Building Base Slab Next to Patio

Our patio was just finished so I can start building my oven! I have a question about the base slab. My patio has a short retaining wall (about 8" above ground). Should I make a 3 sided form and use the retaining wall as the fourth side of the form? If I make a 4 sided form adjacent to the wall would I just leave the adjacent board in place after the base has set and remove the other 3 boards?


Can you attach a few pictures of the patio in question? I need to see what we are looking at here :slight_smile:


Here are a couple pictures. The stone you see is a cap stone on top of retaining wall block, the wall is almost completely buried at the point where I will build the oven. Thanks!

Thank you for the pics -

I’ve been meaning to do a plan for building a base into a hillside, but haven’t had the time.

Since this one decision can make or break the performance of your oven, I will tell you this one thing…

Do everything you can to keep the 3 / base slabs OFF the ground / elevated.

The cold ground will do everything in its power to rob any heat from your oven - and the cold ground WILL win. You need to keep the base / hearth slab at least 2" - 3" off the ground / away from the hillside with a 2" layer of insulation in the base / hearth.

If you can elevate the hearth slabs a minimum of 2" off the ground (preferably a little more if possible)… and have a 2" Perlite / Vermiculite insulation layer in your hearth, your oven will provide you with outstanding performance.


Hi Kevin

Thanks very much for responding. My description is not clear, sorry. The surface of the patio is at most 8 inches above the ground and I plan to build the base adjacent to it. So fortunately, there is no hillside to contend with.

My question: if I butt the base wooden form up against the short retaining wall and cap stones how can I remove it after the concrete has set? Alternatively should I make a 3 sided form with the 4th side being the retaining wall and caps? My sense is that I should leave a gap between the form and the wall, but it would have to be very small so I can step onto the base from the patio.

Hope this makes more sense, thanks again for your help, much appreciated.

I think I understand what you’re asking. Here’s what I did. Hope it helps…

I had an existing 8’ x 8’ concrete slab that used to hold my hot tub. I just tied into the existing pad and
poured concrete right up to the existing edge. Not shown in the picture are some sections of rebar that I drilled and glued into the existing slab to provide more structure to where the new concrete met the old concrete. Seems to be holding up fine.


Thanks Ken, yes that answers my question thank you. After going back and forth, I decided to keep the base separate. I just completed it today. It’s a few inches from the patio, enough room to hopefully remove the form.