Plastering long 4cm channel in cozyboard

boardtc

I have a 4cm wide, 1.8m long channel in a 5cm coxy board (12mm standard plasterboard with 38mm insulation backing). It was created to run wiring from our patio to the fuse board. My plan was to apply PVA generously, leave a while, and then fill it with pre-mix plaster. The only place I found it is this 10KG: https://www.screwfix.ie/p/no-nonsense-ready-mixed-plaster-white-10kg/23226 - a lot would be left over.

Is this the best plan or what do you suggest?

10-10-20

Hi. I'm slightly concerned that what looks to be a standard unprotected electrical cable will be buried in a wall at such an angle with no protection - it doesn't appear to be installed within a prescribed zone (ie a zone indicated by a socket or junction) and you mentioned that the wall is cozy board, so that indicates that it's an insulated slab and hence the wiring probably should be suitably derated. If this was all performed by a registered electrician and you have a cert for the work, then well and good. We'll leave it at that.

In terms of back filling that hole, I have used bonding to perform the initial back-fill as it sticks very well (no PVA required with bonding) and it doesn't suffer badly with suck - so you can keep working it for a good period of time so that the bonding is submerged slightly from the level of the wall. Up to you if you want to PVA it to improve the workable time. Then after that apply skimcoat while the bonding is still wet with a good plaster's trowel. With those two products and patience you can get that joint to be completely unnoticeable from the surrounding wall.

Otherwise, you could try use a large gap filler or Toupret interior filler and build it up before finishing it off with a good knife.

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boardtc

@Mason Parsons did you mean to post something?

con747

https://www.boards.ie/discussion/comment/121924379#Comment_121924379

Probably post building or a bot.

boardtc

Any advice on how to fill/plaster is much appreciated.

DublinDilbert

https://www.boards.ie/discussion/comment/121938123#Comment_121938123

Have a look at this video, https://www.youtube.com/watch?v=Nax6Zxcbhp4 he recommends foam and then mesh/plaster.

If it was me I would bond in scraps of plaster board, leaving gaps every 30 cm or so, then once they are stuck in place i would inject in expanding foam. Then fill / tape over the top of the plaster board. I would push the plaster board in so it is slightly below the surface and use the paper tape when jointing.

boardtc

@DublinDilbert Brilliant thanks, I have secured some scraps from a friend. Can you tell me some more please about the paper tape and what you would use to finish?

kirving

https://www.boards.ie/discussion/comment/121920168#Comment_121920168

Would you reccomend putting in a blank socket at the bottom to indicate that a wire is running there? ie: create a zone

10-10-20

https://www.boards.ie/discussion/comment/122039034#Comment_122039034

I'm not an electrician but I understand that anywhere that the cable comes outside a zone that it should be protected by a galv shield. In this case it's at an odd angle, so in theory you could 'create a zone' by placing an inspection box (blanking plate) lower down, but how is that going to indicate that the wire curves in at the top? But yes, better than nothing.

DublinDilbert

https://www.boards.ie/discussion/comment/122038996#Comment_122038996

paper scrim / joint tape, screw fix will sell it and jointing compound, most good builder providers will sell a small bucket of jointing compound.

The cable is far enough back there should be no issue. If you are worried about it you could add additional protection in front of it.