I’m having an electrician install several new circuits in the house I just bought, which I have determined has plaster walls on rock lath. The circuit installation, of course, means a few dozen holes in the walls that must now be patched.
Right now I’m patching the holes as if the walls were drywall: cutting out drywall patches and using joint compound and mesh tape. Is there a better way? The instructions I’ve seen for patching plaster all assume that there’s intact wood lath behind the plaster, but here, the rock lath gets the same holes as the plaster. Furthermore, the brown coat of plaster is quite tough and is eating up all the blades I’ve used to try to square the holes off.
Also: when you knock on these walls, you hear a hollow sound, like drywall, and not the dead thud that I associate with plaster walls. Our home inspector thought they were drywall until he saw the rock lath in the attic. Are hollow-sounding walls characteristic of plaster on rock lath, or is it something else?
Replies
Can't really help you with your patching. But, Lenox does make some plaster blades. The work good in a hand held saw and great in a sawz-all. Just keep your speed down so they don't burn up quite as fast.
Get some Durabond, joint compound. Try to make the patches as straight, square or rectangular as possible. Then make a "blowpatch" out of the drywall. Use Durabond and imbed it well on the "blowpatch" and into the plaster hole. Affix the blowpatch into the plaster ans straighten out the blowpatch. On the next few coat use Durabond around the blowpatch and on the final coat use a joint compound which can be easily sanded. be careful with the Durabond as it's impossible to sand. I've just done a few of these in NYC.
If the new electric wires are against the wood lathe of the plaster, just fill the snake hole with Durabond and use mesh tape around the edges of the patch. Use joint compound on the final coat.
Another alternative is the drywall patches that are sold, they have a steel and fiberglass mesh and come in various sizes..little expensive but they work well. Use a setting compound on the first two coats and joint compound on the final coat.
Hard to say which of the above methods would be the best..it all depends on the type of patch.
Patching plaster walls with drywall is the norm. There is a metal patch sold at Lowes ( cost is $5 for an 8X8 inch patch) that you can cut to fit over the hole, then just mud overtop. This patch is supposedly self-stick. Seems like it would work just fine...but may be too costly if you have a lot of holes to patch.
I would seriously think about purchasing a roto-zip tool ( approx $50), or else at least the roto-zip blades and install in a router. This tool and the blades make it a breeze to cut through any wall; including plaster. I just used mine the other day to cut out a hole in a plaster wall for installing an "old work" electrical box on a recent job.
My advice, draw outlines around your existing holes so that they become "squared off". Cut your drywall patch first, hold it over the existing hole, now draw the outline, then use the roto zip to cut out around the outline. It is easy to cut these free-hand with the tool...just take your time and continue the cut in one direction...clockwise I believe...you can tell by the feel immediately which direction gives you the most control.
After cutting out the hole, slide a small piece of wood into the opening, pull this stick tight against the inside of the plaster, and drive a couple of drywall screws through the plaster and into this stick to hold it in place. Now, insert your drywall patch and screw it to the stick. Now your patch is in place, simply tape the perimeter and mud it up. Use fast setting type mud ( you mix with water) for the initial first coat. Use a topping coat for your final finish coat. Buy fine grade masonry sand ( it's white..looks just like salt) and mix a few cups of this into a few cups of topping compound...almost a 1 to 1 ratio. then spread this mix on with a heavy brush to simulate a swirl pattern , or use a trowel for a smooth application ( this is of course if your plaster walls have a sand finish...if not a sand finish, omit the sand entirely.)
In addition to the patch, you will have to spackle over the few drywall screws that you initially set to hold the stick in place. No big deal.
Davo
Hey Davo,
I love my Rotozip too for plaster walls, but you forgot to mention that the tilecut bit is what you need for plaster. Over rocklath or wirelath (slowly) you can get away with just this bit. With wood lath, you can cut the hole in the plaster, and then chuck a sabrecut bit to do the lath. I've done 40-50 outlet/light boxes this way, and they generally turn out great!
JK
Big Jake,
Thanks for "filling in the gaps" that I missed. Actually though, I have had good success with using drywall bits...so long as I go at a slow -moderate pace. If I try to hurry, the bit will snap, no doubt about it.
Davo
Your method will work, no problem.
But depending on the availability of plaster supplies in your area, you could do it the real way.
Put in something as a backer. Drywall, with the back side out, will work.
There's a product called plasterweld which is like pink, thin paint. It helps new plaster adhere to existing. It also seals areas where efflouresence (the white powder from water damage in plaster) is. Paint some on the edges of the hole and the face of the backer. If you have the backer inset a little, like 1/8" or so, that would make it easier to level out the finish.
Mix up some lime putty, Autoclaved finish lime and water. Mix it up to a creamy consistency and let it slake (sit for a while). Think cake frosting consistency, or a little wetter.
Mix up some slow set gauging plaster. Add some lime putty, about 25% or so. and mix it really good, so the slow set is homogenous throughout the lime. Apply it like mud. A trowel works well. As it starts to set, you can start troweling it out, making it really smooth by using the edge of the trowel. Use a little water on the trowel for lubrication. Fill all the pinholes with all the stuff you are "scraping off" and keep troweling with the edge as the plaster hardens. It should blend right in with the existing finish coat.
By the way, if using the plaster technique, you don't need the mesh tape. Run the finish coat flush with the existing plaster. No need to feather anything in, and absolutely no sanding.
If you live in Chicagoland, I could show you.
