Importance of cutting insulating board to oven footprint?

[kebwi]

I realize that when using vermicrete people over pour a larger area than the oven footprint, but when using insulating board the photos often show a tight confinement of the board to the oven's footprint (including wall thickness of course).

Is this important? I can imagine that without doing this, rain might sit on the board and damage it. I'm using InsBlock 19, which I've heard can take some moisture without turning to mush, but I don't know if it can withstand veritable puddles.

Should I cut it tightly around my outer wall and arch perimeter?

How do people cut 1" InsBlock? Do you saw it, or just score it. It seems pretty easy to work with; I'm almost worried that a saw will tear it to pieces. My preference would be something like a coping saw or hack saw, but obviously, those can't cut very far into the material.

[kebwi]

Re: Importance of cutting insulating board to oven footprint?

Is this a dumb question, or just one no one knows the answer to? I'm willing to accept the former explanation if people think it's just too finicky a thing to be worrying about.

[Les]

Re: Importance of cutting insulating board to oven footprint?

If you are building a dome, the board would obviously need to be cut round. If you are building an enclosure, doesn't matter if it hangs out well past the walls. I used a jig saw to cut mine. Wear a mask - the stuff is nasty.

Les...

[jmhepworth]

Re: Importance of cutting insulating board to oven footprint?

I used FB Board and cut it with a circular saw. Because I have a gable roof enclosure, I didn't cut it to fit. Later, I discovered that I need to trim some to fit the decorative arch. I used a knife for that.

Joe

[asudavew]

Re: Importance of cutting insulating board to oven footprint?

I know Ken had problems with it getting wet.
I don't remember what type he used but he was careful about keeping it dry after it sank a bit after getting wet.

[kebwi]

Re: Importance of cutting insulating board to oven footprint?

I guess since I'm undecided at this point whether I will do a dome or "building" enclosure, I better just cut it to fit. That way all bases will be covered.

Thanks.

[dmun]

Re: Importance of cutting insulating board to oven footprint?

I let mine just overlap, but I wasn't doing a dome shaped enclosure. It's easy to cut. I used a sawzall, but almost any kind of saw would cut it. They make a carbide toothed saw for drywall that won't dull up on the abrasive material, but you aren't making that many cuts anyway.

[kebwi]

Re: Importance of cutting insulating board to oven footprint?

To beat a dead horse, my thoughts on this topic continue to evolve. It seems to me that even for a dome enclosure the hearth insulating board doesn't need to be cut flush to the bricks, as shown in the photos of several previous builds. My reasoning is that there will be several inches of insulation over the dome anyway, some combination of blanket (or in my case loose fill InsWool) and vermicrete or loose fill vermiculite. The board can extend at least that far past the brick, and that's several inches.

Right?

Here's the thing. I'm making a 36" oven, so 45" on the outside of the brick. I'm using InsBlock 19, which comes in 12"x36" sheets, so that tiles to 48" easily, which is 3" too wide diameter, 1.5" radius, so if I just approximately cut it to shape without adhering to a pure, circular, flush footprint, I have 1.5" extending beyond my brick. Seems to me that even if I eventually choose to do a dome enclosure (I remain uncommitted and have both domed and roofed designs at the present time) this 1.5" extension will still just be absorbed under the dome insulation, the fiber and vermicrete.

Riiiight? I hate to cut off waste. Small funny shaped pieces won't be useful for making a door anyway, so they would just be scrap. Might as well leave them in and them to do useful work and provide a more solid, less "edgy" foundation for the soldiers. I'm only apprehensive because I don't see this in many other peoples' photos.

[jmhepworth]

Re: Importance of cutting insulating board to oven footprint?

Look through the pictures on my thread. You will see FB board not cut to the shape of the dome.

[ThisOldGarageNJ]

Re: Importance of cutting insulating board to oven footprint?

this 1.5" extension will still just be absorbed under the dome insulation, the fiber and vermicrete.

Keb, Im in agreeance with you.. as you can see in the pic, I left a cutout for the vermicrete and laid the board under the vermicrete, (i used vermiculite firplace liners I got off ebay cheap!!!) they were 1 x 12 x 18 so the whole bottom almost of my area was filled,,,

Cheers
Mark

[GianniFocaccia]

Re: Importance of cutting insulating board to oven footprint?

Keb,
After looking at all the builds I decided to surround my hearth insulation specifically to keep it protected from....me! I know that when I start building the dome if I had any exposed insulation I would lean on it or kick it and fray it. Same with exposed vermicrete. The pics show 2" of Insblock 19 on top of 3 1/2" of vermicrete.
My jigsaw cut the Insblock like butter. It was strangely firm enough to make very exact cuts and I could 'shave' off a 16th of an inch with no problem.

John