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Will an oven fit....looks like yes! PA build

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  • #31
    It isnít our intention to worry you but caution and patience are advised. Vermicrete takes up an enormous amount of water in the mix and less than half is used up in the hydration process This leaves a lot of free water to eliminate. Not sure how big your oven is but a 4Ē x 1 m vermicrete slab is around 79 litres (20 gallons) 1/3 of which is water. When you build straight over it without allowing it time to dry some, it makes the job of drying it that much more difficult. Some drain holes in the supporting slab help to eliminate moisture more easily. The same applies for the mortar in the inner dome and the vermicrete in the insulation space. So just take your time with gentle fires. Remember, one litre of water makes over 1650 litres of steam.
    Kindled with zeal and fired with passion.

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    • #32
      Ahhh.....I posted all the pics at once so timing is not clear. That silly round base I though was a good idea took me 3 weeks to build and now another week to build up to match the dome diameter. The vermiculite slab went in July 2 and is covered by a 2 5" concrete slab, leaving just the sides open to the elements to pick up new water. Then a broken truck and his daughter's wedding kept my bother away until september so it's been sitting a long time and should be pretty dry.

      I did add some vermiculite to the stucco covering the insulation...it's about 50/50 motar/vermiculite by volume and about an inch thick, except near the chimney where its thicker to form the radius that blends it into the dome. No doubt that still has some water but is was at least a full day in the hot sun between 1/2" thick layers...but it looked and felt pretty dry each layer.

      Still, probably good advice to heat it slowly.

      It is a 40" oven btw, I didn't mention that.

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      • #33
        Tonight I had at the top with a grinder and sander. I had planned to stucco the brick on the front of the oven and the top....but the front bricks been growing on me so I wanted to see how it would look brick on top.... I kind of like it, Lana's not so sure.

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        • #34
          The front shelf was supposed to be travertine to match the island....it ended up brick to match the rest of the oven. Construction involves a lot of....discussion at my house.

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          • #35
            One last base coat to makes the texture and color more even to be sure the finish coat comes out uniform color.

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            • #36
              I'll add this info. This is built using plain $7/bag mortar, but the inside is pointed with the high heat stuff.

              My bother told me that's how he always builds them, it's way easier......but...but.....and after some digging I found this paper that says under 600C it doesn't matter what you use:
              https://info.ornl.gov/sites/publicat...es/Pub1043.pdf

              only the very surface should ever cross 600C, so normal mortar pointed with heat temp it is.

              Also there is a 2.5" thin slab of plain concrete over the 4"vcrete insulation, then the bricks are set to the concrete with heat temp.

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              • #37
                Thanks for providing that very comprehensive document. It clearly states "In the temperature range from 450-550 C there is decomposition of portlandite". In addition "commonly used aggregate materials are thermally stable up to 300-350 C". In practice oven builders have found that the portland degrades from around 300 C. The home-brew which has proved adequate for the temperature range of wood fired ovens contains lime as well as portland cement which also acts as cementious material but has a higher service temperature (begins its degradation at around 500 C) than OPC. So the lime takes over when the OPC begins its failure. In addition the high clay content provides good refractory properties to the mortar to help counteract the deficiencies of the sand aggregate. If you want a mortar to perform to higher temperatures then calcium aluminate cement (CAC) and high temperature aggregates are required.

                All that aside, you have a very nice looking oven and I'm sure you will find it performs well.
                Last edited by david s; 09-18-2018, 02:21 PM.
                Kindled with zeal and fired with passion.

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                • #38
                  David, There's a ton of data in that paper and that's the way I read it the first time though as well. On the 2nd or 3rd read I realized the the data is for concrete and when they say aggregate they mean the crushed stone in the concrete not the sand that is breaking down so that doesn't apply to mortar. On page 32 you'll find "The aggregate type is one of the main factors influencing the compressive strength of concrete at elevated temperature.". Up on page 20 is this "Results in the literature indicate that the primary factors affecting the modulus of elasticity at high temperature are the type of aggregate". so that's the stone that's burning out of concrete and not applicable to mortar.

                  I think the most important part of the article is on p24:
                  "Figure 25, which presents results for unsealed mortars fabricated from ordinary Portland cement, blast furnace slag cement, and truss cement, indicates little difference in strength-temperature characteristics, except the ordinary Portland cement mortar exhibited a sharper decrease in strength at temperatures greater than 500įC (Ref. 4). Another study utilizing a number of cement types (e.g., ordinary Portland cement, fly ash, and blast furnace slag cement) also noted that up to 600įC there was little effect of the cement type.52".

