Brown streaky stain on plasterboard/plastered/painted internal wall

[Spocksmum]

Quick and urgent question to identify sudden appearance of a streaky horizontal brown stain appearing on ground floor internal wall - fairly high up on wall. This is a garage development built one year ago into a room - so plasterboard and plaster/paintwork still new. Freaking out that we have a major damp problem and no workmen available till next week.

So - here are my theories:

a) having the central heating on a lot recently (so warmer room) has meant that some already present internal stain from the works done has finally infiltrated to the inner wall, by 'dry blotting paper' process eg from wood preservative on wood frames onto which plasterboard was fixed? OR b) damp ingress from outside wall has suddenly occurred or been exacerbated with recent very wet weather - maybe a damaged guttering above? (Difficult to check as horrible neighbours are adjacent to this side of the house so never go near there) OR
c) Freezing weather has caused cracking in outside wall that has then caused damp ingress but no major leaks?

I just really need the problem to be a minor one and not something major and urgent but am afraid it might be bad news. No internal plumbing in that area (which is the inside of an outside house wall), as far as I know.

Does anyone know what a slightly growing (in last 24 hrs) brown streaky stain high up across internal wall might indicate and is it very urgent? If I can't get anyone to come out and look, what can I do myself to check the cause and rectify it across New Year? PigletJohn? Anyone?

brown stain is usually to do with a chimney, where the old tar and soot moves out with the damp.

Disused chimneys must be ventilated top and bottom to prevent internal condensation.

Or it could be rainwater penetration

less often a plumbing leak.

Condensation is encouraged by damp, lack of ventilation, and, especially, wet washing draped around.

Thanks PigletJohn. The wall has no chimney there or nearby either - so it can't be that. No plumbing there at all either.

Could it therefore indicate rainwater penetration? If so, why would it appear in a horizontal streak rather than vertical - ie the way rain falls?

If it's rainwater penetration, however, why would it appear in one discrete brown streak? It somehow seem to be following a horizontal line rather than a 'patch' IYKWIM?

Would it be anything to do with the wooden framework onto which the plaster board was fixed - ie something used for preservative that has leached through, as the room has become warmer? Could this seep through the plaster board and plaster, over 12 months and finally show on the internal wall?

Any further thoughts anyone please?

'mmm

the brown indicates dirt. Clean water usually leaves a clean or yellow stain, depending what it picks up from the wall or wood.

if it is horizontal and you are sure there are no pipes, it might be lying or running along a lintel or timber frame, or it could be rain if there is an old window or door lintel in the wall, especially if there is a spilling gutter or leaking downpipe. Have a good look outside, preferably during rain, for a potential source. Cracked, bubbled or loose render will hold rain.

If the wall is plasterboard, and you can't find the source, you can cut a square out and have a look behind. It is fairly easy to put the piece back, fill and redecorate.

timber preservative is not likely to wash out in damp. Old coal-tar creosote will soak through paint and leave a brown mark, but is not usually found indoors, and has a distinctive smell. Old kitchens often have greasy dirt on all surfaces, but it does not easily move with plain water.

p.s.

could it be a rust mark? Might be orangey-brown. It could occur if there was steelwork (builders do not like painting it) that had got damp.

Plaster sometimes has metal lathing, it should be galvanised but that only holds back rust for a limited period, unless it stays dry.

I think the height of the stain is the same as where there was a makeshift mezzanine built by the previous owners when they partially converted the garage. This platform was taken down by my builders.

Not sure what part of the timber framework they might have left behind when the builders put up the plasterboard. I think they took off old plasterboard and then put new ones there.

So it might be a steel connector or nail/screw left in the timber.

It still might be damp ingress through the external wall (no doors or windows along there at all). I think there may be some ivy growing - just a small patch - up that wall.

Can't get the original builders back in as I'm in the process of making a small claim against them for the worst of the various 'botched jobs' that they did. That's why I'm trying to figure it out myself but as I don't trust the builders to have done a good job, they may have cut corners and left nails/screws/old timber before covering up with new plasterboard.

Good to hear that if all else fails, I can get the plasterboard cut out. Will have to wait until after new Year now though as no one working locally here till then but I'm also then back at work myself, so could be tricky to arrange this....