arch trouble - help!

[timmarhy]

This is attempt number 2 with the dome. inistally on this attempt my key stone wgded itself in before it got all the way in so i cut another piece and fitted it in below where you see a gap in this one.
questions are
1. how much mortor should i be using? this refactory stuff dries almost on contact and is impossible to work with
2. is there a prefered method for taking out the supports for the form? i'd hate to think i put all this effort in to ruin it just but taking out the supports.
http://i43.tinypic.com/501heq.jpg

[timmarhy]

Re: arch trouble - help!

sorry for the double post - my arch is standing on it's own as of this morning and arch number 2 is drying.

[egalecki]

Re: arch trouble - help!

I don't know what mortar you're using, and probably wouldn't be able to help with that anyway, since the AU stuff doesn't seem to correllate well with US products, but I think your arch is too flat. I would think you need more, well, arch to it. You're asking the bricks to hold themselves up by squashing them side to side, not by wedging them in an arch. The forces are not working right- if you look at the right side, it looks like some of the bricks want to fall downward, and since they're all nearly vertical, nothing's stopping them.

When I built my arch I left the form in for a week just to be sure it was dry and set.

Also, I know that the barrel vault is a tried and true oven, but your arch troubles are why I chose the round kind. It just seemed like something I could make stand up more easily...

[timmarhy]

Re: arch trouble - help!

oh the irony. my inital arch was a high dome, and it caved in on me. the barrel vault you see pictured is now complete and has been holding for 2 days now. i pulled the form out after only 8 hours and it's held perfectly without even a crack in the mortor.
i suspect my issues were 2 fold - the refactory mortor i was using needed to be cut with 1 part normal cement to make it useable by mortals, the stuff is rated to about 2000c so i suspect diluting it won't make much difference at the 500c i'm aiming for.
the 2nd issue was how i pull out the supports - I needed more of a drop in the form so it was totally clear when i tried to remove it.
anyway live and learn i guess - will post pictures once it's compelte.

[Neil2]

Re: arch trouble - help!

That is a nice arch. If you can do one that flat on your first project you should be promoted to laborer at least !

As Elizabeth notes, you need lots of side buttressing with a flat arch.

Also, if you soak the bricks in water and then let them drain out the mortar will not dry out on contact so much.

[timmarhy]

Re: arch trouble - help!

yeah that's a nice tip with the bricks, i read that one the night after i finished

[egalecki]

Re: arch trouble - help!

Oh, and another thing with the form- if you use shims under it to get it to the right height, then you can pull them out and the form comes out easier.

[timmarhy]

Re: arch trouble - help!

update - had a party last night and fired the oven up to full temperature and it held together and is still standing this morning.
i've got some minor cracking in the mortor but i guess this is normal? nothing is breaking away or dropping and i think the cracks are only on the surface.
what advice can you give on measuring temp in the oven? the thermometer i got isn't accurate at all.

[Neil2]

Re: arch trouble - help!

I bought the infrared one from Forno Bravo.

Infrared Thermometer :: Pizza Oven Accessories :: Forno Bravo Store

It works well.