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moto127 10-01-2009 10:35 PM

fire clay
can a mix of fire clay ,sand, and portland cement be used in place of refractory cement for joints and flue assembly on a casa oven?????????????

nissanneill 10-02-2009 03:09 AM

Re: fire clay
my whole build was using a similar mix, 1 part fireclay, 1 part hydrated lime, 1 part Portland cement and 3 parts brickie sand. Two years down the track and not a crack anywhere even with plenty of very hot 500˚C cookups.
I would use this again and will for future builds. The refractory adhesives are expensive and many who have used them have reported cracking problems.
I have no doubt that they are good, possiblt too good and cracks are generated through the bricks and not along the mortar joints.
Wet your bricks well and keep your mix nice and workable and you should have no problems.
Check out my build for the finer details and hints.


dmun 10-02-2009 05:01 AM

Re: fire clay
Doesn't the Casa oven come with a bag of Refmix? I'd follow the instructions if it were me.

moto127 10-02-2009 06:33 AM

Re: fire clay
yes it does and i used it for the dome placement and seam. i do have another bag i bought extra i am just asking in case it is not enough for the vent and brick arch assembly. the fire clay i can get locally, and was told a mix of 1 part clay 2parts portland and 3 part sand would work also up to 2000degrees.

moto127 10-02-2009 06:35 AM

Re: fire clay
just another thought in the directions from fb it says you can coat the dome with refratory cement for a better heat retention would fire clay also help this???

dmun 10-02-2009 08:23 AM

Re: fire clay
Yes, the homebrew stuff will work fine. You can coat the dome, but why add mass? It's engineered for the exact right performance the way it's built.

moto127 10-02-2009 09:06 AM

Re: fire clay
that was a suggestion in the forno bravo directions for installation so i was just curious if it would be benificial

james 10-02-2009 10:51 AM

Re: fire clay
Hi Moto,

FB tries to say that the standard Casa oven is perfect for a majority of uses -- though a very serious bread baker can build up the thermal mass of the oven as an option. For a vast majority of users, the standard Casa oven is exactly what you want!

I will double check the text in the installation guide and see if I can tune it up a little to be more clear.


GianniFocaccia 10-02-2009 05:31 PM

Re: fire clay
I just read a post from earlier this year that caught my attention and alerted me that I may have just picked up a less-than acceptable HW refractory mortar from ANH. The earlier post from geisen said that the HW rep he talked to said that any refractory mortar used on a WFO must be hydraulically bonded, which is not water soluable, like the 50lb of Sairbond, I just picked up. I left a message for the HW rep who sold me the bag asking if they sold their hydraulically-bonded product Mortar 413. It's been a week and no call back.

Is the homebrew mortar hydraulically bonded, and if so, could it be the hydrated lime that makes it so? I'm thinking maybe I can just add some lime to the bag of Sairbond I purchased in the event I can't switch it out for the Mortar 413.


nissanneill 10-03-2009 02:37 AM

Re: fire clay

Is the homebrew mortar hydraulically bonded
I am not knowledgeable to answer your question on hydraulics, but these quotes might answer it for you.
Wikipedia states "Hydraulic limes set under water and Non-Hydraulic limes need air to carbonate and therefore set . Modern non hydraulic lime mortars are produced from lime derived from high calcium lime stones . These lime stones are burnt in kilns producing quick lime for other industrial uses other than building. Non-hydraulic lime mortar sets by reaction with atmospheric carbon dioxide (commonly called 'carbonation'). This is in contrast to the setting of Portland cement and hydraulic lime which sets by reaction with water in the mix.
Lime mortar is more porous than cement mortars, and it wicks any dampness in the wall to the surface where it evaporates. Thus any salt content in the water crystallises on the lime, damaging the lime and thus saving the masonry."
My 'poor mans mortar mix' has minimal portland because it cannot handle the heat put into an oven, the fireclay to make the mortar a lot 'stickier' and the lime to adds workability and time to the mix. Apart from that, lime mortars have been used for centuries without real problems.


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