Monday, 3 March 2008

Drying the dome

I left the clay dome overnight, then scooped out all the sand and broken bricks the next day. Although the broken bricks were only there because I'd run out of sand, it made the job quicker as they were easy to remove. I put my 100W light bulb in the oven, and left it for 5 days to dry. The bulb kept the temperature above freezing, but the clay never really got warm. The newspaper soon dried though, and I peeled it off after a few days. The next few pictures were all taken after 5 days drying with the 100W bulb - about 5-8 C temperature outside

You can see the lumps of clay that I used to build the dome on the inside face - it was impossible to get this smooth, because I can't reach in that far and the oven entrance is only 13"...

Notice that as the dome has dried it's pulled the arch and cracked it. Around the base of the oven dome I could see the whole dome was shrinking inwards, but staying as a single intact piece. The whole dome could contract over the flat firebrick base as it dried. The cracks between the base of the dome and bricks show about 1/4" movement after 5 days.
The cracking was worst around the outisde of the brick arch. Stupid of me - because the arch couldn't shrink as the clay dried, it cracked instead. Oh well, I'll fill these in later.

Not known for my patience, after 5 days drying I decided to substitute the 100W bulb for a 500W halogen work lamp. After another 5 days the dome was very dry, and felt warm to the touch all the way round (even at the base, away from the light). The clay was a very different, almost white colour now, with no darker regions (although the photos don't show this well). The arch had cracked a lot now with the extra drying, although all the bricks were still very firmly fixed, and I couldn't extract any with a lot of wiggling about.

The cracks around the arch (there were three) had opened up to about 1/2" on the outside, although hardly showed at all on the inside. A couple of small surface cracks had opened up near them - but no sign of these on the inside at all.

The base had probably moved about 1/2" inwards all round - so that's about 1" shrinkage in total across the dome. The dome was intact apart from the cracks around the arch - no other cracks anywhere else. I'm pretty pleased with this.

I filled all the cracks with the spare clay/grog mix that I'd bagged up from when I made the dome - a very quick and easy repair that soon left things looking good again. I wet the dome around the cracks before doing the repairs to make sure they all stick. The repair's obvious right now - you can see the darker fresh clay.

I'm pleased with that - far less cracking than I had dreaded. The 500W lamp has gone back in, and I'll add some insulation to fill the chimney gaps in the next few days.

No comments: