PLEASE advise - relaying concrete slab in 1912 ground floor bathroom

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MindenRose1912
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Joined: Mon 16th Nov, 2020 1:51 am

PLEASE advise - relaying concrete slab in 1912 ground floor bathroom

Post by MindenRose1912 » Mon 16th Nov, 2020 4:19 pm

Hi guys, I'm wondering if anyone could PLEASE help. The Internet is an absolute minefield of info and I'm at my wits end now.

My house is 1912, so not too old, but equally, not built out of modern building materials or techniques.

Its a 2 up 2 down, typical semi, with a small scullery extension on the ground floor, which is original. The house is suspended timber floor, on dwarf walls, and the small extension is a concrete base. Over the years this has been chopped around a bit, but it is now a bathroom on the back half, and the front half forms my kitchen side of our kitchen diner.

I started renovating the bathroom and I found issues at every turn. ALL the plumbing was leaking, the walls were drenched (plaster had blown and tiles were popping off etc). The ground had multiple layers of tiles, SLC, patchy concrete, bricks, plaster (!?) and mud - i guess that's what happens over 100+ years when you only have 1 bathroom/toilet.

As a result, I moved the door opening and dug out the whole floor to 300mm. In the process, I hit an old clay pipe, which I now have reinstated as I'm moving the toilet. I've added 150mm of type 1, which is compacted down to 100mm.

I've read SO MUCH about DPM's and the pros and cons in older properties. There is an old bitumen/slate DPC in the brick wall. The external wall is solid, with no cavity or insulation - which is not helping with warmth or condensation (remembering that this is a bathroom).

My thoughts are that if I am insulating and tiling the whole room (using varying thicknesses of marmox boards), then it won't be able to breathe anyway, so I may as well lay a DPM and lap it up the walls, past the DPC, and then fixing it behind the wall Marmox Boards (much like you would with skirting boards). Does anyone have any views or opinions on this?

My next challenge is the floor. The waste pipe rises around 45-55mm out of the sub base, before it reaches the upright. How would you lay insulation and concrete, before applying 10mm marmox board and tiles on the floor? I'm also thinking about installing electric UFH.

I was considering laying 100mm concrete onto the DPM, then another 100mm of 'ProofTherm High Performance Insulating Floor Screed'. Then 10mm marmox board and tiling. Has anyone else got any better, cheaper or easier ideas?

Any help is very gratefully received!

Thanks

88v8
Posts: 2807
Joined: Wed 15th Jun, 2011 7:01 pm
Location: Glorious Gloucs

Re: PLEASE advise - relaying concrete slab in 1912 ground floor bathroom

Post by 88v8 » Sun 22nd Nov, 2020 10:56 am

Hello and welcome.

Yes, undoing years of botches can be ... interesting.

So, there is a dpc. That greatly simplifies things. Problems arise when a dpm is installed where there is no dpc.

Tuck the dpm in just under the dpc, don't go above it.

Our previous house was solid-walled, I never felt the need to board it out, but it would save a bit of heat. However, you will find a big difference just from having dried the walls... could take a month per inch thickness... as damp leaches the heat away like billy'o.

Have to watch you don't create condensation behind the board, but the manufacturers should give guidance on that.

UFH, mmm sorry beyond my pay grade. Just don't put a wood floor on top of it as we have seen from time-to-time on here. Wood is an insulator.........

Ivor

paulc
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Joined: Sat 22nd Oct, 2016 7:05 pm

Re: PLEASE advise - relaying concrete slab in 1912 ground floor bathroom

Post by paulc » Sun 22nd Nov, 2020 2:09 pm

If you are insulating the walls, have a look at the warm batten method. This will give a small gap between the insulation boards (rigid Celotex type stuff) and the wall. Leave it open at the top and vented to the roof space - That should avoid damp building up in the gap. Assuming you are using the same material to insulate the floor, insulate the wall all the way down to the floor, then put your screed down. This will avoid any cold spots at the floor/wall junction. Do the same with the ceiling, and you'll have a well insulated and warm room.

MindenRose1912
Posts: 2
Joined: Mon 16th Nov, 2020 1:51 am

Re: PLEASE advise - relaying concrete slab in 1912 ground floor bathroom

Post by MindenRose1912 » Mon 23rd Nov, 2020 12:31 pm

Thank you guys

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