Archive for May, 2009

How to clay plaster

Part of the reason why I am writing this blog is to share the things that we have learned in the process and give a little how to advice on what worked for us. So here is the first How to entry and clay plastering.

The instructions from American Clay are pretty good but I felt that if you have never plastered before, never touched a clay-like material before or never held a hawk and trowel, you might struggle at first and I would recommend a little trial on a some kind of board just to try. Also, if you can avoid it, don’t make the ceiling your first area to plaster.

Here’s a list of things you need:

  • Several 5 gallon buckets (for mixing clay and for clean up)
  • A big mixing paddle
  • A high power drill, you want one that goes slow but has a lot of torque
  • Grouting sponge and smaller sponges for corners and edges
  • Spray bottle or garden type sprayer
  • A pool trowel (rounded corners worked better for us than square)
  • Small trowel or taping knife for corners
  • A hawk
  • Plastic scraper to get clay out of bucket onto hawk
  • A plastic tarp if you need to protect your flooring
  • Ladder
  • Dust mask

Preparing the wall:

Sanded primer is not fun to apply. The sand just wants to gunk up your roller and brush and not really stick to the wall, but be patient. Keep stirring the primer and press hard on the roller. That seemed to work. When you brush, it leaves a thicker layer of sand. It is not the most perfect thing but it seems to work and hold the plaster on the wall. If you need to cover up water stains or have old walls that are hard to clean up, I would prime with a sealing primer before. Especially if you have grease stains on the wall. Clay likes to absorb things so it will pull it through any normal paint or primer.

Mixing plaster:

Mixing of plaster

Mixing of plaster



I used a different method for mixing the plaster than AM Plaster recommended and it worked fine. I added the dry pigment powder to the dry base plaster and mixed it in dry at first. Then I poured the water on top and let it stand until all the water and been absorbed down. Then I mix with the drill and paddle. This is how I mix glazes and it avoids clumping and it worked here too. We only used Loma which is pretty sandy and doesn’t really want to clump. If you are using Porcelina or Maritimo I would test this method first but don’t see a reason why it shouldn’t work. Mix enough plaster to last you through the full job with some extra. If you are coloring, intermix buckets for color consistency. It’s OK to have left over plaster. You can dry it and safe it for repairs down the road. Try to predict ahead if you will run out before your job is done. That way, you can stop at a completed wall and if your new batch color is a bit off, it’s not big deal since it’s not on the same wall. Make sure you adjust that water content but just try a sample and see what works for you. For us, the plaster was very runny, to the point where it would almost run off the hawk but not quite. That way, on the second stroke it was wet enough to not tear behind the trowel .


We worked side by side in the kitchen. A. took the top of the wall and I took the bottom. That worked great because you don’t have to worry about keeping your edges wet so much. The edges are crucial though because when the clay reaches a certain dryness it will sort of come off as you go over it with a trowel and that is no good. The point is to keep it on the wall. If your clay is too wet, it’s not good either and you might get little cracks when it’s dry. Drips running down the wall is a good indication of too much water. Use the spray bottle to keep your edges moist. Anyway. I like to work from the bottom up: Set my loaded trowel at the edge of the wall and pull up. Clean off my trowel and repeat the same stroke. Professional plasterers will work up and then down in the same motion but I could not master that technique. If I can’t work upward, I like to work left to right. A. however, likes to work right to left. You just have to figure out what works best for you. Don’t worry if lots of plaster falls on the floor. There’s no good way to avoid it. If your floors are otherwise clean you can scoop up that plaster and put it back in your bucket. Let the first coat dry completely. Moisten that coat with water from your bottle or sprayer as you go along adding the second coat.


one wall with 2nd coat, and other wall with dry first coat

Plaster that has been compressed with sponge

Texture of second coat

Texture of second coat




I only did the sort of rough sanded finish in our house because I like the irregularities and natural look. It is the softest finish though so its not always the best for certain areas. I waited until the clay was leatherhard. That means when you touch it it doesn’t feel sticky and leaves no residue on your finger but it’s still wet. I you start seeing lighter spots, that means its too dry.  Then I use a clean well rung out sponge and as I spray a bit of water onto the wall, I wipe in circles. If the clay comes off or moves around on the wall, it is too soon to do this. The sponge really shouldn’t leave much of a mark but actually leave things looking smooth. I press down to compress the clay as I wipe in circular motions. This will make the sand corns stand out more but the clay underneath is a bit tighter. Imagine compressing little particles. Don’t use too much water but use enough. You’ll get a feel for it but it might take a few tries. The wall will start looking very gorgeous and beautiful. Loma has a nice sparkle to it that I really like and it has a lot of depth. Finally I let this coat dry completely and then use a very dry moist sponge to go over it again to wipe off the sand. It will come off anyway with time, and especially if you have hardwood floor like we do, you don’t want that sand sitting around because it will scratch your finish.

Clean up:

Wash all tool in your bucket with water not in your sink. The sand will abrade at the metal of the trowel so you might find edges sort of sharp. Be careful not to cut yourself. The sand might also wear through the rust proof coating of your trowel so don’t be surprised if rust shows up. Let your bucket of wash water stand for day and then pour of the clean water off the top. You can let the sludge sit to dry. Once dry you can throw it into the trash. You can spread out the left over clay plaster to dry but crumble it up into little pieces. It gets really hard when it’s dry so if you need to rehydrate it someday, it will be easier with smaller pieces. Remove your tarp and vacuum. If you have hardwood floor or any other flooring that will scratch, vacuum frequently at first and be thorough around the edges.


You might say “Never again” when you are done but your memory of the mess will fade and as you will think about your next project and what to put on the wall, you will be so happy looking at your clay plaster wall, that you will decide to do it again in a heart beat.

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