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Msupsic 06-25-2010 08:15 AM

How to achieve this texture?
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I'm repairing my garage for use as a winery. The walls have some dents and holes in them, looks like one of the previous owners probably drove the car into them or something. The house was built in 1947, but it looks like they may have done the garage interior later in the life of the home.

I first thought the walls might be plaster on lathe or maybe stucco on metal mesh, but after digging in, it looks like it is some form of sheetrock, covered with a textured facing of some kind. Please refer to the picture.

The drywall looks to be standard 3/8" stuff and the texture is about 1/8" thick on top of that. The finish is hard and gritty, like stucco.

Can anyone tell me what this finish is, and what the best approach is for repairing these holes? I don't need the repairs to be perfect, but it would be nice to match them as close as possible.

On first guess, I was going to square out the holes, replace with new 3/8" drywall, then make a mixture of joint compound and #30 silica sand to resurface.


Nestor_Kelebay 06-25-2010 09:44 AM

Are you calling that stuff around the orangey-gold coloured door "texture"?

That isn't texture, that's ordinary base coat plaster.

And the "drywall" behind it is something called "gypsum lath". Gypsum lath is the "missing link" between wood lath and drywall. It was an 16 inch wide by 4 foot long piece of gypsum wrapped in coarse paper that was nailed to the walls. The base coat plaster was then applied directly to the gypsum lath. Then gypsum lath changed into 4 by 8 sheets with a smooth paper on the front and contoured edges and became the product called "drywall" we use today. Gypsum lath was only used between about 1950 and 1960, so those garage walls were finished during the 50's.

Matching the "texture" is not going to be a problem. You just have to make real base coat plaster:
1. Phone around to your local plaster and drywall wholesalers and the guys working there will know which companies in your area still make real plaster. I forget the mixing ratio, but you won't go too far wrong with:
A) mix equal parts of hydrated lime and Plaster of Paris to make the white, hard and smooth "guaging coat" plaster.
B) mix sand (typically 5 to 10 parts sand per part Guaging Coat plaster) into the guaging coat plaster to make base coat plaster.

NOW, the old base coat plasters took a lot of skill to apply because the sand was heavy and if you put too much sand in, it wouldn't stick to the wall. So, dilute some white wood glue with water to make a paintable consistancy and paint the drywall you want the base coat plaster to stick to with that dilute glue, allow time for the glue to dry, and then apply the base coat plaster. The moisture of the base coat plaster will re-emulsify the dried glue.

It's been over a decade since I made real plaster with hot lime, and I found I could get better results just using joint compound, so I never pursued that. However, hot lime is dangerous to work with because it's an extremely exothermic reaction when you mix it with water. Nowadays you can buy "Hydrated" or "Slaked" lime, which is what you get when you mix hot lime with water and give it time to cool down. So, hydrated lime gives you the same stuff without exposing you to the danger of working with hot lime.

You'll do OK mixing equal parts lime and Plaster of Paris, but if you want to get the mixing ratio exactly right, phone around to the Plaster and Drywall wholesalers in your area.

Once you apply the base coat plaster to the wall, brush it with a stucco brush to get that same "texture" as seen in the photo.

Msupsic 06-25-2010 11:32 AM

Wow... thanks so much for the very thorough reply. It sounds like you've nailed it. The "Gypsum Lath" you described would make sense, as the studs are 16" apart center to center, and it seems like every time I break a section of this stuff out, it comes off in perfectly sectioned 16" pieces. I thought I was just really good at cutting ;)

This was the only photo I had available. This is actually a hole in the wall I need to repair. What you're looking at is not a door, but an insulation material on the backside of the interior wall. This partcular stud cavity also serves as a return for the HVAC system. Apparently it was common to do that in the 50s?

Any chance you know what that brownish/yellow insulation is made of? I have another thread running regarding this substance. I wanted to make sure it wasn't dangerous.

Thanks so much.

Nestor_Kelebay 06-25-2010 03:44 PM

No, I saw your other thread and didn't know what that insulation was, so I didn't reply.

You might want to e-mail the picture in your other thread to Owens Corning's "Feedback" people.

Talk to Owens Corning

Owens Corning makes for fiberglass and styrofoam insulation, and I expect someone there might know what that insulation is.

