Slip Straw

David's picture

When you fall down, there's not much else you can do but pick yourself back up. And well, we are on our feet again and it's time to push on. So this morning we slid on our boots, pulled up our sleeves and with the determination like salmon during spawning season, went out to work on the cob studio. The past two weeks have been very windy and very wet, so the job site is pretty much in tatters. Tarps are strewn about, all torn and shredded. And walking around the cob building is a hassle because any bit or clump of clay seems to become magnetically charged to your shoes. If you're not careful where you step, you'll eventually end up with a pair of 20lb. shoes. So we knew a good clean-up was in the work schedule. But first ...

... the roof! Our next major portion of the construction is the roof. We decided to go with metal, mostly because we plan on using it on the roof of our 'real' house so that we can better harvest rainwater. Not sure if we'll harvest any on this roof, but at least we can get some good experience installing the metal. I originally had planned to use plywood sheathing underneath, but instead have gone to using 1x4 strapping. But first things first, I need to get it ordered. So I went and got a couple of quotes on some structural galvanized roofing. As it turns out, a 150 sq.ft. roof costs around $550 to cover with metal. This was more than expected, but we'll have to manage. And now, if all goes as planned, we should have a metal roof delivered next Saturday. We can hardly wait!

Along with moving a huge pile of clay away from in front of the studio, I tossed some old straw around the entire building to keep our shoes clean. It's 100 times better. But the biggest thing we did was starting the slip straw insulation. We've been wanting to do it for some time now, and being how we were done cobbing and now waiting for the roof, it was a good time to get at it. It would have been good to have done it earlier when the sun was high and the temp was hot, but I think we can get it dry before it's time for installation. Oh and in case you were wondering what slip straw is, it's straw that has been covered with a watered down clay (slip). But to get to the thick of it, here is what we did.

First I had made a formwork of 2x6's to pack the slip straw into. I measured it out to give me (2) 2' squares and (1) 2'x3.5' rectangle. We then decided to use some landscaping fabric for the bottom. I just simply cut it to fit, and then stapled it to the form. The idea was that when we finished packing the straw into the form, we could lift the whole thing onto a screen and remove the form to use again while the first dries. The fabric would also allow air to freely pass through the bottom to get a quicker drying time.

All that set up, it was time to start making the slip. I filled a bucket partially with water, and slowly added some sifted clay. I decided to use my trusty potato masher to break up the clay in the water. I was sure this would be an easy job, but it turned out to be some hard work. The masher was working, but not very efficiently. The clay would end up sticking to the bottom of the bucket and not breaking up at all. A quick fix was to use the masher to scrape off the bottom and then mash it again. The real problem was how many times I'd have to repeat the process just to get one shovel of clay broken up. I didn't make note of how many times it took me, but I'm sure if I did I would have eventually gotten tired of counting. Be assured, it was a lot. I decided to try stirring it instead of mashing. I used a simple wooden paddle and began stirring. When I started I could feel the clay, in the water, hit the paddle. And in no time at all, I couldn't feel the clay anymore. I thought I was onto something. I even poked my hand in the water and felt around the bucket for clay, and only found small bits so I thought the paddle idea was the cat's meow. So I added more clay and started stirring again. And again the clumps soon stopped hitting the paddle. But from the look of the water, I knew something was amiss. It wasn't getting thicker like it was supposed to. I felt inside the bucket again, and like the last time, it was pretty clean of clay clumps. Then it struck me! With the smallest of hopes, I pulled the paddle out of the water. And sure enough, the bottom of the paddle was caked in clay. And I was stirring this thing as all get out, so I knew this was a dead end. I then tried to just use my hands to squeeze, smash and stir the clay, but that definitely wasn't working. So, back to the masher I went. But I did come up with a slight fix. I threw in a handful of small stones to help keep the clay from sticking to the bottom. All I can say for that is: I think it helped. I still had to scrap the bottom, but it sure wasn't as thick as before.

Now Patricia, on the other hand, had the right idea. I was using the same sifted clay that I used for the cob, but Patricia took it one step further. She sifted that clay through another, small sifter. The same one I used to get the clay ready for mortaring. She ended up with a very fine clay that pretty much dissolved in water on contact. The sad thing was that she needed dry clay to begin with, and we didn't have very much of it. So she made what she could and I made the rest with my potato masher. In the end we had our slip. Now came time to mixing it with the straw.

We grabbed an old wheel burro to mix it in. We'd toss in some straw, and then drizzle some of the slip on over it. Patricia would then take a garden fork in each hand and start tossing the straw around to cover it with the slip. It was a dandy of a thing. Very easy and very effective. All the straw would be covered in slip in no time flat. Now we just wished we knew how much slip to add. We read that squeezing the straw in our hand, if it stayed stuck together, it was good. Easy enough. But we decided to try a few different batches. We had three bays in our form so we made three different batches. The first was tossed with a very light amount of slip, and the second we were a bit heavier with the slip. When we packed them into the form they turned out just fine. Very similar, but the lighter one, seemed a bit more airy. It's good for insulation value, but only if it holds together. We'll see if it has enough clay to do the job. Now the third was mixed quite differently. We saw a video of some people kinda dipping the straw into the slip, and then squeezing the excess out. So we decided to try it out. I poured the slip from the bucket, into a snow sled so that we have more room for mixing. And then we got down and dirty, literally.

The process turned out ok. First off, it isn't exactly warm outside and the slip was down right cold on our hands. And wringing the straw out with cold hands wasn't very pleasant. But it packed pretty well. Probably because there was more slip covering the straw. More slip, of course, means less insulation value. But if any of the three hold their shape, this is the one.

Now, with all three bays packed, it was time to move it onto a screen. For the screen we laid out a sheet of plywood, then put four blocks on that, and then an aluminum ladder on top of the blocks (the blocks being at each corner of the ladder). And that's about where our plan to move the form failed. When we picked up the form/fabric, the heavy slip straw made the whole length of fabric sag in the middle. So much so that it was immovable. Patricia suggested to just leave it as it lay until it dried a bit. Being how it was near the end of the day, and seeming to be the best idea, we did just that.

With a little extra time on our hands before we turned in for the evening, we decided to fill in the studio floor with sand. We laid out some more landscaping fabric to cover the floor and then proceeded to fill it with a few inches of sand. The sand really defined the spaciousness of the interior. We like it.

Well, I guess that's it. We still have more slip straw to make, but I think this next time I'm going to try and have some clay already soaking in water. Maybe it will make it easier to break up. Here are some pictures we took while our camera was working. Enjoy!