Gypsum and wall stains

[Keithj]

I've mentioned before that the firm that carried out the major repairs on my house did a fine job, until towards the end when the boss was trying to make a bit more money on the deal and started cutting corners. One of those corners was using plasterboard and gypsum on the inside of south and west-facing outside walls where the exterior is lime, and where the lime is "inset" from the plates and studs.

Water pools on the little ledges thus formed, and blows through the wall when it's seriously windy. We end up with "tide marks" of a darker colour staining the bottom inch or so of the inside walls. The rest is OK. There are gaps under the lime where the green oak has shrunk, but I've been filling those each summer and the gaps are now almost non-existent (but enough for water to blow through, needless to say).

Last month, I washed off all the stains, and repainted. It looked very good for a week or so. Then we had a mighty rainstorm and wind, and the tide marks are back again.

I'm wondering what to do (other than just "repaint", as the preacher said). One thought is to chisel off the bottom inch or two of gypsum, back to clear plasterboard, and re-render in lime. I'm inclined to have a little experiment in a corner of the kitchen behind the table, where it wouldn't be too noticeable if it all went wrong.

What is the view of the panel? Would there be other problems where the gypsum and lime meet? Would it prevent the tide marks?

 

[malcolm]

This is the ground floor I assume. Have you got any plaster touching the ground? How about removing the bottom inch of plaster and cover the gap with shirting boards.

 

[Keith Bowman]

If the tide marks came back after the mighty wind and rain, doesn't that mean you still need to stop the water getting in from the outside before you can deal with the tide marks? Didn't you say something about a lead doodah coming up behind the outside lime and down over the oak plate? (Or is that a different wall?)
Perhaps the sinners of the parish should be set to picking oakum to use for caulking the joints like a wooden walled ship!

 

[Keithj]

I like the oakum idea, but unfortunately that isn't in the C of E mandate. Clear mastic might do the job, but doesn't seem "right" to me.

The lead fix seems to have solved the leaks above the downstairs window in the south gable end (various pieces of anatomy crossed).

This problem is different - water is squeezing in above the sole plate, about 18 inches above ground level inside and out. The (new) sole plate sits on a (new) low brick plinth: the original sole plate was replaced due to rot that had been covered in concrete. I'm wondering if lime instead of gypsum wouldn't show the tide marks. Experimentation may be the answer.

 

[Keith Bowman]

We had a similar problem here where the render comes down to the sole plate. The (exposed) studs are only 6-8" apart but the pieces of lead I put in to run up behind the render and step out down over the sole plate by about 1" seem to have cured that particular problem. It meant hacking off the bottom of each panel of render and replacing it over the lead of course.
In another area I tried using tarred string as a caulking - absolutely useless. It might have been good enough for Nelson, but it didn't work on dry land!

 

[Keithj]

Comes down to "keep the water out" or "make it so the water can evaporate away without staining". I was planning to use the latter for this, since it's not making puddles inside - that would have got the lead treatment.

Maybe I'll have a try with the clear mastic. I bet it won't work