Cieling Damage Prevention

[sunbay ac]

How does one install grilles and boxes in an older home with plaster and lathe ceilings without damaging the plaster and leaving gaping holes?

[Toolpusher]

Scratch the surface of the plaster to score a line,
Get a new sharpe blade, Go slow and be lucky.

Last ones I did with a rechargeable circular saw. Along the long sides, then finished with a hand saw.

[berad]

There is a plaster blade for a sawsaw. It has teeth that lean opposite of each other on the blade. It looks like a crocodile. Go slow and wear safety glasses and a respirator or you'll be wiping your eyes and blowing hard boogers for days. I generaly measure to where I believe there will be no joists in the way and then use a 1/4 inch drill bit that is 14 inches long and drill a spotter hole in the middle of the grill location. Then either you have someone up top to measure, or you go up top to measure to make sure you miss what you want to miss.

[hvac4u]

i used metal cutting sawzall blades, wore them out quick but they did the job

later i heard of the plaster blades, but thankfully never needed to use them

[rimek]

If it is wood lath, then be sure your cuts across the lath are next to a joist at the outside edge of the register opening. That is because any reciprocal(sawzall) type of saw blade, even plaster-masters, can grab the wood lath and bounce it, which will seperate the plaster farther away from the edge.. How many u gotta do? You can mark the hole and use a small masonry bit(3/16, 1/8) to drill into the plaster only to the lath and run along the line to clear the plaster away from the lath and then use yer sawzall. Of course, you don't need to worry much when the line runs along the same way as the lath, just try to spot the register opening between 2 whole laths. In real fussy spots, I have drilled a hole all the way through every 1/4"-1/2" or so along the line and that makes cutout easier. If this is an unfinished place with no worries about mess, you can have yer helper run a small circular saw or angle grinder with a thin masonry cut-off blade and cut 'em out that way, just makes a sh*tload of dust.

[amickracing]

I use a masonary bit for a spotting bit, sometimes use my regular long drill bit if needed.

I've found using a masonary blade for a grinder works awesome for making a clean cut. Unfortunaetly it makes a lot of dust and a good size mess, so use it in the right conditions.

[billygoat22]

Depends. If its damaged or was cheap plaster work- less than 1" thick, its much more likely to break, can't really avoid breakage if its already falling apart.

I've used the plaster blades with sawzall. Cut across the lath opposite the joist (one side hole against joist when you can) since the ceiling is pretty stiff before you start cutting, and keep the saw against work or hold the lath down as you cut so it won't bounce. Cut side by joist since it sure isn't going to bounce where its nailed tight.
Then cut the last two sides in the joint between laths (plaster only no wood to snag).

For a return hole I like to cut the ends first then across the lath, since the scrap will fall its so heavy and break back past the cut line. (outside edges in toward center of sides)

[jiminator]

I've had great success cutting plaster in the past with the carbide grit sawzall blades. There are no teeth on the blade that catch and tear and pull. Instead the blade just sort of grinds its way along. It cuts through the wooden lathe pretty well, too, though you'd think it wouldn't..
An easy touch is critical....

Best of luck,
Jim

[t527ed]

carbide bit in roto-zip tool.

[corny]

I always spotted my own holes...On plaster I would do my damndest to let two edges of the register fall in the gap between laths....I would score the plaster deeply at first with a razor knife then cut with a sawzall blade...just a run of the mill roughing in blade.

Ok... Once many years ago I had to cut in a 20 by 25 filter grille in a plaster with lath and that metal stuff wall.....carefully marked and got both holes on each side of the wall cut perfect......perfect ... then I noticed a small "tit" of lath sticking out into the opening... I thought I would just take my hammer and screwdriver and knock the tit off........it knocked off about a 4 inch by 2 inch hunk of plaster....it made me absolutely sick.

The next day while hooking up the air handler and condenser I fixed the wall with several coats of plaster of paris over the course of the day....

[Al Gregory]

When I did my old 100 year old house I tried to be so careful and no matter what I did the plaster cracked. Then when I said I dont care anymore it all went fine. I know live in a new house and need to do the upsatirs this spring and I hate the thoughts. I dont know how you guys do AC for a living. Its bad enough in basements with boilers I hate attics. Anybody in South Eastern Mass looking for work I would rather pay someone to do it for me. I suck at sheet metal I would rather use a pipe wrench all day.