800 mm homebrew cast

[david s]

I’ve not used the silicone treated stuff because it’s not available to me, but it is possible that it reduces the bond with the cement on the surface of the grains, having a greater tendency to wash off the grains. The stuff designed for agriculture and nurseries is not coated and designed to hold moisture. Someone else who’s had experience with both types may chime in.

There is always some reduction in volume (around 20%) when mixed with cement and water. Do not use a mixer as it abraded the grains and results in even further volume reduction. It is better to mix it gently in a barrow with a spade.

[Linuc]

I knew I didn't have enough perlite so I had already ordered another 100 litre. Luckily this was the agricultural perlite. Man, what a difference! This was much easier to work with. More moldable and kept together. The other was more crumbly to work with. It seems fine when It's dried though.

Unfortunately the 100 litre of agricultural perlite didn't last long. The most crucial part - the walls - are now done so I figure the bad perlite is good enough for the remaining parts. But I'm not sure I have enough... Maybe 50-70 litres. That means I have used 300 litres for the slab and over the oven - and that might not be enough. Yikes!

Hopefully I'm done tomorrow night.

[Kris S]

looking good!

[Linuc]

Finally done with the insulation! You can see the difference in colour between the good and bad perlite.

Now rest for hopefully only one week and then start the curing fires. Can almost taste the pizza now!

I'm also trying to figure out what to do about the opening... I'm thinking of only stucco and then mosaic. The alternative is to cast an arch, but I don't want to make the opening any deeper. I'm also not sure what to do about the rest of the oven. Stucco of course, but not sure if I'm going for mosaic or paint. Maybe it could be cool with painted oven with a mosaic opening.

[Linuc]

Only a few days left until I can start curing fires. So excited!

A couple of questions though. I have kept the oven covered two out of five days so far in case of the rain. I might need to do that again tomorrow. Should I wait longer then seven days before I start the curing fires? I figure less water have disappeared since I've kept the oven covered a couple of days.

And is it important to fire and increase seven days straight when I do the curing fires? It may rain a couple of the days and then I of course don't want to fire in the oven. Can I fire one or two days, then pause a couple of days, and then continue the oven curing?

[SableSprings]

Doing a curing series of fires with a couple of "rain delays" is no problem. You're just driving out the internal moisture slowly. Because you've got a good layer of perlcrete over the oven, it is worth going even a little slower than if you'd used ceramic batting. The perlcrete retains a lot of water and it's much more important to keep the oven covered from the rain (which would add more water to the perlcrete ) than it is to "miss a day or three" in the curing sequence.

One of the tricks from David S is to put some plastic sheeting over the perlcrete dome during the later curing fires (or after you've quit for the day)...if you see condensation between the plastic & the perlcrete, moisture is being driven off so continue to go slowly. If you ever see steam coming off the top surface of the perlcrete, back off the fire. Water turning into steam produces a lot of pressure as the volume rapidly expands and can do damage to the perlcrete layer.

[Linuc]

Almost done with curing fires. Fire six out of seven days. Pizza premiere tomorrow!

One question though. Today I fired quite intensely and I saw some steam from my homemade steam vents. I have no idea if this is a good solution but I did cast in three plastics tubes, 50 mm - the same as the thickness of the perlcrete. So the tubes are "standing" on the fire blanket so hopefully they won't melt.
Maybe I should have put them on the perlcrete instead....?

However, I don't know if the steam came from the homebrew or the perlcrete.

And I have no idea if my steam holes will work in the long run. I figured it would be enough if the oven have some holes so the steam can escape?

[UtahBeehiver]

If you are able to see steam venting you are going too hot too fast. David S suggest placing plastic over the dome and as long as you see condensation on the plastic there is still moisture in the oven. When water sublimates to steam the volume increases by 1500 times hence the need for vents to reduce any dome pressure of water going to steam from the build or subsequent water getting into the oven at a later time

[Linuc]

If you are able to see steam venting you are going too hot too fast. David S suggest placing plastic over the dome and as long as you see condensation on the plastic there is still moisture in the oven. When water sublimates to steam the volume increases by 1500 times hence the need for vents to reduce any dome pressure of water going to steam from the build or subsequent water getting into the oven at a later time

Yes, I did that and there was of course condensation on the plastic for the first time yesterday. Maybe I were goding too hot too fast but I did back off when I saw the steam.

The question was more about if you think my steam holes will work in the long run.

[david s]

If your vermicrete layer is 10:1 it should have plenty of little voids between the grains that should do the same job as your vent holes. A vent through the outer impervious outer shell is the more important plan to reduce the build up of steam pressure that can crack the outer shell.

[Linuc]

If your vermicrete layer is 10:1 it should have plenty of little voids between the grains that should do the same job as your vent holes. A vent through the outer impervious outer shell is the more important plan to reduce the build up of steam pressure that can crack the outer shell.

I see. I did cast in the vent holes since I'm going to apply stucco and then paint on the perlcrete. But if I understand you right I should have put them on the perlcrete layer instead? Guess I could leave the current vent holes, and then put a couple more on when I'm applying the stucco.

I understand the plastic tubes ain't the most correct soulution - but it's cheap. Do you see any risks?

[Linuc]

Pizza premiere. Love this. So much fun. Thanks for all the help. A little bit of work left though. What a fun journey.

[Linuc]

A small update. I have not entirely finished the oven yet, but I have been using it for a month and a half now. I think I'm going to put mosaic on the opening of the oven and then maybe paint the rest.

I have made many pizzas this summer! Very fun to experiment with different dough recipes and different flours.

[Petter]

Nice! Enjoy your oven!

[Kris S]

yummy looks very nice!