Sunday, July 17, 2011

Fun With Plaster

Today was a celebration day. We got to do some real work with plaster. Yesterday, however, was a different story because the mortar mixer we purchased last year at a terrific bargain price wouldn’t start even though it had started on the first pull every single time since we purchased it. Maybe it was just putting on an act, and, when we were ready to get down to business, it showed its true colors. Luckily, brother-in-law Doug was patient and persistent, and Mr. Mixer roared back to life this morning and rejoined the team.

Once that big repair was completed, we organized our plaster assembly line beside the mixer so we wouldn’t have to haul the plaster ingredients long distances. Since we are all older than we used to be, we also wanted to be able to lift the ingredients into the mixer without hurting our backs, so we lined up buckets of manageable size and started mixing.

We situated the clay sifting station nearby with plenty of shovels standing at the ready so anyone who drops by for a visit can make themselves useful.

The light clay straw stage is behind us. That’s the straw that is coated with clay slip and stuffed into the gaps between the bales. Now we are applying the first coat (scratch coat) of plaster. When we are completely finished, our plaster will be about two inches thick. This first coat is about half of that thickness. It covers the straw and provides the key for the last two layers. There is no special technique. At a workshop, they said, "Just get a bunch of mud on the wall." That's what we'll try to do.
Here we have applied four sample recipes to the west wall.

Using our Torrey dirt, the best recipe is two parts clay, 3/4  to one part water (depending on the moisture content of the clay and the date of the last rain storm) and two parts chopped straw.

We arrange buckets of ingredients beside the mixer in a fire brigade fashion and hand them to Scott to pour into the mortar mixer.

As each plaster batch in completed, it is placed in black cement mixing tubs near the west wall for easy access. The plaster needs to ”ripen” for a while. This allows time for the straw to become thoroughly hydrated and for the water to fill the spaces between the clay platelets. In the end, this makes a stronger plaster and one that is easier to apply.

While the plaster ripens, we mix a batch of clay slip (clay and water, but no straw). Scott and Doug blast slip onto our bales in order to make a surface that will accept the plaster.

At first we attempted to put slip onto the bales by hand. We are very glad we purchased a used plaster sprayer. It makes the job much easier and faster than hand application.
 But Scott says, "You mean we have to do this to ALL of the walls?!"

Soon the plaster in the tubs was ready and the fun commenced. In short order, but with lots of effort, we finished putting the scratch coat on this small section of wall. Success!