Pete Duffy, Handyman
My son owns a bunch of 80-100 yr old houses around Rutgers Univ. which we are constantly upgrading so I've got alot of experience patching plaster. First of all, be very careful when cutting the holes as the vibration can loosen large sections of plaster from the lath. I'm going to assumer you have the holes cut. Cut a piece of 1x2 longer than the hole, 2 1/2 to 3" longer. Don't bother trying to square out the hole. I run a 2" screw into the center of the 1x2 so I can control it into position and hold it in place if the hole is too small for my fingers. Run a 1 5/8 sheetrock screw through the wall about a inch above the hole into the 1x2. Tighten until the screw sinks just below the surface. Now screw a second 1 5/8 screw an inch from the bottom through the wall and into the 1x2 as you did above. Remove the 2" screw in the center. If it is a larger hole than put a couple of these backers in(you won't need the center screw in this case). Now cut a piece off sheetrock to fit the hole shape. It's easier to carve the sheetrock than cut the plaster & lath square. Screw that piece of sheetrock to the wooden backer strip or strips. I use 1/2" sheetrock usually because it is closer to the correct thickness. Now mix up a batch of regular plaster of paris and fill around the patch and over it until the hole is completely filled. Work fast as this stuff sets up in minutes. Go wash your mixing bowl and knife before it gets hard or you may as well throw them away. Now go back to the hole with a appropriate sized spackle knife and carefully scrape the plaster of paris until `you have clreaned up the edges and have the patch slightly below the finish surface level you desire. Do this by pulling the knife towards you at an angle. If you push foward at an angle the knife will dig in and ruin the patch. The patch will not shrink and will be fully cured in about 20 minutes. There is no need to use tape on the edges as it doesn't shrink and is rock hard. Now give it a light coat of spackle and your done. As soon as the spackle dries, prime and paint. You won't be able to find it after you paint. When the hole is large and the plaster is somewhat loose around the edges I screw it into the lath with sheetrock screws around the edge of the hile before I mix the patch.
My question WHY DO ELECTRICIANS HAVE TO MAKE SO MANY HOLES? At HD and Lowes they have this drill bit on the end of a long flexible shaft.
Does anyones's electrician use it ar do the all just use a hammer? Also doesnt anyone cut a hole with the blade at an angles so the same piece will fit back where it was taken from.
I'm always being accused of being too logical, and I have no Degree in Nuthin'.
Once you get going it takes 5-10 minutes per hole to patch them. The electrician might spend 15 minutes avoiding a hole. How would you rather spend your money?
To Frank and Dan
You'll right in what you say. But, others dont care as much as you guys do. But I can't argue about economics. There are a few plumbers who include patching in their price, but it doesnt include texturing and painting the whole wall to match.
Never seen an electrician include patching in his competitive price.
I have never seen an electrician move the second floor carpeting to cut the plywood floor to run electrical on the 1st floor ceiling.
I have never seen a Plumber run a water line under the width of a 3 car driveway without saw cutting it. I managed to "water bore" that distance, 1st time missed, 2nd time (boring) worked just fine.
Is there a book on the "Fine Art of Fishing"? for electricians.
I feel for electricians when the interior decorator wants that light switch or light fixture moved JUST 2 inches.
We make so many holes because homeowners want wires run where there are no access holes existing. I can use the long D'Versibits to go up or down from a new box I cut in the wall, but not horizontally easily. Also I do not like to drill through pipes, the plumber gets mad. Many times I run into situations like no access to crawl spaces in old houses, the floor joists are almost touching the ground. Two story houses have no access between the two floors. Most customers do not like conduit run on the outside of the house. I could go on, but it is obvious why electricians need to cut holes. I invite you to teach us how to do it without cutting holes. I am always open to new techniques.
Frank DuVal
Re: "My question WHY DO ELECTRICIANS HAVE TO MAKE SO MANY HOLES? "
I have rewired a lot of old homes and for the most part additional holes, other than those cut for junction boxes and covered by mounting the box and device, are not needed. Perhaps one or two in a complete rewire. Usually to get to overhead boxes in a ceiling trapped between floors.
This assumes that there is some access. Attics, crawl spaces, utility chases, closets and cabinets all offer routes for wiring to be run. Trim around doors and windows, baseboards and perhaps a new chair rail all can be used to gain access to wall or ceiling cavities with sufficient planning.
Of course this takes imagination, specialized techniques and tools and a large bag of tricks. It also takes more time. One time a HO estimated having an old twos story house renovated. Rewiring, plumbing, AC, the works. He got estimates for doing the jobs with minimum finish damage.
Someone suggested that it would be far cheaper to remove the finish on a few walls and a ceiling. The plaster was badly cracked and needed replacing anyway. Once he decided to drop some of the plaster he had the trades reestimate. The total cost was almost halved. I have been told that it is often easier to replace the plaster or drywall on complete walls than to patch more than a few holes in the same wall.
Knocking a lot of holes is sometimes a sign of a hack job but sometimes it is a logical conclusion of a negotiation between the HO and the electrical contractor. A trade of the freedom to knock a few discreet holes in return for a promise to complete the job more quickly. If it saves the electricians six hours and your drywall man can, assuming he charges the same amount per hour, seamlessly patch the damage in three the HO is ahead of the game.
Active's approach sounds like the way to go.
How solid the plaster sounds depends mostly on how thick the plaster is over the rock lath. If the plaster is 1/2-3/4 inch thick then it should sound pretty solid, but some plasterers probably cut it a little thinner than that.