Damp related issue (breathable indoor finish)

[AndyZ]

Hi

I'm Andy and this is my first post here. I've been lurking around this forum for the past 2-3 months as my wife and I were in a process of buying our first period property. I have to say that the wealth of knowledge here is impressive and already saved us from making some mistakes (chemical DPC comes to mind straight away
Couple of weeks ago we've completed on a purchase of approx 1780 cottage in Lakenheath, Suffolk. The place is in a perfectly livable condition but quite rough round the edges, so we are slowly tackling various bits that need doing (BTW the property is not listed and is not in a conservation area). Anyway, onto the issue I have. One of the corners of the dining room has a visible damp issue (as you can see in the photos). On that wall there is a large bricked up chimney breast, which had sort of built-in shelving on both sides and the thin mdf board, which was used as a backing, started rotting at the bottom. After getting the shelving out, I exposed the wall to see the extent of the issue. It's not damp to touch, but I want to prevent issues in the future. I removed the mdf and peeled off old wallpaper (which was painted over). Now here are my questions:

1. I would like to install some sort of shelving there (was thinking about reclaimed wood), but I'm not sure what to do with the walls, so the same thing doesn't happen again? If I just put wooden boards against the wall, then they will start rotting again... what sort of finish I can put on those walls, so they look nice (don't have to be smooth) but at the same time, the moisture can escape? The walls are made of chalk blocks, but covered with some hard, modern render.

2. As you can see in one of the photos, at the bottom of the chimney breast the render started crumbling and so did the bricks underneath.... should I be worried? How can I stop it from getting worse?

As a side note - the source of moisture is relatively high ground level (at or just above floor level), as the house is built on a slight slope. I'm planning to tackle that, but it involves smashing a lot of concrete, so this may need to wait until spring.

Many thanks for any advice

Andy

 

[noj]

As a side note - the source of moisture is relatively high ground level (at or just above floor level), as the house is built on a slight slope. I'm planning to tackle that, but it involves smashing a lot of concrete, so this may need to wait until spring.

I think you've answered your own question. Fix the source of the damp and the problem pretty much goes away. Replace blown render with lime, once it's dried out (a surprisingly long time), redecorate with a breathable finish - claypaint or similar, job done

But does the blocked off chimney have a vent? If not this could be contributing to the damp too.

Until you stop the damp coming in, don't even think about cosmetic finishes.

 

[malcolm]

That looks familiar. The mould is due to condensation which forms on the surface normally because the bricks are soaking wet so have no insulation value and are cold. Water gets in from outside and the cold attracts water from inside. It is the path for water getting in from the outside that would be most helpful to fix, though you can dry a bit to the inside with breathable plaster and paint.

Lowering ground levels ought to work. A few of us have dug trenches near the wall where ground levels were difficult to lower. Leaky drains can cause this sort of problem too.

The chimney looks odd. I would never be able to resist the temptation to see what is behind those modern cemented bricks to see if it looks any nicer and occupies less space.

 

[Pennyviz]

Not an expert at all, but would suggest walls need to dry before putting anything on top? this can take ages (6 months) so maybe hack off existing mortar to aid evaporation? I've used ecomortar on my walls as it doesn't take so long to cure to cure as lime and sticks to anything - this gives a rough finish which may be OK. On one wall a defiant plasterer has used limelite high impact finishing plaster which may or may not be breathable - it doesn't seem to contain the dreaded cement, but interested if anyone here can shed light as it has given a very smooth finish ......

Penny

 

[bennoa1]

Is the plaster lime or gypsum? I can see the pointing on the bricks under the plaster appears to be lime. If its gypsum you need to remove it otherwise it will trap moisture and the bricks will eventually turn to sand. If its lime remove the paint covering first (I can see its modern paint as the moisture is making it bubble up) and let it dry. I'd also be interested to see what is behind that modern brick and cement fireplace.

