42" Oven in Raleigh, NC

[boombaby31]

Hi all! My friend and I are building a slightly modified 42" Pompeii Oven in his back yard. We wanted to start this thread to share our project and to take advantage of the wealth of knowledge that seems to be floating around this forum. Both of us are pretty much beginners when it comes to concrete and masonry and so this is very much a learning experience for us. So if anyone reading this has any advice or concerns about what you see please let us know. It will be much appreciated.

Before breaking ground, we built our oven in Solidworks. We wanted to go through everything to make sure we knew what was ahead of us and to be able to better visualize our oven in the space we had. I don't currently have the model but if you'd like to see it let me know and I'll post screenshots of it at a later date.

This project had been in its infancy stages for quite some time but we're slowly starting to make some progress. Here is our job site. Not much to see here...



Our first order of business: dig a hole...



Next we built a form for our concrete pad and filled it with pea gravel.

[NCMan]

Re: 42" Oven in Raleigh, NC

Hi there and welcome to the Forum. That's a good start, from what I see. I guess one of the first few things I'd ask is how thick is the base slab going to be? Any vapor barrier? Reinforcement plans?

[boombaby31]

Re: 42" Oven in Raleigh, NC

Hi NCMan. Thanks for commenting! I was planning to do a succession of posts to get in all of the photos I wanted to but I had to wait for my first post to be approved. So there?s more on the way...to answer your questions, our slab is about 5.5? thick. We covered the gravel with 6mil plastic sheeting and then built our rebar/wire mesh reinforcement. We bought a used harbor freight mixer and ready-mix concrete bags to try to save some money.




We could only mix two bags at a time in our mixer and 68 bags to fill our form. Needless to say, it was a long day and I now have a new found appreciation of sidewalks, roads, buildings, etc. So after smoothing and leveling it as best we could here's what we had:



And the next day here's how it looked...



Not the prettiest concrete slab that I've ever seen but it's level and the more it cures the better it looks.

[boombaby31]

Re: 42" Oven in Raleigh, NC

One concern we had was at the back of our pad, after we removed the form, some of the gravel started slipping out from underneath the concrete.



Our plan is to come back and fill it in with the gravel that come out and then fill all around the pad with dirt. Does this seem reasonable? Or does anyone have a better idea?

Anyway, after pouring the pad, we stocked up on cinder blocks and started building the block stand. We are following the method described in Forno Bravo's plans of using mortar to level all blocks on the first layer, dry stacking the rest, and then filling the cores with rebar and concrete. So last weekend we started on the first layer and here's how it turned out:



This is another place we had a concern. A few of the blocks seem a little loose. They?re still level and they aren't wobbly, it just seems like the mortar didn't bond that well to the bottom of the block. It still seems solid underneath though. Our thought is that the mortar has served its purpose by leveling the blocks and once we finish stacking we will fill the cores with concrete which will solidify the structure. Would anyone else do this differently?

Another question we have...can we keep building during the colder months or will the cold affect the concrete/mortar curing? I don?t think we?ll want to be out in freezing temperatures, but when we get days in the 40s and 50s, is it okay to keep working?

That's all we have for now. We'll keep the posts coming as we make more progress. Thanks for reading and/or offering your insight!

[stonecutter]

Re: 42" Oven in Raleigh, NC

This is another place we had a concern. A few of the blocks seem a little loose. They?re still level and they aren't wobbly, it just seems like the mortar didn't bond that well to the bottom of the block. It still seems solid underneath though. Our thought is that the mortar has served its purpose by leveling the blocks and once we finish stacking we will fill the cores with concrete which will solidify the structure. Would anyone else do this differently?
Proceed as planned

Another question we have...can we keep building during the colder months or will the cold affect the concrete/mortar curing? I don?t think we?ll want to be out in freezing temperatures, but when we get days in the 40s and 50s, is it okay to keep working?
You are venturing into tricky territory if you don't have experience with cold weather masonry. The short answer is yes, you can build in cold weather temps, it's 32* and below that will mess you up. The trouble is keeping the mortar and concrete from freezing before it can develop strength ie:cure. The best way to prevent that would be to have a temporary structure around the whole work area and heat it. Don't use frozen sand..thaw it out, but don't burn it. Antihydro/antifreeze mortar additives can be a help, but I won't recommend them if you haven't used it before.

See bold above.

[NCMan]

Re: 42" Oven in Raleigh, NC

In addition to what Stonecutter said..... regarding your question about the gravel falling out from under your slab. There is no real way you can put it back. The first thing I'd recommend is getting that dirt around the whole perimeter, as soon as you can. Bring it all the way up to the top of the slab all around, pack it tight and be sure it stays that way all winter and pay particular attention to the northern facing side, as well as the direction of the winter time prevailing winds(usually the NW). This will help prevent further gravel movement as well as helping protect against frost heave. You are starting this project at a tough time of the year, but it can be done, especially if you are able to enclose it somehow, as was suggested. Pay close attention to what each evenings low temp is forecasted to be and use caution. If concrete or mortar freeze, it should be removed and this phase you are in now is actually the most important step of the whole build. If you have even a mild frost forecasted and you're not sure, err on the side of caution. Also, covering your work w/a few layers of 6 mil plastic, straw, layers of cardboard and/or some blankets, etc. can make a difference, but only for a mild frost. W/your lack of experience, I wouldn't chance it w/a forecast even below 35?. But, that's just my 2?.

