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  • No blanket. I just did a bunch of ~1:8 perlcrete. That seems to be the typical Austin tradition, since everybody winds up going to the brick yard, and tscarborough tells them not to bother with it. I think I even saw it in action on one of my visits.

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    • I finally am on my desktop long enough to show what actually happened. Here's the layers.

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      • Originally posted by Rocko Bonaparte View Post
        No blanket. I just did a bunch of ~1:8 perlcrete. That seems to be the typical Austin tradition, since everybody winds up going to the brick yard, and tscarborough tells them not to bother with it. I think I even saw it in action on one of my visits.
        Be careful if not using any blanket insulation. Before the safer ceramic fibre blanket matched the price of the older generation blanket, I used Perl/vermicrete insulation layer on ovens that I built. Unfortunately the very deep layer takes way longer to dry and if heated too quickly will make the vermicrete swell and crack. This is not too much of a problem unless you have rendered a hard shell over the top, in which case it can crack the outer shell. When the heat from the inner shell hits the damp vermicrete it produces quite quickly, a large amount of steam. But, if there is a layer of blanket between the inner oven and vermicrete layer, not only do you not need as deep a vermicrete layer, but it takes the sting out of the heat and also acts as an expansion joint. In either case itís best to drive the water out before doing the outer shell to be safe. A vent to allow steam to escape is also a good plan. Also 8:1 is relatively dense and doesnít, leave too many spaces between the grains. I find 10:1 better but a little harder to apply.


        So, go extra slow in drying out your oven. If you hold your hand against the outside and itís hot, then your insulation is wet and not performing well. Back off with the firing.
        Last edited by david s; 10-07-2017, 04:35 PM.
        Kindled with zeal and fired with passion.

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        • It's minimally 8:1 but I didn't precisely measure. It is also a roughly even split of perlite and vermiculite. I just figured out after the fact that what I was doing never closed the ratio any lower than 8:1. Anyways, the timetable has been something like:

          ~September 5th, brickwork done
          ~September 18th, started outer perlcrete insulation
          ~September 23rd, definitely finished outer insulation
          ~September 26th, finished stucco brown coat
          October 1st, completed stucco finish coat

          The brown coat did get rained on, but the bricks and perlcrete got tarped whenever something was coming along.

          Outside of the finish coat, some of that stuff might have finished earlier. I'm just going by timestamps on my photographs, and I didn't necessarily take them right after finishing--or even the day after.

          So given that kind of timetable, should I give it two weeks?

          IIRC the fast-and-dry (haha pun) rule was to wait two weeks. That would mean October 15th would be Pizza Time. The big question is whether I can get up to 900F on the 14th. My wife really wants to do it, but I wanted to practice first. Just disregarding the oven itself, it has been years since I have really worked a pizza oven and I don't have a routine down with this new one. I don't know its personality at all. But such is life. I've been on here long enough to see tons of people always asking, "Can I use it now?" It's like kids asking, "Are we there yet?" I know I was impatient with my first one.

          As it stands today, October 7th, I have a space heater deep inside keeping things warm. Even without it, the current daily weather range is 69F-93F.

          Side thing: The oven smells a little bit like guano to me. I think it might be a side effect of the diluted muriatic acid mix I used to clean up the brick work. My wife thought I was crazy. I was thinking "more like batshit insane, am I right hawhawhaw." But no really it smells like guano and I'm wondering what is up with that.

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          • Originally posted by Rocko Bonaparte View Post
            It's minimally 8:1 but I didn't precisely measure. It is also a roughly even split of perlite and vermiculite. I just figured out after the fact that what I was doing never closed the ratio any lower than 8:1. Anyways, the timetable has been something like:

            ~September 5th, brickwork done
            ~September 18th, started outer perlcrete insulation
            ~September 23rd, definitely finished outer insulation
            ~September 26th, finished stucco brown coat
            October 1st, completed stucco finish coat

            The brown coat did get rained on, but the bricks and perlcrete got tarped whenever something was coming along.

            Outside of the finish coat, some of that stuff might have finished earlier. I'm just going by timestamps on my photographs, and I didn't necessarily take them right after finishing--or even the day after.

            So given that kind of timetable, should I give it two weeks?

            IIRC the fast-and-dry (haha pun) rule was to wait two weeks. That would mean October 15th would be Pizza Time. The big question is whether I can get up to 900F on the 14th. My wife really wants to do it, but I wanted to practice first. Just disregarding the oven itself, it has been years since I have really worked a pizza oven and I don't have a routine down with this new one. I don't know its personality at all. But such is life. I've been on here long enough to see tons of people always asking, "Can I use it now?" It's like kids asking, "Are we there yet?" I know I was impatient with my first one.

            As it stands today, October 7th, I have a space heater deep inside keeping things warm. Even without it, the current daily weather range is 69F-93F.

            Side thing: The oven smells a little bit like guano to me. I think it might be a side effect of the diluted muriatic acid mix I used to clean up the brick work. My wife thought I was crazy. I was thinking "more like batshit insane, am I right hawhawhaw." But no really it smells like guano and I'm wondering what is up with that.
            Allowing the thing to dry naturally is dependant on temperature, air movement and humidity. I have no idea of your weather conditions but I did do an experiment on drying of vermicrete (attached) that you may find useful. Also read the thread on curing under "Heat Management".
            I like to use a combination of Heat Beads (BBQ fuel) and wood and try to avoid direct flame impingement on the dome. The normal regime is 7 fires in 7 days getting progressively bigger.
            Can't offer any ideas re the smell, but the fire should fix that.

