Water impervious surface finish for bathroom

[Clive]

Hi,

In my end-of-terrace victorian house, the bathroom is housed in a brick built extension. It is well built and well =93integrated=94 into the rest of the building. I can't afford to do the internal reorganisation of space I would like but I need to refurbish the bathroom.

The walls are ceramic tiled throughout. Currently tiles are =93blowing=94 off the walls and during the recent cold spells the room is freezing in the morning with puddles of condensation.

I need to pull some of the tiles off the walls before they fall off. If am am going to do this I'm thinking of insulating the walls. My idea is to use Kingspan or Celotex or some =93finished=94 urethane board that I can tile directly. I only want to tile the area around the bath and shower. What =93finish=94 can I put on the untiled boards that will be

100%(?) water resistant given the 100% humidity level created by a shower?

Thanks

Clive

[slider]

In my end-of-terrace victorian house, the bathroom is housed in a brick built extension. It is well built and well ?integrated? into the rest of the building. I can't afford to do the internal reorganisation of space I would like but I need to refurbish the bathroom.

The walls are ceramic tiled throughout. Currently tiles are ?blowing? off the walls and during the recent cold spells the room is freezing in the morning with puddles of condensation.

I need to pull some of the tiles off the walls before they fall off. If am am going to do this I'm thinking of insulating the walls. My idea is to use Kingspan or Celotex or some ?finished? urethane board that I can tile directly. I only want to tile the area around the bath and shower. What ?finish? can I put on the untiled boards that will be

100%(?) water resistant given the 100% humidity level created by a shower?

Thanks

Clive

You need to "tank" the walls.

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[Andy Dingley]

Generally it's better to insulate the outside of the walls, except when you can't, or when the room is intermittently used and you want a fast heat-up. Bathrooms though, they're so intermittently used that even that might not apply (i.e. use time is shorter than even the internally insulated warm-up time). Insulating the inside is certainly easier, except that it does shrink the room slightly and some similar terraces can't spare that much in their bathrooms. Reading the "Yellow House" eco-retrofit project site is interesting if you've a Victorian house.

I'd probably (given that this is what I'm doing in our spare bedroom) go for hacking off the plaster and replacing with Kingspan and plasterboard dry lining. Tiled wet areas would be Aquapanel over a similar thickness of Kingspan instead of plasterboard. If it's really small and it was convenient, I'd use Marmox under the tiles instead of both.

Mostly I wouldn't worry too much about Marmox under a tiled shower, unless it was new tiling work. Shower tiles are cold & wet, insulation won't change that much. My big concern would be the larger areas of untiled wall. Of course if the whole room is tiled, then you might be back to Marmox. I always set up a spreadsheet for jobs like this, both for the thermal aspects and for the costs. A bar graph of capital cost, heat loss, predicted temperature (if you trust this) and heating cost for the various materials options makes the choice a lot clearer.

1930s style bathroom design looks good in small Victorian bathrooms. Looks "clean and modern", but not out of place.

[NT]

Sounds like cavity wall insulation would be a better bet, and probably doable.

NT

[Andy Dingley]

If you have a cavity (and one of useful width) in a Victorian rear extension.

[Tim W]

Andy Dingley wibbled on Friday 15 January 2010 12:04

Agreed. The U-value of Marmox is comparable to the same thickness of PIR board (about 2 W/m K for 12(.5)mm thickness. 20mm would be better at 1.35 W/m K if space allows.

Overall Marmox will beat celotex + surface covering as the surface covering be it aquapanel or PB will not be as good an insulator. Marmox has a surface you can tile to, and it's water proof. You can even tank it fully, but using a special jointing kit (basically mini tanking for the joint), although stuffing the joints with silicone will go a long way.

Although Marmox under the tiles will allow the tiles to heat up very quickly, so they won't remain cold during a shower. But as Andy says, they are going to get cold again fairly quickly afterwards and thus this isn;t a route to making them magically become dry fast.

Good idea from the overall economics POV. I do guarantee to the OP that 20mm Marmox under the tiles will increase the comfort fact in use quite considerably though. Can't comment on 12.5mm, but it will be rather better than nothing.

[js.b1]

IPx4 wall mounted 2kW fan heater. Dimplex FX20VE springs to mind with inbuilt runback timer adjustable

5-100min (turns itself off). Needs to be mounted 60cm from the edge of any bath or shower. Very fast warmup even in solid double brick.

Extractor on the shower & kitchen.

- Elica Krea in Stainless from John Lewis is =A389 or so, looks good as a mixture of "old design, modern finish, stainless, mesh filters rather than ugly holes"

- It needs a 127mm core drill, buy Blue Spot from Amazon UK or hire for a day (about =A330-35 for deliver/collect same day)

You need to get excess moisture out of kitchens vs loading the house - and not drying washing on radiators or in front of radiant gas fires which will saturate a house!

