36" Pompeii Dome - Thailand

[david s]

Hi Danny,
most commercial renders have some waterproofing added which produces some resistance to water absorption at the same time as leaving it breathable. You can tell this by the difficulty in getting water to mix into the product initially. If you make your own mix it won’t have that property, but if you want to make it waterproof you can do that over the top later or leave it porous if it’s under a weatherproof roof.
4:1:1 sand, lime, cement is a pretty good mix and the lime imparts some elasticity as well as some crack self healing.
Random mixed fibres are a much easier way to reinforce the layer than chicken wire, but more expensive. The time saved in labour is well worth it IMO. You can use the nylon fibres, but I find the 19mm AR glass fibres better and easier to work with than the nylon ones which are longer thicker and stiffer. This means you have to pull them out every so often in a thin layer.

[danhem]

Yes, you’re correct. As you’ve already purged the inner oven of moisture it doesn’t matter how you get rid of the water in the vermicrete layer. Sun wind or fire, just get rid of it before rendering over it.

Hi David,

I'm now looking at getting the materials together for the rendering layers. Is there a best practice here? I'm unsure on whether to buy the render or to mix it with the remaining lime I have.

If going the home mixed route, is the a recipe to follow i.e. sand:limeortland etc? I see that other members have also added to nylon fibres to their mix to prevent cracking.

Hoping to get these final steps complete in the right manner so I can put the job to bed once and for all.

Many thanks.

Danny.

[danhem]

When we exchanged notes before, I didn't realize you had a thread. I feel badly about that now. Too late now, but I ordered lots of things from Amazon in the US (especially blades) and they arrived in Thailand no problem, even after everything was shutdown for the CCP virus. The bad part was the shipping costs were really high and sometimes the delivery folks look for any excuse to return it rather than make a residential delivery.

Your oven looks great. You've done far better than we did, especially starting with smaller fires.

I have zero control since I left in March, and no matter how much I tried to explain the construction process or the importance of firing up slowly over a couple of weeks, they just blazed ahead and did their own thing. I'm pretty sure I'll be rebuilding, at least partially, in a year or two.

What are you using for wood? Where are you sourcing your wood?

Hi,

No worries, it's been a tough but fun project, after I saw that you had stopped posting here I realised you were no longer here in TH. Actually the most frustrating part of the build has been sourcing the materials and navigating the weather, which has been particularly bad here in HH this year.

All in all I'm pretty happy with how the oven has turned out, DIY is not one of my greatest attributes but with the help of this forum and a careful approach to each step I'm managing to make some cracking pizzas. My only real concern at this stage is whether my oven is retaining enough heat - I'm not recording much heat loss during a fire but the internal bricks seem to cool down faster than others here have recorded (makes me wonder if the BST bricks are any good or if they are the same rubbish as their refractory mortar ), but patience in this respect has been suggested so I'll carry on with fires and complete the job ready for the dry and cooler season in November.

I feel for you on how your contractors have carelessly f***ed up what started as a very nice looking job. It might sound over dramatic but I'm sure it breaks your heart.

I responded to the wood supply in the other post, if you find anything better, please let me know.

Danny.

[TxGR]

When we exchanged notes before, I didn't realize you had a thread. I feel badly about that now. Too late now, but I ordered lots of things from Amazon in the US (especially blades) and they arrived in Thailand no problem, even after everything was shutdown for the CCP virus. The bad part was the shipping costs were really high and sometimes the delivery folks look for any excuse to return it rather than make a residential delivery.

Your oven looks great. You've done far better than we did, especially starting with smaller fires.

I have zero control since I left in March, and no matter how much I tried to explain the construction process or the importance of firing up slowly over a couple of weeks, they just blazed ahead and did their own thing. I'm pretty sure I'll be rebuilding, at least partially, in a year or two.

What are you using for wood? Where are you sourcing your wood?

[UtahBeehiver]

Should be fine, the ones Gulf and I use are made from PVC.

[danhem]

Got the v-crete layer complete. The first two rings were quite difficult, certainly time consuming making sure the material held up instead of crumbing off to a frustrating mess. The later layers were actually enjoyable as it feels like another step closer to completing the build. About to set a fire and will dry the vcrete out before the stucco layers.

