Continuing to put mud on the walls

There were several things to do this last week that did not involve the house, but we were still able to mix and apply several batches of plaster.

On Monday, the boys and I worked all day plastering the walls in the laundry room. We mixed seven batches of plaster and put them on the walls. Each batch weighs around 240 pounds wet. Once it dries, it’ll lose about 40 pounds per batch (a five-gallon bucket of water). So, that’s 1,400 pounds of thermal mass on just these four walls alone. If we count all the walls we’ve done so far (including the walls we did on Friday that I haven’t mentioned yet), it figures out to about 3,500 pounds of thermal mass, and we’ve only put the first coat on a few of the walls. There is still the second coat on the straw bale walls to be figured and a finish coat on all the walls. I find it interesting to think about the mass of the plaster that will help moderate temperature and humidity (clay is good for that) when the house is done.

I took the photos today of the plaster we applied last week. So, you can see that it is drying nicely. It’ll be cured within the next week, I expect. The places where it is thicker will take longer to dry thoroughly, but there’s not really any hurry. The only concern is mold. If the weather cools off and it is damp, the plaster won’t dry quickly like it does when it is warm with a good breeze blowing through the house. We had a few areas on the walls that we packed with slip straw last fall that grew some mold on the surface because the drying conditions deteriorated after we packed them.

I’m not really worried about the mold. It seems to originate in some of the straw that is used in the mixes, probably because of the presence of mold spores. It can only survive and grow in moist conditions. I have discovered a safe way to kill it and prevent it from spreading – white distilled vinegar. We sprayed walls that grew mold after packing last year, and it took care of the problem. There have been a few places where some mold appeared on the surface of the plaster when the drying conditions were not ideal recently. A little vinegar kills it quickly. I’m sure if it was a major case, not just a little here or there, that there might be some other remedies needed, but this one is working for us.

So, after doing all the walls in the laundry room, we didn’t get back to plastering until Friday. We only had the afternoon, and we worked in the guest room. We were able to get 2 walls done. We’ll finish this room tomorrow if all goes well. And, we’ll do a few more walls, too. It is reasonable for us to finish the first coat on all the downstairs walls this week.

 

Putting mud on the walls

Since we have all the interior walls packed, it was time to focus on plastering. We did a little plastering a few weeks ago – just one batch. The boys both commented that they would rather play in the mud than pack the walls. So, they seemed happy to plaster.

We started with the dining area wall on Tuesday after doing some cleaning up on Monday. This was the largest of straw bale walls to be plastered, considering walls as areas between posts or on one side of a specific rooms. This wall is 9 feet tall and 14 feet wide with only one window. The thing with plastering the straw bales is that we have to work the plaster into the straw. The goal is to get it pressed into the bales an inch or two. Also, around the windows where I curved the bales, I really have to work the plaster in. I used chicken wire on the curves. So, I have to press the plaster through the wire and work it into the straw with my fingers. When the ends of the straw face outward, it’s easier to work the mud in, but when the straws lay cross ways, like most do in the curves and on the ends of bales, it takes more effort to work it in.

So, I worked the plaster in on the window curves while the boys worked on the sides and below. Once I got the curves done, I helped finish up the rest of the wall and make sure it was all pressed in to the bales as desired.

On Wednesday, we decided to plaster some of the slip straw walls. Having done a little of this previously, we knew that it goes on much easier than the straw bale walls. You don’t have to work it in the same way. Our process involved the boys smearing the plaster on the walls with their hands. I would follow with a trowel to smooth and even out the plaster. We were able to finish the wall below the stairs, the wall along the stairway, and almost all of the walls in the hallway, including in the linen closet but not the cabinet above.

We actually finished these walls in the morning and then spent time in the afternoon sifting some more clay dirt. We’re using clay that we excavated when digging the root cellar. I ran the tiller through the clay pile to loosen things up and then we screened it through 1/4” hardware cloth to remove rocks and larger clods of clay. This makes a nicer mix of plaster. We screened it into half of a 275 gallon tote – the same thing we mixed the slip straw in, only we put the metal frame around it to give it some rigidity.

On Friday, we plastered in the mudroom. We were able to get all of the walls plastered in there except for a small section above the interior door. We had two walls of straw bale and two of slip straw. There were curves around and above one window and the exterior door.

I calculated that in the three days of plastering that we mixed and applied 1,500 pounds of plaster. Once the water dries out of it, that is 1,200 pounds of plaster. This is only the first coat, too. The straw bale walls will require a second heavier coat to fill in the irregularities, maybe even a third coat. The slip straw walls will only require one more coat. At this rate, we will have several tons of thermal mass on the walls which should help moderate the interior temperature during the summer and winter.

Each batch of plaster consisted of 2 buckets of sand, 1.5 buckets of clay-rich dirt, one bucket of water, and half a bucket of chopped straw. I mixed it in the concrete mixer, using my hand to help ensure that the sand was mixed through properly. It made a nice easy to apply plaster.

We’ll be mixing up a lot more in the coming weeks.

Straw in the wall: an instructional video on slip straw

I’ve been thinking about and intending to put together a video on using light straw clay, also known as slip straw, in interior walls. The boys and I have packed 1,100 square feet of walls now. So, we have a little experience. I figure that I really was learning how to do it by the time we finished this week, but I’m not going to go back and start over!

Anyway, I figured it would be best to shoot some video on the process before we got it all done. As we worked on the final walls, I videoed different parts of the process, and then I spent some time over a couple of days to put together an instructional video called Straw in the wall: using light straw clay (slip straw) as interior wall fill.

 

Window seats upstairs

A while ago I finished curving the straw bales around all of the windows downstairs and installing 3/4 plywood window sills. Upstairs, I hadn’t gotten all of the window sills/seats put in and had one windows to curve the bales on either side. I got those done today.

After finishing packing slip straw in all the walls, some of the plywood I had been using for forms was now available. I just had to rip the pieces to the proper width and cut them to the right length so that I could install them. There was only one window that needed the bales curved, the one on the west end upstairs.

It looks good to have the windows finished. I still need to do above them, but that will entail putting in some nice boards rather than rounding bales like I did downstairs. I’ll do that later.

The walls are all packed!

On Wednesday of this week, the boys and I finished the last wall to be packed. All of the interior walls have been packed with slip straw, and once the last ones are completely dry (by the end of next week), all of them will be ready for plaster. We’ll be focusing on the plastering job we have starting soon.

We calculated that we packed 1,100 square feet of walls in the house and used about 50 straw bales (give or take). We didn’t keep track of how many hours of work that entails, but it was several. It’s nice to have that part of the project done.