We’ve been watching Grand Designs, and have noticed something that, as an American, strikes me as a little strange. Quite a few projects seem to install drywall and then cover the entire surface of the wallboard with a thin coat of brownish plaster, which is then painted.
IME, here on this side, we tape the gaps between the panels, apply joint compound (aka mud) over the tape, sand it down to make the seams disappear, and then apply paint to the whole wall. But the mud only covers a small percentage of the surface, not the whole thing, as I’ve seen on the show.
Lath and plaster construction, once a standard here, is only seen in houses built 60- or 70-plus years ago, and AFAIK is rare in new construction.
So why do Brits put plaster over drywall, instead of the (presumably) cheaper and easier method we Yanks use? Is there some definite benefit, is it a code issue (if so, why?), or just custom and inertia? If there is a benefit, why don’t we do it? Or is it done in US buildings, too, and I’ve just never heard about it?
Is the plaster perfectly smooth? A common technique here in the US is skip troweling where a thin layer of mud is applied to the wall then troweled to leave a texture behind. This adds interest to an otherwise blank wall and hides imperfections.
This how-to video even states you don’t need to tape and sand the joints, just tape them and depend on the textured mud to hide the tape.
It’s partly tradition from when they would use finish plaster to cover the uneven surface of a brick wall, and partly to give a smooth finish to the plasterboard panels. Simply plastering the joins inevitably leaves bumps.
Plasterers work fast. Two workers will plaster a whole room in an hour or so. The ones doing the ceiling work on stilts.
My house (Massachusetts, built 2008) has blue board and a plaster skim coat for all walls and ceilings. Perfectly smooth finish - like glass type smooth. The plasterers had a giant light bulb that they held up to the wall to look for imperfections, which they smoothed out as they went. It was smooth enough that primer didn’t want to stick in some places.
The closets and garage walls and ceilings are textured plaster. Textured plaster is easier to make, so for spaces that “don’t count” towards looking nice they will shortcut. The plasterer wanted to textured ceilings throughout the house, but I abhor textured ceilings so it was smooth all around.
I’d say about half of the houses I’ve been involved with building in some way (even just a friend’s place I visited) in the past 20 years have had a plaster skim coat for interior walls and ceilings. Massachusetts and Rhode Island.
One of the things I dislike about the old-fashioned lath and plaster walls of the 1952 house I’m living in now is that when you try to nail or staple into it, you’ll probably chip out a little crater, and maybe bend your nail, too.
Does a plaster skim coat chip when you nail into it?
Plastering maybe, but the joint compound used here is sanded perfectly flat and smooth. Here is the basement of my last house after the mud had been sanded down. The short stripes are covering the screw heads in the middle of the sheet.
The plaster finish doesn’t need to get sanded, which saves labor (but needs more skills to do well). Blue board and veneer plaster can be installed in a day. Skim coat and sanding can take a couple of days, while you wait for it to dry.
Depends what you want to nail into it. For pictures and the like, a simple pin seems to be enough: for a heavy weight, you need a plug and screw. I had trouble finding a reliably secure fitting for the supports for my curtain rails in the narrow gap between full-height windows and the ceiling cornice (I don’t know what the original builders had done, but there didn’t seem to be any consistency - bits seemed impenetrable, and other bits had only a bit of plasterboard and a void behind). After taking advice, I ended up fixing a wooden batten the full width with a combination adhesive/filler and masonry nails, and screwing the supports to the batten. Still holding firm ten years later.
That’s most likely because there is a concrete lintel above the window space. I had the same problem and ended up borrowing a nail gun and nailing (with special hardened nails) a wooden batten to the wall.
Most of the drywall installers around here didn’t want to do taping anymore, they wanted to use the plaster technique and charge more. I found a commercial building installer when building an addition that did the old fashioned way and charged less.
That’s actually not entirely true. Drywall has a tapered edge on the long sides to accept some of the thickness of the mud. However the short side is blunt, so the mud mounds up over the joint. That’s why in the photos above, where the drywall was installed horizontally, the vertical joints are much wider to try to smooth out the bump. If you put a long straight-edge on the wall, you’d see those vertical joints, but probably not the horizontal ones.
Actual wood lath and plaster hasn’t really been a thing in the US since the 1920s when they switched to drywall-like plasterboard. They were much smaller sheets than today’s 4’ x 8’ drywall and they still applied multiple coats (scratch coat, brown coat, and top coat, or at least the brown coat and top coat). Metal/wire lath was a thing in the 1930s but it wasn’t any less labor intensive. Veneer plaster (blueboard and about a 1/8" coat of plaster) or Kal-Kote which is similar but uses a thinner harder plaster coat is an outgrowth of those older techniques.
Because cheap is cheap. Skim coat plaster is nicer looking, harder, more durable, and also easier to paint. The exposed paper of drywall absorbs primer and paint more than mud, so extra coats may be necessary to get it looking even. Just because something can be done cheaper doesn’t mean it’s good, or that consumers would want it. Otherwise we’d all be driving Kias and living in tar paper shacks. Look in parts of continental Europe like Denmark, Germany, or Switzerland and the quality of home construction is lightyears ahead of the garbage that’s acceptable here in the US.
I’ve run into some situations where the difference between Level 4 and Level 5 finishes are a bit blurred depending on the contractor. Technically Level 4 has the maximum needed layers of mud on joints, corners, and nails/screws, and Level 5 has all that plus a thin skim coat over the whole wall. I’ve seen a finish which would best be described as Level 4.5 where they skim the whole wall but scrape all the mud off. That fills the pores of the paper and knocks down any fuzz, so it paints just as well as a full skim coat, but it doesn’t even out any slight ridges. Unscrupulous contractors would call that a Level 5 finish (we skimmed the whole wall!), whereas the higher end contractors would consider that their Level 4.
If it’s just a skim coat of typical joint compound/mud then no. Real plaster undergoes a chemical reaction with water and sets/cures into a harder almost crystal-like matrix. Drywall mud mainly just dries, and it’s softer and easier to sand than plaster when dry, plus feathers out great when wet (i.e. it can be tapered out to basically zero thickness without tearing or leaving ridges), making it easier to smooth out. It dries slowly though, and can shrink a lot, so you can’t put it on too thick in one go, hence why so many coats are required for high level finishes. Wet plaster is thicker and more gloopy so it’s harder to work, and it sets up faster too. Some would probably argue that “true” plaster requires multiple coats of different grades of plaster, and that’s still harder than skim coat, but I think it’s splitting hairs at that point.