Friday, April 20, 2007

Finally, Plaster.

I’ve got walls! It feels good too. I got the scratch coat on all the bathroom walls today. It took about 3 hours. I think I could have done it in under 2 if I had someone to mix plaster while I troweled it on.

There was nothing too exciting about the plastering today. It went well. I did notice a few things that might be helpful to any would-be plasterers out there. In the great Plaster Repair PDF made by Dave from The Worley Place, he says to mix the plaster to a consistency of “Cake Batter but just a tad soupy”. I found this difficult to imagine because I’m not a baker. What is the consistency of cake batter? I made the first few batches of scratch coat too soupy. This was one of the reasons I think my Keys were so large.

I tried to come up with a better way to describe it. For me, I like it to be the consistency of warm peanut butter. That’s sounds good to me, but what if you’re allergic to peanuts, you’re probably thinking, “Warm peanut butter!? What the hell does that look like?” I ran in to similar problems with other analogies for consistency.

Soft shoe polish: shoe polish allergies
Soft serve ice cream: lactose intolerant
Squished cockroach innards: cockroach innards allergies

The list goes on. No matter what the analogy, someone will be left out. Then as I was mixing up a perfect batch of plaster the perfect analogy came to me as if by some unseen force. As I was mixing the plaster with my little 2-inch wide trowel, I thought to myself, “Wow, this is just a perfect batch of plaster”. As I scraped the bottom once more with the trowel I noticed how the deep valley I created in the pail looked kind of like when Charlton Heston parted the Red Sea in the movie The Ten Commandments. That’s when it came to me. This is the analogy everyone will understand. I mean, I’m an atheist and I’ve seen that scene dozens of time. It’s part of the collective consciousness.

So when you’re mixing your plaster for the scratch coat get it to where you can “Part The Red Sea” with your trowel and have smooth sides. The sides of the "sea" should be smooth, and maybe sag just a hair. If they flop in too much, the mix is too wet. If you get any cracks or breaks, the mix is too dry. Go Unto Thee And Be Like Moses...Or Charlton Heston, Which Ever Works Best. {Said in a loud, booming voice}.

Other helpful tips: Don’t put the pail of plaster at the base of the ladder where you can step in it. I’m not going to say how I know this is a good tip, you're going to have to trust me on this one. Also, don’t wear expensive Italian loafers when plastering. Trust me on this one as well.

And one last thought on the origins of plaster. I can’t shake the train of thought about how and when gypsum plaster became the preferred method to lime and sand plaster. It’s easy to see how drywall supplanted them all. It’s a quicker method. Quicker does not necessarily mean better, it’s just quicker. And for a professional, the quicker you can work, the more money you can make. That’s easy to see. There seems to be little difference in the methods for the two types of plaster, though. So why the switch. Then it dawned on me: Marketing! The great un-equalizer.

I’m sure that’s the missing link. US Gypsum had a product that they wanted to move. Plasterers that used lime plaster did not buy US Gypsum plaster. It was probably through a series of clever marketing campaigns, discounted merchandise to get shelf space, and maybe some threats and intimidation that they were able to get there product in to the hands of more and more plasters. Lime was used in enough of the other building trades that the use of lime in plaster could have lost the focus of the lime producers for a short enough period that the switch was made among plasterers, and even more importantly, those that sold products to plasterers. Or maybe the lime producers were cocky and assumed they could never lose the market. A fatal mistake for many industries though out the ages.

The old saying goes, Build a better mouse trap and the world will beat a path to your door. A modern twist on that could be, Market your mouse trap better, and you can beat your own path.

Tomorrow: The Brown Coat


Anonymous said...

Great analogy! Are you taking pictures? If so I would love to see them! We love our plaster walls but now have quite a few places with drywall. We tried to find a plasterer to do a ceiling that had had furring strips nailed into it when the PO installed acoustic ceiling tile (that looked lovely) but ended up installing drywall over it.

