Pump House: Window Headers and Door Archway

The finish line for the pump house is in sight! Ryan and I made a list of everything that has to be done for that structure to be completely, 100% done and the list fit on one small notebook page! AND, since making that list we have already checked off like 5 things!

The pump house is going to have an arched doorway. Cobbing an arch is something that should be done with some care. Before I even arrived Ryan had built a form for the arch using masonite and fastened it in place with screws going into the cob. Contrary to what I have heard some people say, Ryan has found that you can screw into cob using a drill and, ideally, ceramic coated wood screws. To keep the screw heads from going right through the masonite Ryan has invented a ingeniously simple method of putting the screws through bottle caps and using the bottle cap as a big, temporary washer. When building forms it is also important to realize that it is usually easier to take cob away then to add it once something is built, so our archway form is fastened a bit lower than the door will actually be. Once the cob is all dry we can easily shape the arch to the exact shape and and height we need using chisels, grinders, and lathe to basically sand away what we don’t want.

Archway before mudding but with the form in.

In addition to having a form we also created what Ryan calls “porcupine blocks” which are attached to the frame of building but stick out into the cob. These are just blocks of scrap wood with a handful of nails or screws sticking out of them, sometimes with bottle cap washers on them as well that help to give something for the cob to grab onto and provide extra strength. It is the same idea as putting rebar in cement, and it will all be covered up so it doesn’t matter what it looks like, just that it performs it’s function structurally.

Once you start mudding an archway it is important to make sure to not let any one lift dry out too much as it will be much stronger if each lift is fulling keyed into the previous layer. It’s like working with clay; things can’t be too wet because then they will slump, but if they are too dray it is hard to create a strong bond. So once we started mudding the archway we threw up an inch or so every day until it was done. Now, the exterior archway is DONE. That is one thing checked off the list!

Window header in, not yet cobbed. Notice the porcupine nails sticking up from the top of the header, and the barbed wire which will also reinforce the cob. (note: this picture taken from the inside)

Next focus for the pump house was getting in window headers above both windows. You don’t want cob to be bearing down directly on a glass window as that is a lot of weight for the window to handle so you usually install a header, which is usually just a piece of wood. This sounds simple enough but, as with everything in the building world things generally take at least twice as long as you think they will. The first step was making the walls plumb around the windows. It is easy to carve away cob, but once the wooden headers are in those can’t be moved or shaped easily so we wanted the walls to be plumb before we installed these headers. Our choice tool for plumbing the walls is a long plastic level with paint scrapers screwed along one side. This tool allows us to make plumb line channels every six inches or so in the wall and then we chisel or sand away the excess cob between the plumb channels.

Interior of the window with the first layer of cob above the header in.

Once the walls are vertically plumb we had to create a level surface on top of the windows for the headers to sit on. This also required some carving away of cob, checking every so often to see if the header would lie flat on the window top. Once this was accomplished we porcupined the top of the headers with scrap nails and screwed the headers in, using some shims to give them a bit of a reveal for both aesthetic effect and to allow more light in.

Then, finally, we were ready to cob again! Except, our walls had started to dry out quite a bit…. So, for a few days we stopped at the pump house morning and night to give the area we would be cobbing a good misting with the hose (use the mist setting on a spray nozzle so as not to erode your work!), slowly rehydrating the cob.

Then, finally, it was time to cob! With the headers in, it is just a matter of putting up a few inches of cob every day or two until we meet the roof. This is the last area on the pump house that needs to be mudded. It will then be time for shaping, hanging the door, plastering and other finish work! So exciting!

Exterior of Pump house with the archway fully mudded and window headers in! Note that the archway form stays in until the end of the drying process if at all possible.

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