42" Pompeii construction in Adelaide

[P3 Stoaker]

G'day All,
Back to something a little more familiar today, brickwork. Completed the decorative arch and after considering different methods I ended up using mortar and laying like the rest of the bricks.
Great idea from David S, got a garden moisture meter to check on the vermiculite and after just 3 days there was only the slightest indication of moisture in one probe hole, the other 2 showed no moisture at all. I should note that the dome brickwork was completely cured and dry when the insulation was applied. The dome was completed 2 months ago, I've run a full set of curing fires and we don't know what rain is here.
Anyone have any tips on how to get a nice round shape when applying render on the dome?
Regards
Greg

[P3 Stoaker]

Thanks David, I'll get a moisture meter, I had one but ?? I am in a different situation I think in that the brick work is fully dry. I didn't realise about insulating before firing but I'm lucky it survived quite well ( I think) with only only minor cracking as seen in the earlier posts. Once most of the moisture is gone I'll paint with kemcrete and render the next day as the kemcrete is thin and will dry quickly.
I've tested a little kemcrete on the v-lite. Its a milky liquid mixed 1:1 with cement powder and can be painted on to reduce any crumbling when applying the render. Seems to work well and locked that v-lite in tightly.
Thanks again
Greg

[david s]

It’s hard to say without looking at your oven and knowing your weather conditions. I do know how hot and dry Adelaide can be. I also know that the appearance of the surface is quite different to what’s deeper in. You can dry it too fast with damaging consequence, but you will never damage it if you go slower than required. If you fired it uninsulated you may have already damaged it. Do the moisture meter thing and if you see visible steam back off, you’re going too hard.

[P3 Stoaker]

G'day David,
Thanks again for the feedback. I aimed for 50mm (2 inch) of v-lite but I suspect it went on a little thicker in places. The whole dome was well and truly white the day after application as its warm and very dry here. I can fire the oven should I need to. The brickwork was completely dry though before insulating and applying the v-lite. I have already run a full set of curing fires up to and including very hot on the 8th or 9th fire. I don't really want to cover the oven and leave it for 2 months unless I really need to as the v-lite is quite fragile and anything rubbing on the surface will cause crumbling.
Do you see a problem rendering after a week or so? I will use a garden moisture meter as suggested. How dry do we need it to be for rendering? It will sit then for around 2 months.
Thanks again
Greg

[david s]

48 litres is still a lot of water. I've not used the silicon coated vermiculite as it's not available to me. If it was I'd try it as it prevents quite a lot of absorption into the grains.I can't find how thick your vermicrete layer is, but from my experience I've found about an inch and a half sufficient. Any thicker and it takes way longer to dry out. Once it's gone white ( around three days of good drying weather) you could probably start some drying fires. I always give it at least a week. A cheap garden moisture meter plunged deep into the vermicrete layer, not at the top because that'll dry first, but about half way down the dome, will indicate when most of the moisture has gone. Alternatively or in addition, you can throw some sheet plastic over the dome during firing to see if it is condensing under the plastic.

If you can't fire it for two months then you'd be better to wrap it in plastic until you can get back to it.

[P3 Stoaker]

I just measured the jug. It was a little bigger so a total of 48 litres was used. Keen on any thoughts in relation to previous post.
Many thanks.

[P3 Stoaker]

G’day all.
Mark, thanks for the positive comments.
David, thanks for the feedback. The oven won’t be fired now for at least 2 months. The main goal at the moment is to get it waterproof as it’s outside, starts raining here in a month or so but I’m completely out of action after two weeks from today.
The ratio I used was 30 litres vermiculite, 3 litres of concrete and I haven’t actually measured the little bucket but I’m guessing about 4.5 litres of water went in that mix. It it a coated vermiculite to somewhat waterproof is so as to reduce the water needed. So for a max of 240 litres of vermiculite I estimate I used 36 litres water.
So for me it’s a question of when can I render ??? I’d appreciate any thoughts/comments on how long I should wait to render. I really want to render 5 days later, and it is quite warm here and dry. What do you think?
I’m not confident I can cover the dome successfully to keep rain off the vermiculite for two months and render later.
regards. Greg.

