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30" cast dome design

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  • #46
    Your dome looks great, I like the idea of how you made the dome form instead of sand... what did you use to harden the paper... also how many sacks of refractory cement did you use for your dome? I too am a cement newbie so I am worried about how fast David says that it becomes unworkable, it looked like a nice sunny day but what was the temp, I see you worked up a sweat... I am thinking I'll need to wait for the cooler season here before I do my dome.
    Looking forward to seeing your build progress...


    • #47
      Thank you! The paper gets very hard when the glue dries. But it was the ribs that made the form rigid. Also, syrene wrap protected the paper from all that water. Overall, this is probably more work than building a sand dome if I had to guess.After all,we glued together 17 layers of newspaper though my daughter really enjoyed it.
      I have used Harbison Walker KS-4 PLUS castable refractory mix, 5 55-lbs bags and I still have 3 more for the entrance and I added SS needles. I think it's important to get castable mix because it has lots of things in it including fibers to help with water removal. Recommended temp range for the mix is below 27c. They tell you to use ice water above that. Also, they warn that temps above 35c may reduce workability of the concrete, whatever it means. The temps were around 30-32c when we cast the dome. Thank God we were in the shade but I was soaked! The time frame for a batch is 20 minutes so we mixed only 15 lbs of concrete at once which also allowed us to use a cheap electric mortar mixer without killing it (but it still tried to smoke once in a while)
      Being a newbie, what really helped me is a small casting practice I did with an extra bag I got specifically to practice (see my other thread if curious)
      Removing the paper mache today, fingers crossed!


      • #48
        As far as I can tell, the dome turned out REALLY WELL! Very happy with it! The only blemish is on the front top of the arch but it is not much. Everything inside of the dome is nice and smooth. So I hope it is good then. The paper form came out fairly easily. On to the entrance!!!

        David, david s please let me know if it is OK to cast the entrance in place (please see a couple of posts above for more details if needed)

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        • #49
          Getting ready to cast the entrance

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          • #50
            Mullster Mullster

            I have forgotten to thank you again for posting about the problems you have experienced with your cast. I would not packed that concrete as tight as I did if I have not seen your pictures! Thanks!


            • #51
              Originally posted by sergetania View Post
              Mullster Mullster

              I have forgotten to thank you again for posting about the problems you have experienced with your cast. I would not packed that concrete as tight as I did if I have not seen your pictures! Thanks!
              Glad it helped!
              My cast oven build thread



              • #52
                Completed another step - the entrance. It took over two hours and just two 55 lbs bags of the castable mix. Interestingly, this time the temp was around 74F vs close to 90F when we did the dome. We have not used ice water this time but still the window to work with a batch was noticeably longer, at least a half an hour. Ambient temps matter!

                Making a facade is next. Planning to wrap wires coming from the facade either around the bolts under the chimney adapter or the entire concrete hump around the chimney under the insulation. Not sure which is better. Anyone sees a problem with either method? Thanks!

                It is quite roomy inside while the outside looks rather small!
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                • #53
                  At this point in the build, I do need someone to look over the following plan of action to complete the oven because I am not quite sure what I am doing. David david s or anyone else, PLEASE help me finish the oven!

                  I believe I know enough to make and attach a facade. Once that's done, I have just under 4" of space on the base around the dome to insulate the oven and build an outer layer. It will have to be waterproof and I am planning to build a device to release water vapors through the outer layer. Based on what I have seen and read, including this thread, I should do the following

                  1. Cover the inner core with 2 layers of ceramic blanket (I got enough material for 3 layers but David said it gets harder to work with after 2 layers)
                  2. Fasten the blanket with stainless chicken wire
                  3. Lay at least 30mm (probably can do even more) of 1:10 cement to perlite mix (install a breather device)
                  4. Anything else on top of that before the final waterproof layer?
                  5. Apply the final waterproof layer of material like this (Elastomeric flashing sealer)


                  Do these steps look reasonable? Am I missing anything? Thank you very much for your help! I can't say I am very excited because that would be an understatement!
                  Last edited by sergetania; 09-02-2020, 06:07 PM.


                  • #54
                    Click image for larger version

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ID:	429331 I would see how it goes after two layer of ceramic blanket and if going good add the third because you have it and any irregularities can be corrected with the vcrete. I would also make yourself a curve trowel for holding and shaping the vcrete,especially 10 to 1. The blanket can be secured with tie wire as well, just a few tapcons in the hearth and weave back and forth.

                    Google Photo Album []


                    • #55
                      Thank you! Got the trowel made already for the dome casting but didn't use it much. I will adjust the radius and it will come in handy. Glad I can waterproof the vcrete layer directly. Based on what I read it seems perlite dries faster so I planned to use that instead of vermiculite. Is that ok? Not sure I have ever seen either. The wire method seems simpler than chicken wire. How thick is the wire?What gauge do you use? Do you attach the wire to the base (insulation board,for example, because it is easy to do and it's what it looks like on the picture)?
                      Edit: just looked up tapcons, got it! Can I do wood screws into the ceramic board?

                      Thanks a lot,
                      Last edited by sergetania; 09-02-2020, 08:52 PM.


                      • #56
                        Tapcons are for the concrete hearth. I am not sure the CaSi board has enough strength but you can try it with longer screws place horizontally but in the hearth is better. Tapcons or equivalent can be installed with a regular drill and concrete bit. Most any wire will do, I just used some wire I had laying around.fairly small diameter and flexible. You can interchange perlite and vermiculite although perlite has a better K value but mixed with portland the difference moderate. P or Vcrete have a ton of water in it, do not go by the surface dryness only.
                        Google Photo Album []


                        • #57
                          Thank you for the help, Russell! I think I have a pretty good understanding of what I need to do now.


                          • #58
                            sergetania great progress again. Just checking - are you suggesting simply sealing the vcrete layer? I’m no expert but I would have thought you need a render layer on top of the vcrete first?
                            My cast oven build thread



                            • #59
                              Yeh, scratch coat, then final coat. Some even put two thinner scratch layers on i believe


                              • #60
                                Mullster Thanks!
                                Yes, that's exactly what I was hoping for. A vcrete layer and then paint over with a waterproof coat. Do I need anything on top of the vcrete before waterproofing? Won't it work? I have no idea hence I have asked.