Insulating and waterproofing external bathroom wall

[powernun]

Hi all,

We have stripped our bathroom walls back to brick and are lining them with NoMorePly fibre cement boards. The reason we went for cement boards was for the moisture resistance and for supporting the large-format tiles we’re planning (90 x 90 cm).

The tricky part is the exterior wall. This wall has the following complications:

• Has a window
• Has a heavy basin mounted on it
• There are water pipes close to the wall (about 50mm distance from the brick
• The bottom half of it will be tiled, and the top half just painted

We want to ideally insulate this wall, while also making it as moisture-resistant as possible and being able to hold large tiles.

Our current plan is to use 40mm Thermaline insulated plasterboard on that wall and inside the window reveal, cutting around the pipes as needed and filling with expanding foam before putting the tiles over.

Would this be the right approach, or is there a better way to handle insulation and tiling on that wall? Is there such a thing as fibre cement insulated board?

 

[Deluks]

Marmox multiboard, available in a variety of thicknesses.
If you put heavy tiles on it be sure to use adhesive and the proper fixings. Basically follow manufacturers instructions.

 

[mikeey84]

As above, I did Marmox 40mm. It's not quite as good as PIR insulation, but much better than nothing.

Dot and dabbed to wall with tile adhesive, then fixings drilled through dabs (as per installation instructions)

Easy to cut with an old saw.

I'd repipe rather than foaming, but it's a lot more work- will help prevent condensation.

 

[powernun]

Marmox multiboard, available in a variety of thicknesses.
If you put heavy tiles on it be sure to use adhesive and the proper fixings. Basically follow manufacturers instructions.

As above, I did Marmox 40mm. It's not quite as good as PIR insulation, but much better than nothing.

Dot and dabbed to wall with tile adhesive, then fixings drilled through dabs (as per installation instructions)

Easy to cut with an old saw.

I'd repipe rather than foaming, but it's a lot more work- will help prevent condensation.

Thank you both, Marmox looks exactly like what I was looking for.

For fixing, I was planning to use the same technique as for the rest of the bathroom boards: SBR first, then adhesive expanding foam (most likely Soudal plasterboard adhesive foam), and the mechanical fixings they recommend. I will double-check with Marmox if that's OK.

Also, I remeasured the pipes, and with a 40mm board and 10mm tiles on top of it, I should just be able to make it fit without cutting out in the sink area. But in the toilet area, the soil pipe is concreted in, so the water inlet cannot be rerouted closer. So, for there, I will most likely need to cut out a small 10cm x 5cm x 3cm area, which I'm OK with, as it's behind the toilet anyway.

 

[mikeey84]

If your putting large heavy tiles up, I would use a good powdered tile adhesive and not foam if it was me. I also ran a bead of ct1 or similar along the edge of each board, like mortar in a wall, to aid with waterproofness and help prevent movement.

 

[powernun]

If your putting large heavy tiles up, I would use a good powdered tile adhesive and not foam if it was me. I also ran a bead of ct1 or similar along the edge of each board, like mortar in a wall, to aid with waterproofness and help prevent movement.

Thanks, I'll keep it in mind. Maybe I'll do a test to see how well it holds up, since on this wall, only the bottom half will have tiles; the top half will be painted.

On another note, looking at Marmox's instructions for plastering (for the top half of the wall I want painted), it looks like it will need a bit more proper plastering with two coats, rather than a skim coat that I can probably get away with on the cement fibre boards. I might need to get a plasterer in, as "proper plastering" is something I really don't have patience for. Plumbing, electrics, building, carpentry, decorating, all fine, plastering is the bane of my existence

 

[mikeey84]

I've never regretted paying for good plastering work!

 

[camerart]

Hi,
I'm no expert, but insulated downstairs walls 100mm foam. Ad as I was also doing building work, I needed building control, who made me add battens, and through the wall (4 1/2 inch) ventilation, for the condensation on the wall side of the insulation to escape.
C