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How to detect leak in bathroom?

Hi All!

Hope to get some advice on what the best course of action to repair the wall paint and stop the bubbles from coming back.

We have moved into a new home last year and have noticed one of the bedroom's wall is patchy with bubbles on the wall. We have removed the old paint and repainted the wall and added a layer of waterproof primer. However, the bubbles are now returning.

On the other side of the wall is a bathroom that was renovated 2-3yrs ago so i would hope the waterproofing is still intact. We only use the toilet and sink and have never used the shower since moving in.

We have had a builder who had inspected the wall and believe its because its an old building and condensation. They suggested to render the wall however my concern is that it doesn't address the wet patches on the wall and if its a leak that we are simply covering up the problem and waiting for it to become a bigger issue.

Looking forward to hearing your suggestions. Thank you!

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MitchellMc

Welcome to the Bunnings Workshop community @furmanzhang93. It's a pleasure to have you join us, and many thanks for your question about waterproofing.

If you have already stripped the paint once, repainted, and even applied a waterproofing primer, and the bubbling has returned in the same area, that is almost certainly the sign of an active leak inside that wall. Paint does not fail like this unless moisture is continually present. Even very high humidity in a bedroom would not cause bubbling this severe, especially after a recent repaint.

Because you are not using the shower, it is quite unlikely that the waterproofing membrane is the problem. A far more common cause is a slow leak in the pipework inside the adjoining bathroom wall. This could be from the toilet supply, or even the shower pipework feeding the mixer and shower head. Those lines remain pressurised whether you use the shower or not, so they can leak quietly for months.

At this stage, the most sensible next step is to investigate the wall cavity. That means cutting out a decent sized section of plasterboard in the affected area so you can see what is happening behind it. You will probably find damp insulation, wet timber studs, or visible signs of water tracking down the cavity. Once exposed, the source is usually much easier to identify. A leak detection specialist is an option, but in cases like this they often tell you what you already know, that the wall is wet and needs opening up.

I would not recommend rendering over it or continuing to repaint. That simply seals moisture in and delays the inevitable repair, allowing the leak to cause far more structural damage over time. Since the issue has returned after your first repair, that indicates an ongoing leak rather than a one-off moisture event, so it is important to address it now. Once the cavity is open and the leak repaired, you can replace the plasterboard, allow it to dry thoroughly and repaint without the problem recurring.

Please let me know if you have any questions.

Mitchell

furmanzhang93

Thankyou for your reply Mitchell. Would you advice the same approach of opening a hole if its a brick wall?

MitchellMc

That's a bit more complicated @furmanzhang93. If it's a brick wall, it might be worth calling in a lead detection specialist first to try to pinpoint the area of the leak. They'll be able to scan the wall and determine the most likely location of it, then you can decide on the next steps. I guess the positive side of that would be that there is less chance of the water damaging timberwork, but I would still strongly encourage you to resolve the leak instead of trying to cover over the damaged wall.

Mitchell

furmanzhang93

Thank you Mitchell! We will go with that suggestion and see where it takes us from there.

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