Hole In The Wall Cafe

Posted by Steve on Wed, 06/28/2017 - 11:26pm

Yeah, Cafe. Because there are several things on the menu... several tips from my tyromaniac's bag o' tricks.

First thing, I apologize for the long lapse in updating BrookynRowHouse.  Fact is, there haven't been anybuild-y things to talk about around here.  The house is just about done, and "just about" is the same as "done" in a DIYer's vocabulary.  So I don't promise to be more active here. I also accept the fact that my Google ranking has dropped like a pigeon dipped in plaster from its #1 position five years ago under "Brooklyn Home Renovation" to, hell, I don't even know where it is now.  Probably where they hide dead bodies

Anyway, a friend asked me a couple of years ago to write an article about fixing large holes in walls.  He had recently installed central air and wanted to remove all evidence of where the in-wall air conditioners used to be. IIRC, he had plaster-over-wood-lathe walls like me.  If you've read my blog you know that I prefer the look and sound control attributes of plaster better than drywall.  In a nutshell, I use drywall for new construction but I always repair existing plaster walls. 

Coincidentally, an air conditioning installation is why I have to repair these holes too. I had an 18,000 BTU split-unit air conditioner head installed in my living room and the installers had to open up some 10" holes in the wall to pull the copper, control line and drain.  I also replaced my absolute CRAP Fujitsu split unit system with a new Mitsubishi.  Warning: if you have a Fujitsu spilt unit system, the company doesn't stock parts for old products. Mine was only 12 years old when one of the compressors croaked yet Fujitsu America told me it couldn't help me. A local Russian A/C tech found a compressor for me in a shop in Moscow and it cost me nearly a thousand bucks!  But I'll end this rant for now.

The Mitsubish installer is Russian as well and gave me a great price for this three-head system.   He also did a very clean job.  The last guys took sledge hammers to the walls, which loosened the old plaster all over both sides of the wall.  These guys used an oscillating saw which makes very clean cuts, as you can see from the photos.  I'm happy to give them a recommendaton: EDITA MC CORP, Heating and Cooling, 646-719-4559.  NYC only though.

Okay, on to the repair.  First up are the two holes in the plaster hallway wall that were made to pull the pipes and wire across the basement ceiling to the compressor under my back yard deck.

This was the easier hole because the installers exposed a stud for me to which to fasten the wood lathe. 

By the way, finding wood plaster lathe is a challenge.  Modern plaster uses either extruded metal or blue board.  I suspect part of the reason is fire code. This stuff makes excellent kindling. 

I found eight foot lengths of smooth 2x1/4" poplar at Lowes.  Ideally, you want to use rough cut wood because the plaster clings to it better but it's secondary to the 1/4" gaps between the lathing.

After you cut the lathing to size you want to soak them in water for a few minutes. This will raise the grain a little bit but, more importantly, it keeps the lathing from sucking moisture out of the plaster. 

This hole is more of a problem.  The studs are located about six inches away from the edges of the hole. Because of that I'm going to have to use another technique to fasten the lathing.

Back to Hole #1, one side was flush with a stud so there were two options: either make the hole wider so both studs were exposed or sister some scrap lumber to the left stud to expand its nailing surface. Being lazy I chose option #2.  I had some old 2x2 in my wood bin. I aligned the 2x2 just shy of the old lathing and fastened it with a couple of 3" screws.

The rest of the job was self-evident.  Just leave gaps between the boards so the plaster can curl behind and lock, i.e. "key",  behind the lathing. Looking at the picture below -- the other hole -- you can see what it's supposed to look like on the other side of the wall.  That's 110 year-old plaster!

The only tip here is to pre-drill those screw holes otherwise the thin wood will split when the drill jacks the drywall screw tight.

Neatness doesn't matter.  Just avoid leaving gaps larger than a half-inch or so otherwise you'll lose a lot of your scratch coat plaster behind the lathing. That's why I filled in the bottom with a split piece of wood.

On to the next hole.  Here's where it gets a little tricky.  The studs are located too far away from the holes to make sistering an option.  I also didn't want to make the hole larger.  What I did was drill holes through the plaster and the existing lathing.  Then I drove a 1-5/8" drywal screw into the new lathing behind the old lathing.  I put a temporary screw in the new lathing to use as a handle while driving the screw.  In this case it's just for demonstration purposes. You only need it when you get to the final piece of lathing and can't get your hand in the hole to hold it in place. 

So that takes care of the lathing.  It's actually a pretty simple job.  It took me twice as long to write about it than to actually do it.

The next step is plastering, and here's the next tip:

Plaster walls are actually layers of different kinds of plaster. In old construction there's the brown coat, followed by a scratch coat followed by the finish coat, which is the thinnest of all. The brown and scratch coats are what make up 95% of the thickness of a plaster wall. Brown coat is also a different kind of plaster from finish plaster. First it's lighter than plaster so it has less of a tendency to slump on the wall as it dries. It usually contains bonding agents to make it stick to lathing and it's fairly coarse so the scratch coat has something to "key" to.  In the olden days, horse hair was often used to make the brown coat stronger... hair rebar, if you will. Brown coat also dries fairly quickly.  It can usually take a scratch coat the next day. 

I use Structolite, a very common brown coat product available at the hardware box stores. It's best to add it to water rather than vice versa. That way you can ensure a thorough and even blend.  You want to get it to a consistency somewhat like oatmeal -- not soupy but also not too dry.

And did I mention to wear gloves?  Any kind of plaster or concrete will turn your skin into beef jerky. 

Applying brown coat is a LOT cleaner if you use a hawk, basically a pallette with a handle.  Dump a pile of plaster on the hawk, rest it against the hole and just push it in.  Pros use a trowel but I use a six-inch dryway knife.  I never got the trowel technique.

What you want to do is force the brown coat behind those gaps in the lathing. Really push it in there.

I only play a plasterer on blogs, so I make the brown coat my thickest coat. Plaster purists would rap my knuckle for that but I find that it makes the job quicker and less problematic to build up the brown coat to about 3/16" shy of the finished wall.  Again, neatness isn't a priority.  A good mechanical fastening of the brown coat to the lathing is. 

Let the plaster set up for an hour or two (depends on temperature and humidity) than run the edge of your blade though it in a crosshatch pattern.  This will give the scratch coat a better bond. 

This was Part 1.  The next article will dive into the scratch and finish coats. 

There's also another hole upstairs that needs fixing, this one in the bathroom drywall.  Maybe that will be Part 3.