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!

Finished Stacking Straw Bales

John places bale at top of wall

Riley transfers bales to building site

Last week, with the help of family and friends, we finished stacking all of the bales. They had been sitting in our garage since last summer and were certainly making themselves at home in that comfortable, dry space. The great thing about that storage site is that we knew exactly the conditions under which the bales would winter: no mice, no moisture, no sad stories. The challenging things about that storage site were they took up all of the space in our garage and we had to move the bales again - from the garage to the house. (Many times during our research it was recommended that bales be delivered to the building site and stacked directly where they would be used. This removes the necessity of moving bales so many times.) Nevertheless, we now have a building made of straw, but it’s not a house...yet.

Scott checks the wall to see if it is level and plumb.

Using a weed trimmer, Riley smoothes the wall’s surface.

 There are many next steps but we decide to begin playing around with plaster a bit. Our printed references include Scott’s notes from our workshop with Bill and Athena Steen plus the book entitled Using Natural Finishes: A Step-by-Step Guide by Adam Weismann and Katy Bryce. Both are proving to be invaluable.

First we set up our plaster mixing station. This consists of a mortar mixer, a large sorting screen used to sift the earth from our building site into piles of 1/4 minus particles, piles of earth to be sifted, shovels, mason’s sand, a water source, a wood chipper, straw, a wheel barrow,  a mixing table, large cement mixing tubs, several white buckets and many pairs of rubber gloves.

Riley moves earth to the mixing station.

Doug and Scott shovel earth through the sorting screen.

We experiment with our soil to make a clay slip. (This clay slip is the basic ingredient in all of the future plasters we’ll be working with.) Using Torrey clay soil, we need a mix of 4 parts water to 7 parts soil.

 Adding long, unchopped strands of straw to the clay slip, we create light clay straw which  used to fill all of the empty spaces between the bales and between the bales and the framing timbers.

Scott begins filling gaps between bales with straw clay.

Before we work on other walls, we want to create several different mixes of plaster in order to determine the best “recipe” for the first layer. Some sources call this layer the scratch coat. When we are completely finished, every wall will be covered with approximately two inches of plaster. This first coat will be about one inch thick. The main purpose of the scratch coat is to get a bunch of mud on the wall and fill in the major irregularities in the surfaces of the walls. The success of the last layers of plaster depends on this foundation coat. It must stick to the walls and it mustn’t crack. Once it’’s on the walls, we’ll put scratches in its surface, hence the name “scratch coat.” This scratching will provide a surface that can support and hold the next layers of plaster.

Scott and Riley add straw to chipper in preparation for mixing a plaster "recipe."

The chipper transforms the long straw into small, fairly uniform small pieces.

Soon we will use this chopped straw, sand and clay slip to create the scratch coat.

Straw

After all of this time and planning, we are finally working with straw! It seemed as if this moment would never arrive, but here we are with bale number one in hand.

Before this first bale could be set in place, we attached burlap to all of the exterior timber frame surfaces that will have plaster against them. We did this because plaster and wood don't really like each other very much. They'll sit together quite nicely for awhile, but, as time passes, the plaster dries and contracts a bit leaving small gaps between itself and the wood. These gaps could eventually become conduits for moisture to enter the bales, and this is a big problem in the straw bale world. We love new experiences, but this is one we would like to skip. The burlap will act as a relationship reinforcer. When we get to the plaster stage (which isn't far away - hooray!), that burlap will be pressed into the first layer of plaster which will give strength to the bond, thus reducing the chance of future separation.

Next we pounded 12-penny nails part way into the sill plate at four-inch intervals. The nails stand about two inches above the sill plate in a zig-zag pattern. As the bales of straw are set in place, the heads of the nails dig into the bottom of the bales and provide a very strong hold. This prevents the bales from moving off of their foundation.

