Mortar specs for front arch - different to dome?

[jab49]

Perth, Willetton - should close the dome today and start on the outer arch that will support the chimney (but 6 weeks to get one to Perth from the US! )

Given that I'm using proper refractory cement - Silaset 40d, it's a heat setting mortar - should I modify this for the outer dome? It never really goes "hard", so will it ever, given that my efforts to insulate the front arch from the dome might end up being reasonably successful? yes, it will all get hot from radiated heat and even some heat leakage from the dome, but will this stuff ever set hard enough for long term purposes out there? Silaset doesn't mix up fluffy like portland cement and sand, so laying the first three side bricks might be a little weird too.
Any advice, faithful woodies?

Thanks
John

[jab49]

Re: Mortar specs for front arch - different to dome?

Maybe that question was too dumb? Anyway, I closed the dome and with some satisfaction, especially as I seem to be the only person in Perth who's building such a beast. Everyone here seems to build the simple barrel shaped kits available, and none of the local suppliers know what I'm talking about if I go outside the usual. Oh well, we press on, and hope the chimney kit arrives before summer. For those interested, a couple of pics of my keystone going in.

[Tscarborough]

Re: Mortar specs for front arch - different to dome?

As a rule, for any area without direct flame contact, normal Type S or N mortar should be fine depending upon the type of brick used for the outer arch.

[jab49]

Re: Mortar specs for front arch - different to dome?

Thanks Tscarborough. I'm using refractory bricks, like the ones I used in the dome, so I guess "type S" (structural) is the way to go.
One more quick question - how long after you set the keystone in the dome do you pull out any supporting formwork? I'm guessing even refractory mortar and the fact that it's a dome means you should be able to pull it out and have it self standing after a day or so. Any caveats here?

[Spinal]

Re: Mortar specs for front arch - different to dome?

I think the reason that you never got a response is that you're one of the few using proper heat setting mortar instead of homebrew

[jab49]

Re: Mortar specs for front arch - different to dome?

:-) Probably right, Spinal. Anyway, have answered my own question in relation to "how long to wait until pulling out the dome formwork- I just did that and wow! She ain't pretty in there but she didn't fall in! In a rustic kind of way, she is a beautiful thing! I'll have a job cleaning up and doing some pointing, but it's a big oven and I'll fit alright - you could fit a couple of large wombats in there! Sooo satisfying, I must say.

[Spinal]

Re: Mortar specs for front arch - different to dome?

Once you get a fire in there, she'll be the prettiest thing you've seen (just don't tell swmbo that I said that! )

[texman]

Re: Mortar specs for front arch - different to dome?

Hey from Texas. Nice job there John.
I used heat setting mortar as well (alsey) and have yet to fire it. Seems strong now but really gains strength when fired. Keep those pics coming.
Tracy

[Bacterium]

Re: Mortar specs for front arch - different to dome?

Hi JT,
on my first build (with just normal brickies mortar) I cleaned out the supporting sand cap after about 2hours...... by which time I had worked up the courage that it had enough holding - then it was a matter of climb in and clean up while it was still moist enough

....... although a local brickie mate reckons technically it should be self supporting.

[jab49]

Re: Mortar specs for front arch - different to dome?

Thanks all - I'll close this thread and start a new one when I get my chimney and start on the outer arch and vent support. For the record, I've pointed and cleaned up as best I can in there, with help of skinnier son to reach that back parts, and I'm really pleased with it. Nothing as clean and nice as most I've seen on this site, but pretty good for a bloke who's a clerk by trade.