Trouble with ceramic fiberboard foundation?

[Rosewood305]

Long time reader, first time poster. I've been following this forum for well over a year and thanks to all of you I gained the confidence to build my own. I made a mistake when cutting the fiberboard/insulation floor and now a part of my first course hangs slightly over. How big of a problem is this? I sort of ignored it and started building the dome so, if it is a problem, any suggestions on how to remediate? Thanks!!!

[SableSprings]

First of all, welcome to the forum community! The dome is going to be covered with some type of insulation and as long as you tuck or fill that slight overhang gap at that time then it's no problem. Remember that the goal is to insulate the oven bricks completely from "the outside world" & you can still easily do that. Do try to leave a gap between the foundation slab and the batting to eliminate the possibility of wicking moisture up. Relax & enjoy the build!

[david s]

If that were my problem, I’d be filling the space with 4:1 vermicrete, which at that ratio is still insulating while providing some strength and support.

[UtahBeehiver]

Plus one on David's suggestion. It will also act as abrasion protection for the CaSi board and FoamGlas insulation

[fhausback]

I had the exact same issue. I feathered out the gap with a bit of mortar, and will insulate the heck out of it. My dome has been done for a couple months, and haven’t noticed any movement or issue yet

[ultrasport]

This would be a perfect time to lay in some thin aluminum flashing in that area down to the slab with a right angle onto the slab. Secure it in with some stainless screws and then fill everything up with a vermiculite insulating mixure. This will help insure no water getting in.

[Gulf]

Aluminum will degrade until the lime in the vecmicrete is completely dry. Which can take a while. Thick aluminum flashing may work. But, I wouldn't advise using it in this situation.

[Rosewood305]

Thanks for the help! Will perlite provide the same protection as Vermiculite (I ask bc it’s easier for me to get perlite…)

[SableSprings]

Yes, perlite will work just fine. You might even use some bender board to make a form around the perimeter since the perlcrete will want to fall away until it hardens (5:1 will give you a little compression support which you don't need, so consider using 8:1 or 10:1 if you use the form).

[Rosewood305]

Thanks everyone. I took your advice and filled in the gap with perlite. In so doing I also realized 2 things:
1- my spacial planning is very bad
2- there’s about 2 in at the back of the dome before the platform ends. I have 4in ceramic blanket to put on followed by render, so I’ll clearly hang over the edge. Any advice on how best to address this problem?
thanks!

[Sixto]

Two ways to handle it (at least two I can think of right now)
1) live with the overhang and return the render horizontally to meet the edge of slab (leave 1/4" gap between render and concrete and seal that with silicone caulk)
2) drill slab and attach some stainless studs to connect existing to a rounded slab extension in the back. That will close off the bottom of your insulation/render overhang.

if it was my oven, i would do #1 'cause the difference in looks between my 2 options is close enough and you don't need structural support outside the bricks....