Plaster board butting to existing plaster on wall

chuggypig

Hi

I have a wall which has had an opening knocked through and i will be tiding up the opening with dot and dabbed plasterboard. I dont want to strip all the good plaster that is already on the wall and replace with board so i have just trimmed to existing plaster back and given it straight edges and want to butt the plaster board up to this. My question is do i need to scrim tape between existing plaster and plaster board before skimming

Cheers

Richard C

How much of the plaster have you stripped back? Is the opening to have a door liner fitted or is it a form of arch?

A D&D plasterboard repair is not ideal & it’s best done with a base coat plaster & then finish. You must use reinforcing tape but because of the different expansion & contraction rates (old & new), even that may not stop it cracking open again where the 2 meet. A nice straight edge where the new meets the old is not a good idea either as that will be more liable to crack. Blending in to existing with plaster skim is not easy if you want to avoid seeing the join or it cracking & I will more often than not, re-skim the entire wall. I usually break away the edge of the original plaster with a hammer to give a rough dog toothed edge, make good around the new opening with base plaster or render & blend this flush with the surrounding original, I then apply 3 layers of overlapping reinforcing tape before PVA & re-skimming.

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Richard C

PrenticeBoyofDerry · Posted: Mon Nov 02, 2009 10:27 am Post Subject:

Yes, tape the joint, if you take about 30-40mm of the finish off the plastered wall, where joint between plaster and board is. You can then the tape can sit level over the joint so no hump when you skim. remember to fix the board so they are a few mm recessed to existing. plaster so new wall can be plastered level to existing wall.

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Dum Spiro Spero

chuggypig · Posted: Mon Nov 02, 2009 11:17 am Post Subject:

Hi

I will be skimming the whole wall covering plaster board and original plaster so assume just dot and dab plaster board keeping this level with what's on the wall then skim.

I have trimmed back the original plaster about 400mm either side of the opening all the way to picture rail which is about 400mm above opening. Normally i would have stripped the whole wall back and dot and dabbed the full thing but the wall is quite long so seemed pointless stripping good plaster off just to put board on, and the other reason is the wall has previously been treated for damp long before i moved in at the bottom meter of plaster is like concrete and an absolute nightmare to get off taking the bottom meter x 400mm wide to either side was enough for me
to realise it was gonna take ages to remove.

Could i not just dog tooth the existing plaster and plaster board then leave a gap between both fill this with bonding then re skim the lot to prevent having a straight edge being a week point.

Cheers

Richard C · Posted: Mon Nov 02, 2009 11:51 am Post Subject:

Stripping the whole wall back is not necessary & a total waste of time if the original plaster is sound. I would still use a base plaster or render to fill out, depending what the original is but I assume your choice to D&D some board means you’re not comfortable with that.

Dog tooth & fill is better than a nice straight line. Keep the new board flush with existing wall fill out any gaps as you suggest & tape it well. Boarding it out may work fine but it rather depends on individual circumstances. The problem is that as the internal temperature of the property varies, it will expand & contract at a slightly different rate to the original plaster/render finish & this can cause the finish skim to crack along the join between the 2 even though it’s been well taped; the larger the area of boarding, the greater the problem.

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Richard C

chuggypig · Posted: Mon Nov 02, 2009 11:57 am Post Subject:

Cheers.

I'm not comfortable re-doing the plaster i can skim spot on but that's it. i would porbably make a right mess if i had to replaster as i've never tried it and would'nt want try my first time in my living room. Plus the hole left has raggy brick edges and i assume this would be easier plaster boarded.

cheers for you help i'm gonna get a start on it tonight

Richard C · Posted: Mon Nov 02, 2009 12:15 pm Post Subject:

Go on, go for it; it will add another feather to your cap

If you can skim as good as you say then you’ll be just fine; use some depth guides or battening to rule off against if you need to. In your case I would suggest Bonding plaster as it sticks well, is very easy to use & will give you a fair amount of working time to get it right; it’s not meant for high suction backgrounds but I use it a lot on such jobs, you just need to PVA seal the background the day before, PVA again before you plaster & keep the surface moist (not wet) while it’s going off.

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Richard C

chuggypig · Posted: Mon Nov 02, 2009 12:22 pm Post Subject:

If i was to replaster instead of plaster board how would i go go about covering the new steel lintle it's and "I" section and i was advised to cut some dry timber so it was tight fitting to the inside of the flanges and knock it in place then fix plaster board to this as well as it being dot and dabbed to the brick above steel

Richard C · Posted: Mon Nov 02, 2009 1:50 pm Post Subject:

That makes a little more involved but basically, do it exactly the same. Fit the timber so it’s tight as advised & screw a lump of PB to this so the face is flush with the brick wall (not the plaster). Fix some steel lath (mesh) over the lot so it overlaps the wall at least 150mm both top & sides & then apply your base plaster over the lot, build up in layers no more than 10mm at a time; using the lath will help prevent it cracking around the lintel. Fix a strip of PB to the bottom of the lintel but I would use a trade grab adhesive rather than drywall. What are you fitting to the opening, is it to be left plaster finish or are you fitting a door liner?

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Richard C

chuggypig · Posted: Mon Nov 02, 2009 2:10 pm Post Subject:

Is that all??? pffffff - "Simples" as Mr meerkat would say.

Thanks for all your great advise but that sounds a little out of my league. Think i'll go back to plaster board idea or else i can see me making a right a**e of it and that wont go down very well, and to be honest the misses is already doin her nut with all the mess and dust at the minute without big blobs of bonding all over the floor.

Cheers