Mistake in foam size for base

So, kicking myself. I’m making the Mattone Barile Grande. I just went to place my 3 slabs on top of the cinder blocks, and then I noticed it seemed a little off compared to the pictures. I don’t know how I got the measurements wrong, but somehow I cut the foam to be 23" wide instead of 29". All the other dimensions are correct.

How much is this going to be an issue? I’m just trying to gauge what my response should be. Would I be better off repouring the whole thing or doing something like cutting the extra 3" on each side with an angle grinder? Or is this really just not going to be all that big of a deal given the extra layers of sand and fire brick that go on top.

Thanks for any advice on my blunder.

I mad the same mistake in the other dimension, front-to-back. I used the grinder with a diamond blade, a diamond blade in the circular saw, and a brick chisel and 3lb hammer. That insulation layer is very important in the performance of the oven, otherwise you end up trying to heat up the entire slab every time you want a pizza.
Keep building.

Hi Patrick and welcome to the BrickWood forums.

@gdiscenza is correct. Although most of the uninsulated area would end up under the base of your arch, what you will end up with is the arch sitting on a heat sink and thus pulling heat down into the slab.

His solution will take care of the problem cleanly and get you back on track. You can use the angle grinder with a diamond blade (eye protection, mask, and long sleeves). Score along the side at the proper dimension, then cut perpendicular grooves every few inches. Finish the job with chisel and hammer.

As building errors go, this is an easy one to fix and you won’t regret it.

Good luck and let us know how it goes!