All About Slip Straw

Workshops throughout this process. If you want to be involved, ask!

This Saturday and Sunday mornings the 24th and 25th, I will be collecting clay at the river.  I haven’t figured out where…but I know I can.  Anyone want to come, you are totally welcome. Let me know.  Saturday will be more of a search, hopefully with results.  Both days probably around 9am

Awesome finished slip straw wall. This would then be plastered after the straw completely dried. Plaster to keep water out!

Slip Straw is also known as Light Straw-Clay.  This is coming from the German “Leichtlehm” which means light-loam.  So we have three names for the same thing:

  • Slip Straw
  • Light Straw-Clay
  • Leichtlehm (light-loam)

I like Slip Straw the best.  It is fun to say and the most descriptive of the technique. Literally, Straw put in a slip.

Light Straw-Clay can lead you on.  It is HEAVY straw content to light clay content. It is neither particularly light nor heavy in weight.

I like Leichtlehm because I like to speak German, again very descriptive (light loam content, to straw).

So Slip Straw.  You take a bunch of straw.  NOT hay as that can seed in your walls and lead to living walls which, unfortunately you don’t want in this case.  Leads to rot.  Also, less tensile strength than straw, as straw is all stalks.  Also! Hay is a food source (nutritional as it has the seed and grain content) for many animals around here! So let the animals have theirs and you can have yours.

You take any amount of earth loam with a high clay content, sift it to get rocks and larger pieces out, and mix water into it.  Water is mixed until it is kind of syrupy or creamy in consistency.  It really doesn’t matter, the thicker (milkshake-ish)  it is, the more slip you will have to straw, the heavier the straw will be and the longer it will take to dry.  Some people are fine with this.  In this project, it will not be a thick mixture as it is very important that the drying process does not take very long.  As it gets colder, the longer something will take to dry as it will start freezing first. Then it will start molding and I will live in a mold house.

After you mix the slip, you throw straw over it and throw it around so that every bit of straw is lightly coated in slip.  THIS MIX IS SOMETHING LIKE 90% STRAW 10% CLAY.

I have used a wheelbarrow for this process in the past.  I like this way a lot because the slip will settle at the triangular bottom, so you just keep folding the straw in on itself down into the slip while being able to keep parts that you feel have been sufficiently wet down on the sloping sides.  I don’t have a wheelbarrow and would appreciate  if anyone who has access to one could let me know!

So apparently, some people then leave the straw that has been put in the slip on a tarp to soak for a few days.  I don’t really think this is necessary and won’t be doing this.  I’ve come to this decision because I didn’t let the slip straw soak in the last project I worked on and it was fine and soaking will make the project take longer and I am on a tight time schedule.

So after you pile your available slip straw on a tarp at your work site, collect yourself a good study stick from the forest. Diameter of 1.5-2 inches/~4-5 centimeters. Three feet or under a meter long. Or whatever you like after you know what you like.

So you have all this.  Now let’s go back in time to what you did to prepare the work site.

As mentioned in an earlier post, the structure I am working on is a three walled, raised hut.  Before you can create walls made out of slip straw, you need a frame.  So, we already have one side of the frame in each of the three existing exterior wall.  The other side of the frame will be about 3 or 4 feet/1 meter high, running the length of each wall.  It should be a piece of plywood or something similarly light-ish, thin and easily put in place.    Since I want walls with a thickness of 9-10inches/22-25 cm, I will be placing the plywood about that width from the existing walls.  Stabilize this in any way possible, most likely screwing it into the support beams, so you can remove it easily.

So now you have a 3 or 4 foot/ 1meter  high pocket.  This is where the slip straw comes in.  Start throwing some down in the pocket and tamp it with the stick you collected.  It is important to compress the slip straw as much as possible and get it into every corner and cranny. As the slip straw dries, it shrinks.  The more compact it is, the less shrinkage, the less holes to fill in.  And as one of our frames is an exterior wall that will not be coming off, it is even more important to compress it fully because we will not have access to the other side of the slip straw wall when we are done.  Also, the more compact it is, the better an insulator the wall is.  And that is the whole point.

After tamping ~2 feet, you want to take the form off and  let it dry for a few days.  Really, I don’t know how well this is going to work out.  Mostly I am worried about it not drying out properly.  Also, depending on what I experience, perhaps more than 2 feet high can be done at a time.  You can decide this by the amount of splooging occurring.  Splooging is a very technical term used in cob building…It is when you have put too much cob clay up at once, and the walls start bulging and sliding down.  Splooging is bad.  It means that you have put too much on top of a layer and it will therefore take much much longer to dry and it will mean more sawing (yes with a saw) of the wall in order to make it even (Because it has to be even!).   After the few days, place the 3-4 foot form you used for the bottom layer of insulation above it, going along the length of the wall again, same distance from wall, and over lapping the first finished part of the wall a bit so straw is tamped directly on top of  the first layer. Repeat what you did before, tamping slip straw into the form until it is about 2 feet high. The reason why I suggest a 3 foot high form is so that you can tamp down more than 2 feet if you decide that it is working ok, and not splooging in the same way as cob.  At points in the growing wall, put in horizontal beams.

As I get closer to the roof, this will be harder to do as the roof was not secured to the structure with cob in mind.  What I will most likely do for this is leave a frame up near the roof and fill it with dry straw as thickly as possible.

If this process continues every 4 days, this part of the project should be done in about two weeks.

Things to remember while working on these walls:

where windows are going (don’t put slip straw there, accommodate with a wooden frame WITH LINTLE!) (later windows to be put in using cob and or corbel cob)

The pieces of wood extending to the right and left of the window on the top and bottom are lintles. They displace pressure or that the window doesn't crack!!!

Other things to do while doing this:

  • reinforce floor especially on open wall of structure as this will be where the stove is going
  • attach door to open wall from corner beam.

The Wall that does not yet exist must have a non-combustible component on wall and floor as this is where the wood burning stove will be.  Rock/bricks on floor, rock/brick wall for half of it. Don’t really know what to do.  IDEAS APPRECIATED!

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