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Yahoo-Archive 03-20-2005 02:10 PM

fireclay mortar ratios
we are at the dome building stage and i wonder about the sand/cement/fireclay mix you suggest.
you seem to use quite a bit more cement and fire-clay to sand ratio than allan scott suggest. is this necessary for a better placidity while building the free standing dome??
i just want to make sure that more cement is better than less, since more cement will also cause likely more cracks......
anyhow, i am very excited about the progress we are making.

thanks for your suggestions and help


Yahoo-Archive 03-20-2005 02:11 PM

I used 10:3:1.5 sand/Portland/fireclay. I believe this is the same as
Alan uses. It's fairly similar to the composition of firebricks so it
has pretty much the same thermal properties (in terms of expansion, etc.).

One suggestion is to remember to dip each brick in water before
mortaring it. I took 4 of them and dropped them one by one into a
bucket of water and then just took them out as I mortared each into
place. The mortar sticks a little better, the bricks won't pull as
much water out of the mortar, and it helps slow the curing a bit (slow
curing is better than rapid curing in terms of ultimate strength).


Yahoo-Archive 03-20-2005 02:12 PM

thanks jim!
i was just getting confused, since the pompeii write- up suggests a mix of 8:3:2.
would it matter one way or the other?


Yahoo-Archive 03-20-2005 02:13 PM

It's not an exact science. The 10:3:1.5 mix very closely mimics the
thermal properties of the firebrick. Variations may make it stickier
(more fireclay will do that) but will react differently to heat than
the brick.

This isn't nearly as big an issue with the Pompeii design as it is
with Alan's as the joints are unexposed to the interior (no spalling
or flaking mortar falling into the food) and there aren't the places
where there are huge gobs of it (like the front of the vault on Alan's
where the bricks lean into the lintel).

A stickier mix makes it easier to mortar and to be honest, I tend to
add extra sand/Portland/fireclay at about a 2:1:1 ratio when I need to
make up for too much water in the mix.


ricocamus 04-14-2008 12:19 AM

Re: fireclay mortar ratios
Has anyone tried using just Portland Cement and sand for their oven? My final problem to doing this oven is finding refractory mortar. Neither can I get any fireclay to mix up with lime to do the "homemade" refractory mortar. I am going to go with clay bricks (since I can't get any fireclay bricks) but I am stuck (pun completely intended) at finding the mortar. Any tips?

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