Time limit

[Wozza]

I’m on a time limit…

Building a 940mm internal diameter Pompeii and I’ve just started the 6^th course. Internal arch built and I have all the materials I need to complete. I now have a time limit for grandsons birthday in a few weeks so I’ve got 6 three day weekends. Is this feasible?

W’end 1: Finish 6^th and 7^th courses. Start 8^th.
W’end 2: Finish 8^th, 9^th and 10^th.
W’end 3: Finish dome and build outer arch.
W’end 4: Wrap with 3 layers insulting blanket and vermicrete the dome (and render?).
W’end 5: First fires to cure.
W’end 6: Take to pizza temps.
W’end 7: Party time…

I’m not sure about the vermicrete and then rendering it (stucco?). Do I need to leave time between these two operations? I don’t mind leaving the final finish for a while if I have to. In fact, if everything goes pear shaped, could I leave the insulation off completely and fire up the oven with no insulation? Just make sure no-one leans against it…

And it seems logical to me to get a few fires going to dry out the dome before I put the insulation and vermicrete on. Then a few more to get the moisture out of that when it’s complete. Any comments?

[david s]

It is better to fire the oven with the insulation in place IMO, otherwise you have a greater risk of cracking. You can fire away up to pizza temp before doing the render coat, but just ensure the oven does not get any rain on it. Make sure you push the water out slowly and try to avoid direct flame impingement on the dome for the first few days of firing.

[Wozza]

OK, so I should aim to get the vermicrete on before curing the oven - and getting to pizza temperatures. The render can wait if I run out of time, but a tarp on the dome will keep it dry in the meantime. What mixture do you use for the vermicrete, Dave? I've read 10:1 for initial bulk coat (30 - 50mm thick?) then a final coat at 6:1 to skim it off (with some lime thrown in).

[cobblerdave]

G'day
If you above the arch and past the arch transition you have considerably less bricks to lay as those rings get smaller you might find yourself closing faster than you think.
It's August the airs dry and those August westerly winds are due, it's going to assist drying the dome faster than fires alone. Don't forget to leave the dome bare and unfired for 10 days for a chemical cure, before any drying fires.
Regards dave

[david s]

With three layers of blanket you have plenty of insulation. The reason a vermicrete layer is added over ceramic blanket is just to even out lumps and bumps as well as creating a firm substrate to render against. If you make it any thicker than an inch it will take ages to dry. If you want to use it as an insulating layer then make it lean. I find that anything leaner than 10:1 makes application difficult. Adding a little powdered clay works really well to improve the workability of a lean mix. Anything richer will be stronger, but not as insulating. If creating a thicker layer than one inch, I leave it for a week to dry before adding another layer. Like I said you have plenty of insulation at 3" of blanket, so a 1" vermicrete 5:1 would work well for your build.

[Wozza]

Up past the arch now, Dave. Should be plain sailing to finish the dome. And cheers, Steve, good info on the vermicrete. That's exactly what I'll do - a 25mm layer on top of the 3 layers of blanket.