Preparation for bonding/hardwall coat

[Bedrock9]

Hi, I am trying my hand at plastering and have a few questions about preparing for skimming the walls.

I have had a rewire and removed some loose plaster so have some patches back to brickwork, some cutting in with plastic conduit etc and some exposed copper pipework to cover prior to beginning skimming the walls. The bricks are oldschool & very porous.

What I am not sure about though is

1. Should I wire brush the brickwork or similar to remove any dust, old lime plaster etc and try to get a bit of a mechanical key or am I just wasting time?
2. I understand I should wet the brickwork a lot before bonding/hardwall to slow suction but should I also be putting on a PVA mix to try and control this too?
3. On the conduit would it be a good idea to do something like Roughcasters solution for Gloss paint, like neat PVA and bonding coat slurry to give the bonding coat something on the conduit to stick to? Or should I just rough it up with sandpaper, or 3 to 1 PVA, or not bother?
4. Existing plaster work is at least an inch deep in places, I seem to find different points of view on whether I should be using drywall or bonding.
Should I be doing something like drywall scratch, bonding coat, skim?
5. Been told plaster will corrode copper pipe work, is it ok to just cover it with duck tape as someone suggested?

Thanks in advance!

 

[Bedrock9]

40 Views and no responses... have I exposed myself as the village idiot or committed forum suicide?

 

[Alastairreid]

40 Views and no responses... have I exposed myself as the village idiot or committed forum suicide?

Clear the walls of any loose plaster/debris and dust with a light brush no need to wire brush.

A damp down will suffice but using pva wont do any harm.

I would put scrim tape over the conduit.

A couple of coats of bonding to bring it up to below flush before skimming.

Wrap copper pipes in duct tape!

 

[Bedrock9]

Hi Alastair, cheers for that will see how it goes! Ta

 

[Bedrock9]

Hi Alastair,

One more ting!

Would the plasterer normally seat the knockout boxes I take it? I.e unscrew them level them up with the new skim so set about 3mm proud and then just fill the sides with bonding to hold them in at the right depth and level?

 

[Alastairreid]

The plasterer wouldnt normally touch the pattress boxes, that would be down to the spark to set them out.

 

[Bedrock9]

hi, yeah funny that an old mate has done the rewire and one of them is almost an inch deep behind the plaster, not sure if that's going to be a problem. I suppose it would just mean sticking longer screws on the fixture anyway. Will give him a buzz and find out.. Cheers

 

[Bedrock9]

Hi Alastair,

I have been building up with bonding where it was back to brickwork and have my window reveals plaster boarded ready to go and a couple of other bits skimmed.

Where my bonding will meet up with existing plaster should I scrim tape or something similar the join in order to prevents cracks where the two backgrounds meet? I believe I should tape the joins between the plasterboard and bonding as well before skimming yes?

Also as the existing plaster below the window was so deep I need to either stick an extra layer of bonding over the front of the reveals or stick another layer of board on to double it up. I am thinking that the whole wall has so many patches of different things going on that the best finish might be achieved by doing a thin coat of bonding over everything once they are all at similar level and then skimming over this. Is that best practice anyway? Or am I just worrying over nothing? Thanks again.

 

[Alastairreid]

The only time you really need to use scrim is if there are differing surfaces, ie gyproc to brick etc or if there are cracks in the existing surface.

A tight coat of bonding over that lot is what i would do.

 

[roughcaster]

Agree with Alastair, spot on as usual.

 

[Bedrock9]

I take it by a tight coat you mean almost like a skim of bonding floated rather than just scratched and a bit rough? Thanks again

 

[NickB_99]

I take it by a tight coat you mean almost like a skim of bonding floated rather than just scratched and a bit rough? Thanks again

Yes. In noddy terms (which I always like!) it is not too hard as Bonding has little lumps in it and make it straight forward to gauge the thin (tight) coat of Bonding as it goes on.
Usually ends up reasonably smooth and don't scratch.

(Ps I think the little lumps are called vermiculite or something like that. I'm sure roughcaster told me a long while ago, but I've slept many times since then!)

 

[Bedrock9]

Thought so, cheers! Will post some picks of my bodging when done... see whether it falls off in two weeks