I would just like to know what you think about this. We have a house from the 1930s that we are restoring. We are currently working on the basement windows. We have removed an old, poor basement window. I have cut new wood myself, from which I have made a frame. The wooden frame is precisely sized to fit the opening. The opening is built with stone and gravel mixed into the mortar. In the upper part of the opening, there is a wooden beam that belongs to the house's sill. My question concerns the bottom of this opening. I have brushed away loose old mortar and sand at the bottom, and now there is a small depression there of about 1-3 cm. The depression varies because small stones and gravel are embedded in the old mortar. When I now install my custom-sized frame, there will be quite a large gap at the bottom. Cold air will blow in there. How should I seal this gap? Should I mix some kind of mortar and apply it? If so, which type of mortar? We have hemp fiber that we plan to insulate the walls with. Could I place some of that in the gap? But there is quite a risk that moisture might get in there at some point, so maybe it's not so good to fill it with an organic material? Otherwise, I thought of hemp or flax, but as I said, I am unsure about that. The mortar itself has a certain moisture content, so perhaps I should avoid flax and hemp? How would you do it? Do you have any advice to offer? I gratefully accept any advice on this.