[david s]

If you've gone through almost two 100 bags, then you've added around 60 litres of water. Some is used up in the hydration process, but there's still a huge amount of free water left. Allow a couple of weeks drying in the sun and wind (hope your conditions are favourable) before doing any drying fires.

[MarkJerling]

That looks very tidy!

[P3 Stoaker]

G'day All,
Vermiculite all done. Its a fine v-lite and it's coated to be somewhat waterproof, unsure if it made a difference. I worked out I needed about 140 litres I had about 40 already. Sold in 100 L bags I thought to play it safe and get 2 as the place of purchase is an hour away. In the end it probable went on thicker and I was sweating it all day as I thought I'd run out. Made it with about 10 L to spare.
Regards
Greg

[P3 Stoaker]

G'day All,
Thanks for the info Mark. I ended up cornering myself in that I'd never found a vent, despite searching and the weekend was here, insulation and vermiculite. I needed a vent fast and made one. Hope it will be alright but seems fairly simple, let pressure out !!! I just plugged the elbow but I drilled a couple holes in the cap. I jammed steel wool in both ends. Ref photo 5.
I had a gap to fill, photo 6. The floor bricks are on calsil board (cannot see). The grey strip is concrete foam and the white bit is vermiculite. So filled the gap with v-lite.
I ended up using wire running across the dome to hold the blanket in place. I anchored wire loops at the bottom, photo 4. Worked well.
Started the v-lite yesterday as recommended and that provided a firm footing to continue this morning.
Todays photo's in the next post.
Regards

[MarkJerling]

Try these guys: Xylem Australia 2 Capicure Drive, Eastern Creek, NSW 2766

[P3 Stoaker]

G'day David S and Mark,
Thanks for the reply and info. I think I'll put the vent towards the back, probably half way down?? I'm not really sure yet.
I found a business here in Adelaide called Construction Chemicals. They are most helpful on the technical advice side and their products are more than meeting my needs, or will I believe, yet to use many.
When I asked about a render I wanted water proof and was planning on adding fibres. They sell a render covering these requirements, waterproof and fibres already added. I'm yet to use it but seems like it should do the trick.
Question for any Aussies, what vent did you use? I have seen plenty of pictures from Russell and others but I'm not having much luck here in Aus. Has anyone purchased one? Do you know the name of the item?
Kind Regards
Greg

[MarkJerling]

G'day All,
David and Mark, many thanks for the feedback.
David, if I may, I'm interested in a little more info on firing the oven insulated as I'm not really grasping the point. Whether insulated or not the firing and heating initially from within the dome through to the outside would surely be the same with or without insulation, after all the bricks will be the same temp throughout when starting the fire?? What am I missing here? Also, how would one know the extent or degree of cracking if the dome is covered?
Mark, cracking as shown in photo's. No detectable heat rise using a heat gun near the cracks suggesting no hot air is escaping, and the last fire was real hot. I do have 2 minor cracks through the inner arch along joints at the top, not shown in photo's, very minor.
Thanks again, it's all great info.
Kind Regards
Greg

Sorry for the late reply. That does look like very minor cracking to me. I would not worry about it.

[david s]

G’day all. Google assisted, the apex is the top.
Can anyone see why the vent can’t be at the back towards the bottom?
Also, anyone got any good ideas how to best seal the render at the bottom of the dome? My oven is outside and therefore want to prevent water getting in under the render. I an laying bluestone slabs around the oven on the hearth and have them slopes away but water is likely to ‘wick’ in.
Regards
greg.

I don't think it really matters where the vent is, because it's a bit like the hole in a saucepan lid just to relieve pressure, but make sure wasps and other insects can't make nests in it and block it up and make sure water won't run in. Steam pressure is more likely to build up at the top of the dome where it'll be hotter so you could make a case for placing a vent at the base of the dome where the steam pressure will force water out. When firing a new kiln for the first time, empty and to service temperature typically water will start dripping out from at least one bottom corner at around 400 C. so perhaps that's where its drain should be.

Regarding the dome to hearth joint I use Flexible Pointing to seal up the whole dome and make sure there's a pretty thick coating at that joint. If you water down the stuff 20% you can simply paint it on.