Greg said...

I forgot to take pictures yesterday before I left the room. Once out and cleaned up, I didn't want to go back in. The floor gets a lot of dry plaster and the occasional drop of wet plaster. I don't want to track through the house. I'll gets some shots today of the scratch coat before I start the brown coat.

Anonymous said...

Ummmmmmmm what if you're to young to have watched the Ten Commandments? I'm not saying I haven't watched it. (Because I have thank you very much 12 years of parochial schools!) But ya know......... (Sorry it's the smart alec in me.)

Greg said...

I thought about this and it's no problem. Just wait until Easter and it's sure to come on TV. Don't have a TV, then hang out at the mall. It's bound to be on a TV in a store showroom someplace. It would be hard to live in North America, or be a Christian without seeing that movie at some point. For non-Christians living outside North America, I'm sorry, this is the best I can do.

Anonymous said...

You mention Gypsum replacing Lime due to marketing. Sorry, that's wrong. Pure lime plaster will take months and even up to a year to cure properly before paint and other decorative finishes can be applied. Gypsum takes much shorter time. But that's just a partial reason. A great book all you should read is "Plastering Skills" by F. Van Den Branden & Thos L. Hartsell. It even tells you about the Lightweight aggregates again, NOT a marketing ploy. Lightweight aggregates sych as vermiculite, perlite, and pumice increase insulation & sound absorbtion, increase fire protection, and are lighter than sand.
BTW, I'm not by ANY means an experienced expert. I've been yearning to learn more about the craft of plastering for years, that book really helps, as do experiences such as yours, thanks.

Greg said...


I don’t always let facts get in the way when I’m writing. I still think that lime is a more forgiving plaster in the long run, and therefor may be considered better by some. Also, it is superior for wet areas.

As for the cure time, a fellow old house restorer has done traditional lime plaster and painted within a month of the completion. I speculated at one time that maybe the long cure times you hear about for lime was due to the old paint formulas and not the plaster. The plaster would absorb the linseed oil as it cured and so you would be left with a mottled finish. This does not seem to be the same for modern paints.

And don’t kid yourself, marketing plays a role in everything in our society, and has for a long time.

Anonymous said...


gotta say I spoke too soon. I had just dropped by your Blog and had not fully read everything on the plaster subject. I now see that many others, (especially Roger from Spring City PA) have helped you with a LOT of facts. They have helped me also.

I gotta thank you for this all. The discussions have been great.

As to lime being "more forgiving" than gypsum. From my limited experience, yes and no. That's why we get to MIX them. Best of BOTH worlds <G> I was determined to be a purist and make my repairs with lime, but then realized gypsum is just as authentic.

I'm a wallcovering installer by trade and in the past a painter. The alkalinity of lime can raise hell with wallpaper (brown "burn-outs"), and also oil based paint (saponification). Gypsum is not as alkaline and does cure faster. BUT lime is easier to work due to it's slower set time. Both have their strong points.

You doing good with this blog !!


Greg said...

Thanks Bill,

Yes, the whole plaster discussion was very helpful to me as well. Just five years ago when I first started working on my house I found almost no information about plaster. It was very frustrating. Slowly, different people got help from old-timers and learned things through experimenting. Over at the discussion forum there is a new Reference section with some good posts on lime plaster.

Anonymous said...

OOOOPS, fogot to answer one of your comments.

you said:
"I speculated at one time that maybe the long cure times you hear about for lime was due to the old paint formulas and not the plaster. The plaster would absorb the linseed oil as it cured and so you would be left with a mottled finish. This does not seem to be the same for modern paints."

The "modern" paints you are talking about are latexes. Latex can deal with a higher alkalinity. There is one that has been promoted as dealing with a pH of 13 (talk about your "marketing" <ROFLMAO>)

As I said before, oil paints saponify (hydrolyze with alkali to form a soap and glycerol) with high pH.