The way to fix that hole would be to use ordinary drywall to replace the missing gyproc lath. When I fix holes in plaster (which is what you have), I'll use 3 inch long drywall or decking screws to fasten short pieces of spruce 2X2 to each side of the hole so they're flush with the existing studs. (You might not have room for those 2X2's if there's a duct or something in that wall cavity.) I use pieces of spruce 2X2 because trying to nail or screw within 3/4 of an inch of the CUT edge of a piece of drywall is invariably going to result in "break outs" (which is where the part of of the gypsum between the screw and the cut edge breaks away from the rest of the gypsum core). Putting up the 2X2's allows a luxurious amount of room to screw the replacement drywall panel in without breakouts.

(There's a bit of skill involved in plastering, and one of them is knowing how thick to mix the base coat plaster so it doesn't slump, but if you're new to plastering, then I'd cheat and use some horizontal wood supports to both apply a uniform thickness of base coat plaster over the drywall, and prevent the plaster from slumping as it dries if you mix it too thin.)

So, if it wuz me, if you widest putty knife is 4 inches wide, I'd use horizontal wooden screeds spaced about every 3 inches. If your base coat plaster is 5/8 inch thick, I'd use about 1/2 inch thick wood screeds made by having any scrap board in the lumber yard's junk barrel cut down to that thickness and then ripped into strips on their table saw. (And, being the perfectionist I am, I wouldn't stick the screeds to the drywall directly with double sided mounting tape. I'd probably stick some strips of painter's masking tape to the drywall first, then use double sided mounting tape to stick the wooden screeds to the strips of painter's masking tape. That would allow me to pry out the wood screeds after the plaster was dry, and pull off the painter's masking tape easily without tearing the surface paper off the underlying drywall.)

Then, paint over the drywall panel with diluted white wood glue and allow time for the glue to dry. Don't paint the wooden screeds cuz you don't want your base coat plaster to stick to them. Try not to let the glue drip behind the wood screeds, too. And, allow time for the glue to dry before applying the plaster.

You can also BUY Base Coat plaster, but the stuff you buy nowadays doesn't have sand in it, and it will often have shreaded news print in it, so it won't end up looking like the real base coat plaster you have now. Normally, base coat plaster is covered by the smoother whiter guaging coat plaster and so you're probably the first one in the history of the World that's wanting to match the appearance of existing base coat plaster. But, if you want to match what you have now as close as possible, you pretty well have to make the same stuff you have, but that not hard to do.

You should know that your base coat plaster will have a working time you can use it for. After a certain length of time, the base coat plaster will go from soft and easy to spread, to stiff and unworkable. I know that's the case for Guaging Plaster (which doesn't contain any sand) but whether or not you'll notice that "kick" as much when most of the material is sand is something I can't remember any more. So, maybe mix up and apply your base coat plaster in small quantities until you learn how long your working time is.

You probably want to run a putty knife around your wood screeds while your base coat plaster is still workable to make it easier to remove them later.

Anyhow, after your base coat plaster sets up, predrill some shallow holes into your wooden supports, drive screws into those holes and pry the wooden screeds out, and then you'll probably need a pair of needle nose pliers to get the masking tape out.

Then paint over the dry base coat plaster (and the screed notches) with more diluted white wood glue, allow to dry and apply another coat of base coat plaster so that it's flush with the surrounding wall. The old plaster will support the new plaster from slumping, and of course, the thinner the coat of plaster, the less it's gonna slump.

Here's the kicker: The thing you're calling "texture" on your old base coat plaster is nothing more than the natural roughness of any dried slurry that's made mostly of sand combined with the impressions made by the stucco brush. (They'd brush the old base plaster so that it was rougher so that the guaging coat would stick better.) If you brush your base coat plaster when it's too wet, then the brush strokes will be more pronounced, and if you brush your base coat plaster when it's too dry, you won't see them at all. You're going to have to experiment as your base coat plaster is drying to see when to brush it to have it look about the same as the surrounding wall.

Anyhow, if your house was built in 1947, it definitely has plaster walls, so maybe it's good you're learning to plaster in your garage as everything you learn from this project will be applicable in your house too. Nowadays, however, no one uses hot lime and sand to make plaster any more both because of the danger in using hot lime and because it's harder to spread smooth and get good results. Nowadays everyone uses drywall for the gyproc lath and a manufactured base coat plaster like Domtar's Perlite Admix Hardwall or USG's Structolite as the base coat plaster. And, of course, drywall joint compound is used as the guaging coat plaster. The only time real plaster will be used is when you're restoring a historic building where it's important to stay true to the materials and methods that were used in the era that it was built.

Msupsic 06-25-2010 04:05 PM

Excellent information, very detailed. Good point about the breakouts, too. This is going to take some experimentation on my part, no doubt. I have a few pieces of scrap drywall that I can practice on before I hit the real thing.

