Pizza Oven Dimension Changes - Slab and Stand (Actuals) - Cinder Block Construction - May 2024

This past weekend, I went out and began to assemble the frame for the concrete slab pour that will sit on top of the 4" or so layer of gravel for our backyard pizza oven.  I have posted about and pretty much considered my dimensions for this oven done.  The last time I shared the dimensions, I called them 'final, final'.  That was this post - where I included these as the final dimensions:  

Slab: 78" wide, 86" deep. 6.5' wide, 7'2" deep).

Stand: 72" wide, 80" deep (4.5 blocks wide, 5 blocks deep)
Leaving reveal of 6" total both dimensions. 3" all ways.

That's what I have now - for lumber.  78" wide slab x 86" deep slab.  But....after I assembled the forms, I decided to lay some of the concrete blocks inside the footprint to make sure I was accurate in my dimensions.  And, that's when it looked like this:

I put down 4 blocks wide and 2.5 blocks (so far) deep.  Knowing that I spec'd a 3" reveal, my mind started racing what I was doing wrong.  Then, I think I figured it out.  There are/were two things going on: 

First, I've gone back-and-forth with stand builds.  4 blocks wide x 4.5 blocks deep.  Vs....4.5 blocks wide x 5 blocks deep.   My LEGO model is 4 blocks wide x 4.5 blocks deep.   

The second thing going on is that cinder blocks aren't actually 16" wide x 8" tall.  Like dimensional lumber, they're a fraction smaller in each direction:

That means the stand (and hearth) aren't going to be even dimensions.  

Using the LEGO model numbers, that means - the stand dimensions would be 4 blocks wide x 4.5 blocks deep.  Using 15 5/8ths, here's the stand dimensions:

and....

Rounding up, the stand would be (roughly) 63" wide + 71" deep.  

Leading me to the big question:  Is my slab too big?  Or...do I need more blocks?  

To figure that out, I needed to go to the dome calculations.  The dimensions of the hearth, stand and slab all come back to the dome.

My current plan is to create a 39" interior dome + 8" to exterior of dome + 2" insulation on both sides = 51" side to side.  That means the hearth needs to be (AT LEAST) 51" side to side.

39" dome + landing + 2" insulation on back = 64" from back to landing (leaving 2"+ for insulation).

Dome = 51" wide x 64" deep.

Stand = 4 blocks wide (62.5" wide) x 4.5 blocks deep (70.3125" deep).  

Allows for 10" in width + 6" in depth on the stand for the specified dome size.

Now....take the stand and add face materials.   

Stand = 62.5" wide x 70.5" deep + 6" each of face brick (3" each side) = 68.5 x 78.5.  

Plus a slab reveal.

Leads me to decision:  

Shrink slab to 72" wide x 80" deep (6 foot wide x 6 foot 8 inches deep) - or leave it where it is now.

Shrinking it would lead to a six-inch reduction in both width and depth.  That also means a reduction of concrete needed - from 48 bags down to 41 bags (estimated).  That's about forty bucks, so I'll take it.

Using a 4-block-wide stand also means that I'm going to have to cut down my angle iron in front.  That piece that you see in the image above is 48" long.   With just 3 blocks of clearance needed, here's how the math works out - below.  46 7/8ths is all that will fit, so I'll need to cut angle iron down by an inch and 1/8th.  Eek.

I'll likely need to alter the back storage locations and associated angle irons pending the spans.  

I think I've now decided now.  

I've written about this before - posted here on my 20th anniversary of blogging - and linked to a post by Paul Graham where he talks about the actual act of writing being the sorting/solving mechanism when problem solving.  I LITERALLY just experienced that very thing:  the act of writing this post allowed me to really understand things - and make a decision.  That's wild.  

So....For now, I'm going to back out there and trim the slab forms to allow for a smaller slab:  72" wide x 80" deep.  

And, for the final, final, final numbers, here's what we're going with:

Slab:  72" wide x 80" deep

Stand:  4 blocks wide x 4.5 blocks deep - 62.5" wide x 70.312" deep

Hearth:  Same as stand.

Oven:  39" interior, 51" exterior side-to-side x 64" front-to-back.

This also allows me to finalize my materials order.  Concrete, rebar and concrete/cinder blocks.