            Vermicrete insulating slab copy.doc.zip
            Kindled with zeal and fired with passion.

            Comment


            • Originally posted by david s View Post

              Allowing the thing to dry naturally is dependant on temperature, air movement and humidity. I have no idea of your weather conditions but I did do an experiment on drying of vermicrete (attached) that you may find useful. Also read the thread on curing under "Heat Management".
              I like to use a combination of Heat Beads (BBQ fuel) and wood and try to avoid direct flame impingement on the dome. The normal regime is 7 fires in 7 days getting progressively bigger.
              Can't offer any ideas re the smell, but the fire should fix that.

              [ATTACH]n401701[/ATTACH]
              I never saw that document! I feel like the forums have slowed down because I've been around those subforums, but then stuff like this shows up. That's a really cool science project they did.

              I looked up your neck of the woods based on Townsville. It looks like you get a bit higher and drier than Austin, TX. The past summer wasn't too hot here compared to some previous years--the 2011 drought comes to mind--but we were over 100 degrees Fahrenheit (~38C) for most of July and August for our summer. September saw mostly 90s for the highs. In terms of humidity, it got very miserable due to a few chance storms and them Harvey rolling in. Humidity was around 70% and higher based on circumstance.

              Anecdotally, I was having trouble applying the stucco properly because sections would dry before I could connect them. I eventually sucked my wife into it to help finish it off.

              As I sit here, the oven is burning a 2x4 and a few larger bits of branches. The bricks in the dome did cross 300F/149C. The outer dome shows no temperature difference based on my IR thermometer. Well, technically the dome is one degree cooler on the outside than the oven's base. I will be keeping an eye on it to see the delta over the next two hours, but I don't expect much to happen. I discovered that some of the gravy in my perlcrete ran bled into the bricks inside the dome. The bad news is that it negated all the work I had put into cleaning those bricks. The good new is that is less water in the perlcrete to deal with. I hope subsequent firings will take care of that.

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              • I've progressed to burning logs--if that is actually a step forwards. The logs don't shoot off a large flame, burn longer, and don't burn quite as severely hot as split ones. I was about to get just over 400F yesterday inside the dome without any noticeable events. I haven't even been able to spot the inevitable crack yet. I'm hoping to get just past 550F for a time today.

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                • You have two problems here. Firstly the thick vermicrete layer directly against the inner oven without the blanket insulation between and secondly that you've rendered over the vermicrete before driving off the water which is going to trap the water in the vermicrete layer. It will eventually find its way out though, just take longer. Do you have a vent hole to allow steam to escape. If not it may help you could cut a hole with a masonry hole saw. It allows you to more easily feel the moisture coming out, or you can plunge a cheap garden moisture meter through the hole into the vermicrete layer. Also if the insulation is wet it won't insulate very well and the outside shell will feel hot. If it's working ok i.e. dry then the outside shell will get no hotter than cosy warm.
                  Kindled with zeal and fired with passion.

                  Comment


                  • Originally posted by david s View Post
                    You have two problems here. Firstly the thick vermicrete layer directly against the inner oven without the blanket insulation between and secondly that you've rendered over the vermicrete before driving off the water which is going to trap the water in the vermicrete layer. It will eventually find its way out though, just take longer. Do you have a vent hole to allow steam to escape. If not it may help you could cut a hole with a masonry hole saw. It allows you to more easily feel the moisture coming out, or you can plunge a cheap garden moisture meter through the hole into the vermicrete layer. Also if the insulation is wet it won't insulate very well and the outside shell will feel hot. If it's working ok i.e. dry then the outside shell will get no hotter than cosy warm.
                    My wife will probably drill a hole in my head if I put a hole in the oven right now.

                    As it stands today, it felt like a step backwards. Sixteen hours after yesterday's firing, the inside was still ~140F, which I regarded as a good sign. To me that implied that it wasn't cooler off by "sweating" water and evaporating. On the other hand, it might also mean the oven is finally saturating with heat--including a potentially very wet insulation layer. When we fired it up, we got a five degree (Fahrenheit) differential between the base and the dome. So I pulled back on firing hot. Instead, we have spread some wood out inside and have had it going pretty gently for around six hours now. I don't think it's then went over 300F inside.

                    I thought it was this thread where I saw--but I cannot find it--that I should avoid over a five degree differential in temperature. I wondered if that was in Fahrenheit or Celsius. I mean, if it's Celsius then I have some more play room hehehe. The base was about 68-70F depending on the time and the dome was 72-74F at its hottest. However, under the floor inside my base, I was reading upwards of 90F. This was pretty odd to me because I don't really recall my old oven getting that hot. I am wondering if a lot of the water got wicked into my bottom perlcrete layer. That layer certainly had plenty of time to dry before then; I cast that in early July and did not set my first bricks until early August. It was roughly an 8:1 mix.

                    FWIW I'll go see if tscarborough's answering the phone tomorrow and see what he thinks of this mayhem.

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                    • The range that you are likely to get problems is when the top of the dome is around 500 F and the bottom of the dome is still around 300 F a 5 degree difference is nothing.. Just keep going with the fires, itíll dry eventually. Do you have some weep holes in the supporting slab to allow the water to escape from the under floor insulation?
                      Here is the curing thread. https://community.fornobravo.com/for...curing#post833
                      Last edited by david s; 10-12-2017, 12:47 PM.
                      Kindled with zeal and fired with passion.

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