Fixing boxes to a tanked wall.

[flyingsparks]

Got to fix socket boxes to a tanked wall, and clip cables down. The wall will be dot and dab too, so I have sunk the boxes in 10mm ish, and the customer is going to apply more tanking to this area. How would you go about fixing the boxes to the wall? Glue with plasterboard adhesive stuff, wall plug and screw and paint over them? Also where cables are clipped down the wall, would you paint over them with more tanking slurry?
Cheers all...

 

[333rocky333]

Reminds me of when i worked at "number 1 london", they had dampproof rendering, and the contractors used a sort of grip adhesive to stick small moulded wooden panels where our fixings were to go, that was all surface galv conduit

 

[viewer]

Please could you explain the construction?
Your description suggests that a plasterboard wall will be built in front of a tanked solid wall and the plasterboard waterproofed on the back - is that right? The cables go between the two? Where is the sunken box section?
A lot depends on your answer as, although the electrical answer might be fairly simple, tanked walls are always a nightmare and any answers and subsequent problems could lead you into expensive "it's your fault" arguments in a year's time.

 

[flyingsparks]

No it's basically a block wall tanked and then plasterboard dot and dabbed onto it. Just wondered about the fixing of the boxes to not compromise the waterproof tanking by drilling it.

 

[securespark]

Leave the Dot & Dab alone.

Glue battens to the D&D with NMN. Screw plasterboard to that, then fit dryline boxes to this board with the cables running in the void between the two plasterboards.

 

[bernardgreen]

In some circumstances tanked walls can be damp from condensation so look out for the vapour barrier.

If it is a tanking wall ( a wall purposely built to be a tank ) then it was probably designed to tolerate short screws but if it is a tanked wall ( a leaky wall lined with a water proof layer ) then best not touched.

 

[pjcomp]

Talk to the tanking company. They're responsible for the waterproofing and will carry the guarantee that it stays dry - they should be working with you to ensure that whatever you (and the plumbers etc) do doesn't muck up their warranty.

PJ

 

[Lectrician]

Concur with that. They will normally advise what they want done. You don't want to make it up yourself.

 

[flyingsparks]

It's not being done by a tanking company. Basically a bloke who is building his own under build extension, but I'm doing the wiring. He is the one doing the tanking etc.. I think the building inspector asked for the walls to be tanked even tho it's knot a retaining wall and there is a dpc....

I don't think he will want to change the plans by fitting battens etc..

 

[Lectrician]

It is more usual on something like that to find plastic DPM placed over the wall, and a stud wall built in front - That's what happens around here on single skin garage or basement conversions.

 

[viewer]

Not easy, but I'd suggest telling him that boxes have to be surface mounted or you won't do it. Sounds dramatic, but I have seen cases where tanking has failed or has been the wrong solution and when problems arise the tradesmen working inside the building have been blamed by the householder or their insurance company. Even where it was shown that the problem had been caused by a DPC in the wrong place, it still cost the builder a small fortune in solicitor's costs, time on site, lost work etc. TBH the whole concept sounds a bit dubious. Tanking has to have a certain amount of flexibility and yet he's using dot and dab. As others have said there are lots of problems with condensation, salts and movement. Protect your back. Maybe worth talking to the building inspector.

 

[bernardgreen]

The two sucessful tanked rooms I have seen had a stand-alone room built of stud work inside the tank. Nothing touching the walls of the tank. The extreme one had drainage channel to remove condensation that ran off the walls to a pumped sump.

 

[stillp]

have sunk the boxes in 10mm ish, and the customer is going to apply more tanking to this area.

Where is the customer going to apply more tanking? Inside the boxes? Behind the boxes? What about the fixing screws?
I'd take those boxes off, fill flush, retank then do as others have suggested and glue timber to the wall and fix the back boxes to that.

 

[ban-all-sheds]

Maybe he'd go for this sort of thing (but with BS 1363s)

 

[flyingsparks]

have sunk the boxes in 10mm ish, and the customer is going to apply more tanking to this area.

Where is the customer going to apply more tanking? Inside the boxes? Behind the boxes? What about the fixing screws?
I'd take those boxes off, fill flush, retank then do as others have suggested and glue timber to the wall and fix the back boxes to that.

No I have chiseled out the block. He will now tank the bit which has been chiseled out. I will be back on Monday to fix the boxes. Was thinking of glueing the boxes hence no screw holes. I can't see really how anything I am doing should cause the tanking to not be effective?