Aquapanel in shower enclosures

[dundeediy]

Im building a three sided timber stud wall to create a shower enclosure and using aquapanel cement board over the studs.

Theres a lot of conflicting advice online re whether to install a vapour control barrier behind the aquapanel or tank the surface before tiling (or both!) to ensure its waterproof. Most of the online advice states that aquapanel is not waterproof so there is a requirement for additional methods to prevent water from seeping through.

In an effort to get a definitive answer I contacted the UK Knauf Technical support team - this is their response:

We don't advise that you use to VCL behind the Aquapanel board as it is not needed, also you wont need to tank the surface of the boards.
​

So there we have it - according to Knauf theres no additional methods of waterproofing required - or does anyone disagree?

 

[opps]

Surely you need to tank the joins though?

I had always assumed that aquapanel is waterproof. (I am often wrong though).

 

[dundeediy]

I agree - the guy from Knauf didn’t specifically mention tanking the joints but I think it makes sense to do so.

 

[opps]

I guess that tanking the whole sheet will reduce the weight bearing load.

 

[oldbutnotdead]

Do Knauf supply installation instructions with the sheets? Any detail about taping joints and that sort of thing should be in there- have a trawl on their website

 

[ktuludays]

I helped a builder install some earlier this year and no instructions came with them.

What I would advise as the op has done is that they are mechanically fixed. The builder dot and dabbed them and they fell off the wall twice. He then used nails into the brick and plastered the walls. 3 months later when I went to install the bath all the plaster had fell off due to movement in the boards. In the end I ripped it off, added battens and used no more ply.

 

[opps]

He used nails!

Are you sure that he was a builder?

I agree - the guy from Knauf didn’t specifically mention tanking the joints but I think it makes sense to do so.

I would also tank the screw holes (just in case...).

 

[dundeediy]

Just to clarify further I contacted Knauf tech support again asking for more detail re joints etc - this is their response:

You will not need to tank internal corners, between the boards or over the screws heads. As long as the board has either been butted together using the Aquapanel joint adhesive (method 1) or taped and jointed with the Aquapanel interior joint filler along with the Aquapanel joint tape (method 2), topped over with the Aquapanel skim coat, you will be fine. ​

So interesting stuff - if it works as stated this certainly makes for a relatively simple method of building a waterproof shower enclosure.

 

[opps]

Thanks for the update.

I am surprised that they don't consider it necessary to cover screw holes.

 

[oldbutnotdead]

If Aquapanel tape is the same as Marmox tape it costs about £5 per metre and you end up needing

Thanks for the update.

I am surprised that they don't consider it necessary to cover screw holes.

Me too. And watch out for the price of the special Aquapanel skim, tape, jointing compound- I found with Marmox that all the 'special' bits added about 100% to the price per sq metre for the panels

 

[opps]

Just to clarify further I contacted Knauf tech support again asking for more detail re joints etc - this is their response:

You will not need to tank internal corners, between the boards or over the screws heads. As long as the board has either been butted together using the Aquapanel joint adhesive (method 1) or taped and jointed with the Aquapanel interior joint filler along with the Aquapanel joint tape (method 2), topped over with the Aquapanel skim coat, you will be fine. ​

So interesting stuff - if it works as stated this certainly makes for a relatively simple method of building a waterproof shower enclosure.

Duh, I missed that bit...

So tanking isn't necessary if you pay bucket loads more for their cement based coating. That certainly seems like a case of cross selling by the rep.

Personally, I would rather save time and money by tanking the joins and screw heads.

 

[Paul C.]

Oh dear. I don't think Knauf are up-to-date with the latest British Standards!

BS5385 Part 1, 2018:
6.1.1.3 - In wet areas, e.g. showers, wet rooms and steam rooms, substrates should be protected with a suitable proprietary tanking membrane system.

The likes of Aquapanel and Hardie Backer are water RESISTANT, not water PROOF. This means any water coming into contact with it, the board will soak it up and hold it without losing dimensional stability. When the shower is not in use, the theory is that the water in the board will slowly evaporate away, either back through the tile joints or into the wall cavity (where it goes from there is anyones guess). Water can still pass through it, and although its going to take a serious amount of water for that to happen, it leaves open an element of risk, one that if I was an installer, I would not be prepared to take.

Foam-core panels like Marmox, Wedi and Kerdi, are water proof. As with the Aquapanel, the joints and screws need tanking over, but the remainder of the surface is completely water repellent and water cannot pass through.

Ok so I await the backlash - people saying that British Standards are overkill and to some degree I agree...... (wow, that rhymed, check me out! ) but they still need to be considered. If any case went to court for some kind of installation failure or leak, regardless of how much experience a tiler has, commenting with the usual "been doing it like this for 30 years and never had a problem", theres always a first time and he would be held liable for not fixing to the recommended standards. If knauf said it would be fine, then at least he could in turn take them to court to claim back from them, but then they'd even try and find fault in the fixing and find somewhere to hang blame as long as they don't have to pay out.

Sounds like alot of hassle doesn't it? when all along it could have been prevented with a £40 tanking system.

 

[foxhole]

Or forget the tiles and use shower panels.