Wall chasing and replastering - any tips?

Hi all,

the time draws nearer to when I'll have to chase out all the walls for new electrics.

Got the ALDI chaser and a funny cranked chisel bit for my SDS.

But, I've been thinking - how hard will it be for an eejit like me to plaster in the chases afterwards? And what should I use? Bonding, then a skim coat - or browning, or a mixture of Bonding and finishing plaster (IIRC) laid in one go (heard somewhere that someone swears by this for patching up).

Is it best to cut the chases tight to the oval conduit, or leave a gap for the plaster to get round the sides (better grip?)?

The walls appear sound and the final finish will probably be a lightly textured paper painted with emulsion (no, not woodchip!).

A mate was recommending re-skimming the lot, but it seems a waste and a lot of work if the rest of the plaster is good. Granted, you could paint a re-plastered wall directly and it would look good, as he has (Hello Mark!)

Cheers

Tim

Reply to
Tim S
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Bonding won't polish up nicely as it's got large particles in it (looks like mica and other stuff).

Liberally paint the cut edges and the exposed plastic trunking with dilute PVA to seal the edges, and make the plaster stick to the PVA. Try to avoid it getting into the accessory boxes or down the trunking (it will permanently stick PVC to the inside of the trunking).

I use just finish coat, and if possible an old bag past its date, as that means it will set quickly (you don't want to be waiting

2 hours to finish polishing off the surface of the chases). I do two coats -- the first is bonding made from the finish coat plaster (mix in a little PVA), which saves lugging a separate bag of bonding coat around. Bring that up to 1-2mm below finished surface. It will crack (being too thick for a finish coat), but that doesn't matter. Then use finish coat (no PVA) to do level it off. Apply the finish coat whilst the bonding coat is still damp (but set, or very nearly so).

Cut to exactly the conduit size. Chasers normally come with spacers which give you exactly the right size. Cut the chase freehand following a pencil line -- the inevitable slight curve you'll get holds the oval trunking in place without any nails needed. First time, I cut against a straight edge and got a perfectly straight chase, which meant the trunking just fell out of it;-)

If it's a small piece of wall, and you're good at skimming, and the wall isn't perfect, then I would reskim. Otherwise, it's not necessary. If you're not good at plaster finishing, you would be advised to allow for sanding the chase down afterwards. They do have to be perfect to be invisible on a painted wall, and your eye is easily drawn to the tiniest imperfection of that sort.

Reply to
Andrew Gabriel

The point is to get a good adhesion to the brickwork and the existing plaster, so anything that will let this happen is a good thing. I've heard of a stretchy tape that will bond to the brick surface and grab the plaster to it. It is something like the plaster bandages they use for setting broken bones I think. Apply dry and wet and press into the channels to get it stuck.

Plaster is normally built up with a coat of bonding and a coat of finishing, so if you can copy that in any wider chases, then great. But it might be better and cheaper to stick with just finishing plaster throughout the job.

The making of a smooth finish is in the soaking and polishing. After applying the plaster, leave it for an hour and then soak the surface of it thoroughly with a paint brush. Slide your plastering float firmly over the surface to make it smoother. Do this a few times until you are happy that it's level with the original surface, and is as smooth as a babies whatsitmabob.

Remove any wallpaper before plastering as well, or your new plaster will be level with the paper instead of the original plaster surface.

I bet you get the knack of it in no time at all.

Reply to
BigWallop

Andrew Gabriel coughed up some electrons that declared:

Thanks Andrew. Looks like I'd better plaster up after 1st fix and get any required sanding out of the way as it's as messy as chasing...

I know it's hard to get a good patchup on a wall to be painted with emulsion - that's why I'd resigned myself to hanging paper, either lining or textured, then painting. Fortunately my paper hanging skillz are OK, except on ceilings.

I'll certainly employ the PVA. With any luck if I sink the backboxes with care, I might avoid much pastering around them.

For protecting the accessory boxes, I was going to poke the conduit through the knockout, then add a blob of sealant to bung the hole up, and cut out a few bits of plastic sheet (like 3-4mm thick stock) to stick in the front. Probably only need 4-5 as these will be resuable.

Cheers

Tim

Reply to
Tim S

You'll probably find the knockouts are deeper than the conduit, except in the case of very shallow boxes. You can make the channels deeper as they approach the box, although you might not want to make them that deep everywhere.

The trick I mentioned in the other thread about plastering over back boxes is actually what I do with all back boxes when I'm skimming (with the wires tucked in behind). I get a much nicer finish if I'm not worrying abour stearing the trowel past wires and avoiding filling backboxes with plaster. I then cut out the plaster and the card when it's half set (except those boxes I'm leaving plastered over). It's often occurred to me that someone should make a piece of semi-flexible plastic for this purpose.

Reply to
Andrew Gabriel

Pack the boxes with old newspaper. You can throw it away after you're finished. But it stops you filling the boxes with plaster.

Reply to
BigWallop

I'm sure I've seen them somewhere.

Reply to
<me9

snipped-for-privacy@privacy.net coughed up some electrons that declared:

You're not thinking of Yoozy boxes are you? These are similar in concept but are used when plastering is done after 2nd fix (they are effectively a spacer that holds the plate out from the wall and fills the gap to stop the plaster getting in. Doesn't help the plasterer, except in as much as the electrician won't go and kill him for filling his boxes with muck.

Cheers

Tim

Reply to
Tim S

I don't think so, but their website is so bad, I can't actually see what the product is. The pictures demonstrating it all show a installation where the cable doesn't run in a line from the accessory box too, which is not good ;-).

I remove all the accessories, and coil the wires up so they are hidden in the back box and not sticking out. May temporarily connect with chocolate block connectors or leave the circuit turned off, depending. If you're going to the lengths of replastering, you're usually at least replacing the accessory plate items with new ones too. (Keep new ones away from damp plaster -- it can stain some finishes.)

Reply to
Andrew Gabriel

Maplins used to sell something like this. They stopped selling it years ago (at least 10)

Adam

Reply to
ARWadsworth

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