My first oven ever

[Amalgam]

Hi there you guys first of all HAPPY NEW YEAR. I am moving my thread from the introduction forum so all newbies can follow my first ever wood oven. it is done with a gym ball. The first layer is a 2-inch thick layer of the Home brew sand, cement, line, clay mix. Following recommendations I will cure it covered with wet rags and plastic for a week then I will proceed with a 3-inch layer of a 10:1 vermiculite/cement. A couple of questions though

1- should I air cure this first layer after the week long wet covered curing before the next step with vermiculite/cement?

2- Also, can I demold this first shell and move it to the final resting place (stand) and do the vermiculite/cement layer once it has been placed on the oven floor; or I should finish the entire oven and then do the floor stand process

[david s]

Good questions.
http://www.holcim.com.au/products-an...echniques.html scroll to the bottom of the page in this link.
Once you've attained good strength you then need to remove the water, but because you are covering it with a vermicrete mix which is also wet, you may as well proceed as soon as you've removed the covers. Because the vermicrete mix is so water absorbent it requires around double the amount of water that is required in the hydration process, leaving you with a large amount to remove.
I presume you cast the dome in a single piece which means its going to be very heavy to move. Most folk cast in situ over a sand mould and then remove the sand once the casting has set, which eliminates the need to move it.
When you demould the casting you will no doubt find some voids that need to be filled. This should be done while the casting is still damp which it should be after being wrapped for a week. Force some of the home-brew into the voids and smooth it over as best you can.
The oven can sit on the floor or you can sit it on the underfloor insulation and fit the floor bricks into it. There is no difference in performance. With the oven sitting on the floor it is much easier because you don't need to make precise cuts of the floor bricks. The dome will cover them. Fitting the floor after the dome has been placed is a lot more fiddly, but any bricks can easily be removed at a later date if need be.
Because the vermicrete mix holds so much water it is easier to do it in 2 or 3 layers of about 1.5" each with a week of drying in-between. The reason is that wet vermicrete sitting deep against the dome will take ages to dry if done in one single layer. The recipe for over the dome 10:1 vermicrete is 10 parts vermicrete or perlite (I prefer a 50/50 mix of the two), 1 part portland cement, 3 parts water. For every litre of cement a handful of powdered clay makes the mix more workable.
After the vermicrete appears (and it won't be) you can proceed to use gentle drying fires (refer to the curing thread under Firing your Oven). A simple cheap garden moisture meter will help you. Plunge it as far as it will go into the vermicrete layer and when the light flashes red you have driven out the water. You can then proceed to do the outer stucco shell. With wet vermicrete sitting against a cast dome that does not contain burnout fibres you must be extra careful not to go too hard with the fire or you'll get steam spalling. If you see visible steam then you are going at it too hard, back off.
Good luck and happy new year and oven,
Dave

[Amalgam]

Thank you David here are some pics. I guess I will demold and set it on the stand before I put the vermiculite outer layers, that way it is not gonna be so heavy.

[david s]

Well done. Don't forget the underfloor insulation. Is that pipe you cast around made of stainless? Reason I ask is that it looks a bit like just galvanised in which case it won’t last too long. Also it is a good idea if the pipe is a somewhat loose fit because being conductive it will expand before the casting that surrounds it. I cracked oven 2 and 3 before realising it can place a lot of stress on the casting if it’s tight.

[Amalgam]

David thank you so much for that information about leaving the chimney a little loose to compensate for expansion. And indeed it is a galvanized pipe, but I am using it as a form to create the void where the chimney is going to be placed. I am in my 7 day wet curing period and excited to continue with this project

[Amalgam]

Ok after 7 days I just demolded the first shell made of the 3:1:1:1 home brew mix. As you guys can see in the picture and as David predicted there are some voids that I will cover immediately. Quick question though, because of one schedule problem I will not be able to start covering this shell with the 10:1 vermiculite cement just yet it could take me up to a week; would that be a problem? Will the outer vermiculite shell still stick to the inner shell? Thank you

[david s]

Yes it will, but even if it din't it wouldn't matter. Folk using insulating blanket don't stick it to the dome with anything. Waiting a week will allow the casting to dry out more and as you need to rid it of moisture anyhow, the wait won't hurt a bit. Although i’d doubt it would dry much in a week in your prevailing weather conditions.

[Amalgam]

Ok base is done and I am ready to pour the floor and install the bricks. David, reading all the valuable information that you kindly have given me and in the forum I found that you recommend to use 10:1 vermiculite cement for the outershell but for the floor you recommend a proportion of 5:1, would you mind telling me the reason why? And also should I bond the bricks permanently with the same vermiculite mix? Thank you

[david s]

The underfloor insulation needs to be strong enough to bear the load of the oven and floor sitting on top of it so it needs to be stronger. 4" thick is adequate. Any thinner is insufficient insulation. The equivalent is to use 50 mm of calcium silicate insulating board. This is a more expensive option, but has the advantage of being dry. If you make your own vermicrete it will take ages to dry out.

[Amalgam]

Ok finally after a few weeks I could continue my project. Now I just covered the oven with a thick layer of vermiculite cement mix. A couple of questions, how long should I wait before covering it with stucco? How long should I wait until start curing the oven? Should I cure the oven before covering with stucco, so it helps the layer of vermiculite to dry? Thank you for any info you guys share with me.

[david s]

Yes it,s better to remove the water from the vermicrete before you do the stucco. A little cheap garden moisture meter will help you establish when its dry.Don't go at too hard or you may crack the inner dome and or the vermicrete layer will also swell and crack.
#2

[Amalgam]

Thank you David, regarding the curing can I start the heating and cooling process while the vermicrete is drying or I should wait until it dry is completely?

[david s]

I like to leave it for a week and let sun and wind do much of the drying, but that’s also dependant on weather conditions. I did also mention that doing it in layers of around 35 mm and allowing a week of drying between layers also helps. Some gentle fires will push the moisture away from the fire to the vermicrete surface.

[Amalgam]

I am posting this question here because there are not too many visits to the “Firing Your Oven” forum. I have been trying to start a fire in my new oven to start the curing process but the logs do not catch fire. I’m using dry wood that burns quick and easy in a fire pit but they don’t inside the oven. I have used a propane torch to start the log and it catches fire but dies immediately, I have used one of those little fire starters that burn the log but it doesn’t turn into an active fire. So my question is what is wrong? Maybe lack of oxigen? Just to let you guys know the inside dome is 14 and one quarter inches tall and the door is 8” by 16” does that have anything to do with it? Any ideas. Thank you
Alfredo