castable refractory

[fxpose]

Re: castable refractory

If anyone wants plans or more photos, please ask. Easy to build, great to use.
Happy cooking to all.
Willy

If possible, can you please post some more photos here in this thread. I'm especially interested in how you set up the sand mold. I'm assuming the sand mold was demolished and excavated afterwards? Or was this a reusable mold?
Sorry about the newby question.

Thanks!!

[mr g]

Re: castable refractory

Hi to fxpose and cuba. Wild Willy inspired me and a group of friends to make our domes out of castable. In all we have about 10 domes to build so we intend to reuse the sand dome. We are tossing up whether to make a fibreglass inner and outer mould from the sand one or whether the sand dome will hold up during multiple uses. I have attached some photos of the sand mould which is simply bricklayer's sand. The dome will have an inner diameter of 1000mm and an inner height of 450mm. The door opening is 450mm x 300mm. You'll notice that the mould has a narrower portion where the opening meets with the dome entrance - this is for the door jam. Since we intend to reuse the mould for multiple domes I have decided to paint the sand using ordinary houshold paint to bind the sand together. This has worked quite well and now the sand has quite a tough outer layer to help preserve all the edges. I also intend to wrap the dome in a plastic layer of some sort (possibly cling wrap) and then spray it with canola oil as a release agent. My only real concern is how thick to cast the dome. I don't think I want to go over 70mm thick but is this going to be strong enough and how long will it take to heat up? I'll post some more info when I have gone to the next stage. Hopefully next weekend.

[sonomacast]

Re: castable refractory

Really nice job on the sand dome. How are you going to cast the cement and keep the thickness constant? Will there be an outer mould? Will the ovens be segmented? Thanks

[mr g]

Re: castable refractory

Hi Sonomacast, yes I'll be using a couple of outer templates similar to what I used for the sand dome only 3" bigger to guide me. Yes, we will be making the first one in three sections - two pieces for the dome and one for the entrance. It may be that two pieces for the dome will be too heavy so there is a possibility that the next ones will be in three/four pieces. I'll post some pictures when I have the outer template and separators ready. There's a good chance that the first dome will be cast this weekend.

Cheers
Mr G

[sonomacast]

Re: castable refractory

Excellent, Good luck and keep us informed and up to date Mr g.

[david s]

Re: castable refractory

Mr G,
I think you'll be very lucky to release a casting from a sand mould without damaging it. I have to use a hammer and screwdriver to release my castings. If you are doing a one piece casting it's going to be extremely heavy.

[mr g]

Re: castable refractory

Hi David, it sounds like you make these domes regulary ? Is that right? If so
I have a few questions for you.

Regards
Mr G

[diy]

Re: castable refractory

Proper refractory castable should dry out very slowly so then it won't crack

[jonkendall50]

Re: castable refractory

I may have missed this earlier, but what kind of castable are you using? I went to a local place and they had insulating castable and non-insulating. I was thinking that it might be smart to use non-insulating as the dome, cover it with a thermal blanket then a layer of insulating castable.

[david s]

Re: castable refractory

diy,
The product information I was given on castable refractory says that it does not require extended curing like portland cement. It uses calcium aluminate cement which, unlike portland, only needs 24 hrs to set hard before going through its heating schedule. It's chemical process is different.The clay content in the mix has already been fired (grog) so the shrinkage is zero.

[pacoast]

Re: castable refractory

I'd be really interested if you figure out a way to reuse your sand forms. It might work if you mixed enough cement into the sand to hold it together - but that is just speculation, I haven't tried such.

Sand is often used as a form e.g. for low domes. And sand molds are used to cast metal pieces. In which case a reusable pattern is used to set the next sand mold up quickly. I suspect that you want a reusable form. I think that if you "glue" the sand together with more cement than is usually used, it might be reusable. But are you sure that your refractory mix is stiff enough to simply apply it to the sand form? The castable refractories that I've used are runny like concrete and need a female form (second shell) to hold the refractory in place until it sets.

.

[mr g]

Re: castable refractory

Hi Pacoast, yes that is the big question - will the castable simply run down the sides and not hold. I'm casting my first one tomorrow so I'll post an update soon. What I intend to do is cast the entrance part first which will only take two to three bags so if things go bad I haven't lost too much money.

Regards,
Mr G.

[Johnny the oven man]

Re: castable refractory

Castables should be mixed to a consistancy that is niether runny or too dry. If you can get a ball of the mix in your hand, it should not ooze through your fingers when squashed, and should not crumble when thrown in the air about 2 meters and caught.

[pacoast]

Re: castable refractory

I'm not disagreeing with anything that Johnny just said. But mr g, I think you'll find that the castable will slump, that is shift downwards before it sets even if you tried to mix it thick. I haven't seen any castables that are thick like putty.

I hope that it works the way you want & you may have found a thicker product than I have seen. But perhaps give it five minutes thought as to how you will handle it if it doesn't go according to plan. Perhaps a partial second form or something that would help if you run into problems.

Best of luck on the pour!

.

[Johnny the oven man]

Re: castable refractory

Perhaps mr g might want to give me a call, we are in the same town. 95604477.