32 Inch Cape Build

[CapePizza]

Question about mortaring bricks to concrete. I'm planning on mortaring a row of bricks up against the Foamglas/CaSi insulation board as a border of sorts. The bottom side of the brick will sit on the concrete pad the oven sits on. Can you just mortar the brick to the concrete pad or is it necessary to use some kind of additive to ensure adhesion. I've read conflicting advice. Thanks for the help.

[Neil.B]

As long as the base is clean/dust free you should be able to mortar directly. It will be no different from when you built your brick base. I normally do a 4:1 mix of builders sand and cement.

[david s]

If you have used a vermicrete layer over the blanket a significant amount of it ends up on the concrete supporting slab where you are wanting to mortar your bricks to. Clean this up really well. Vermiculite tends to leave behind a kind of slimy residue that should be cleaned up, perlite doesn’t seem to do this. I wash and wire brush the surface to be joined on to really well as well as making some grooves with the angle grinder and diamond blade, to provide a good key for the mortar join. This is worth doing IMO as sometimes a crack develops between the outer shell and the supporting slab which can be an entry point for water intrusion.

[CapePizza]

Thanks all for your suggestions regarding mortaring the bricks to the concrete slab. I went ahead and mortared 4 bricks yesterday to the concrete slab at the oven's front in preparation for installing the decorative arch bricks, using just Portland cement. Having only been using the home-brew mix, the Portland cement was quite different. Kind of sticky and dense, but nice to work with. Thanks again!

[CapePizza]

Question about CaSi blanket wrap on the vent tunnel. The blanket I have is one inch thick. On the vent tunnel (with chimney flue) I was planning on 1 layer of the blanket (1 inch) covered with about 1/2 inch of
P-Crete and some kind of render on top of that. My question is, although the blanket is "1 inch thick" when it's installed in place, with the wire lath holding it down in place, does that 1 inch get compressed? I squeezed it between my fingers and seems like it compresses to maybe 1/2 inch. Is it like when you install fiberglass insulation in a stud wall it shouldn't be compressed to preserve it's insulating capabilities?
The reason I'm asking I've got about an inch and a half to work with before the P-Crete and render extend beyond where I want it to go. The other option I guess is I could forget about the insulation blanket on the tunnel bricks and just put 1 and 1/2 inch of P-Crete and render. So back to my question, does the blanket get compressed when installed or should an attempt be made not to compress it? Thanks for the help.

[david s]

The blanket does not really compress under the weight of a lean vermicrete mix, although the density of it varies. I use 96 kg/m3, but you can get 128kg/m3 which would have less compression issues, although being denser has slightly less insulation value. I don’t use chicken wire to hold the blanket in place because it’s very time consuming to install, will compress the blanket if tightened which reduces insulation value and adding conductive steel between insulation layers can only reduce insulation value. If the blanket is covered with 10:1 vermicrete it is so light that it won’t compress the blanket at all. A 1/2” thick layer is very thin and may not have sufficient strength to act as a suitable substrate for the render to be applied over it. I think you really need a min of 1”, but if you make it stronger, say 5:1 it’ll probably work ok. Because the entry is significantly cooler than the dome, the reduced insulation there won’t make much difference.

[CapePizza]

david s Thank you for your thoughts. Not sure I phrased my question correctly. Since I only have 1 and half inches to work with I was thinking of purposely compressing the blanket to a half inch to be able to get 1 inch of P-Crete in place. Maybe best to just forget about installing the blanket on the tunnel and just put 1 and half inches of
P-Crete. I am planning on 3 inches of insulation blanket on the dome covered with P-Crete. Thank you again.

[david s]

Yes, that’s an alternative. On my build only the rear half of the flue gallery is covered in one layer of blanket. The front half is vermicrete only.

[CapePizza]

Sharing some updated photos. Just completed the flared entrance tunnel. Wound up taking almost as much time as to do the dome... well, not really but seemed like it took forever. Just completed the outer decorative arch yesterday. Need to add a few more bricks to the chimney and install anchor plate for flue pipe.... and add a few more bricks to top of concrete pad to buttress tunnel arch on the 2 sides. We've been having some great spring like temps so am able to keep working for a bit longer before winter arrives

[MarkJerling]

Sharing some updated photos. Just completed the flared entrance tunnel. Wound up taking almost as much time as to do the dome... well, not really but seemed like it took forever. Just completed the outer decorative arch yesterday. Need to add a few more bricks to the chimney and install anchor plate for flue pipe.... and add a few more bricks to top of concrete pad to buttress tunnel arch on the 2 sides. We've been having some great spring like temps so am able to keep working for a bit longer before winter arrives

That is a true work of art John!

[CapePizza]

MarkJerling Thank you, Mark. That's very nice of you to say that.

I also like the chimney design on your oven. I've wondered if that is a layout you came up with or is it some traditional old time design? At any rate, it's interesting. I've not seen that type of design before.
Thanks again!

[MarkJerling]

MarkJerling Thank you, Mark. That's very nice of you to say that.

I also like the chimney design on your oven. I've wondered if that is a layout you came up with or is it some traditional old time design? At any rate, it's interesting. I've not seen that type of design before.
Thanks again!

I got the idea from here John: https://www.fornobravo.com/blog/pizz...-good-and-bad/
What contributed to my idea was the fact that, where the oven is, near our home, there's a window which lines up with the oven landing and I figured it would look better if the chimney was therefore set back to the top of the dome, as that takes the chimney out of line of sight from inside the window. So, it had both practical and aesthetic considerations. Lastly, I have a friend who's an "expert" on almost everything and I enjoyed building it this way so that he would say when he saw it the first time that it's "wrong", the chimney can't come out the top of the dome as all the heat would be lost. (Which he did!)

[CapePizza]

Hello...Breather vent cap question....... I'm starting to plan for the insulation blanket and P-Crete on the dome. I'm planning on inserting a breather cap vent/pressure relief valve embedded in the P-Crete layer sitting it on the insulation blanket. I was planning on only using one vent on the very top of the dome. Is that enough, just the one..... or is there any benefit to having more than one, and if so.... any suggestions on how many and where to lay out the pattern?
Thanks very much for the help.

[Baza]

John - I'm completely blown away - remarkable work, sir!
You have revived the confidence to continue with the flared opening - wow

[CapePizza]

. Thanks for the nice words, Barry Baza. We've had such great weather these past couple of weeks I'm still plugging along. We did have a (rare) small earthquake here last week which made me think
about the stone pedestal my oven sits on. This was a left over from a cob oven I had a few years ago and I reused it. I sometimes regret not building a typical cinder block base that most people use. At any rate, that earthquake got me thinking, if that pedestal were to weaken and break up, my oven would be lost. So I spent the last few days installing 2 concrete columns on the two front corners of the hearth. Poured them yesterday with a steel tube bridging the columns. Hopefully that will add a some support and a little peace of mind. The rear of the hearth is supported by earth (dirt and rocks).