 

[AndyZ]

Thanks for all the suggestions

Stupid question first - how do I tell the difference between lime and gypsum plaster?
Once I know what this is:
If it's gypsum - hack it all off, leave it open to dry for a while and then finish with lime or ecomortar.
If it's lime - remove the loose bits and paint and patch it up with lime.
Did I get this right?

Regarding the high ground level - it's definitely on my to do list, but it involves breaking up concrete path first (which goes alongside the house but at least is sloping away from the house.. for the most part), and then digging... so it will take a while.

Regarding what behind the the bricks... I assume a fireplace similar to the one below, which is in my living room (in a fully working condition. The dining room is next to it, in an extension which as far as I'm aware was built shortly after the house, so c1800. There is no chimney stack on the roof and the whole thing has been unused for decades. I'm tempted to open it up, but I don't want to bite more than I can chew, so this will have to wait.

 

[bennoa1]

Lime is a white colour, gypsum is darker and is hard to break up. Lime fizzes in something but I can tell by looking now so never had to do it. A close up picture may help. Is this chimney stack shared between the 2 sides then?

 

[MatthewC]

Lime is a white colour, gypsum is darker and is hard to break up. Lime fizzes in something but I can tell by looking now so never had to do it.

Vinegar

As above, sort out the high ground as a priority! Forget decorating until it's dry.

 

[AndyZ]

Lime is a white colour, gypsum is darker and is hard to break up. Lime fizzes in something but I can tell by looking now so never had to do it. A close up picture may help. Is this chimney stack shared between the 2 sides then?

Thanks, I'll check tomorrow when I'm back home and take some close up pictures.
There are two separate chimneys. The unused one terminates at the roof height and it bricked up/tiled up as far as I'm aware.

 

[AndyZ]

Here are a couple of close up photos of the plaster.

 

[AndyZ]

After looking up close and testing with vinegar it appears that the plaster on the left side of the fireplace is lime, while on the right side is gypsum.
Ground level is actually around 2-3 inches below the floor level, with the exception of the left-hand side wall, where it is around 2 inches above the floor level. This should be much easier to rectify than I originally thought.
The plan is to:
- lower the ground level
- inside - hack off everything down to bare stone/brick
- replaster in lime

 

[Zebra]

Your Photo 6 above looks like a sand and cement internal render to me. As already mentioned, if you chip a bit off and drop it into a cup of vinegar, if it is lime it will fizz a bit. If it is cement or gypsum it will just sit there looking at you. But also, lime will be much much softer, whereas cement or gypsum will be hard.
Your plan sounds like a good one, as long as you're not hacking off any remaining original lime plaster, which might be a shame.

 

[AndyZ]

Yes, I'm planning to remove all loose/swollen/cracked stuff and then double check what the rest is made of, before removing it.

 

[Hazel7000]

I would also open up the chimney in that room. The natural ventilation from the chimney will help - lighting a fire in it will help too! Replastering with lime would be my suggestion also. After drying out.

 

[AndyZ]

Ok... slightly stupid question now - how do I know that the wall is dry and ready for re-plastering? It is completely dry to touch now - even the parts, which are damaged. Even that bottom left corner, where it's all black is also dry. I know that the previous owner lowered the ground level shortly before selling the property, so as it's dry now, is it possible, that these are just the results of dampness that was there before? Or in other words - how can I check if there is still an issue with damp or is it just the case of fixing the damage that was done before?

 

[Zebra]

Good question. My suggestion is rather unscientific, but if you have some lime plaster, and you stick some on, you would see the line of damp in it once it has gone off.

 

[noj]

Have to agree with the stripey one - and since lime is happy with a bit of moisture (and may well even carbonate faster if it's still passing out of the wall) I'd plaster it up and watch it dry - exciting stuff!

It will take a few months to fully dry out after plastering anyway - and in the heating season you may have a bigger problem of stopping the plaster from drying out too quickly

 

[AndyZ]

Thank you for the advice