Insulation on the inside.

- The idea behind insulation on the outside is you keep the thermal mass of bricks which heat up over many weeks. The downside is for that "thermal mass" to work you need continuous internal heating to build up that store of heat. Additionally insulation on the outside shuts off any solar gain if you are south facing, which even in winter is still something.

- The idea behind insulation on the inside is you only have to heat the air in that room "on demand" rather than trying to build up a store of heat in bricks, which in a bathroom/kitchen is not practical.

- Insulation on the inside gives rapid heatup from limited heating (towel rail, wall mounted fan heater).

Marmox behind the tiles.

12.5mm is barely noticeable, 20mm is noticeably, 30mm should be very good indeed. It is not cheap, but does work.

Going Kingspan/Celotex (PIR) insulation...

- Wall is covered in a wood batten frame

- 25mm Celotex is pushed into the wooden frame

- 12mm Celotex covers the wooden frame (cold bridge)

- 9.5-12.5mm Plasterboard covers the lot

- Skim of plaster

- Tiles

That gives you 50mm total thickness, of which only 37mm is Insulation which also loses 5-10% of its U-value due to cold bridging from the wooden frame.

Going Marmox insulation...

- Wall is Mapei Primer G or S (sealed)

- 20-30-40-50mm Marmox is bonded by Mapei Keraflex

- Skim over with plaster

- Tiles

The key difference with Marmox is 100% of the thickness is insulation and there is no cold bridging or wooden frame to rot. Marmox is thus ideal for rooms tight on wall thickness (small kitchens, small bathrooms).

Bare Insulation figures...

- 20mm PIR =3D 29mm Marmox

- 30mm PIR =3D 43mm Marmox

- 35mm PIR =3D 51mm Marmox

- 65mm PIR =3D 94mm Marmox

Installed Insulation figures...

- Solid 9" brick wall, U-value =3D 2.11

- Solid 9" brick wall with 30mm PIR & 12.5mm PB =3D 43mm combined, U- value =3D 0.43 =3D=3D 43mm Marmox (same thickness)

- Solid 9" brick wall with 35mm PIR & 12.5mm PB =3D 47.5mm combined, U- value =3D 0.40 =3D=3D 50mm Marmox (same thickness)

- Solid 9" brick wall with 40mm PIR & 12.5mm PB =3D 52.5mm combined, U- value =3D 0.37 =3D=3D 58mm Marmox

You can see how PIR whilst better suffers due to space "lost" to plasterboard. It's surprising no-one has stuck XPS to PIR foam or done a Marmox with PIR foam (XPS is somewhat stronger than PIR).

Real world:

- Solid 9" brick with 30mm Marmox =3D 66% less heat loss (U value falls from 2.11 to 0.72)

- If it took 1000W to heat it before, that figure is now 340W

- Comfort wise the room will also warm almost instantly

The downside.

- Marmox is very expensive.

- 25mm PIR for 2400x1200 is about =A312

- 30mm Marmox for 1250x600 (1/4 the size) is about =A318

That is =A312 v =A360 for the same area. Admittedly Marmox is easier to fit re labour, plus no wood battens, plus no plasterboard, but it does need =A36 Mapei Primer-G/S and =A37/5kg Mapei Keraflex.

So Marmox is good for those tight situations or where waterproofing is key (solid wall kitchens, bathrooms etc).

What we need is a PIR version of Marmox (cement/PIR/cement), I believe one does exist - but I've never seen it for sale. I think Kingspan make it. A simple PIR (Kingspan) rather than XPS (Marmox) board which can be bonded to a wall & plaster skimmed, job done fast, ideal for DIY sheds.

[Andy Dingley]

IMHE, the price of Marmox is heavily weighted by where I get it from.

If I just have to go "somewhere" and buy "something", then it might as well be Marmox.

If I'm buying Kingspan anyway to do a lot of wall area, then _also_ needing to go somewhere else (as it happens, in the opposite direction) to get a small quantity of Marmox too, is going to discourage me from using any Marmox at all - when Kingspan and Aquapanel would do the same job to very close to the same insulation value.

This would change if it wasn't so hard to find a Marmox stockist. (in my locale, at least)

[Tim W]

Andy Dingley wibbled on Friday 15 January 2010 15:37

It's easy enough to buy online.

This is where I get mine:

[js.b1]

Kingspan Purlcrete was the name I was thinking of, but it is Extruded Polystyrene just the same not a PIR core. As its name suggests it is aimed at roof level insulation.

[Bruce]

My local Wickes (Buckinghamshire) sells it.

[NT]

if its an extension its quite likely. Easy to drill a few holes & see.

NT

[Andy Dingley]

8-( My two local Wickesen don't sell even half of what's in their own catalogues. They don't even do white polystyrene in full 8x4 sheets, you have to buy two of the narrow ones (which cost nearly as much each).