Pdx 42" update

[david s]

Oil your forms and vibrate the sides of the mould when you lay up the slab. This will ensure a good release from the forms and eliminate voids.

[Macrinehart]

I saw one ameture using a Sawzall without a blade for vibration, and WD40 for oil. I've got both, will that work?

[mongota]

If you have a roll of packing tape, cover the inside faces of the 2x4s with tape. It'll give a nice smooth surface if that's what you're looking for. The packing tape being more smooth that the wood will also allow air bubbles to more easily escape the mix when you vibrate the form, and it'll also act as a form release when you wreck the forms.

If you want a more decorative edge, I used a few sections of PVC pipe as a form to dress up the edge of my hearth slab: https://community.fornobravo.com/for...771#post254771

[Macrinehart]

[QUOTE][If you want a more decorative edge, I used a few sections of PVC pipe as a form to dress up the edge of my hearth slab: https://community.fornobravo.com/for...t254771/QUOTE]

That's a nice look, and probably lower on material cost than cove molding. I take it your quartered pipe is behind the 2" pipe for support?

[Pizzarotic]

I saw one ameture using a Sawzall without a blade for vibration, and WD40 for oil. I've got both, will that work?

Yes, sawsall or sander will work fine, also use a rod or small shovel around the edges to work the mix into the sides first. Any voids can be filled after with a rich mortar mix and sponge off.

Any oil will work. Spray cooking oil is another option. Just apply it before adding the Reo as you don't want release agent on that.

[mongota]

[QUOTE=Macrinehart;n444762]

[ I take it your quartered pipe is behind the 2" pipe for support?

The quartered 2" is supported by a small piece of wood so the 2" stands 'upright'. The halved 4" sits on top of the quartered 2", with screws slightly below center holding the 4" to the 2x6 perimeter form. With the screws being slightly below center, the force of the screw rotates the 4" down on the 2", clamping them together so to speak.

[Macrinehart]

Hi everyone - I've been thinking about weep holes and thermocouples and want to be sure of my plans before finalizing the hearth form. Reading the forum I've seen some suggestions of installing stainless steel tube to run thermocoupling through, and I also saw one individual had installed flexible steel conduit normally used for electrical wiring to allow installation of thermocouples under the oven later. I have some leftover flexible steel conduit from another project.

Is there any advice on placement of weep holes and how to install? Should I have a put something in like paper tubes to form the weep holes or just drill them out while the concrete is set and curing? Thanks!

[Giovanni Rossi]

Macrinehart,

I’ve read a ton of posts here on adding thermocouples and it seems as though current opinion is they are more trouble than worth. Many have moved to the shoot and read IR thermos. Do another search and see what you think.

Also a lot about weep holes can be found. From what I've read, 4-5 placed to meet your drainage pathways (mosaic tiles or whatever) should do it. 1/2" PVC placed during the form build is best. While drilling after the pour can be done, some worry about hitting rebar or mesh.

“Gulf” aka Joe Watson’s current Simmental Farm build also has good instruction on weep holes and the corresponding mosaic tile drainage system- Link. I also like Joe’s recent comment on another build about further elevating the insulation layer by putting a layer of 2” pavers under the mosaic tile if planning an exposed dome.

Enjoying watching your progress,
Giovanni

[Macrinehart]

Thank you Giovanni. I have read up on both thermocouples and the IR thermometers and find myself more in the camp of those that like to geek out on instru.ents and charting things. It's actually how I make a living in my day job. the idea of having temperature plots from multiple points is very enticing!

I also have excess PVC, so that's handy!

One other question, should the insulation go under the wall and floor? I think yes, but for some reason I have seen a clear example that illustrates this step.

I am planning on calcium silicate board, which is very pricy but the climate here is wet so I want something that can handle a little moisture without breaking down or loosing it's insulating properties. Just want to purchase the correct quantity. I think I might be in over $800 on Calsil board. Does that seem about right?

Also plan on using the mosaic tiles to elevate the insulation layer.

[Giovanni Rossi]

I think the main issue was durability. Again going from memory, I believe "K" type thermocouples is what should be used. Those more knowledgeable will probably chime in.

I haven't priced Ca Silicate alone as I'm working with a kit, but I understand it's a big part of the cost of a DIY oven.
I'm planning a layer of Foamglas under the CaSil. Also expensive and tough to source.

The insulation board goes under both floor and dome wall. Ideally it should extend beyond that as some would argue not to have all of the weight of the dome right on the edge of the CaSil board.

[Gulf]

.......should the insulation go under the wall and floor? I think yes, but for some reason I have seen a clear example that illustrates this step.......

I agree with Giovanni Rossi, at least by by 2" imo. If you do 3" of 1" ceramic fiber blanket over the dome, a 3rd layer could overlap and extend down to the the tiles.

....I think I might be in over $800 on Calsil board. Does that seem about right?...

Absolutely Not! There are sources for CalSil that are hundreds of dollars cheaper for an oven this size.

[JRPizza]

I didn't use thermocouples, and other than the geek factor (I"m also a graph and data guy) probably would not use them when firing for both a short and long term cook. I do however wish I had a way to see what the outside brick temperature was when we are doing a same day cook with retained heat. As soon as the soot burns off the inside of the dome the IR gun says the dome is in the 800's (for example) but the IR gun will never tell you when the bricks are saturated. I have in the past closed the oven off too soon only to have the temp rapidly drop to the low 300's, which would not happen if I could see that the heat had not transferred through the thickness of the bricks. This could also likely be accomplished with a probe thermometer poked through the shell touching the brick, which would probably be lower maintenance and more durable. I have gotten better at timing when the oven has got enough heat into it to hold a good cooking temperature, but some data would be nice to have.

[Chach]

I used to use my IR gun now I just look at it and barely use it for the oven. I would have liked to see what the outer brick temp is as well so I agree with JR out of curiousity, but I don’t see it a necessity. If you want to geek out over your oven now is the time.

Ricky

[fhausback]

I’m adding thermocouples to mine for the geek factor. When I was building bbq smokers I used that info all the time. Once I learned how to run a particular smoker, I used the probes less and less.

Knowing that, I’m not too concerned about long term durability, but will make sure a couple of them are easily replaceable. As others have said, knowing when the bricks are saturated would be handy.

[Macrinehart]

Almost there! Today I made quite a bit of progress on the form with most trim pieces cut to size, the rebar laid out and zip-tied. The weather is still not great, several days of freezing and thawing plus rain today is causing a lot of ground movement, which in turn resulted in most of my form legs getting loose and collapsing.

Another issue, rebar is too high. Will be cutting supports down to 1".

The concrete crew came by to check out progress and liked what the saw. Will have to wait a week for better weather before pouring. Tomorrow I hope to finish trim, weep holes and final prep before pouring concrete.