Staining from ceiling joists

[Harvey Van Sickle]

We're finally getting around to redecorating the back bedrooms; these were built (an extension to the house) about 25 years ago. They've been redecorated since then, but I suspect that the ceilings -- artex on plasterboard -- have never been painted.

The problem is that I can see the lines of the ceiling joists in parts of the room -- dark lines, as if dirt from the joists has leeched through the ceiling to leave a sort of ghost-staining showing through the artex. (I know -- dirt doesn't leech. That's the effect, though.) I know the roof up there is sound, and the ceilings are dry.

I'm pretty positive, given previous experience in this house, that the artex isn't sealed -- a lesson learned in the sitting-room, which absorbed coat after coat after coat after coat of ceiling paint... So I'm planning to treat the artex with a Unibond-type of sealant wash, then paint in the hope that the dark "follow-the-joists" lines will be covered.

Has anybody encountered a similar "dirt staining" problem? Did painting cover it, or is there some other treatment I need to do to those particular areas?

[John Armstrong]

My guess is that it is caused by condensation. The bottom of the joists will be colder than the bottom of the insulation that I assume is between them. These cold bands will tend to get more condensation than the rest of the ceiling. You could add a second layer of insulation crossways over the top of the joists. Makes access and storage difficult though. Don't block the roof ventilation.

[Harvey Van Sickle]

On 15 Jan 2005, John Armstrong wrote

That makes a lot of sense; it wouldn't be difficult to cover the joists up there -- that part of the loft isnt used for any kind of storage.

Thanks; I'll think seriously about that.

[Christian McArdle]

I wouldn't seal it. Unsealed, it is much easier to steam off and replace with smooth proper plaster.

Christian.

[Harvey Van Sickle]

On 17 Jan 2005, Christian McArdle wrote

An excellent point, but it's a back, extra room which houses a spare TV, ironing and overspill guests (we have a different primary "guest bedroom"). So cleaning the artex off and plastering to make it look that much nicer just ain't gonna happen in my lifetime!