I'm now researching the stucco layers and the oven vent as recommended in another post due to the wet and humid climate we are in for 6 months of the year. Came across this post by Gulf - Vent Planningand it looks like a pretty simple addition during the stucco layer. I had a wonder around the hardware store for ideas and settled on a pipe attachment. Not sure if the plastic material is ideal for the vent pipe but couldn't really anything else that would do the trick.

[david s]

Yes, you’re correct. As you’ve already purged the inner oven of moisture it doesn’t matter how you get rid of the water in the vermicrete layer. Sun wind or fire, just get rid of it before rendering over it.

[danhem]

Once the V-Crete layer is complete, do I need to let it dry naturally or can I start to fire the oven again to drive the moisture out of the v-Crete.?

Other than letting the layer firm up for a few days I can’t see why some slow and steady fires will do any harm?

I don’t mind waiting a month or so for it to try naturally but would rather speed the process up if at all possible.

thanks,

Danny

[danhem]

Danny, if you want the vermicrete to dry leave it uncovered. Keeping it covered holds the water in.
As you have already driven the water out of the inner dome there’s no need to hold the moisture in the vermicrete layer.

OK great, thanks for pushing me in the right direction.

The first ring of v-crete did set overnight. It's a very flimsy and light layer that could be cracked and broken down very easily, hardly surprising considering the structure of vermiculite itself.

I guess this layer isn't intended on adding any structural integrity to the build, more to act as another layer of insulation and a firm (firmish) base to stucco over. The stucco will likely set much harder over the v-crete adding strength the to eventual dome finish.

Completed ring 2 today and I expect that the remaining rings will be much easier than these first 12 inches or so. Tricky stuff to work with.

Thanks again,

Danny.

[david s]

Danny, if you want the vermicrete to dry leave it uncovered. Keeping it covered holds the water in.
As you have already driven the water out of the inner dome there’s no need to hold the moisture in the vermicrete layer.

[danhem]

What are your curing plans for the vcrete? Will you start all over again? Or is the vcrete not really adding a lot of water to the layers underneath?

Hi,

I will complete the layers then leave to dry under plastic wrap for a month or so. After that it will be back to low and slow fires. I will keep the vcrete later wraped in plastic during the fires and watch the condensation coming off. This seems to be a good indicator of how dry the layer is becoming.

Seems that the vermiculite soaks up a lot of water and it takes some time to dry it out fully.

i have followed the advice of DavidS on the curing processes and note that being over cautious with heat is the best way to go. I am petrified of overdoing the heat too quickly and then having to deal with the consequences.

Cheers,

danny.

[Kvanbael]

What are your curing plans for the vcrete? Will you start all over again? Or is the vcrete not really adding a lot of water to the layers underneath?

[david s]

You will be surprised. After 24 hrs it will be firm enough. Doing a little as you've done then leaving it is a good idea as the higher you go the easier it becomes.

[danhem]

Finally got the oven to the target temperature (900F Dome / 750F floor). It took a lot of wood to get there. The temperatures were retained for quite some time so was satisfied with the striking of that milestone.

On to the v-crete layer now and completed the first ring. Followed the recommended mix of 10:1 and added water to achieve consistency as explained by DavidS. David also recommends to throw in a hand full of powdered clay to make the mix more workable - I don't have access to the powered variety so left some kiln clay in water overnight to help dissolve and used that in the mix instead.

If I'm honest - I'd be absolutely amazed if the first ring sets with any degree of firmness. The mix is incredibly crumbly, and whilst I have read of similar here on the forum I just can't see at this stage how it will firm up with any kind of integrity. I hope to be proven wrong.

The ring is now covered in plastic wrap. I am guessing that I will need to leave it a day or two to firm up before progressing on to ring two. I am wondering how long to leave the first ring before deciding that the mix I used is good or not. I have a feeling that a 8:1 ratio of vermiculite to portland would be better but time will tell there I suppose.

[UtahBeehiver]

As you said, the oven firing get better each time, just be patient.