We have been very fortunate with the weather this year. Lots of warm weather, dry weather, and even a mild autumn so far. However, there was a week at the end of July when it was very, very, wet. On the 25th, water started collecting around the Peerie Hoose, so S called our groundworks contractor who came and dug a dry well. This was a hole two metres wide on both sides and two metres deep, which was then filled with stones to give the water somewhere to drain. Sorted! Or so we thought…
To prevent moisture rising from the ground and up into our walls, it was necessary to lay a damp proof course (DPC) after a few layers of brick and stone. These days this is typically accomplished by using a plastic membrane, but as our materials brief stated:
We want to avoid synthetic materials wherever possible. The ideal house would biodegrade over a couple of hundred years of non-use.
We therefore went with one of the traditional methods of damp proofing which is to lay a double layer of slate (the second layer offset from the first and so covering the cracks between slate pieces). The slate we used is second-hand Welsh slate. As you can see in the final image below, after the DPC was laid, further courses of brick and stone were put on top to complete the plinth walls.
To avoid damp getting into cob walls, it is necessary to build a plinth wall at least 450mm above ground level on the foundations, on top of which the cob walls will be built.1 To save money, the bulk of the plinth walls have been built in brick. S looked for second-hand bricks. Most ‘modern’ second-hand brick can’t be reused because it tends to be mortared with Portland cement. The binding strength of Portland cement is stronger than the material of the brick itself, so it’s difficult-to-impossible to clear the mortar off a brick without breaking it. You can find older second-hand bricks, but because it’s labour intensive to clean them off properly (even with older mortars) and tend to be used by people who need to match existing bricks when repairing or extending an existing building, they are expensive.
What S did find is brick seconds from a brick manufacturer in Glasgow. They are cosmetic seconds – bricks that aren’t the right colour or are slightly burned — but structurally sound. Normally they would be broken up for use in aggregate and concrete so as well as using a product that would otherwise be degraded, they are a lot less expensive than ‘normal’ bricks. A win-win!
Technically a plinth wall might not be necessary. Some old cob houses don’t have them, and they are clearly situated in such a way that ground water isn’t an issue and hasn’t ‘melted’ the walls over the years. What we don’t know is how many old cob houses without plinth walks did fall down over the years. It is certainly highly advisable to build a plinth wall to keep the cob from sitting directly on the ground. ↩
It might seem like we’ve been offline, but it’s just that a mix of things has resulted in an overly-long gap in posts. It was a combination of being very busy with the construction; an old computer without a functioning battery; beautiful long summer evenings when I wanted to sit out chatting by the fire instead of in the site cabin on the computer; and an overload of photos. But I’ve now got the photos in order and will catch the blog up to the current situation, and then stay on top of them. Hope we haven’t lost too many interested readers!
This is a long overdue post. We were away for a week in the middle of June and intended to return to the site soon after. But delays in securing our stonemason means that we’re still in Edinburgh. Not to worry, we will be back down on Sunday, and full steam ahead on Monday when the building of the plinth wall starts.
In the meantime, I thought I’d post some photos from when we were last down at the beginning of June. We (well, Scott and his team) finished off the foundations and construction of the scaffolding started. It will be tented scaffold so that we can work even if it’s raining. The roof wasn’t finished before we left, so no photo of that, but it is apparently all up now and waiting for us!
Yesterday, we arrived back on site. It was great to be back, a warm sunny day, and the internet connection is now live!
We’re only here for a week, but there are a few key things that need to happen before we return at the end of June for the bulk of the work. First up, the surveyor returned and put marking pins in the ground to show where the walls need to be built. These can’t be moved until the stone wall is up!
This showed up a little problem – one of the foundations was slightly too narrow.
When we moved onto site to start the foundations, we had no electricity, internet, or running water. We did have mains water to the site, but it required two people to fill up a 5 litre bottle – one to wrestle the 32mm supply pipe into the bottle, and the other to turn on the toby1, which is the main valve controlling the supply of water to our property. All cooking (and heating of water) had to be done over a fire. This was fun at times, but challenging at others (especially when it starts snowing early in the morning and we had not sorted dry tinder the night before). Charging mobile phones and computers or accessing the internet required a 300m walk to Wiston Lodge (who have kindly allowed us to use theirs). This might not sound like a big deal, but when you need to check something quickly or send an email in the middle of building works, it can be quite problematic. Continue reading
Called a mains stopcock outside of Scotland – don’t ask me where ‘toby’ came from. ↩
Over the course of three days, the trenches were filled with Type 1 aggregate. Luckily the weather was much improved from the beginning of the week – both warmer and with a couple very sunny days. The aggregate is deposited in 150mm rises and then packed down with a ‘wacker’. There are two variants if this machine – one that looks like a lawnmower and another that looks like a pneumatic drill, both with plates on the bottom that vibrate up-and-down. Both types were used in our case, and resulted in a closely-packed foundation, the cross-section of which can be seen in the previous post about aggregate.
The result is about 700mm of packed aggregate with a solid and level surface. The latter is thanks to an electronic measuring stick they have which ensures the surface is truly level, not just following the surface of the surrounding land which falls away.