My first WFO design, any comments before I build?

[Mark1986]

Re the smoke and smell… the smoke will be burnt away inside the dome on route out of the chimney but not until the oven is dry and functioning properly at high temperature .
Re the drying fires … it does take time and patience but is very important to go nice and slow if you dont want to many cracks!

Can you also comment on the flue width and height? I'm a bit worried that I might messed up with the size..

There are many ways to go about drying the oven, lots of small fires gradually getting bigger over 5-7 days is pretty standard

Personally I always start with a BBQ brickettes suspended off the floor on a baking rack or similar. I start with only 5-6 bickettes and buildup the amount and time over the first two days.
Then begin the fires, if possible I keep the fire going for a few hour's in the morning , let it cool and do more fires in the evening so quite time consuming !

Thanks for the tips! I follow this video for curing the oven: https://www.youtube.com/watch?v=5cb3aAkU5R8 . I didn't know that you can also use brickettes. I'm going to try that tomorrow!

[fox]

Re the smoke and smell… the smoke will be burnt away inside the dome on route out of the chimney but not until the oven is dry and functioning properly at high temperature .
Re the drying fires … it does take time and patience but is very important to go nice and slow if you dont want to many cracks!

There are many ways to go about drying the oven, lots of small fires gradually getting bigger over 5-7 days is pretty standard

Personally I always start with a BBQ brickettes suspended off the floor on a baking rack or similar. I start with only 5-6 bickettes and buildup the amount and time over the first two days.
Then begin the fires, if possible I keep the fire going for a few hour's in the morning , let it cool and do more fires in the evening so quite time consuming !

[Mark1986]

I have started curing the oven since yesterday starting with small fires. I did this for three hours and there were no cracks. You can see it in the photos below.



One thing that did startle me a bit was the amount of smoke and the smell of it. I wouldn't want this to be a problem with my neighbors and girlfriend. Do you think this problem will go away if I start making hotter fires? I'm also wondering if my flue is large enough. Dimensions of the oven and flue:

- chamber > 65 cm wide and 32.5 cm heigh
- Flue/chimney > 12cm wide and 50cm heigh (from opening ceiling)

I'm also thinking about making two doors, one for closing the front and one for closing the oven chamber. Last one will be hard as I didn't make a ledge for it to stop on.

Any advice?

[david s]

Yes, That's what I do, but use an acrylic sealer over the render before tiling it. The render layer can be strengthened with the addition of AR glass fibre random mixed reinforcing.

[Mark1986]

david s



Ok, and if I apply a cement layer over the prelitecrete, can I then put tiles on it?

What kind of cement should I use? And how thick should this layer be?

Cheers!

david s

I found a page where someone describes a cement render consisting of: "... 4 parts plastering sand with 1 part lime and 1 part cement.."




https://gardengeek.net/pizza-oven-build-part-9/

Would this be a suitable render to use before putting tiles on the oven?

If so, can I just use a small layer of about half an inch over the perlitecrete?

Cheers!

[Mark1986]

david s

The 6:1 mix is not strong enough as an external coat or as a suitable substrate for tiling against IMO. If it were mine I’d be doing the drying fires and finally with the inside white, apply a cement render over the vermicrete.

Ok, and if I apply a cement layer over the prelitecrete, can I then put tiles on it?

What kind of cement should I use? And how thick should this layer be?

Cheers!

[david s]

The 6:1 mix is not strong enough as an external coat or as a suitable substrate for tiling against IMO. If it were mine I’d be doing the drying fires and finally with the inside white, apply a cement render over the vermicrete.

[Mark1986]

Update

I finished rendering the dome with the 6:1 mix, I did have some inconsistencies in the mix but I think it will turn out fine. I added a small steam vent as I live in a wet area.




david s My girlfriend thought it would be nice to put mosaic tiles on the render as a finish. Would I need to flatten the surface with some kind of cement layer and then use tile glue? Or can I work with a thick layer of tile glue to flatten it out?

