DPM around shower drain - appears missing or nothing to worry about?

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gedc

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Topic # 150995 10-Aug-2014 14:45

Hi folks

14 year old house - single story concrete pad. Shower in bathroom is acrylic base and sides. It started to leak and get a bit spongy when stood on and noticed carpet through adjoining bedroom wall had a damp edge and skirting was swelling. Gave me a good excuse to redo the bathroom as it has been a maybe aye /maybe no project for a while.

Ripped it all out and the concrete pad beneath it was indeed wet and some of the framing along the bottom edge was damp so will let that dry out. The pad has the shower drain in the centre and it appears to have been patched into the main pad - about 20 inches square. - From what I gather, they box this section out during the original pour for the plumber to have a bit to play with re setting the drains etc. The main pad all dried out within the day but the patch is still pretty much soaking wet.

The patch isn't the best of efforts and appears to have been chucked down to a rough finish. There is also a big bit missing around one edge of the drain which gave me access to the area beneath the patch. Its full of 30 to 40mm rounds which makes sense but having scooped out a few handfuls of these I have found the edge of what I assume to be the DPC/ DPM - black plastic sheeting, with a nicely cut edge. It would appear the rounds are sitting on bare earth and the 1inch patch is spread on top of them.

I'm not sure if I'll put down an acrylic base or a fully tanked / tiled base and side but either way, they require some surface prep and gluing of bases down. Should I be cutting / chipping out the infill and repatching a membrane into place before filling back in or is this bit of damp fairly normal given how it's done this side of the planet?

Would appreciate your thoughts.

Ged

timmmay

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Reply # 1105917 10-Aug-2014 15:47

Confused. Photo?

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gedc

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Reply # 1105925 10-Aug-2014 16:24

Excuse the quality. Just dumped it from a phone.

The patched in piece ( dark square ) is wet and doesn't appear to have any DPC/DPM under it so Im assuming has been sucking up water from the ground and also from the leaking shower base . Is this normal for concrete slab construction in NZ and all is well or should I chip it out and redo properly with membrane underneath or does it not really matter in the grand scheme of things.

Hope the picture clears up my explanation of what I found :)

Cheers

mattwnz

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Reply # 1105930 10-Aug-2014 16:39

Is there just earth underneath it? If so that looks like very poor construction, as there should be a DPM. I would suggest getting a builder in to look at it, as they would be the best to advise. If it was built in 2000, then if it doesn't have a DPM under it, that would be a worry. I would also contact the council to see what info they have, they should have the plans and details on on reccrd so you can check things.

gedc

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Reply # 1105939 10-Aug-2014 17:05

I'm fairly confident the slab has a DPC underneath it -standard black plastic as its sticking out a couple of inches from underneath the dry bit of slab. It has a nice straight edge on it as if it was cut away. I have a builder friend coming around at the weekend to look at but also spoke to another mate who is in the building trade. He was fairly bullish it was common and most folks in the trade didn't get worried as nothing perishable was being installed on top etc i.e a shower base etc.. He joked that the void gets taped up and made good for the inspection then the plumber comes along and stabs holes in it to let any standing water drain out...I can just picture that LOL.

Ive got a disc with the plans somewhere so will go look that out as well

Still keen to hear from those in the know if this is indeed common and if it needs attention. Given I'm in CChurch I'm also thinking re liquefaction etc forcing up through this weaker area if another bad wobble occurred.

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Bung

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Reply # 1105943 10-Aug-2014 17:12

The gravel under the patch would be full of water if there was ground water problem. It depends on the situation, I have a shower over a hole in the pad that isn't patched and the soil.is bone dry. In many places they use gravel under a pad rather than a DPM. The object is the water can't maintain pressure against the concrete.

timmmay

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Reply # 1105967 10-Aug-2014 17:32

If it was wet for a long time it could take a good while to dry out. I know in my new bathroom there's the wooden floor, some kind of white polystyrene base to create a slope, two layers of very thick orange waterproofing that's painted on, then tiles - I'm not 100% sure of the order. Actually the whole floor has the orange membrane, and it's behind all the tiles too.

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DarthKermit

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Reply # 1105978 10-Aug-2014 17:52

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That concrete looks like crap. I don't think you'd have anything to lose by chipping it all out to see what it's like underneath.

Whatifthespacekeyhadneverbeeninvented?

D1023319

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Reply # 1105996 10-Aug-2014 18:36

DarthKermit: That concrete looks like crap. I don't think you'd have anything to lose by chipping it all out to see what it's like underneath.

I agree with Darth, it does not look like they used enough cement in the concrete / mortar to patch the floor.
However i doubt that enough water would wick into your house to wet the wall frames and next room so I think it was probably due to a poor connection of your shower floor into the drain or the walls to the floor.

Also are you sure the drain isn't blocked or that there's no back-flow from the drain e.g. during high rain fall due to storm water entering it?
Obviously we cant see the outside of your room in relation to ground level or if you are in a valley to judge what ground water level is like.

In liew of the above thoughts, as a layman i'd suggest ,
1 knock out the patch,
2. dig to natural ground level including 6 inches under surrounding slab,
3. backfill with metal,
4. put plastic down and tape to drain pipe
5. fill with cement rich concrete

gzt

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Reply # 1106006 10-Aug-2014 19:38

Other possibilities. Leak fault in the piping down below (or something unrelated to the shower) that is eventually causing water to rise up around the outside of the pipe and emerge underneath the acrylic and make it's way to the wall. Try and test that somehow.

That wet patch - does it actually feel like proper concrete or a bit sandy? It looks really wrong from here.

gedc

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Reply # 1106046 10-Aug-2014 20:48

Thanks for the feedback. The concrete is sandy in texture, hard to the touch but gritty and is most likely a crap mix. The connection to the drain inside the shower wasn't hellish tight when I was looking to take it apart and that may have caused the leak. That was a good excuse to get cracking on the new one. Whatever, its been like that since the house was built and we've only just noticed the leak so either the base had a crack in it or the connection wasn't watertight. We do get flooding in and around the garden when it rains very very heavily - duck pond flooding but never seen this happening and its hardly been raining of late here so thinking its more mechanical failure than water coming up.

I'll confirm with the builder at the weekend then cut / chip out the middle section and make good again.

Will let you know his thoughts. He's done a few houses in his time :)

Cheers