Hi,

We are putting a new south facing single story extension on the side of our solid walled Devon house (just ruble on that side). The house and extension has UFH (pipe in screed) and DPM etc. We need to decide what to do with the old external wall (now internal) which is covered in a scat coat. The lower 3 foot is damp (it has been tanked internally and with the DPMs no big suprise there).

Any views \ preferences \ votes for :

a) Take up to 3 feet high off and tank it and finish with plaster (builders preference - of course!).
b) Take up to 3 feet high off and lime render just there.
c) Take up to 3 feet high and box it in (battons and plasterboard) and finish with plaster.
d) Take it all off an box in (battons and plasterboard) and finish with plaster.
e) Take it all off and lime render.

thanks

Andrew


Andrew

Take off renders and tanking and let the wall dry out before covering up again

If you plaster directly on to the wall with anything while the wall is still damp, there is a good chance the new finish will get discoloured etc


Do you mean footings, or just the lower part of the wall?

Many thanks for the responses.

It is the lower section but the extension is below the house to has exposed down to the footings. We have taken the render off and it is visibly damp to 1-2 foot.

I think dry out and review after a few weeks. We have had a very wet month and it was exposed to the elements for a few weeks of that while the pad was being laid.

many thanks

Andrew

Andrew,

I'd go for lime and accept that sometimes it will be moist on the surface (and a bit mottled, decoratively), rather than looking dry on the surface but being known to be wet behind.

Cerisy, were tey the sort of toads which can inflate a bit of their throat? Given the insulation value of still air....

Andrew,

I may be teaching you to suck eggs, but if the builder says he 'does lime', check what he really means - does he do pure lime mortar, or sand/cement mortar with a handful of 'bag lime' thrown in? My suggestion is for pure lime. Sand/cement with a little bit of lime is unlikely to breathe like you want it to.

I would advise using a St astier 3.5 NHL as a render, if you are going onto a very hard type of stone then you may want to look at applying a stipple coat which would consist of a lime slurry mix, apply using a Tyrolean gun or harling trowel, can be a bit messey if its your first time so tape up the sides and put down a sheet, let this set for a couple of days to allow a good key. You could apply the first render coat using the same mix say 2 sharp sand 1 soft sand( quarried sand not dredged) to 1 lime but a dryer mix to the slurry. When green hard which should take around 2 to 3 days us a comb scratcher to apply a diamond patten for the keying of the second coat. Then when green hard again brush over with a stiff brush ( churn brush) to leave a slightly open course finish. Let this dry out and lightly mist down and add a lime wash which you could make out of the hydraulic lime which will help with the setting. You could add some natural earth pigment if you like a natural buff coloured finish or if you want a pure white finish i would go with a wash made from mature lime putty. If the outside has any cement then remove it and re-point with the NHL, cement only traps the moisture in the wall and forces it out from the face of the stone causing spalling or back into the internal wall.

Pure hydraulic lime has a chemical set when added to water, so will drive out any damp from an external or internal wall during the setting process. If using on internal walls, you would need to make sure whatever you use to decorate with, that it is still able to breath. This is where lime washes or lime paints come in. Fat lime is made from 95 to 100% pure lime stone calcium carbonate which does not have the same chemical set, as this will only set with contact with air CO2. We specialise in the use of lime mortars so have good understanding on how to remove damp from period properties. You will still need to repair any leaking gutters or pipes. Dpc's didn't come in until the public health act of 1875.

£1000 sounds good, make sure he lets it mix dry for around 10 minutes then wet for 15. We sometimes make a mix the day before as this fattens up the mix and makes for a smoother render to apply. Also make sure the finish is not polished with the steel trowel it needs to be sponge finished or cross grained float finished to let it breath.