It's surprising to see how quickly the straw bale phase of the building goes. In just four days, a handful of people have completed almost half of the wall installation. Most of the work in done in pairs which change as needs change. Shanna, Doug, Scott and Riley have done most of the straw bale work. This involves stacking bales, retying them to fit the space, notching bales to fit around posts, tying bales to the timber frame with eye screws, and shaping bales to provide curved surfaces at the window and door openings.

Scott and Doug place eye screws into timber frame posts.

 Scott tamps the first bale securely onto nails in the sill plate (or toe up).

 Scott shapes a bale with our precision chain saw.

Riley tamps a bale into place.

Doug takes a moment to evaluate.







As a section of wall is completed, bamboo poles are attached to the wall at the base of the sill plate and at the ceiling. We used conduit straps at the bottom and drilled holes in the ceiling at the top. The poles are placed directly opposite each other on the inside and on the outside of the wall. Using a bale needle and baling twine, the opposing poles are "woven" together very, very tightly across the wall. This "weaving" compresses the bales in such a fashion as to create one very solid wall rather than just individual bales stacked on top of each other.

Close up of bale needle.

Wayne demonstrates one of the "weaving" knots.

Knotting bamboo pole in place.

Shanna "weaves" a wall together.

Riley pounds bamboo pins into bales below a window opening.

The completed west wall.

Scott spoke with our window provider yesterday. The first shipment should arrive sometime next week and I'm sure we'll have our straw bale walls done just in time. We only have half a house worth of straw to finish.

The team.

The team in front of the completed west wall. (Click on the picture to see us celebrate.)

More Insulation

On Thursday of last week, we had visitors from an another planet. At least that's what they looked like once they had donned their gear.  This is how the visitation came about.

Earlier this year, Scott spent three days installing tons of cellulose insulation in the ceiling of the main part of our house. Now that we were nearly ready to raise the straw bale walls, we needed to get the insulation into the ceiling of the kitchen on the north and the sunroom on south sides of the house. Our architect planned for us to use nine inches of Owens Corning Pink Panther rigid foam. That would have involved many, many hours of cutting sheets to size, gluing them in place and then filling any remaining gaps with expandable foam. That's the yellow foam dispensed from spray cans. If you've had even a little experience with the stuff, you know it's a lot like silly string gone mad. Plus, all of this work would have been the overhead sort that is so "fun" to do.

Since Scott had had such a positive experience with the blown-in cellulose insulation, he thought we might be able to use it in the remaining ceiling spaces as well. Unfortunately, when we presented this idea to our architect, Wayne confirmed Scott's fear that moisture condensation could be a problem. Wayne suggested we look into icynene insulation instead.

We had never heard of icynene, but with a little research and a few phone calls we learned that it is a foam insulation which is sprayed over the area we wish to insulate - our kitchen and sunroom ceilings. Once sprayed it expands and fills in every single void it can in just a few seconds. This creates a very tightly sealed space. Icynene is made from a friendly material, castor bean oil. If we were looking for LEED certification for our house, it could also contribute points for that certification. You can learn more at http://www.icynene.com/green-building.

The deal sealers for us were that using icynene would mean we wouldn't have to cut all of that rigid foam and then do all of that work over our heads. Plus it was less expensive than Pink Panther foam and gave us better insulation value for our money. We were sold and that is why aliens showed up in Torrey last week.

Edwin and Juan arrive.

This is their product.

This is what a room looks like before foam insulation is applied.

Juan encloses this space with plastic.

This room is ready for insulation.

All of their equipment is covered with protective duct tape.

Even their shoes...

Edwin and Juan must each wear a respirator during the application.

Edwin is completely protected in this suit. He has also wrapped his head in plastic wrap to prevent even the smallest molecule of liquid foam from entering his nose, mouth and eyes.

Edwin pushing a ladder in place.

Edwin applying foam to the ceiling.

Edwin applying more foam to the ceiling.

Foam insulation is in place and Juan is cleaning up.

A close-up of the foam insulation.

This entire room is done.

Edwin and Juan give a thumbs up.

Not only can the foam be used for insulation, but it can also make a great party hat!