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M365Certified t1_iyb6ek9 wrote

There's bad advice here. The lathe originally was covered by a plaster blend, plaster mixed with horsehair (readily available then) and sand, both of which added strength and "bulk". You can look it up with some research. If you want it "restored", find a plaster who knows the old ways.

Far more practical, and what I've done, is to cut drywall to fit, screw it to the joists/lathe, using 5/8, 1/2, and 1/4 inch boards to get as close without going over to the original thickness.

Get some 90 minute setting type plaster/joint compound (NOT the bucket of pre-mix) to fill in the "gap"; Don't over fill because sanding is a huge pain. Use paper tape to bridge from old plaster to new to prevent cracking

Final level happens with the sandable pre-mix stuff, then sand smooth.

Make sure what is left is well attached, there are kits to help secure remaining plaster if its loose.

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Mr_Czarcasm t1_iybuwh1 wrote

this video is exactly what this guy said. Do this.

https://youtu.be/hKxya3jNhYg

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tacotimes01 t1_iybyyx7 wrote

I used to manage an old building and this is the way, but there is one problem: leaks. If there really is a leak issue, that drywall is going to mold, turn black, and stink up your apartment.

Old buildings have lots of leaks: old galvanized drain lines, internal roof drains, rainwater intrusion from rotted tin lintels, poorly sealed ancient windows, retrofitted shower pans on old ass flooors, etc. from my experience, catching the leak and fixing it was one thing, but ripping apart walls to find mold from old Sheetrock repairs and abating that was a nightmare (and potentially a reoccurring one).

Plaster doesn’t rot, just gets wet and dries out.

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adappergentlefolk t1_iyc5kf5 wrote

depending on the backer and the composition plaster can definitely lose structural integrity from damp. things like gypsum on brick can get absolutely shredded by salt migration from the brick. then instead of dealing with moldy drywall you have to deal with a wall section that has disintegrated into fine sand, ymmv what you prefer

even lime plaster on lathe can disintegrate if damp is trapped in the plaster behind an impermeable layer like thick paint or wallpaper

definitely source of water intrusion needs to be fixed before any repairs are done to the area. simply a waste of money and effort otherwise

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tacotimes01 t1_iyd3fnx wrote

Thanks, completely agree you have to fix the moisture issue. I’ve definitely had plaster repairs fail in this way when leaks persist. I guess my point was that it’s been preferable in my experience to go the plaster route and deal with this rather than the effects of mold growth in the walls. You always “think” you fixed the underlying cause of a leak in an old building, but sometimes it’s less apparent or there are multiple causes. I’m getting PTSD thinking about managing this leased 120 room 1909 San Francisco nightmare.

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NightGod t1_iyc65a5 wrote

OP could use glass mat drywall and avoid that issue

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[deleted] t1_iyby695 wrote

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M365Certified t1_iydbqmw wrote

Final result is softer

it must air dry, so thicker coats will take forever to dry, vs the powder that "cures" via chemical reaction with water

As the others noted, it shrinks more, which creates problems when filling in big/deep areas

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WAREHEIMER69 t1_iybk97m wrote

Can you say a little more about the product to use for the final coat?

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superbigtunajim t1_iybl03w wrote

You can get in a bucket or a box normal sold in a couple gallons. Drywall mud not spackle. https://www.acehardware.com/departments/paint-and-supplies/patch-and-repair/joint-compound/12922

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7point5swiss t1_iybr6jn wrote

I would use a lightweight, not all purpose, for the final coat. Much easier to sand.

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M365Certified t1_iybma6s wrote

That is the stuff, instead of setting when mixed with water via chemical reaction, the bucket/premixed stuff dries, you can't apply it too thick, hence the setting type for the main leveling. Its also a lot softer than the setting type, so its easy to sand.

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WilliamWebbEllis t1_iycnj5r wrote

If you're taping onto existing painted walls I would use a premix taping compound or all-purpose compound. Powders don't stick well to paint.

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dougc84 t1_iycb6n1 wrote

You seem knowledgeable - I'm going to hijack and ask a question. I have a section of plaster that was adhered directly to brick. A less-than-knowledgeable about old houses contractor (and I won't hire again) cut a section out, about 8"x8" square. Now I need to fix it. I don't even know how I would go about putting drywall on that. Any suggestions?

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mawktheone t1_iycda2p wrote

You get a gypsum based adhesive for putting the drywall directly on surfaces. Call dot and dab attaching. Just cut out a square of drywall, throw a handfull of adhesive on the wall and stick in the square.

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For a pro tip, cut the patch a few inches oversize, and cut off the plaster on the excess leaving the paper attached. put a layer of jointing compound under where the paper overlaps the old drywall and it'll be much easier to feather out and blend later

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adappergentlefolk t1_iycx4bk wrote

a section that small is also possible to just fill in with new gypsum in one or two coats and level it off to be quite flat with the existing wall. i guess drywalling is a more useful skill to develop in general however, depending on region and materials availability

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sub-hunter t1_iycfg9j wrote

100% what you said with the addition of five minute mud 25 minute mud and 90 minute mud

The only goal with each of the types of mud is to not create anything to Sand

Final coat with wet mud with some water added

I totally understand this guys only gonna buy one bag of mud

And he could probably just fill the entire hole with five minute mud like the way they did the plaster

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M365Certified t1_iyddjjn wrote

I'd stick with 90 minute mud as a beginner, more waiting but more time to figure out what you are doing. Pure mud you'd need to get it pressed through to create new keys for adhesion, and the horsehair & sand in the greycoat adds strength, not sure pure plaster would last as long

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