Once the Cabin site was cleared and marked out, it was time to put in the foundations. We needed to put in 16 stumps and 7 posts to meet our rapidly evolving design.
The soil profile at the site was a thin layer of loam top soil which progressively gets sandier down to a compacted clay which was 500mm below the surface. By 800mm, the clay was so compacted that sparks would literally fly when you drove the crowbar into it. As a result, all of the holes for both the posts and the stumps were only 800mm deep which is a fair way from recommended depths in the textbook.. particularly for a 5m 300kg hardwood post!
You can’t see it in this video but the two little stumps at the topside of the hill have been built up with another block secured on top with straight brackets. This was to bring the height of the floor up as far as possible as they were way too small.
On the plus side, the compacted clay came out in big clumps which then rammed down into a really secure, hard, water-repelling substrate for the stumps to sit in. With that in mind, we only used this rammed earth to secure the stumps. For the posts, we put the best clay we could find around the base of the post up to about 200-300mm. We then used post-mix concrete (you can buy from any hardware store and don’t get the rapid set stuff), mixed in a wheelbarrow, and poured to the top. We mounded that concrete a little around the base of the post to ensure water would be directed around the post rather than sit next to the bottom.
Once the concrete had dried a little, we put the empty wet concrete bags around the top and secured with a few shovel loads of dirt. This lets the concrete cure slowly, keeps it damp from baking in the sun and resulted in crack-free concrete collars.
This was a massive and seriously labour intensive job which took us about 10 days of hard work. Does look great once everything is in though as you can see the skeleton take shape.