EBC: Interior Finishing – Walls, Ceiling, and Trim

We finished infilling the interior walls of the cottage at the end of August. You typically want to give light clay straw a month or so to dry out completely. Fortunately, we had several things to do before plastering the walls:

1) Framing and infilling interior walls

2) Finishing the ceiling

3) (Building &) Installing Doors and Windows

4) Building the sleeping platform

5) Installing baseboards, trim and sills

Interior Wall Foundation and Subfloor

A few days after we finished infilling the exterior walls with light clay straw we started in on the interior walls. I built the form work using the 2x8s from the perimeter grade beam. The cottage will have a half bath and a sleeping nook. Here’s a Sketchup drawing of the interior plan.

Sleeping nook on the right and half bath on the right

The sleeping nook is a platform elevated about 12 inches above the finished floor. We’ll use 1×6 tongue groove boards for the platform surface. There will be long slide out drawers under the platform. We’ll put ship lap on the bottom half of the wall and apply earthen plaster to the upper portion.

The half bath will have small vanity and bucket compost toilet. We’ll frame the interior walls with 2×4 lumber and infill with cob. The half bath will have standard a 2 foot wide door.

Jean and Tom were my crew again for pouring the concrete grade beam. The form building and pouring process was almost identical to what we did for the perimeter grade beam.

Since the interior walls aren’t load bearing we the made rubble trench much shallower and the grade beam is only 6 inches wide rather than 8. We tied the interior grade beam to the perimeter grade beam by drilling into the perimeter and inserting rebar.

We’ll be installing an earthen floor in the main area and in the half bath. An earthen floor is composed of many layers of different materials, the first being several inches of gravel. We’ll build up materials until the finished floor height is ¾ of an inch above grade beam so you can see I have a ways to go. I will make another detailed post about earthen floors. Here’s a preview video about installing the floor.


Before framing the interior walls, I wanted to install the ceiling which will be 1×6 tongue and groove pine boards. I putting in R-19 fiberglass insulation batts between the rafters. I also had to run the rest of the wiring for overhead lights and fans.

Wall Framing

I framed the walls fairly closely to my Sketchup design. After running the last of the wiring I infilled the walls with cob. I ran out of dirt towards the end so I finished up with light clay straw. I thought I might put a bottle window above the half bath door but a few days later I filled in the area with cob.

Doors and Windows

I built the front door. It’s a 2×4 framework with quarter inch plywood sheathing. I’m still working on the hexagonal window. I’ll take a deep dive into building the front door in a future video.

The windows two large windows are off the shelf aluminum double pane single hung windows. The half bath window is a vinyl awning window. The awning window was white but I primed it and painted it black. There are four transom windows that I’m still working. I’ll touch on them in a later video.

The Sleeping Nook

I framed the sleeping nook platform like a deck hanging 2x4s with joist hangers. There’s a lower set of joist hangers that will support the hardware for the underbed storage. I fastened the 1×6 tongue and groove boards to the joists with trim screws.

Earthen plaster will sometimes dust off if you brush against it. The nook is only about six inches wider than a queen sized mattress so I decided to install shiplap about half way up the wall to prevent dust winding up in the bed. The shiplap will also serve as a headboard. Tongue and groove and ship lap boards only come in 8 and 12 foot lengths so I was extremely fortunate that all my measurements work out so that there was little waste.

Baseboards, Trims and Sills

After building the timber frame cabin I discovered that it was much easier to install baseboards and all the trim work before plastering the walls. All of my baseboards and trim are ¾ of an inch thick. The finished plaster will be ½ to ¾ of an inch thick. The trim is good guide to maintain a consistent plaster thickness. It’s also easier to apply plaster to the trim rather than to the ceiling and/or floor.

I also installed horizontal furring strips in the kitchen at 36”, 60” and 84” (above finished floor height). These will provide me good connection points and ensure the wall is good and flat for the kitchen upper and lower cabinets.

Here are a couple of other tips for prepping for earthen plaster:

1) Staple burlap onto your window and door headers and any other place where you have large sections of wood. This will provide a good mechanical key for your plaster.

2) Put a screw or nail into each of your studs at a consistent height. I like to use my shoulder, waist or knee as reference points. Stud finders can’t find a stud buried in a cob or light clay straw wall but it can detect the buried screw or nail.