Bathroom

[Rusty10]

Hi

We currently have plans approved to move our bathroom. One side will be against an external wall and we will need to build three partition stud walls.

Would just like some info' on what would be best practice please?

Therm' board the external wall and then use marmox/wedi?

Internal walls use moisture resistant plasterboard then marmox/wedi where the bath shower will be?

As I understand it we could tile directly onto the marmox/wedi board and maybe plaster the rest?

Thanks for any help

 

[mypetearthling]

Hi Rusty,
Cement based backer boards are definitely the way to go for wet areas (bath, shower) as they are dimensionally stable even when saturated. Remember that unless you use expoxy grout it will not be completely impervious to water so it is important that your substrate can cope. Backer boards can also hold a lot more weight than normal gypsum plasterboard. Grout and adhesive is about 4kg per m2.
Plasterboard can hold 32kg per m2,
Plastered plasterboard can hold about 20kg per m2
Backer boards can hold about 40kg per m2, depending on brand.
This is something to bear in mind if you're using large format porcelain or natural stone on the walls. Also type and brand of adhesive is important. For larger tiles its best to use cement based adhesive because ready mixed won't go off. DON'T use DIY stuff, it's rubbish
And don't be tempted to use PVA as a primer. Use only acrylic based, (ideally made by the same company as your adhesive)
Have a look at the Tiling Sticky, and the archived posts in the forum there, it's probably the best place to ask further questions too.

Good luck with your project!


K

 

[Richard C]

What sort of “approval” have you got? Planning Approval is not normally required but the work is notifyable, subject to inspection & must comply with several Building Regs. Have you submitted a Building Notice?

Stud walls between a room containing a w/c & another habitable room need too comply with minimum sound insulation standards, drainage, forced ventilation + electrics.

By thermo board do you mean Thermaline? Why do you want to use that, is the external wall solid brick? Are you planning to fix tile backer boards over the top of that?

Watch out for the max tile weights specified by mypet but you can get tile backer boards that will take in excess of 50 kg/sqm if you need it. You can tile direct onto backer boards & some (but not all) can be plastered. Moisture Resistant PB you can tile direct but use acrylic primer if cement based adhesive is being used which you will need for tiles larger that around 250mm. MRPB must be primed before plastering.

Marmox & Wedi are fine but Aquapanel or Hardibacker will be equally as good unless your constructing a wet room; use 12mm boards for walls not 6mm. If you plan on tiling the floor it needs special consideration & possibly prep.

As mypet said, read the tiling forum sticky & archive posts to avoid making disastrous & potentially expensive mistakes.

 

[Rusty10]

Hi guys, many thanks for the replies.

Initially I am just wanting to know if I would be wasting my time using 27mm Gyproc thermaline on the exterior wall (I have used it throughout on the exterior walls on the ground floor), I was then going to fix marmox/wedi or similar on to that?

Would Aquapanel/Hardibaker be used on the internal stud walls as substitute for plasterboard or does it go on top?

Building notice has been submitted and fully approved btw.

Sorry if the questions seem very basic!

 

[Richard C]

Initially I am just wanting to know if I would be wasting my time using 27mm Gyproc thermaline on the exterior wall (I have used it throughout on the exterior walls on the ground floor) I was then going to fix marmox/wedi or similar on to that?

If you use Thermaline I would be inclined to tank any wet areas rather than fix backer board over the top of it; apart from increasing the wall thickness still further, it seems an unusual thing to do. I still don’t understand why you want to use Thermaline, I see little point if it’s a modern cavity insulated wall. How are you proposing to fix it? You need to be aware of tile weights, you can’t rely on dot & dab fix if you’re going to hang tiles off it, especially heavy large format ones.

Would Aquapanel/Hardibaker be used on the internal stud walls as substitute for plasterboard or does it go on top?

Use instead of plasterboard in wet areas. Aquapanel meets noise insulation requirements but you need to check the spec for the others. Use MR Wallboard in dry areas but note what I said regarding sound insulation requirements; here you need to use Soundblock MR.