Any idea why the original plasterer would just use base coat and not finish it off? I guess, for a garage, finishing it with a top coat wasn't economical or necessary at the time?

I should have mentioned that I plan to throw a coat of matte paint over the walls, ultimately. So what I really care about is matching the texture, not necessarily the color of the original plaster. I just want to make sure there isn't a distinguishable difference in surface texture, where I did the patches.

Also, good idea about the insulation issue. Of course, OC would probably be able to identify it. It is what they do...

I'm excited to get to work now... thanks.

Nestor_Kelebay 06-25-2010 08:59 PM


Any idea why the original plasterer would just use base coat and not finish it off? I guess, for a garage, finishing it with a top coat wasn't economical or necessary at the time?
Most likely something like that. They weren't going to paint or live in the garage, so why make it nice to look at?

Instead of painting the base coat plaster, you might want to consider using drywall joint compound to put a skim coat over the whole wall to make it smooth. Painting over base coat plaster is like painting over concrete blocks. No matter how nice the colour, it's still going to look kinda ugly.

There are two ways of skim coating that work well for newbies:

1. Use a "V" Notch adhesive trowel to spread joint compound over the base coat plaster, allow to dry, scrape off any blobs that are sticking out proud of the trowel ridges, and then hold the trowel upside down to fill in the trowel ridges with more joint compound using the un-notched edge of the trowel. That will give you a uniformly thick coating of joint compound over the walls.

2. Use a "V" notch adhesive trowel to spread joint compound over a small area of the base coat plaster and immediately mist the joint compound with water and trowel it smooth. Repeat that process until the walls and ceilings are done. That will also give you a uniformly thick coating of joint compound over the walls.

The base coat plaster is rough enough for joint compound to stick well to, so I don't think you'd need to paint with dilute white wood glue before applying the joint compound.

Also, the plastering experience you get in your garage is going to help a lot next time you need to fix any plaster in your home. You'd prefer to get your troweling skill working on your garage rather than your home.

I made wine kits and beer kits for over 20 years. I just stopped making beer within the last 12 months. I even have my own fridge that magically turns homemade wine into home made champagne. But, I haven't made wine for quite a while now. When I did, I would buy wine kits that had the tannin in a separate package and leave the tannin out. Instead I would make the wine without tannin and drink it young, mixed with soft drinks to make wine coolers.

Msupsic 07-15-2010 11:35 AM

Next step...
Finally got all of the dents/holes cut out and replaced them with new drywall. I'm going to paint on the glue mixture this weekend... I'll let you know how it all goes.

Msupsic 07-20-2010 08:01 AM

What gives?
Hey Nestor,

I just started laying the base coat yesterday.

I'm using your recommended mix of 1 part plaster / 1 part lime / 5 parts sand.

I can get the mix to a nice spreadable consistency, but the stuff is drying up almost immediately. No kidding, no sooner do I mix the bucket up then it is already clumping up and becoming brittle. I have a window of about 5 minutes to get the stuff up on the wall before it is useless. Needless to say, I didn't get much done last night.

The feel, look and texture are nice when it dries, otherwise.

Is this right, or am I doing something wrong?

Nestor_Kelebay 07-20-2010 09:04 AM

Hydrated lime helps retain moisture. I would increase the lime content and see how much increase in working time that gives you.

Mix up a small batch (a couple of ounces) with twice the lime content and see how much longer a working time you get. Also, when that small batch stiffens up, try mixing it again to see if working it thins it out again. (Don't add water when mixing it the second time, just see if working it will thin it out again.)

And, of course, the more lime or gypsum in the mix, the smoother the slurry is going to spread. So, to get the same surface roughness you had before with the 1:1 lime to gypsum mix, you'd have to add more sand. But, for the time being, just add more lime to see how much that increases the working time, and then worry about matching the surface roughness.

Msupsic 07-20-2010 10:03 AM

Thanks, I'll give it a try... I don't know if I indicated it in my previous posts, but there are some pretty large areas that I have to cover. The little patches were no problem, but in some places I have patches that are 12" high and 5' long. It's a little hard to cover these big areas when your mix is drying out every 5 minutes.

As I said, I'm not hell-bent on getting this perfect, as it is only the inside of the garage. "Close to very close" will suffice. I'm most concerned about getting the thickness of the patches level with the existing plaster.

Of course, that's not to say I don't want to do the best I can. Your help has been invaluable so far. The few areas that I have covered, look great, and the base coat is sticking well with the wood glue coating.

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