How to improve shower drainage in 1980s slab house?

LorenClayton

Hello

My house is 1980s brick on slab. All the plumbing is down one side of the house, kitchen, bathroom, toilet & HWS (see photos). Some time ago I did a flood test by taping the drain in the shower, and the next morning some water leaked across the floor tiles to the wall, but the water level looked about the same and it wasn't a lot of water at all. This test was above tiles though, something fixed by new grout or silicone, which I did myself recently. But this doesn't test the integrity of the drainage system below.

About a year ago, a plumber with a good Tramex meter said the tiled floor adjacent to the shower was maximum 99% moisture after turning on the shower tap. He said I needed new grouting and silicone but this is all he did. But what if the main problem is below tiles in the drain below?

It's the potential drain leak I'm worried about. And why I don't want to pay a plumber $$$ for re-grouting & re-siliconing if the expensive problem is the trap / drainage leaking under the shower pan. This was an IP before I bought the house.

Any idea what kind of bathroom drainage I would have? The roof gutter pipe is right next to my bathroom (closest window in photo). Is the gully under the pipe for stormwater or sewerage? I suspect I have no real bathroom waterproofing at all, as this didn't become code until after the 1980s.

I basically want to know what kind of bathroom drainage I probably have and how much roughly it's going to cost to bring up to code. Shower drain is 40 mm and I think it's PVC pipe. Would appreciate any advice. Thank you.

JacobZ

Hi @LorenClayton ,

With a concrete slab home, the drainage pipework is installed before the slab is poured, so the pipes beneath the bathroom will typically be fully encapsulated within or beneath the concrete. This is quite different to a timber-framed floor where there may be a crawlspace allowing access to the plumbing from underneath. This means that any alterations to the pipes would typically involve cutting out the concrete, altering the pipes as need, then repouring concrete around the new pipes. If there is a waterproofing membrane in place, as they must be poured in one continuous layer over the whole area, it would mean you need to gut the entire bathroom to reinstate the membrane as per the relevant standards.

Unfortunately, it's impossible to know exactly what is happening beneath the shower without a proper inspection. Given your concern is specifically about a possible leak in the drainage pipework or trap, I'd recommend contacting a licensed plumber who can carry out further investigation, ideally using a drain inspection camera where appropriate. They can determine the condition and layout of the pipework and advise whether there is actually a drainage issue before you start considering more extensive repairs.

There are systems that can be used to reline pipes without the need for cutting out the concrete, so if there is a leak, this could be a possibility, although it would need to be confirmed by your plumber.

Also, the pipe you've referred to beside the bathroom does not appear to be a stormwater downpipe. As it continues up through the eave, it is much more likely to be a sewer vent pipe. The gully at ground level would need to be identified separately by a plumber rather than assuming it is connected to the roof drainage.

Considering the age of the home and the moisture readings you've already had, an inspection by a plumber would be the best next step before trying to estimate what work might be required or what it could cost.

Allow me to tag some knowledgeable members to see if they have any info they can add - @R4addZ, @Nailbag, @Noyade.

Jacob