Smearing clay slip on a light clay straw wall prior to plastering
Clay slip is an essential material for coating straw bale and light clay straw walls prior to plastering. Basically, it serves as an adhesion coat, essential for getting the first coat of plaster to stick to the wall. There’s not much science to making clay slip, and it’s really fun to smear. Here are a few really simple tips for making and using clay slip for natural walls.
Mixing clay slip with a heavy duty drill
How To Make Clay Slip
Clay slip is a liquid mixture of clay suspended in water. Clay bonds to itself really well, and that is the primary reason for smearing slip over a straw bale or light clay straw wall. Try putting clay plaster directly on a straw bale without slip and you’ll see what I mean. Depending on the application, you will add either more or less water. For the purposes of applying an adhesion coat to your natural wall, you’ll want something thick enough that you can pick it up without it completely running between your fingers.
Depending on the quality of your site clay, you may need to run the slip through a screen. A piece of 1/4″ hardware cloth mounted to a wooden frame makes a great screen. Be sure the slip is wet enough (but not too wet) that it easily pushes through.
Application is really easy… pick up a handful of sticky clay, and smear it on the surface of the wall. You don’t need to build it up thick, just give the wall a good coat so that your plaster will adhere. I personally see no issue with immediately following up with plaster. If your slipped wall dries out, you’ll just have to spray it down to allow for the proper adhesion.
That’s all there is to it!
p.s. On a side note, I know that some people add a small amount of sand to their slip… I’m honestly not sure why. It just makes it more difficult to stick to the wall. I don’t personally recommend adding sand.
Ready for the Next Step?
Read on for a base coat clay plaster recipe, and tips for applying the plaster to a light clay straw wall… one of the most fun steps of all.
Don’t forget — see my previous two articles in this series of light clay straw how-to building guides: