Firebrick for a wet outdoor location rocket stove.

Have been lurking this site for quite some time and researching rocket stoves for extreme high temperature use. Most information found cautions against using commercial fire brick in moist locations. Being that I plan to install an outdoor rocket stove in South Louisiana (20 miles north of the Gulf of Mexico and 20 miles east of the Texas state line) - resistance to moisture is a must. Even covered areas get surprisingly wet with high winds coupled with heavy rains. The main use of this rocket stove will be to rapidly heat large amounts of water to boil crayfish (cooked properly they are delicious) - typically 5 gallons at a time and sometimes 10 gallons. Most crayfish boilers in this area use 100,000 BTUH propane burners that often require 45 minutes to heat the water, make a heck of a noise when they are in operation and require trips to town to refill the propane tank at the most inconvenient times. The crayfish are contained in a basket that is sized for the pot so the pot does not need to be removed while the rocket stove is operating.
I have access to perlite, vermiculite, commercial clays, commercial sands and local clays on my property. Long ago I noticed some fairly white colored clay on my property, but more commonly red clay is found.
So far my plan to is to cast the rocket stove core in modular pieces that can be easily assembled to allow for easy experimentation and build a 6" throat diameter core J-tube. Will then experiment with chimney height, etc.. to obtain the highest BTUH possible. Effective BTUH (British Thermal Units Hour) will be determined by timing how long a measured amount of water requires to come to a boil.
Is there any proven mixture of clay, sand, and perlite that could hold up to this extreme temperature? Any assistance would be greatly appreciated.

I know this is a rather old thread, but I'm wondering about firebricks and stoves outside in the rain (and how William got on with his project). People do build outdoor kitchens, so do you put a shelter over the stoves or make some sort of waterproof layer over the stove either removeable or permanent?
I'm thinking of building an outdoor forge my thread and am contemplating making a more multifunctional permanent arrangement, but am not sure of how the brick will stand up to my climate. At the very least I expect they will need careful drying before running the stove very hot. Does anyone have any experience or knowledge to share?

I'm about to find out the hard way. I've built a quick and dirty J-tube core in the paddock as a heat engine to drive a pyrolysis retort. It's partially torn down at the moment while I retrofit with some black pipe to convey the syngas from the retort into the burn tunnel. It's raining a lot this week and the whole contraption is pretty saturated, so when it comes time to test it again I'll be driving off a fair bit of water.

Other than the obvious potential damage due to explosion of trapped steam, I'm not sure what happens when firebricks get wet. Please let us know how you get on Phil!

Dense firebricks probably don't absorb all that much water compared to soft red brick (I could probably measure this by comparing dry and wet weight). So I'm banking on this to mitigate the potential for trapped pockets of superheated steam. It's outdoors and I plan to stand back during the initial stage of the burn.

Phil,

Dense firebricks have apparent porosity (closed pores not included) around 13-19%. Very dense 90% high alumina can be 18% counterintuitively.
For comparison I have measured porosity of two brick types I use for buildings - modern structural brick was 11% and hand-made terracota bricks 22%.
I would make sure that your outside stove is covered when it rains.

Ok, that's good info. I will do a small, low-intensity fire to start with and try to dry out the burn tunnel before I involve the retort, because that could make things really hot. The plan is to have a cover for the whole thing when I quit messing with the design, but at this stage I'm still knocking out bricks and putting them back into place.