Is this old damp proofing?

Just taken wallpaper off a house built about 1905. There is damp, probably rising in some of the house but not this room.

Is the grey plaster up to about a metre off the floor special waterproof plaster from damp-proofing? I can't see any injection holes but guess they might be under this layer.

I want to put insulated plasterboard in the alcove. I know it's not like insulating the whole room but it's solid brick walls so gets cold (ripped up floor to insulate that too). Would there be any problems with interstitial damp or anything? I would probably just attach it with foam, that has worked ok before.





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Grey paint over lime plaster? Used to have a dado rail as I can see the fixing holes.
If the paint is a modern acrylic emulsion (vinyl Matt) will stop the lime plaster breathing and cause damp.
Damp sponge the emulsion as older paint or breathable paint will wash off

Wayners said:

Grey paint over lime plaster? Used to have a dado rail as I can see the fixing holes.
If the paint is a modern acrylic emulsion (vinyl Matt) will stop the lime plaster breathing and cause damp.
Damp sponge the emulsion as older paint or breathable paint will wash off

Click to expand...

Think grey stuff is a different type of plaster, it's not multi-finish or the old original (probably lime) stuff. There was a dado rail yes, an old one, looks like they replastered up to it? But also about the height they do damp-proof render I think.

Could be Limelite plaster..

Chris, As above, Its a specialist Damp Proofing plaster such as Limelite - one of the oldest remedial "plasters".
That flooring carcass is also Remedial work from whenever. The whole original floor joisting was replaced with what you see. Possibly because of lack of through ventilation from front to the back of the house?
How many air bricks are there on the front elevation at sub-floor level? Is there an air brick venting any hallway?
Photos showing the front and rear elevations at ground level might help?
There's damp looking stains on the ends of some of the joists.
The hearth and the joists around the hearth will need attention.
Strips of DPC are needed in various places.

Thanks very much for that.

Can you put an insulated plasterboard, attached with foam glue and with a vapour barrier, over Limelite?

I have now found a slate damp course in the external walls. The sleeper walls also have some basic plastic damp-course.

It is a semi-detached house and think no ventilation through the party wall to the other semi. Also no ventilation to the rear. There are currently three air single air bricks on side wall, and one in front elevation. They are not 75mm above the ground but it's sheltered so no risk of flooding. I've cleaned them out and they are letting in air.

But I don't think they provide much ventilation and there is rot on some beams and a bad smell in the middle of the house. I also plan to insulate between the floor joists and build a few small new sleeper walls to help with deflection - those 4x2" joists are right on the max span permitted for C24 (which they may not be). So the airflow will get worse than it is now.

To help subfloor ventilation I have already cleared out rubble and knocked some bricks out of internal and sleeper walls that are not supporting anything. But I think it will need more. Here are my ideas for improving (see pic):

1 and 2 - try to put some new air bricks in?
3 put a bathroom fan under the stairs to push air from hallway down into the subfloor, at the point furthest from the current airbricks and where the stale smell is worth. It could be on a timer so it comes on for an hour a day or so. It would be mounted in a ventilated cupboard above ground so accessible for cleaning etc.

Would any of these work? If there is no cross-flow from air bricks, does it make more sense to put a fan in to push air down into subfloor and out of the airbricks rather than hoping air blows through them?

Stick insulated board on with foam over single skin walls.
Then the correct mechanical fixings through board

Thinking about it, I think blowing warm air from the house down into the subfloor would be a bad idea. The moisture in it would condense on the colder surfaces like underside of beams in the subfloor.

Perhaps just a fan under the floor to circulate the air in that part furthest from the airbricks?

All sleeper walls should be honeycombed to allow thro or cross ventilation.
Your hearths might be full of fender wall soil, & lack any DPM or DPC's?

My view fwiw, is dont put any kind of electrical appliance under a floor.

Thanks. I haven't investigated the hearth fully although the beams feel quite solid there.

Would you leave the solid timbers in place or replace all with new treated timber (with 5mm shims to make up to the same height as the old true 100mm 4x2" timber).

I would only consider a fan under floor in the cupboard under the stairs, where I could make it fairly easily accessible.

Leave.

Thanks the sleeper walls are not honeycombed but I might be able to knock a few bricks out here and there to make them better.

I'm going to add 75mm Celotex on galvanised nails (joists are only 100mm deep), then tape over the top and seal round the sides.

Would putting in more air bricks in front of house be worth it?

Are you going to leave the fireplace in situ and buff up the blacking?