| Alexbenjm |
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| #1 |
Hello, I came across this website when researching how to repair and skim plaster walls. I am currently cleaning and restoring my first room in my 1923 house. I've taken off the layers of wallpaper and paint to reveal blue-green pigmented plaster walls. I've identified the pigment as calcimine. A TSP solution easily took care of that.
The exposed plaster walls are rather rough textured, but in overall excellent condition with visible trowel marks along with usual holes, gouges, and cracks from 80+ years of life. There are two large holes with lath exposed underneath the windows where I've removed badly cracked plaster due to moisture. I will be stabilizing the plaster first then I plan to use Structo-lite to patch up those holes, but should I use a bonding agent? Would a mesh be recommended for those two holes?
Should I use mesh for every single crack, no matter how fine? I've come across people saying one should apply mesh to the entire wall, is that a good idea?
One issue I'm trying to figure out how to repair are the corners of the room which are extensively cracked. I can see all the way inside the corners and see lath. What would be the best way to repair those corners? I'm thinking the corners should have some flexibility to accommodate seasonal movements of the individual walls and ceiling.
Eventually after all the repairs are made, I intend to skim using master of plaster. One last question, the glasslike polished finish sounds quite attractive but would paint bond to that kind of finish well?
Thanks!
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| | | Clarence Bauer |
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| #2 |
First make sure all calcimine paint is removed.
Your repair method is correct no adjustments need to be made.
The use of mesh tape should be as follows, Mesh tape all cracks over 1/16 inch.
Mesh all joints of new to old (patch areas)
Inside corner cracks mesh tape with wide mesh say at least 6 inch wide.
For a bonding agent on exposed wood lath use one part bonding agent with 2 parts water wet lath than apply plaster.
No bonding agent required for Master of Plaster
Yes paint will bond to the high polish finish of Master of Plaster follow painting instructions of paint manufactor.
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| | | Jim Burkhard |
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| #3 |
Wow, lots of good questions. This might be a long response! I will respond with some advice from a fellow amateur. I've been using M.O.P. for 10 years in my own home and have had great success. There may be some seasoned actual pros on here with better thoughts or ideas, though. Please listen to them if they correct any bad advice I am giving. I'm only saying what has worked for me (or what I've gotten away with) in the past, which isn't necessarily the right or the best way to do things.
You mention exposed existing lath where the plaster had failed and been removed. I'll assume that this is WOOD lath and not metal. Patching with Structolite will work very well (I've done what you are suggesting). If you are putting the Structolite over wood, a bonding agent is a good idea but not strictly necessary if you get the wood lath good and thoroughly damp first. Clear any old plaster residue from the lath surface (old toothbrush maybe) and mist the exposed wood and old plaster edge throughly prior to applying Structolite (spray it a couple times the hour prior to make sure it's soaked well) . The wood should be damp, but no standing water to dilute the plaster. When the plaster is subsequently applied, the pre-dampened wood allows the plaster to retain its water long enough to set properly. Without pre-dampening, you may end up with light powdery Structolite. Structolite darkens when it sets and gets nearly hard as concrete. If this doesn't happen, it didn't cure right and drying out too fast is a common cause.
I've put Structolite over damp wood lath without any problems. Where I did run into problems (dried out plaster that never cured) was where the wood lath *itself* was nailed to a heavy (4 x 6 or thereabouts) horizonal framing timber for a long run. The direct contact with a framing allowed the water to be pulled from the plaster, which ruined the set. I had to knock the failed plaster out and reapplied with the bonding agent. No troubles that time and has been OK for the 4+ years since.
All that said, what I would do in your case would be to cut a piece of metal lath to fit *inside* each hole and screw the metal lath right into the existing wood lath. I use K-Lath screws for this (wide flat heads), but since they'll be buried inside the whole, almost anything that secures the metal to the wood will work fine. The metal lath is a LOT less fussy than the wood lath at providing a good surface for the plaster to key into. I'd still mist the wood which will be in contact with wet plaster thoroughly to keep from drawing out the plaster's moisture, but the metal lath will key very well.