                  Basically portland based mortar is good to 500C-600C, which is well above wfo operation temps which is why I agreed to building the dome with the cheap stuff and just pointing the inner 1/2" which could see higher temps with the high temp stuff.

                  I'm not in ANY way saying its wrong to use the high temp stuff for everything, but I think there is data to support the use of the low temp stuff for most of the work and its cheaper and easier to work with....but in my case with the bricks fitting pretty well and all the mortar buried under the dome I'm not sure I'll ever know if the mortar burned out...I guess.

                  The weather looks good for a couple days so I took a vacation day and tomorrow will be finish stucco coat day. There is still some question about what th finish will be. I'm pushing for a sponge finish so I know I can make the curves look nice but my house and garage are textured and Lana like things to match.....we'll see what tomorrow brings.

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                  • #39
                    We will have to agree to disagree. Reference to aggregates in concretes also includes sand as it is just a fine aggregate around which the cementious paste does its bonding, so it applies to both mortars and concretes containing larger sized aggregates. . Practical experience demonstrates that mortars only containing Portland and sand do not handle WFO temperatures, however, as I previously explained, the addition of both lime and clay improves the resulting materials capability to withstand the temperatures we fire to, just. I donít want to harp on about this, but other builders may get the idea that a conventional OPC/sand mortar is adequate and itís not.
                    Last edited by david s; 09-19-2018, 05:10 AM.
                    Kindled with zeal and fired with passion.

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                    • #40
                      I totally agree with Davd. The made from scratch formula (Portland/lime/sand) for general purpose mortar is inadeqate for temps that our ovens reach. It will degrade. But, there is an even worse problem with using premixed masonry cement or premixed mortar. The lime is added for workability in general pupose mortar, not as a refractory. So, here in the states, manufactureres are allowed to substitute part of the lime in the recipe with what the industry calls "or the equivalent". The "equivalent" will usually be crushed limestone and other proprietary additives. This allows the manufactuer to make the product more economically and produce a mortar that is not as caustic. Crushed limestone expands more so than lime when heated. In a fireplace fire box that results in damaged firebrick.



                      Last edited by Gulf; 09-19-2018, 07:35 AM.
                      Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build

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                      • #41
                        Originally posted by david s View Post
                        We will have to agree to disagree. Reference to aggregates in concretes also includes sand as it is just a fine aggregate around which the cementious paste does its bonding, so it applies to both mortars and concretes containing larger sized aggregates. . Practical experience demonstrates that mortars only containing Portland and sand do not handle WFO temperatures, however, as I previously explained, the addition of both lime and clay improves the resulting materials capability to withstand the temperatures we fire to, just. I donít want to harp on about this, but other builders may get the idea that a conventional OPC/sand mortar is adequate and itís not.
                        It does not include sand. They are clear about what reactions are occurring and they don't include the sand components. Sand melts at about 1700 C, it doesn't decompose until well above that....or we wouldn't be able to make glass and the homebrew would also decompose.

                        All the literature I could find say conventional mortar is perfectly adequate up to 500-600C...not good to point up 5he inside of the dome but fine for EVERYTHING else.

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                        • #42
                          Originally posted by Gulf View Post
                          I totally agree with Davd. The made from scratch formula (Portland/lime/sand) for general purpose mortar is inadeqate for temps that our ovens reach. It will degrade. But, there is an even worse problem with using premixed masonry cement or premixed mortar. The lime is added for workability in general pupose mortar, not as a refractory. So, here in the states, manufactureres are allowed to substitute part of the lime in the recipe with what the industry calls "or the equivalent". The "equivalent" will usually be crushed limestone and other proprietary additives. This allows the manufactuer to make the product more economically and produce a mortar that is not as caustic. Crushed limestone expands more so than lime when heated. In a fireplace fire box that results in damaged firebrick.
                          Joe
                          I have no reason to quote anything you posted about lime....but like is not required below 500C so I don't think it matter if mortar has the right line or not.

                          Mark

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                          • #43
                            Got outside a little before 7am...inside a little after 7pm. Things just didn't go to plan. I did the dome....it turned white so I had to do it a second time.

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                            • #44
                              Lana did love the way I did the texture...so I had to escape and redo that. But the result is good

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                              • #45
                                I have no idea what's in the stucco mix I'm using but it destroyed my hands...burned right though the skin on my fingers. What I realized I put on gloves...it got worse so I went to vinyl under the work gloves...it got worse on my fingers and burned my wrists wear the gloves ended and where the hawk touched me.....hurts like he!! ....good excuse for another drink.

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