Hi all from Aussie

[Aussie Pete]

Re: Hi all from Aussie

well...she's been raining pretty hard here all weekend, so didnt get to form the dome yet, hopefully next weekend with any luck.
What is the suggested time to allow the cast dome to set?
I will place plastic sheet over the top of the dome once finished to keep moisture in for a few days atleast, then i will take it off to fully dry.
I think i'm just going to make a butterfly damper in the flue, seems the easiest thing to do. Still after a good idea though.

[david s]

Re: Hi all from Aussie

Castable refractory (calcium aluminate cement) does not require extended curing like Portland (calcium silicate cement) . You just cover it for 24 hrs and it has achieved max. strength. If you plan on making your own castable with lime and Portland cement it will be slow to cure. I'd cover that mix for two weeks.

[david s]

Re: Hi all from Aussie

Sorry, just re-read your thread, when you said "cast dome" did you mean casting, or are you doing it all in brick?

[Aussie Pete]

Re: Hi all from Aussie

sorry David, yeh, i have pyrocrete mix, (just add water),i'll be using that to form a cast dome myself. (layering it over a sand dome).
I know it goes very hard pretty quick, so i'll keep plastic on it for atleast a few days.

[david s]

Re: Hi all from Aussie

Check the manufacturers recommendations on curing. I'm pretty sure it's calcium aluminate so 24 Hrs should be all you need.

[david s]

Re: Hi all from Aussie

I suggest you mix up only half a bag at a time using the manufacturers recommended water addition. With the mix fairly stiff it will stand up vertically without the need for an outside mould. As you get the feel for the stuff you can mix larger amounts. If it gets a bit stiff wriggle it in your hands and it will become more fluid again. If it is hot use chilled water to get more working time. Good luck.

[Aussie Pete]

Re: Hi all from Aussie

good advice there david, thanks very much.
1 question...even if its a hot day, and i use chilled water with the mix, and mix only small amounts as i go, when i've finished the dome, do i only need to lay plastic over the top, is that enough to help stop it drying too quickly. I do have a gazebo over the top of the oven, so i suppose it should be enough, maybe a sprinkle of water over the top every now and then, what do you think?

[david s]

Re: Hi all from Aussie

Pete,
Because it's a different reaction than calcium silicate cement, you do not need to add any more moisture. I cover castings with cling wrap when finished. It sticks closely to the surface. Throw a tarp over that as well and leave for 24hrs. After a couple of hours you will feel the heat the reaction generates, just like plaster of Paris.
Dave

[Aussie Pete]

Re: Hi all from Aussie

cheers dave, much appreciated.

[Aussie Pete]

Re: Hi all from Aussie

Well, its been a while, but some progress has been made, i've made the refractory dome, everything went pretty smoothly, ( with a little help from the missus). I've put plastic over the dome, has been now for about 5 days, i will take it off in a day or 2.
I'm picking up some more refractory cement on friday, with some calc. silic. board (for the door), i need some more cement for my flue transition (still not sure how exactly i'll do it), plus i need to work in the damper somehow. Any thoughts or ideas welcomed.
would it be safe to take out the sand cast now?, i want to try and put some heat lights or heat beads in there to help with the curing....(cant do it with sand in there).
I've got the blanket, then i'll be ready for the verm/perl mix.

[Aussie Pete]

Re: Hi all from Aussie

i've been trolling a bit for some ideas, and i come across this statement made on another thread somewhere.

"Just go with straight portland cement/perlie (or vermiculite) for the whole depth. No reinforcing. This layer will act only in compression therefore no structural benefit to reinforcing it. In addition, the pearlcrete is quite porous and the reinforcing will rust inside the layer."

My question now is.... do they just mean not to reinforce within the verm/perl mix, or any kind of reinforcing?, so do i still layer some wire mesh (chicken wire, whatever) over the blanket then put on the verm/perl mix. I always thought that you make the dome, put blanket on, then mesh over the blanket, then insulation layer.
Do you really need to mesh over the blanket?

[david s]

Re: Hi all from Aussie

The mesh really just helps to keep the form spherical by pulling any folds in the blanket tight IMO. There is really not much point in trying to make the vermiculite layer stronger because you are trying to use it as insulation and to provide a good surface to stucco/render on to. It does give the vermicrete something to hang on to though.

[david s]

Re: Hi all from Aussie

Well, its been a while, but some progress has been made, i've made the refractory dome, everything went pretty smoothly, ( with a little help from the missus). I've put plastic over the dome, has been now for about 5 days, i will take it off in a day or 2.
I'm picking up some more refractory cement on friday, with some calc. silic. board (for the door), i need some more cement for my flue transition (still not sure how exactly i'll do it), plus i need to work in the damper somehow. Any thoughts or ideas welcomed.
would it be safe to take out the sand cast now?, i want to try and put some heat lights or heat beads in there to help with the curing....(cant do it with sand in there).
I've got the blanket, then i'll be ready for the verm/perl mix.

The reaction is complete you don't need to keep it moist for longer than 24hrs. Remove the sand ASAP and try to let the weather (ha ha) dry it for a week. Don't begin to light any fires until you have finished the entry.

[Aussie Pete]

Re: Hi all from Aussie

thanks dave, i will empty out sand tomorrow (RDO), so will clean it out. Cant wait to see what it looks like on the inside,...hope it turned out ok.
there does seem to be very small hairline cracks along the brick arch, where the refractory cement meets with the bricks of the arch...i know everyone says.."dont worry, nothing to worry about"...but its hard, should i put another thicker layer over the top, or just leave it.
it will have blanket then verm/perl over it anyway.

[david s]

Re: Hi all from Aussie

If it decides to crack there, another layer over the top probably won't make much difference. I'd be leaving it for a week to dry and then proceed to curing and then applying the blanket.