We had the issue but on the other side of the wall. Knocking off the cement render was a fair bit of work but a good DIY project. Now have NHL based render on top and much happier.

If you can learn to plaster it's easy enough to mix your own NHL based plaster. The 'magic sponge' trick here (https://projectdingle.co.uk/the-magic-sponge-the-secret-to-internal-lime-plastering/) helped me a lot!! I found 'Breathaplasta' smooth for the top coat quite forgiving as a novice, and also a long plastering edge quite helpful. Cheaper to mix your own NHL + Plastering sand for the base coat though.

We've also added wood fibre insulation which has made a huge difference. And a much warmer room. Of course adds to costs. But it's easy to install.

What thickness insulation did you add? Was it just a case of screwing to the wall and then plaster over?

 

[lizziecupcakes]

hi @larry - I found your comment super helpful. I am thinking of using wood fibre boards for insulation. I am curious: did you use it on the ceilings too? Also, did you have building control approve this by any chance? I just don't know if my building control department have much knowledge of period properties and won't understand why I'm adding wood fibre boards and lime plaster to my 1906 Edwardian brick walls

 

[larry]

I stripped old gypsum back to original lime plaster and then made good gaps with NHL and sand.

I used 3x2 studs (treated CLS) with 40mm of flexible wood fibre insulation between. Steicoflex from eco merchant.
I then counter battened to add another 40mm. The counter battening reduces thermal bridging. I then put plasterboard on top (in one room) but in the last room I've done instead used 20mm rigid wood fibre (steicotherm) fixed with insulation washers.
Stainless steel screws throughout as they have (I read somewhere!) lower thermal emmisivity.

I then plastered it myself.

I did one room with the rigid wood fibre (steicotherm) at 80mm direct to the wall with ejot fixings. Also works well, but I quite like having studs available for fixing.

Take loads of pictures so you remember where everything is!

No you don't put wood fibre on the ceiling. If you wanted to do this rockwool is fine

Can't help you with building control... But you aren't using a completely out of whack product

Good luck with it

 

[lizziecupcakes]

Thanks @larry . Sounds exciting and a lot of work! I appreciate you writing out the materials you used!

Silly question, but can the lime plaster (after drying) and wood fibre boards handle kitchen and bathroom shelves being put up? After the plastering, I want to do the kitchen and bathroom, but I just don't know how "strong" the walls will be.

 

[paulc]

Silly question, but can the lime plaster (after drying) and wood fibre boards handle kitchen and bathroom shelves being put up? After the plastering, I want to do the kitchen and bathroom, but I just don't know how "strong" the walls will be.

Shelves fixed to just plaster/woodfibre might be OK for a few light trinkets. I wouldn't trust it for anything heavy though.
When I insulated some walls here, I used multiple layers of insulation with battens - Fixed vertical battens (2x1) to the walls, filling the space with insulation. A second layer of insulation added on top, and battens on the surface horizontally and screwed through to the first set of battens. The spaces between battens again being filled with more insulation. Where I knew I needed a solid surface for curtain rails, a 12" wide strip of 12mm ply got screwed to the battens. The ply will help to spread the load, and I don't need to worry about where battens might be.

 

[Flyfisher]

Silly question, but can the lime plaster (after drying) and wood fibre boards handle kitchen and bathroom shelves being put up? After the plastering, I want to do the kitchen and bathroom, but I just don't know how "strong" the walls will be.

There are no silly questions if you don't know the answer and asking them is how we all learn.

Plaster - any sort of plaster - is not really a structural material and has little strength. OK for hanging a (light) picture or ornaments but not to be trusted for anything substantial. Wood fibre board might be a bit stronger but still not to be trusted with anything heavy - I wouldn't anyway.

For a solid fixing, you need to get to the structure of the wall, be it brick or stud frame, and transfer the weight of whatever you're fixing into the load-bearing part of the wall. Also, bear in mind there are two type of 'load' you are dealing with. The downward weight of whatever you're hanging on the wall and the 'tear-out' force trying to pull out whatever fixing you use. Think of a shelf or cupboard fixed to a wall. It will weigh a certain amount, which will result in a downward force through the wall but there will also be an outward force trying to pull the fixings out of the wall. Imagine a wide shelf with a heavy object sitting on it but away from the wall. This will cause the shelf to act as a sort of lever to pull out the fixings.

Bottom line: You must make a solid fixing into the structure of the wall. If it has been insulated and plastered then you'll need a long fixing - a 2-inch screw is not going to hack it! And consider both the weight-bearing aspect as well as the 'pull-out' aspect of the fixing, depending on the nature of the item being fixed to the wall.

Fortunately, there are a wide range of suitable fixings readily available these days. If in doubt, use something stronger than you think necessary.

 

[Stevers]

The brackets for the currently fashionable floating shelves must exert a fairly significant tear out force, as apparently did the TV+TV bracket in my mother-in-law's room - fastened into an 2" of dried mud with a skim of original lime plaster (1879). That seemed perfectly OK until the TV (and bracket) hit the floor after a couple of months!

 

[larry]

Thanks @larry . Sounds exciting and a lot of work! I appreciate you writing out the materials you used!

Silly question, but can the lime plaster (after drying) and wood fibre boards handle kitchen and bathroom shelves being put up? After the plastering, I want to do the kitchen and bathroom, but I just don't know how "strong" the walls will be.

If you use flexi wood fibre then you need studs, so you fix to the studs. If you use rigid wood fibre there are some weird plugs which you can use that fix into the insulation but only v limited loads I imagine. All else needs to be fixed with long screws to the wall behind (creates a small thermal bridge)

 

[lizziecupcakes]

Thanks so much everyone.
I was really embarrassed to ask the question!
This is such a lovely forum