[Mark1986]

david s That's great to hear! I will finish the rest of the dome with the 6:1 mix today, I'll send an update later!

[david s]

6 cm of blanket is quite a lot of insulation so you are not relying so much on the perlcrete as additional insulation so if it were mine I’d be leaving it rather than removing it. Just allow the perlcrete to dry out really well before doing any drying fires and before applying any outer render layers over the perlcrete.

[Mark1986]

I’m not quite clear on what you mean, but a 6:1 perlcrete is not a very good insulation layer (see table). You don’t say how thick the blanket layer is, but if you are hoping for decent insulation value from 6:1 perlcrete it is about half as good as ceramic fibre blanket. A 10:1 mix is far better, over which you can apply a dense cement render. But you need to do the drying fires to eliminate the moisture before the outer rende
r is applied.

david s
Sorry for the confusion..

I have about 6cm of insulation blanket around the dome. I could remove the perlite layer and reapply a 10:1 mix of perlite concrete. Would you advice that? Is it possible to remove the render layer without damaging the insulation blanket too much

Also I have left over ceramic fibre blanket I can add, but this can only go on the top part, as I don't have any space left to expand in the width.

Cheers

[david s]

I’m not quite clear on what you mean, but a 6:1 perlcrete is not a very good insulation layer (see table). You don’t say how thick the blanket layer is, but if you are hoping for decent insulation value from 6:1 perlcrete it is about half as good as ceramic fibre blanket. A 10:1 mix is far better, over which you can apply a dense cement render. But you need to do the drying fires to eliminate the moisture before the outer rende
r is applied.

[Mark1986]

Update

david s
I had a little break from the project as I needed help with lifting the cast on and off the stand and I went on vacation. I did finish the oven floor which turned out good!

Today I started putting on the insulation and chicken wire. It was quite a job, but it wasn't that hard. I did ran into a problem that I hope someone can help me with. I started putting on the perlite render with a 6:1 ratio, but when I used a different bag of cement, the mix turned out really wet. I started panicking and mixed more cement and perlite in, as I thought I miscalculated the amount of water needed. The mix turned out lumpy and wet, but I did put it on. I finished about half of the dome. Below you can find the photos.

I'm thinking about a couple of options to fix the problem:

- See how the render turns out, buy new cement and finish the rest of the render.
- Repair the render with a layer of a good mix of perlite.
- Remove the render and start over.

I'm thinking about the second option, as the layor may not isolate at all of crack easily. What would you do?

Cheers Mark

[david s]

Unless the fibres are mixed for quite a long time they will clump together and not disperse throughout the mix. I’m not sure what you have , they should be finer than human hair.

Regarding the slumping, normally solid inner and outer moulds are made and the mix can be vibrated to eliminate air. This is a lot of work and not worth it for a one off casting. It does mean that you can’t vibrate the mix against the sand mould or you risk moving the sand at worst and slumping at least. Most of the air can be eliminated by carefully wriggling the mix against the mould which results in a pretty smooth inner surface requiring only minimal void filling on the inside.

[Mark1986]

Ok thanks for the information on the fire bricks all!

Update on progress:
First on a positive note, the cast seems to be set properly and looks like it is going to tield a good end result. See video: casted dome.

Today was a bit of a set back. I bought new polypropylene fibers from a different brand, these were not a lot of individual strands, but patches of strands 1cm by 1cm. The result of the homebrew mix looked different, and I didn't trust the end result. Here is a photo of how it looked: homebrew mix. Maybe I overreacted by not using it, but I didn't want to take the risk. I re-ordered the first fibers I used. Was this the right call?

The next thing was that the dome was way thicker around the base of the oven. Which was to be expected from the downward pressure and vibrating the homebrew. This is a problem because the dimensions now don't fit on the stand I build. Is there a way to trim the dome? I got an angle grinder I could use. Any ideas?

Cheers!