42" Pompeii Oven in Jamaica

[wthwaites]

I was told it was glass fibres for concrete; I will double check tomorrow. If they aren't, they can't be used?

Apparently the glass fibers I got are purposed for building boats. I guess they are not the correct fibers needed.

[wthwaites]

I got the correct fibers! So i managed to pour the slab for the squirrel tail chimney.
Now I can move on to the final stages for the build - insulation and then the final render!

[MarkJerling]

I got the correct fibers! So i managed to pour the slab for the squirrel tail chimney.
Now I can move on to the final stages for the build - insulation and then the final render!

Nice! How did you do it? Did you do pre-cast slabs, or did you cast it in place over some form of formwork?

[wthwaites]

The cast was done over some formwork (thin plywood cut to size and wedged on top of bricks). It was several layers over a two day period until it got to the same thickness of the side walls.

[MarkJerling]

Aha, thanks for explaining!

[wthwaites]

I've laid out 4" of ceramic fiber blanket and have started my stucco render as a finish. I'll post pics tomorrow.
For the stucco recipe, I have been using david s recommended recipe ratio of 4:1:1 (Sand: Hydrated Lime: Cement) but without hydrated lime as I have not been able to am not able to source it. So, technically the ratio is really 4:1 ( Granite Sand: Cement).
Will the lack of hydrated lime be a problem? I hope not since I'm about 1" thick so far with the render and approaching the finishing coat!

[david s]

The lime makes the mix more workable, making application far easier. It also makes the resulting hardened render slightly flexible and also imparts a self healing crack quality. All these are pretty important. IMO. Most commercially blended render mixes contain lime as well as a waterproofing agent that makes the render partially waterproof, repelling water from entry, but maintaining the ability to breathe.

I find that rendering directly over the blanket extremely difficult because it is lumpy and springy. I always apply a 35 mm thick 10:1 vermicrete mix over the blanket which sets up a firm enough substrate to apply the render on to as well as evening out all the lumps and bumps of the blanket.

[wthwaites]

Thanks.
I couldn't find vermicrete to do that mix. Some materials are hard to find here in Jamaica - even hydrated lime seems to be scarce; can't find it anywhere. However, its likely that I will build more ovens in the future so hopefully I can source then and try that way in the future builds!
The render seems to be pretty solid so far and wasn't too hard to apply since I've been taking my time - 1/4" layers at a time. I also believe that the chicken wire mesh helped a lot with the first layer.

[david s]

Have you tried hydroponic suppliers? Either vermiculite or perlite or a combination of the two work ok.

[wthwaites]

Have you tried hydroponic suppliers? Either vermiculite or perlite or a combination of the two work ok.

No, I did not. I don't think vermicrete is available. Everybody I ask doesn't know what that is.
I thought that perlite used for gardening was not a good option? Isn't the perlite used for concrete blocks a different type?

[SableSprings]

No, I did not. I don't think vermicrete is available. Everybody I ask doesn't know what that is.
I thought that perlite used for gardening was not a good option? Isn't the perlite used for concrete blocks a different type?

Perlite for construction often is coated so it flows better into spaces. That coating makes it more difficult to mix with cement, that's why we point people towards the agricultural perlite which is not coated. I used perlite for both my base and covering insulation and it works very well. Pumice should be available and would be an acceptable substitute. Remember that vermicrete & perlcrete are terms used for the insulating mixes we make & use and are not a product you can buy. You need to specifically ask for vermiculite or perlite...those are available. That may be why you are having trouble finding either one.

[wthwaites]

Thank you for the tip!

[wthwaites]

Approaching the end; almost there! Some pics of progress.
Just applying the finishing coat of stucco (still working out the color) and then installing the granite countertop landing.

[SableSprings]

Normally we suggest doing your curing fires before you apply the finishing stucco coat. The escaping steam during the curing process wi!! Most likely crack the outside render. Leave an area on the top insulation if you can and do the curing before completing the outside of simply accept that you will probably need to recoat the outer shell. I really do like the squirrel tail vent design, looks great. If you don't choose to cure before completing the render, go VERY slow with the curing process.

[wthwaites]

Normally we suggest doing your curing fires before you apply the finishing stucco coat. The escaping steam during the curing process wi!! Most likely crack the outside render. Leave an area on the top insulation if you can and do the curing before completing the outside of simply accept that you will probably need to recoat the outer shell. I really do like the squirrel tail vent design, looks great. If you don't choose to cure before completing the render, go VERY slow with the curing process.

My intention was to do slow cure fires over a period of at least 9 days. But, I thought that the vent pipes that was suggested to be installed at the sides and top would prevent cracking. No?