Building notice has been submitted and fully approved btw.

Unusual to make a full plans submission rather than a Building Notice for a new bathroom; LABC will still want to inspect for B Regs compliance though.

 

[Rusty10]

Oh dear I ma sorry looks like I have totally confused the whole issue!

Maybe a diagram would help?

Untitled

• Rusty10
• 12 May 2011
• 1

I would thermaline the exterior wall as its single block, maybe get it plastered and tile from floor to mid point using small tiles?

I would then build three stud walls using Aquapanel or Hardibaker and tile from floor to ceiling

The bath with shower over would be in the corner so maybe extra tanking needed there?

 

[Richard C]

I would thermaline the exterior wall as its single block, maybe get it plastered and tile from floor to mid point using small tiles?

OK that’s’ now clear; problem is that although Thermaline Plus (which I assume is what your using) has an integral vapour barrier, the internal face isn’t moisture resistant & you should really be using MR board in a bathroom! I have used standard wallboard rather than MR in bathrooms in the past but no longer do it & if you plaster it will reduce your max tile weight. With the MR board I now always use in “dry” areas on ½ tiled walls I mark the tile line, skim down to this & waste the skim into the area immediately below the tile line, tile away & you’re then left with a nice plaster finish above the tiles. You should also mechanically fix the Thermaline Plus, don’t just rely on dot & dab.

I would then build three stud walls using Aquapanel or Hardibaker and tile from floor to ceiling

You only really need to use tile backer board in wet areas, MR plasterboard is fine in all other areas & you can tile directly over as long as your tile weight don’t exceed 32 kg/sqm; but, as I said, if your ½ tiling any areas & want to plaster above you must prime before plastering but if your getting someone in, any “proper” plasterer should know that.

The bath with shower over would be in the corner so maybe extra tanking needed there?

You can tank if you want additional piece of mind but IMO it’s not necessary & I wouldn’t; a wet room is another mater. If you use a backer board on the back wall behind the bath & at the back end where the shower will be, taking it slightly beyond the shower screen (300mm), it will be more than adequate; then use MR PB everywhere else. Again mark the tile line & plaster any non tile areas before you tile but remember what I said about not all backer boards accepting Gypsum plaster; well they will but the manufacturer doesn’t recommend it & you have to do extra prep!

 

[Rusty10]

Once again thank you for taking the time to help, its very much apprerciated!

problem is that although Thermaline Plus (which I assume is what your using) has an integral vapour barrier, the internal face isn’t moisture resistant & you should really be using MR board in a bathroom!

I was thinking of fixing MR plasterboard ontop of the Thermaline? My thinking was as its single block external wall this would aid the thermal property of the wall and not have 'cold' walls?

You only really need to use tile backer board in wet areas, MR plasterboard is fine in all other areas

Understood, I would use MR throughout for internal studs walls and soundbloc on the outside, I was thinking of using tile backer board in the corner where the shower/bath is?

Thanks again

 

[Richard C]

I was thinking of fixing MR plasterboard ontop of the Thermaline? My thinking was as its single block external wall this would aid the thermal property of the wall and not have 'cold' walls?

You can I suppose but I doubt you’ll get cold walls with the Thermaline; I’m just concerned about multi layers & how this will affect support when tilling; as I said you must ,mechanically fix, don’t just rely on Dot & Dab.

Understood, I would use MR throughout for internal studs walls and soundbloc on the outside, I was thinking of using tile backer board in the corner where the shower/bath is?

To meet the minimum sound insulation requirements the boards must have a minimum mass of 10kg/m2 on BOTH sides of the wall; where your new walls require sound insulation, use either Soundblock or Wallboard 10 on the outside & MR Soundblock on the inside of the bathroom. I would use tile backer board on the whole wall behind the length of the bath & on the adjacent wall, taking it around 300mm beyond the shower screen.