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Discussion Starter · #1 ·
I am astounded by all the YouTube videos that tell people to do plaster repairs with drywall compound. Plaster resists adhesion of drywall compound. I always start with a thin application of Durabond or at the very least a high adhesion primer where the plaster would meet the compound. Won't repairs done with drywall compound, alone, have a failure problem? :cautious:
 

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I've learned most plaster repair stuff from Kirk Giordano on Youtube. He's a complete wealth of information on plaster.

Generally his advice on all repairs is to use PVA glue (in UK terms as a generic) as in, Plaster Weld or Quikrete Concrete bonding agent to seal the wall first, and then he generally uses Easysand for most of his repairs. I've never seen him seal anything with painting primer. I've followed his advice quite a lot with my own things and found the Quikrete Bonding agent really pretty great. If a surface is extremely dirty or covered in wallpaper glue or something, sealing it with a paint primer and then using PVA glue is probably best, though. Stuff like wallpaper glue even with PVA glue on it can still be a bond breaker or cause PH wonkiness.

I think a downside to using a paint primer is if a surface isn't stable, and you have a typical latex primer that you simply slap over an unstable surface or a surface with a possible moisture problem under the surface you run the risk of it peeling in sheets under the plaster, whereas using only PVA glue it doesn't really dry in a sheet of latex/acrylic goop, and integrates directly into the plaster itself. To apply it, too, is very easy as it's essentially the same thickness/etc of Gardz, and penetrates like Gardz. In UK and Australia some people even use it before painting as a cheap clear primer, similarly to Gardz.

For big repairs I find joint compound is not very ideal, even though Kirk likes to use it a lot because it can set off quicker and he can be in and out of a job faster. I find for large things to fill or big repairs simply using Structolite or if it's not available some other sanded plaster with aggregate, as it tolerates being put on thicker than Easysand does, is stronger, due to the aggregate allows itself to be flattened/leveled out better, either screeded or troweled down. Then use Easysand as your veneer, as being an unsanded "plaster" it's not really meant to go on beyond 1/8" or so per layer.

Basically all joint compounds have their own glue component to them on some level, including Durabond, Easysand, and All Purpose/premix. Plasters do not have their own glue or bonding agent built into them, they're just whatever parts gypsum, lime, sand, perlite, etc. So beyond those components naturally bonding (ie, lime and gypsum) they really only can bond through suction or mechanical key.

The purpose of a bonding agent is halfway as a secondary glue to literally glue the plaster to the wall, but also to stop suction from happening on a dry or porous surface. So for example, if you're plastering a masonry wall, you could get away without bonding agent entirely, as long as you wet the wall first, if you plaster to a wall that's completely dry, the plaster will dry before it fully cures, from the masonry/whatever sucking out the water from the plaster. With wooden lath in the 1800s or so, they used to need to wet the lath extensively before plastering it, before figuring out bonding agents. This even applies to veneer plaster as well over drywall, unless you're using Blueboard (and even if you are) it's better to use a bonding agent as without a bonding agent the plaster dries before it cures from the paper sucking the water out of the plaster too quickly. This is a problem as without glue built into the plaster, it then can crumble, flake off the wall, etc, because plaster needs to dry after it cures and not before, to reach full strength.

Anyway, though it's long, it's one of my favorite videos from Kirk. On this job he plasters a brick fireplace with Structolite and top coats with Easysand as the veneer coat.
 

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Discussion Starter · #3 · (Edited)
@celicaxx Yup! I agree, he gets most things right. In fact, he is the only one I saw using a bonding agent. Durabond is the only one I trust to bind with plaster. I would also trust a good bonding primer or anything that actually bonds to the plaster. I do not trust the repairs done with drywall compound alone. The cracks are bound to reappear. I [pity the poor DIYer that follows some of those instruction videos! Ive done a lot of plaster repairs from the keys up and Durabond always builds a strong key as well as binding to the residual plaster. For minor cracks, I've always found a good superior adhesion primer works well. A lot of the stuff available in the UK can not be had in Canada. (Actually, a of of products in the USA can not be had here.)
 

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Discussion Starter · #4 ·
I think a downside to using a paint primer is if a surface isn't stable, and you have a typical latex primer that you simply slap over an unstable surface or a surface with a possible moisture problem under the surface you run the risk of it peeling in sheets under the plaster, whereas using only PVA glue it doesn't really dry in a sheet of latex/acrylic goop, and integrates directly into the plaster itself.
If that were the case no repair will last! Moisture problems must be fixed prior to repair. I would not use a "typical latex primer", as noted, I'd use a good bonding primer such as Aqua Lock. In any case my methods have worked for 40 years and the work holds up over time. There are many ways to do such repairs but just slapping some mud in there is not one that will stand the test of time.
 

