Showerroom - partly tiled

[Tim Watts]

Pics:

or short

Tiler did a great job tiling (I diy'd the screed and concrete slab) and I have tested the fall with water and it runs into the drain nicely.

I woke up this morning with one huge panic though:

I wish I had insisted on tanking membrane.

I took advice from the tiler (who's old school) and he said not to worry. Asked a builder mate and he did see it was necessary as it's ground floor, on it's own concrete/celotex/screed self contained in its own DPM wrapper isolated from the rest of the house.

I see that and that coloured my thinking - after all, the worse that can happen is the screed gets wet and maybe waterlogs the celotex and rots its foil face off over years (that can happen apparently). In one respect the problem will at least be isolated and not affect the house.

The stupid thing is that I said I was worried about the edges to wall as there may be movement there, so tiler added tanking edging strip - and seeing how easy that was, I wish I'd said: stop, get some sheet membrane and complete the seal.

But I was working at home, and juggling a dozen things and didn't have time to think it through. Conversely I was also worried that membrane might fail mechanically at some point.

I cannot see anything in the Building Regs approved docs that mentions wetrooms let alone specifying membrane. Although I found a vague mention of a British Standard somewhere. I've keyword searched Part A structure, C Site preparation and resistance to contaminates and moisture, G Sanitation, hot water safety and water efficiency and H Drainage and waste disposal.

Strange - would have thought there'd be a mention...

So, kicking myself here... Might ring the BCO (new one, #3) and double check - he's going to see this for the drains, and therefore might ask... Pain to redo this section, but less of a disaster than if the thing is complete.

I don't see a huge risk myself, but like putting marmox on the walls, it would have been a fairly small inexpensive not difficult extra step...

I'm surprised the tiler didn't say "just do it, we always do that" unless they don't always do that?

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That's what I hate about doing this project - all the technical stuff is on my shoulders and I don't know any experts (apart from relevant people here) so I don't have anyone to really confer with. Kinda assumed a tiler would know what was necessary. Builder mate is more "relaxed" than me too...

Sorry - bit of a depressed moan :(

[Andy Burns]

On a similar note, how worthwhile are the 'uncoupling' membranes (e.g. DITRA) that I see on youtube? Have some bathroom floor tiling coming up over floorboards, so was planning on cement board first, is isolation an issue above that? Need to know my finished floor level before I can do other work, so can't change mind later ...

[Tim Watts]

Based on my state of mind, over screed, I'd say "use one because (in retrospect) it's not hard". I thought these things were hard to use, but it seems you just use tile adhesive to put them down (some others are paint on, some use primers, this is the one Topps Tiles sell - it's a "fabric" covered sheet about 1-2mm thick).

Based on me just noticing you said "floorboards" I would say it is mandatory - even I would have done that.

Have a look at Marmox - I *believe* you can use their sheeting with some additional edge seals and jointing tape to form a wetroom. They even have floor panels with slope angles built in that will make life simpler.

[Tim Watts]

Oh and they have a great tech support line you can phone in Kent where you can speak to a guy who knows his stuff... I rang them to check weight loadings on the board if screwed to the wall.

[Andy Burns]

This one? At the price, no point in not using it for extra precaution against cracking.

I'm not aiming for wetroom, but anything that stops 'enthusiastic splashing' ending up on the kitchen ceiling is a bonus.

Marmox, hardybacker, no-more-ply ... much to choose between them?

[Tim Watts]

That's why I'm kicking myself...

Bah...

Ah - not mandatory then. But wise to design.

Marmox will be warmer to the touch and goes from 4mm to . 4 or 6mm will do you.

It's lighter to handle too - Hardibacker boards weigh a ton.

I've had 20mm Marmox multiboard under my bathroom ceramic tiles for 8 years and it's been very good. I did leave it out from where the bath feet and bog go and screed that level with SBR/3:1 cement after priming the existing screed with SBR then cenement/SBR slurry.

That avoids risk of deformation under high load parts.

[Tim Lamb]

In message , Tim Watts writes

Hmm.. I plan to tank mine. 'kin expensive materials though!