[jeeppiper]

Re: 42" Oven in Raleigh, NC

Boombaby, I noticed you designed your oven in solidworks. I did the same when building mine. I was constantly running in to my computer to tweak the design, check measurements, etc. Since I didn't know what the heck I was doing in terms of construction, masonry, etc, it helped me work through some real tricky spots. I would like to see your solidworks model sometime. Good luck!

I concur with Stonecutter and NCMan regarding cold temps. Obviously, you want to keep the moisture inside the concrete from freezing and expanding.

[boombaby31]

Re: 42" Oven in Raleigh, NC

Thanks for the feedback. I think we'll take your advice and only build when the forecast looks good. Hopefully we don't get another winter like we did last year. We will definitely fill in around the pad as soon as we can. Luckily we still have all of the dirt from digging the hole.

Jeeppiper, I will try to post the model in the next few days. It was a little strange modeling the oven since I'm used to designing parts for a machine shop. There are lots and lots of patterns. We've definitely already found it helpful for building the form and figuring out quantities for our materials. We probably should spend some more time detailing the dome so maybe that's what we can do when we get bad weather.

[boombaby31]

Re: 42" Oven in Raleigh, NC

So I guess a Solidworks file is a little too big to post here. Here are a few screenshots though. Actually looks like we still have some work to do on it. Is there another way I can get the model to you, jeeppiper?

[fremen325]

Re: 42" Oven in Raleigh, NC

Boombaby,

Have you been able to make any progress this winter? I suspect you didn't get very far this past week with the low temps and ice. I am just starting to dig my foundations so am about 3.5 months behind you in the build. Of course it is always fun to be digging in wet NC red clay that is partially frozen. I think I was sliding around in the mud more than I was digging.

Greg

[boombaby31]

Re: 42" Oven in Raleigh, NC

Hey Greg,

We have kind of put the project on hold until the spring. So we've done a little planning and started building some of the supports we'll need for the next pour but that's it. I guess we've had a few weeks this winter where it probably would have been okay to pour but we've just decided to wait to be safe.

Sounds like you've got your work cut out for you. We were lucky in that most of out soil is actual dirt and we were digging in warm weather. Hopefully we don't get any more ice/snow and it warms up so we can all get some work done. Have you started a thread? I'd be interested to see some other NC builds.

David

[boombaby31]

Re: 42" Oven in Raleigh, NC

Okay, we've finally gotten back to work here in the last few weekends. We poured archways across both of our openings. Here's the form we used for those.



Then we built our form to pour the hearth.



We decided to put some crushed glass on top and we are planning to polish it down. I think we messed up on this part though. We were hoping to drop it in and go over it with the float to embed it into the concrete. But by the time we got to spreading the glass a lot of the concrete was already too hard to get the glass down into it far enough.



We got some diamond polishing pads and used a couple 50 grit and a couple 100 grit on it already. We've smoothed it out some but not as much as we were hoping. In a lot of places, the glass is still higher than the concrete.



We are wondering what we can do with it now. We were hoping to be able to polish it and seal it to have a relatively smooth countertop but we're not sure if we can achieve that at this point. We think we'll try more polishing, but it looks like it's going to take a lot more work not to mention that these diamond pads are not cheap. If we sealed it with polyurethane would that fill in some of the gaps and smooth things over a little bit?

[Tscarborough]

Re: 42" Oven in Raleigh, NC

Forget the diamonds until you are below 120 grit, use cheap carborundum and get it somewhat flat, then begin with the diamond. The problem you will be up against is that the glass is much harder than the concrete, thus making your efforts very difficult. Get as large a grinding pad as you can use to prevent removing the soft matrix while grinding the glass.

Technically, the glass goes in at the hard trowel stage and is at or a tad below the cementious surface. If it becomes unworkable with what you have, skim coat the surface with a high polymer skimcoat and grind from there.

[fremen325]

Re: 42" Oven in Raleigh, NC

David,

Have you been able to make any progress on your build? Did you end up having to do a skim coat and grinding back to the glass from there?

Greg

[boombaby31]

Sorry haven't posted on here for a while. We have slowly been making progress on our oven. We moved on and built the dome and plan to come back over the countertop with tile.

We have a 6" chimney that we are planning to use but I'm seeing now that fornobravo recommends an 8" for a 42" oven. Will it be a colossal mistake to use the 6" chimney?