Plasterboard above shower discolouring - help

stanley knife and lump hammer ... plasterboard is straightforward to repair afterwards

If the roof is leaking it may not be where the plasterboard is discoloured. Possibly better to check from the roof side first.

If it's a lack of insulation it could be condensation forming on a cold spot.

Unlikely a plumber is the correct tradesperson unless you suspect leaking pipework above the ceiling. A plumber is unlikely to repair plasterboard work.

You can cut out a section of plasterboard with a Stanley knife or multi-tool but you will need to destroy the section you cut out to remove it. If it has become damp it needs to be discarded anyway.

Juts cut it out . Its not hard to put it back with some filler or bonding plaster then sand it smooth and repaint it

No.

Not necessarily: I keep those sections as they are the perfect size and shape to refill the hole later on.

The secret is to mount them back a little below the original surface and skim over, And angled cut makes this a bit easier

It is almost certainly a seeping joint, probably an elbow joint,

Maybe an excuse to buy a multi-tool :)

Any recommendations - it will only get occasional use.

A stanley knife is better, the multi tool will generate a lot of dust, knife is much less messy.

If you want a multi-tool I like my Parkside cordless one.

Even easier is to use a circular hole saw.

I'm quite liking my Ryobi R18MT-0. It has a pivoting head which gets into places other tools can't. Use it with an adapter to Makita batteries. Bought it on ebay for a fraction of the new price.

Theo

If it's "above the shower" - as mentioned in the Subject field, I would at least admit the possibility of condensation from the shower being the cause. (Possibly aided and abetted by skimpy insulation above that bit of the plasterboard.)>

use foil backed plasterboard..

Often not as simple as that. The edges of what is left in the ceiling and the edges of the patch have to be fixed to something solid. This may involve adding battens in the ceiling to support the exposed edges. The edge of the exiting ceiling and the edge of the patch are screwed into the same batten(s). Any plasterboard patch that could move relative to the surrounding plasterboard needs scrim tape over the join or the filled crack is likely to re-appear shortly after skimming. You should not apply skim tape if the patch is below the rest of the ceiling - pre fill any disparity in surface levels before applying scrim tape.

Use plasterboard screws and not nails.

If trying to detect a leaking pipe joint first thoroughly dry it off and then wrap it in tissue paper (soft toilet roll paper) to find where it first gets wet. This method is good where a weeping connection possibly only results in one drip of water every half hour.

Golly., Why make such work for yourself?

Tape the piece back with masking tape and tack in place with something fast setting. Or wedge in place with some wedges and then tack using plaster.

Once that's gone off remove temporary supports and skim the lot.

Sand and paint

That may work for a very small piece of plasterboard patch but unlikely to work well on anything larger. How much is the OP thinking of removing? When I had a 'small' leak I found I had to remove a 2x3 ft section of board.

I had a major leak. I removed around 1ft square No joists there - the water of course was in fact held there BY the joists

I just bodged it all back in place and skimmed it. Once you accept that you are going to have to skim and possibly sand, it doesn't matter how neat or otherwise the fix is.

I think it unlikely to be a leaking pipe as most builders avoid putting pipework in flat roofs for obvious reasons. It may also not be a problem with the roof itself but an inspection of the outside should reveal any suspect areas. As mentioned already condensation could be the problem especially if it is what is called a cold roof that has been insulated. In such a case there should be an air gap between the insulation and the roof deck and ventilation provided at the fascia boards. If condensation has penetrated the PB and is unventilated and has collected in the insulation this will increase the cold bridging making the problem greater and may lead to damage to the decking material. I would remove the PB and give it a good inspection. If you are concerned about replacing the PB and having it skimmed there are plenty of alternatives such as PVC panels. I have these on our shower room ceiling these come as planks that slot together and can either be directly glued to the ceiling or attached to a framework as is in my case.

Richard

I've found an effective method is to cut the plasterbaord at stud centres - it then simply slots back in, whatever the size.

If you can't do that, do the cut at an angle from the outside in. So when you replace the piece you've cut out is doesn't fall through the hole.

The watermark is at an edge running into a corner for the length of about 1ft at which point there is a joist. So initially I plan to remove a 1ft x 1ft section that will have support on 3 sides.

Hopefully that will allow me to deal with the leak.

All the services, gas, water, electricity, go above the ceiling. It is a pain as I'd like to thread a signal cable from one end to the other but it would have to cross all the joists.

Much of the extension has not been well designed.

The roof is sound and was redone just a couple of years back.

The shower space has a fan in the ceiling vented via a tube to the outside. We've been here 10yrs and this problem has just manifested itself in the past couple of months.

The pipe connections to the wash basin weep with tell-tale copper blue marks on the floor even though I've never seen a drip. I've stuffed some toilet paper around the connections so that any water will evaporate. The paper is blue after a few months.

The water pipes come up from the opposite side of the shower, over the shower/toilet room and then T down to the toilet and wash basin and the other leg continues along the wall to presumably an elbow where the plaster is marked. It would then have to find it's way to the middle of the wall to the shower inlet.

Plan view of ceiling - use fixed font

===================================| I damp | I | I | I S| I | Fan |

I = expected water pipe path from supply S = Shower control

If the flat roof was built as a 'warm roof' then the PB must (=should) be foil-backed with the joints and edges sealed to stop H20 molecules getting into the space above the ceiling (which is sealed and without cross ventilation from the outside).

If so, then this vapour barrier must be repaired, so for a small area like a shower it might end up needing the whole ceiling to be pulled down and re-done.