Stains coming through paint

[malcolm]

I've not actually painted yet but I have got some bits at the bottom of some walls where water will continue to want to come through and evaporate unless I do something very time consuming. I am concerned that stains will come through.

The walls are ground floor and are coated with concrete render and gypsum. The internal ground levels on the other side of the walls are 8 inches higher than room floor level. I've removed impervious coatings from the wall and the plaster has dried out over a few months.

What is anyone's experience for this sort of thing? I'm planning to leave things as they are as much as possible and let the water come through and evaporate. I'm worried I'll get stains.

[Feltwell]

I think you'll get tide marks on the paint Malcolm. We get this a bit on the chimney breast in our kitchen - despite it being in the middle of the house, if the weather is exceptionally wet for a while the bottom 6" of the chimney breast get damp. It dries out but leaves a tide mark.

Presuming that tackling the source of the problem is out, might you be better off at looking at having a ventilated gap behind your decorative finish? Panelling ventilated top & bottom perhaps?

[a twig]

We had exactly the same problem, went for NHL lime plaster skim over woodwool boards attached straight to the wall, then painted with earthborn clay paint.

As long as you make sure you keep everything away from it (don't put furniture against it for e.g.) you'll get a darkening when it gets wet then back to normal as it dries, but no tide marks and no damage in our experience

[malcolm]

I had forgotten about the potential wet patches. I removed impermeable wallpaper and paints in the summer and the walls have dried out apart from in a couple of areas. The walls were soaking wet when the wallpaper was removed. A radiator in front of the largest wet area helped. I guess some equilibrium has been reached, and that might change in the summer when the radiator is not on.

I've been doing plaster repair over the last month and painting with a coat of Earthborn clay paint to make the walls look nicer. I guess if I do that on the previously damp areas I'll have at least 6 months to see what happens before any skirting boards go on.

Cleaning the walls properly before paint will probably help. I didn't do that with some bare plaster on the ceiling and the stains from a long repaired roof leak were sucked into the new paint.

[BladeRunner]

Twig, regarding your suggestion to attach woodwool boards with NHL skim, did you attach the boards directly to the wall as is, or did you remove the plaster/cement back to brick and then attach them?

[Feltwell]

Cleaning the walls properly before paint will probably help. I didn't do that with some bare plaster on the ceiling and the stains from a long repaired roof leak were sucked into the new paint.

If you've got areas like that that are properly dry now and it's just old residual staining coming through on an area that doesn't need to be breathable, then stain block paints do work OK I've found.

https://www.decoratingdirect.co.uk/shop ... tain+block

[CliffordPope]

I've never found any stain-block paint to work for very long - they appear to, but then a year later I find the stain is coming through again.
The only solutions that work in my experience are;
a) stick-on foil-backed paper
b) physical barrier and air gap using panelling on battens
c) change the colour scheme to one that is the same as or darker than the colour of the stain. The most imaginative is to paint the entire dado strip in a variable colour wash that imitates the staining - use it rather then fight it.

[a twig]

Twig, regarding your suggestion to attach woodwool boards with NHL skim, did you attach the boards directly to the wall as is, or did you remove the plaster/cement back to brick and then attach them?

Got the wall back to bare stone then attached direct to that. Did the same in my living room as well, might be able to find some pics later on if that helps

[a twig]

Ah, posted about it before here:

viewtopic.php?f=1&t=16738&p=227203#p227203

[88v8]

....a coat of Earthborn clay paint

In my experience, clay paint does not stick to damp or does not dry.

I have used stainblock in the distant past on a chimney breast with soot staining, but as Clifford said, in the end the only fix for that was Foildamp, which you definitely do not want low down, it will just send any damp up the walls.

Bedec do a stain block for use in conjunction with their MSP.

Ivor