I've opted for a wall side linear drain 900mm long. This came with a bit of pre-trimmed tanking material. There seem to be two schools... always tank over a boarded floor/might be a good thing with an in screed heat source.

Ground floor, no heat, little worry:-)

[Tim Watts]

That was the ambiguity I faced - it did not seem cut and dried...

I sounded it out with the less technical people at home and drew a decision diagram...

If we tile the walls and BCO asks "is it tanked", "no", "do it again" - big disaster. He's going to inspect the room for the drains and ventilation so he might well ask.

If we phone him and say "er, might have a problem, do you *require* it to be tanked":

Yes) We redo the floor. 4 days of cost and 3m2 of tiles. Not a disaster but annoying.

No) We run the risk and the worse that *could* happen is the celotex gets waterlogged. That could take maybe 10 or more years (guess)

And we have some exposed screed in the under basin cupboard - it is monitorable.

No risk of damage to house as DPM isolates the floor on all sides.

So I guess I should phone the BCO's office on Monday.

But I cannot find a single thing in the Approved Docs and I bet they never used to tank these things in the 1960s? Or did they?

[Tim Watts]

Oh: yes there is heat, but wet, not electric. So no danger...

[Tim Watts]

PS Thanks :)

[Roger Hayter]

I put the damp proofing under the electric heating and under a 10mm insulating layer. It is the builder's choice of a paint-on 'membrane' and I have no faith in it. But since with the heating and ventilation the floor never stays wet more than half an hour I have no worries about it at all. Even if the celotex, which is now about 150mm down did get soaking wet I can't see any significant harm resulting. FWIW, our BCO had no interest in the issue.

[Tim Watts]

Thanks mate. As I was saying, when you have no one to talk too, ito's easy to lose perspective... Good job I can come here :)

I never have this problem at work - I work in systems admin, where non optimal solutions are easily undone or fixed - in fact it's how I get stuff done - rough it for 80% of the benefit, then tart it up for the final polish later.

But equally, we try to work to "best practises" too, and that's damn hard in building when most people don't give a monkeys :)

The only thing I'm nervous about right now is spending £200k on new server infrastructure - if I f*ck that up, I get to be reminded of it every day for the next 5 years. Or not at all if I f*ck it up enough!

That's heartening - I will ring our office and see. Last bloke I spoke to seemed quite helpful.

[Tim Lamb]

er.. movement due to expansion? The floor heating advice is adamant about expansion foam next to internal walls as well as 25mm PIR insulation at the external ones.

I plan to use wallboard rather than tiles although I might run a row of half tiles around the bottom and use silicon rather than grout for the joint.

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[Tim Watts]

I did add the foam around the edges. My calcs suggest the expansion of a

3m long floor from 10C to 40C would be about 1mm overall give or take. All my edges will be sealed 3 times (sealed gap around tiles yesterday), will seal Marmox to floor and tiles will have finishing sealant. And we do have edging membrane on all edges under the tiles too - so that's a 4th layer.

That was the bit I thought of and I feel confident that will be fine.

The weakness in the scheme, if any, will be due to any porosity of the surface I think...

That's what I've done in every place - even the main bathroom which has a cold floor.

[Tim Lamb]

The screeders blurb wants expansion joints if the run exceeds 8m. Fortunately I have a convenient doorway so I can hide the expansion strip under that.

I'm planning on ceramic tiles:-)

[Roger Hayter]

About 20mm stainless steel coving looks nice, is easy to seal and will take up a little movement. Not entirely cheap. But the do prefabricated 90deg, 135deg, 180deg, 270deg joining bits, which is good.

[Tim Watts]

That is nice - I've never seen that before...

[Tim Lamb]

In message , Roger Hayter writes

Interesting. Ta.

The seating looks wide enough for a range of tile thickness.

My efforts at running mastic sealant do not find approval from the boss:-( Tooling and tiles don't go well either.

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[Roger Hayter]

There's some flexibility by varying adhesive thickness, but they do different tile thickness ones from about 6mm to 15mm.