New Oven Flue Size

[MattP]

David, by using the threaded rod the top portion of the polystyrene mould can be placed at final stage thus allowing a stick to work the mix into place. My immediate issue is how to hold in place the polystyrene vent recess mould while pouring/casting and then be able to remove following the removal (sliding out) of the timber door recess underneath. I thought of using silicone for temporary "glue" which should come off at the time of withdraw. Any comments.

[MattP]

Hi David, just before I embark on cutting the floor tiles and CalSil board for the oven base could you please clarify the following for best results.
1. Should the refractory tiles be cut along the outer perimeter of the dome castable and flue chamber? - this allows the castable to rest on the floor tiles
2. Should the CalSil board be cut along the outer perimeter of the 50mm insulation blanket?
This is what I have allowed in my design.

[david s]

Apart from being easy to cut and shape, polystyrene also breaks up readily. Just attack it with a screwdriver.
Regarding the floor, you can have the dome sitting on the floor or outside it. The advantage of sitting on the floor is that you don't need to be as accurate in cutting around the perimeter because those cuts will be hidden. The disadvantage is that it is very difficult to remove a brick if it has a dome sitting on it.
Regarding your insulation question, it makes no difference, so long as the oven is completely surrounded in insulation.

[UtahBeehiver]

Dome on or off, like David says both will work. I do not recall of anyone having to replace a broken brick though, that said I have seen some builders have broken "large" refractory Tiles, ie 12" x 12" square. Your plans call out 50mm refractory pavers so I am not sure if they are tiles or bricks. So the choice is yours.

[MattP]

Thanks David and Russell.
My drawings indicate "refractory pavers" they are in fact refractory tiles 305x305x50mm.
Yesterday I started to shape the dome with polystyrene blocks for bulk volume and wet sand combination adjacent to front entrance formwork. The done has been covered with plastic sheeting to prevent the sand drying out overnight. Today is very windy and I decided to postpone works to prevent sand drying too quickly.
The questions I have are:
1.How wet should the sand be during application and is it best to maintain it wet/moist until the dome is cast? I intend to use wet paper on top of the sand prior to casting.
2.Is a temperature gauge with a 300mm probe best to be installed during casting or is it best to drill a hole into the dome and fit the gauge during the render or pericrete layer after casting in order to avoid any possible damage during works.
3.Where is the best location for the gauge in view of protruding probe restriction to dome internal area?
Attached are progress photos.

[MattP]

Hi David, this is the almost complete "sandcastle" and general formwork. Possible pour during weekend.
Any advise on maintenance of the sand surface until then and any other comments?

[david s]

Cover it up so the surface doesn't dry too much.
Try a spray bottle and water. Cover the surface with strips of wet newspaper trying to avoid any folds, before applying the mix.

[MattP]

Thanks for the advise David.
Due to constructability issues mainly relating to the flue section plastic bucket formwork, as well as not being able to hold the 50mm insulation in place around the flue casting, I have modified the design again.
Essentially the idea is to use timber formwork for the flue casting and then drape as much insulation as possible around it holding it in place with chicken wire and tie wire, then cover with pericrete all round as shown on attached .pdf. The question however is the ability of the pericrete/vermicrete to be a suitable base for the decorative tiles adhesive. Do you think it is possible? Or perhaps simply cast around the flue and don't use any insulation. I appreciate your thoughts.

[david s]

You can use a thin layer (around 10mm) of render over the vermicrete and then tile onto that, but make sure the vermicrete is thoroughly dry before rendering over it or trapped water can turn to steam and crack your outer shell.
Regarding the uninsulated flue gallery- you risk cracking it if you don't insulate around it. Just a layer of vermicrete should be sufficient.

[MattP]

Thanks again David.
From your advise I assume I can decrease the thickness of vermicrete for the front of the flue gallery arch from 30mm to 20mm, then apply a layer of 10mm render and after thorough drying tile.
Please verify if I undertand correctly.
Another problem that I can see is this.
Essentially the flue gallery consists mostly of 50mm castable, 50mm insulation and vermicrete. Where the insulation ends flush with the entrance at the front, how can the vermicrete be applied without chicken wire for support? I would appreciate your ideas on this.

[MattP]

David, just to clarify my concerns please refer to attached.

[david s]

In my build I have overcome this problem byI having a small gap, around 8 mm between the front of the flue gallery and a decorative arch which sits in front of the flue gallery. This gap is filled with 10:1 vermicrete. This allows the oven and flue gallery to expand without placing undue stress on the front decorative arch. The front of the flue gallery doesn't get that hot. The carbon never burns off that part of it so it would be below 300 C. I'm not sure how it would go with your set up as planned because your tiles will get hotter than mine.
Check your message box, I've sent you a PM for better explanation.

[MattP]

Thanks David. I have reviewed the design and I think I have addressed some issues. I don't have the luxury of casting the oven in portions hence the restriction in design for the flue gallery/arch interface. I have incorporated pericrete/vermicrete layer at the front of and around the arch and flue. I would appreciate your comments.
Could you please indicate what your cladding around the dome consists of in order for the wire tire to be fitted.

[david s]

I've PM'd you.

[MattP]

Thanks for PM David. I understand you well.
I forgot to mention that I may omit the decorative tiles for the moment, just adopt the pericrete finish and possibly a render coat. I will review once the oven is up and running and well dried out. I would appreciate your comments on my latest attempt to solve the design issues.