You had questions about using mesh.
By mesh, I assume you mean either a sheet of fiberglass mesh or mesh tape. Yeah, I think that's a good idea. If the hole is fairly small, just cutting a piece of mesh to fit over (bigger than) the whole patch may be easiest. If it's large, you might just want to tape the periphery.
You also asked about mesh-taping cracks in general. I tend to err on the over-taping, so sometimes yes the wall has a lot of tape on it when I'm done. If the wall is really heavily spider-cracked, though, it probably does make sense to mesh the hole wall at once with roll mesh as you have been advised. Later, you'll find it's easier to overall skim that uniformly than if you had a zillion individual lengths of tape that you needed to blend in everywhere. Usually, I tape the cracks individually, but one ceiling had so many fine cracks I bought 36" wide roll and did the whole ceiling at once. It's 2.5 years later still no cracks. It does add a fair amount to the overall cost of you do this, though.. the rolls of sheet mesh are a bit pricey. It's a judgement call... If the walls aren't that bad, buy a couple rools of 2.5" tape and go to town. It goes pretty quickly. Make sure that the plaster you are taping is sound though -- I judge how much it moves on either side of the crack when I press about 1" from the crack with my thumb. If I have doubts, in goes a plaster washer.
Qs about dealing with corners:
I'm not sure if the cracks you can see inside in the corners are just the lines right where wall meets wall (or ceiling) or are something wider that travels into the plane of the wall/ ceiling. I's hard to say w/o seeing it, but I'd say if it's smaller than 3/16" or so and just the line right where the walls meet to just use caulk. I always use siliconized latex (like DAP 230). It holds up a nearly forever (unlike regular latex), is water spreadable (unlike silicone) paints perfectly, sticks to porous surfaces (unlike silicone) and remains very flexible. If the "cracks" are bigger than this, you might need to do some underlying relairs first. In general though, I think you are right... without some flexibility cracks can occur where wall meets wall (or especially where wall meets ceiling). Unless they are really big, I do not attempt to fill these with M.O.P., joint compound or anything else non-flexible -- it's just going to recrack. Rather, I just use the DAP 230 siliconized caulk and tool it completely level with the surface with a wet finger. It will be completely invisible It takes paint fine and (generally) won't recrack. In your case with your big cracks, you might need to joint compund (or Structolite if they are more than just cracks) them first and if they recrack in a year or 2 be prepared to caulk the crackline. After that, you should be OK.
Oh, one very important thing: I always caulk those corner joint cracks AFTER the room has been primed. Caulk sticks a LOT better to primer than dusty plaster. So, after I am done skimming the whole room with M.O.P., I primer, then go around and lay a very thin wet-spread caulk bead on every wall:wall or wall:ceiling joint. It's so thin that it doesn't fillet (radius) the corner or anything ... You are just trying to get a *tiny* bit in where the two planes meet. That spot it is probably going to crack at some point and the thin (thin!) layer of caulk hides the inevitable. Just keep a little jar of water to keep your finger wet and the siliconized latex caulk will smooth easily and invisibly.
Your Q on paint bonding:
The paint bonds fine to M.O.P. finish coat. You do want to use primer first of course, but you'd do that for drywall as well. It's "glasslike" to the eye and touch, but I think there is still plenty of tooth for primer to grip.
Keep us posted. I'm sold on M.O.P. for plaster restoration work. Good stuff. |
| | | Alexbenjum |
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| #4 |
Wow, great advice there, Jim, thanks for your post!
I have a few pictures of the damage to the walls and the corners, I'll post them as soon as I get the chance to help you better understand the issues.
I can say that there are both fine cracks and large gaping cracks in the corners where the planes of the walls meet. I would say two of the corners definitely need some repairing before covering and one corner just needs a touch-up. I like your idea of using siliconized latex because I am concerned about the corners recracking in the future.
In the two larger holes with visible wood lath, no metal, they are on the wall bordering the exterior of the house, underneath the window sill. Upon a closer examination, I can see the lath is actually nailed directly to the wood bulkhead, so what you said about moisture being wisked into rest of the wood structure and ruining the new plaster sounds like it probably will be the situation here. I might as well go ahead and use a bonding agent just to be on the safe side.
