Monday, 21 April 2008
I got a bit nervy after the first foot or so, as I was concerned about the mortar bonding tightly to the thermalite blocks. To help the bond I screwed 2" screws into the blocks every 6", leaving about 1" sticking out that I embedded into the mortar. All finished on the masonry work now - just need to leave this to cure, then clean everything up.
Looks good in the summerhouse, especially now I've finished the front and side boarding off. Just need to do the back now, then lay the floor.
Two hours later I had this large pile of flints, just from my own garden. I cleaned them all up the lazy way by putting them in my cement mixer with a bucket of gravel, filling it with water, and running it for 10 minutes. It also cleaned the mixer brilliantly, and I'm sure the neighbours will have enjoyed the din it made. I then spent a happy hour bashing them all in half with a hammer. Goggles are a must for this, along with thick gloves.
I fitted two switches to the front of the oven, one for a light and the other for the thermometer power switch. I'll wire these up later. Then it was time for the flint jigsaw - this took a long time, and was very fiddly. This was about three days work, using a lime and sharp sand mortar. Here I am about half a day into it. The radio was essential to keep me entertained.
I like this next picture as it shows what a con artist I am on this build. The front half is all nice rockery stone and flints, the back is waste concrete and render. No point making the back look nice as nobody will see it!
The first job was to finish the walls on the front using the thermalite blocks. The front is a real patchwork quilt, as I was using damaged and broken blocks. I tipped all my vermiculite into this hollow cylinder. I used 6 bags, so the oven has 6" of vermiculite at the bottom, and about 18" of vermiculite around it at the top. Plus the 4" of insulating blocks. The top is open at the moment, to help with drying it (it's covered by the roof anyhow).
The back of the oven won't ever be seen, so I decided to have a go at rendering it. I was really dreading this, as I've tried plastering before and made a dreadful job of it. This time I used a 4 parts grit sand, 1 part cement, 1 part hydrated lime mix (first time I've ever used lime, and got a lovely cement burn on my hands because my rubber gloves leaked). It went on like peanut butter, and stuck beautifully. The lime makes an enormous difference to the 'stickiness' of the mix - it also helped that I'd coated the blocks with a dilute PVA solution too. I was so pleased with this that I considered using it on the front of the oven too. I still can't believe I did this - it was much easier than I had had dreaded.
Thursday, 3 April 2008
This will give me a nice insulating outer surface (4" thick), and I'll fill the space with loose fill vermiculite. This is a cheap and easy insulating option - you can see the bags of vermiculite stacked up on the left hand side below, ready to go in.
I'm tipping the loose vermiculite into this gap - this will eventually fill up all this space. I've filled all the cracks in the dome with powdered fireclay, and have coated the whole dome with ~1/4" of dry fireclay. You can just see this in the picture below. The idea is that this will sift into any cracks that form in future and fill them up - a good tip from Alan Scotts book, if I remember right.