If possible I would recommend building your window and door frames before starting your walls, that way you can build up to and around them and keep everything nice and flush. However with the construction method we are using at this site this was not posible for the doors at least. The windows can be built first, and cobbed around no problem but the doors cannot. The reason for this is that the bottom of the door frame sits on a small part of your rock wall foundation, as you can see below.
This means that this small section of rock will be taking a very heavy point load under the door frames. So what you effectively have to do is hang the door from the horizontal lentil piece, which will sit on top of the ground floor cob. Then the verticals are connected to lentil and also drilled in to the cob walls using dead men. This is what I will explain in this post.
This is what I mean by fitting your frames and building around them >>
So. The process is as follows…
First you need to make your deadmen which will fit in to the vertical parts of your cob wall. You will need a nice block or stump of wood, with nails sticking out all sides, and no wire wrapped around. As you build your wall up, add a dead man at the bottom, middle and top. These will provide a wooden surface for you to drill your frame in to. As you can see in the picture below, you have to really pay attention to how straight up your stones and cob are. If they are uneven then you are going to have gaps between your frame and your walls. This can be filled with cob but looks really ugly. This is why I would receommend to build the frames (or maybe mock frames) firstso you can build your stone and cob right up to the edges.
If you forget to install the dead men as you are building with the cob, you can cut a big hole in your wall, place them in, and back fill really tightly around the dead man. This will not be as strong but should suffice.
As you can see above, the two circular ends of the wood are what you are going to be drilling your frames in to. So it is important to make sure that they remain a little bit exposed. The dead men in the photo below are a bit too exposed and had to be cut down a bit.
Use a spirit level to make sure the deadmen are in line on the vertical axis, as well as in line with regards to how much they protrude from the wall. If one is sticking out more than the other you may have a wonky window frame.
Once your space is ready with dead men you can place your frames and bolt them in. If you have gaps around the edge you can fill them with a mix similar to cob. Just make sure the space is really wet before filling the gaps so it sticks.
Fill in those gaps well and make them join to the wood in a style you like. We found that curving in to the wood like this reduces cracking and hides the gap which will inevitably form through the shrinkage as the cob dries. The mix we use to fill is called Margarida Mix. Also, shown below, you should try to have the vertical sitting on top of the horizontal so you do not get a point load on your cob. The horizontal beam will help distribute the weight a bit more evenly.
There are a few things to consider with windows, as they may be taking some rain on the outside. Firstly, the outside horizontal parts of the frame should be sloped downwards so that any rain that lands on them will run out of the house rather than in to the wall.
Also the cob above the top of the window should protrude out a bit so that any rain running down the wall will fall in front of the frame and not on top of it.
Finally you can add a drip guard under the horizontals. This is a groove that runs all the way along the underside of the wood which stops rain running in to the wall, and lets it drip to the ground.
The more protective elements you can add in these cases the better. I have shown three lines of defense against water penetration around windows, which I know work with a cob house, but there could be many more that you could learn from modern building techniques.