The walls themselves have some cracks, some rather wide, some very fine, I'll mesh tape them up as necessary.
There is a part where the wall curves into the ceiling, it's a nice smooth arch but when I removed the wallpaper, there were several cracks in that area which isn't surprising. I plan to stabilize that area and a few other areas where there are large cracks.
A bit of history about the house. Some time in the past, the house was actually raised up and its foundation replaced. So I can see that some of the more serious cracking are probably from the house being levered up.
The area under the windows has been repaired in the past but seems the repairs didn't take, because the paint in that area was peeling and some efflorescence happening in there, along with poor plaster crumbling away, that's where the two large holes are. I'm working on removing the poor quality paint and the calcimine underneath.
It's my first house and my first time renovating a house too so I've picked that room to be my first attempt and my Experimental Room where I can try out things and learn from my mistakes before applying techniques to the rest of the house.
Clarence, thanks for your help too and confirming that my repair method is sound.
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| | | Jim Burkhard |
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| #5 |
Alexbenjum-
Good job on your approach and welcome to new home ownership with an old house. I did the same thing myself 13 years ago with an 1830s house. I'm an engineer by training, any excuse to buy tools and learn new skills is a good one. My house has proven to provide LOTS of said excuses.
A couple things I didn't mention about Structolite which may be useful if you haven't used it before. While Master of Plaster truly *dries* (and can be easily repolished if rewetted), the Structolite sets nearly hard as a rock, first turning to a modeling clay consistency and then darkening as it fully sets into a very hard substrate that is ready for topping with M.O.P. or finishing plaster. It will also give off a noticable amount of heat in the process. If you find it isn't rock-hard and didn't darken, it didn't set right for some reason Likely it dried before it set. When I apply it (especially in hot dry weather particularly over wood lath) I monitor it afterwards checking it occasionally over a few hours to make sure that it starts to actually set (dark hard areas start forming) before it dries. If it starts to dry before setting, I lightly spritz it with a little water mist every hour or two. You generally don't need to do that, but just be aware to monitor that it is setting OK.
Structolite is not the stuff you want to use if you want to apply a real thin layer or fill a small crack-- it's for larger repairs or building whole walls. It needs a certain mass of itself to set right, so if you mix up a little bit, then immediately apply it thinly, you might find it just dries into a powder. It likes going on fairly thick and patching *holes*. If the repair is on the small side, you might want to let it slake briefly (i.e. rest for 15 minutes or so after mixing in a ball in your mud tray) before applying, to make sure that the necessary reactions have begun. Mix it up in a big plastic mud tray on the floor with a mason's hoe (has holes in it). Add only enough water to make it workable like fairly stiff mashed potatoes... too much water and it weakens. If it starts to set while you are using it it's done. Do not re-add water.
The USG website has some downloadable PDFs to explain working with it, so go with their advice if they conflict with something I am suggesting.
When you buy it, be sure to check the manuafcturing date stamped on the bag. Ideally this should be fresher than 6 months old. I've used stuff a year old that I had stored in a dry place and it was fine, but it starts getting a little risky, especially if it's your first time. Fortunately, if it's too old, you'll generally know because the main symptom is that it will start to set MUCH faster (within minutes) than normal. I had that happen once and I knew to pitch it and go buy some more. Where I live at least (Western NY), the stuff is not a big seller so sometimes the plaster/drywall supply places have some old inventory they try to sell you. Caveat emptor.
Near me, one (only one of several... odd) of the Home Depots used to carry it, but they quit about a year ago. So you might need to call around and find a real plaster/drywall supply firm. Be advised that there is a similar competing product called Gypsolite that is the same sort of idea, but made by National Gypsum instead of US Gypsum. I haven't tried it, but apparently it's not *exactly* the same and some folks online like Structolite better. I can get either, so I stick with the Structolite hwich I know, but if you can't find Structolite by you, be aware this is another optionwhich will probably also be fine.
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