New build in Sunny Canberra

[Steady]

Looking good timechanter

[timechanter]

I hope it will be looking better in a couple of weeks. I've just ordered my SS needles reinforcement and will head out to the pottery place this weekend to grab powdered clay for the sand form. Other than that, just some ply wood templates to knock up.

[timechanter]

Stand is complete, and form-work removed. Got a 10kg delivery of SS needles, my week is looking up.

[timechanter]

Well I've cut up the Board and marked out the floor tiles (300x300x50mm) . It appears I was a little eager and ended up with 6 tiles and 1 sheet of 600x1000x50mm CF board left over. Chances are Ill have a few bags of castable left as well. Maybe I should build a very small oven for my dad, or maybe I should take up pottery and build a small kiln.

I'm looking good for the dome this long weekend.

[timechanter]

Tracked down the fire clay and the floor cut and ready for the weekend.

[timechanter]

Floor down and level. Notched trowel and 50/50 sand/fireclay worked a treat.

I'm building the sand form for casting today, temps are looking a little high for the afternoon (31C) concerned about my ability to cast in that temp.

Any suggestion here david s ?

[david s]

Are you planning to cast your dome on top of the floor or around it. You can do it either way, but if cast on top of the floor bricks makes replacement of floor bricks at the perimeter very difficult.
The brew for the sand cast is 10 parts sand, 0.25 parts powdered clay, 1 part water.
Are you using a proprietary castable refractory or making your own? SS needle addition is a min of 2% by weight of dry castable. Handle the mix with respect, they're not called needles for nothing.

[timechanter]

Thanks david s .

I'm using proprietary castable on top of the floor tiles with 5% SS needles (should I make it only 2%? They are rather pointy) . I have made the dome today (picture attached) which took longer than I expected to get the shape right. Its currently 31C here and the wind is blow strong , making it a challenge to put wet news paper down (it keeps blowing away).

Big question is is 31C to hot (espeically with strong hot winds) to attempt the castable?

[david s]

5% is good. 2" thick is enough to give you required strength, sufficient thermal mass, reasonable heat up time and fuel economy. In hot weather I always use chilled water because calcium aluminate cement goes off very fast. Don't mix up more than half a bag at a time and make sure your barrow is cool. ie not left in the sun.
The castable is quite thixotropic so wiggling it a bit will make it more fluid. When done, cover it for 24 hrs, but it does not have to be damp cured for a week like Portland cement as it achieves its full strength in 24 hrs.

[david s]

You should cover the sand mould to prevent the surface from drying. Cover its surface with strips of wet newspaper to give your casting a good smooth surface and prevent sand sticking to the inside surface of the casting.
if it were mine, I'd be making another door face 2" higher and 2" wider at each side to trowel against so you create the oven door mouth with a nice flat front face of the correct thickness. You also need to oil its face as a release agent, to prevent the castable bonding to it

[timechanter]

Thanks Dave,

I had another piece as a front for the entrance to cement up to that I left out of the previous photo. I missed your message so I didn't put oil on its face, I hope the melamine board will release okay. My finished dome is below. If/When I do it again I will make a template for the dome curve out of something stronger than foam-board (which broke first measurement.

I'm planing on making the gallery slightly larger to create the inside reveal of 2 cm.

When finishing I realised I had left a couple of section rough and it had hardened already. At those points its about 6cm thick, so I'm hoping other than cosmetic issues (which will be invisible once the blanket goes on) it shouldnt have to do anything ?

[david s]

You can remove the sand after 24 hrs as calcium aluminate concretes achieve max strength then. While the casting is still damp you can fill any voids with some castable. I find it works best if you sieve out the more coarse aggregate then make it into a peanut butter consistency. It won't work very well if the casting is dry. I find 24 hrs after demoulding is good. 2 cm for the rebate is not much, there are advantages to making it bigger in that working the oven is easier with the extra space, it also gives you more wriggle room for the door.

[timechanter]

24hrs are up and with the help of a giant umbrella and a tarp I was able to remove the sand whilst the skys' opened with rain (well for Canberra it opened with rain). As I feared there was a slump at a couple of sections, only one that looked big enough to fill (doesn't appear significant, just unsightly). Out of interest, how do you get the Newspaper out (without using fire)? I want to fill the void but the paper is getting in the way.

I'd like to say those needles are damn annoying in the inner shell. I pull a few out and bent the rest my hands found (the hard way) on themselves. Is there anything I should be doing specifically for them?

The rain stopped me dead preparing the entrance, and I am evaluating the bigger reveal any way. Currently the front flue entrance will be 200mm deep and 520mm wide (interior). The Door width into the Dome is 420mm.

[david s]

If the newspaper is jammed in a crease that you want to fill try a stiff scrubbing brush, failing that a wire brush. The fire will deal with any other bits that are difficult to strip away.

[timechanter]

Just built my gallery out of foam board and sand. So excited to be laying blanket tomorrow. I'm thinking of just render if I can get the blanket smooth.