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@celicaxx Yup! I agree, he gets most things right. In fact, he is the only one I saw using a bonding agent. Durabond is the only one I trust to bind with plaster. I would also trust a good bonding primer or anything that actually bonds to the plaster. I do not trust the repairs done with drywall compound alone. The cracks are bound to reappear. I [pity the poor DIYer that follows some of those instruction videos! Ive done a lot of plaster repairs from the keys up and Durabond always builds a strong key as well as binding to the residual plaster. For minor cracks, I've always found a good superior adhesion primer works well. A lot of the stuff available in the UK can not be had in Canada. (Actually, a of of products in the USA can not be had here.)
What's his name, the Vancouver Carpenter, he doesn't always use bonding agent but sometimes he mixes extra PVA glue in his mud.

Weirdly while it's sort of hard to believe if you handle them side by side, USG rates Easysand and Durabond the same in strength. I don't know if that's actually true, though. Durabond however doesn't really sand well, and Easysand does sand a lot better. For me personally in my kits I kept the bonding agent and Easysand, just to not carry a third bag of joint compound I couldn't use anywhere else except for deep fills. I also didn't want to deal with the potential of Durabond being too "hot" and causing paint adhesion issues like real plaster can have. Plus Durabond 45 or 20 isn't really easy to find here, whereas Easysand 20 is everywhere and sets off faster for second or third coats in some scenarios.

If that were the case no repair will last! Moisture problems must be fixed prior to repair. I would not use a "typical latex primer", as noted, I'd use a good bonding primer such as Aqua Lock. In any case my methods have worked for 40 years and the work holds up over time. There are many ways to do such repairs but just slapping some mud in there is not one that will stand the test of time.
Plaster is overall a hard beast, and there's a lot of things that I've dealt with in old plaster houses that were far from ideal but I couldn't push jobs further to make them more ideal, if that makes sense, as it wasn't my own work and I was a sub. I've had situations of entire small walls near doors losing key but not being able to do anything as it was outside of the scope of work to properly fix it. Same with cracks with movement where they didn't really want to pay to fix it with plaster washers first, etc, just mesh tape it and move on. :(

Thankfully for the moisture thing I've only had one repair go that way thankfully, and obviously yes I know that, but some people will just insist it's fixed and then it's not and you have a problem still. One rather creative repair I did was initially on a house that leaked was I told them they needed to resolve it (eventually I ended up troubleshooting it better than an actual plumber they hired, but that's besides the point...) was after I patched in sheetrock and it felt down on a ceiling below a sink, I used Wonderboard tile cement board, bonding agent, Structolite basecoat, and Easysand. So after it did eventually leak again, instead of a crumbly mess of drywall, I had one paint bubble to cut off with a razor and lightly sand out, and a very small area to recoat with Zinsser Permawhite and that was it, haha. The cement board nor the plaster in that area got moldy or decayed at all from a couple months of dripping. I also have a test sheet of Hardiebacker plastered with Structolite outdoors that's only now beginning to have the Structolite erode off, and it's been out there since 2018. So there's still ways to make your work somewhat more bulletproof, so to speak, but ideally stuff would not leak and everyone would do their jobs correctly, but it's not an ideal world.

UK painting and plastering obviously seems like an entirely different ball of wax compared to US, but I absolutely love watching UK construction stuff on Youtube as it always gives me a fresh perspective compared to USA on how jobs are done, and unlike watching something absolutely foreign, they're still speaking the same language/etc as you, which is also cool.


I've found the sponge float method like that actually works well for Easysand skim coats, you can bring it back to life with the sponge float in that manner and trowel it down.
 

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@celicaxx I was trained buy an old European painter. The standards across the ocean are much higher! He made sure I always sanded every coat from primer to finish AND that meant ceilings too! Lordy! How I came to hate sanding ceilings! I also was trained to thin the paint by about 10 % and do a minimum of 3 coats. (The walls looked like silk when we we done!) Trims were done with semigloss as a rule and wet sanded between coats, a beautiful fined look. Though few want to pay for that level of paint job now. As for Durabond VS drywall compound, yes it is much harder with powerful bonding capabilities; it is much harder to sand and my finish coats are most always drywall compound. I hate both the easy sand and the dust control varieties. The ideal is to build the keys with Durobond and then mix proper plaster for the finish work. However, we are all bound by client budgets. I will work as cheaply and efficiently as possible BUT if what they want to do is not reasonable I say "Sure, you can do that but you need to hire someone else. I won't have my name on it or be responsible when it fails or falls apart." No job was ever worth a hit to my reputation!

I might mention here, I easing into retirement. I am trying hard to refuse most work but still get called in for clients I've worked for for years. It's hard to say no to them. Mostly I'm retired and doing more wood refinishing these days and for my own pleasure. 45 in the business years and a changing world make me happy to put the bush down more often.
 
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