Gypsum plastered interior walls

[fallschirmjager]

I've noticed that the only interior walls that are damp in the house I'm purchasing are those where the other side of the wall is open to the elements (concrete rendered with cracks). As such, in old houses do all interior walls usually require lime plastering or just the inside of outer walls?

Thanks.

 

[malcolm]

In a properly built breathable solid wall in reasonable East English climate the water would tend to move from the inside to the outside, drawn that way by evaporation from the outside. In that case non-breathable inside doesn't really matter for dying the wall. The problem is if you have a waterproof coating inside it will be prone to condensation. That condensation would otherwise just soak into the wall and be extracted by evaporation in a healthy old house no modern mould sort of way.

That doesn't work when you have a waterproof coating outside which will inevitably have failed so the wall is soaking wet. Wet walls are cold so you'll get more condensation inside. Lime plaster and breathable paints will help reduce mould, but aren't the fix.

The only peely wallpaper I have is on internal walls downstairs painted with the modern waterproof emulsion paints. Those walls presumably don't have a very effective damp course so water content in the ground (you'll find the ground is damp if you dig a little hole) balances with the walls making the internal walls wet, and that bubbles the paint or pushes off lining paper painted with modern paints.

I've not noticed any problems with internal walls upstairs apart from the one painted in plastic paint that was underneath the cold water tank when it overflowed. Then it did the wet wall plastic paint thing.

My aim is to make everything breathable. Outside was the priority as there is more water outside to get into the walls. Inside I'm not removing gypsum plaster unless I can see a problem (it is more breathable than the modern paints that tend to be on top), but where I strip off layers of waterproof paint and lining paper and get back to lime plaster I've resolved to put lining paper back on before painting again so the building can be restored again in the future when someone causes problems with silly paints just by removing the lining paper again.

 

[Abi Cott]

I'm going lime on all walls on the ground floor.

On the two upper floors I'm thinking of lime on the external walls, repairing in lime where it's extant on internal walls, and repairing in gypsum where it's already gypsum on internal walls.

 

[MatthewC]

I did lime on all walls upstairs and down; the only plasterboard was on the downstairs ceilings - and even that was skimmed with lime (on DG27). The plasterboard was only used because the problem was found too late. You cannot really go upstairs for many weeks if there is lime plaster drying under your feet, and we were moving in 8 weeks later with much to do upstairs.

As mentioned above, the issue on internal walls downstairs is whether they have a good DPC or are actually pretty well resting on earth with no foundation. If the latter then lime will help address the damp problem on those.

Matthew

 

[fallschirmjager]

Thank you for the replies. For now I am going to lime plaster the interior of the outer walls and see how it goes with a view to lime plaster all walls eventually.