Bought this 10" cardboard Quik-Tube building form to use as the inner form for pouring Kastolite 30 refractory mix in the keg foundry.
About 1/8" wall non-corrugated cardboard w/ what appears to be a thin paper covering outer. This refractory mix will not be as wet as mortar mix but still wet enough to act on the cardboard form. Being thin wall cardboard it will need 3-5 spars on the inside to prevent deformation, it will likely go egg shaped w/o, so spars are a must.
First thought was fiberglass resin which may add structural rigidity as well.
Google says Rustoleum Never-Wet. Enamel paint may work as well.
Contact paper w/ no seams
HVAC foil tape w/ seams
What else may work?
Although a 5 gallon plastic bucket could fit the bill (and be waterproof) I'd rather use this form if possible for consistent diameter.
TIA
Just spitballing an idea— fill the tube with concrete first, pour your refractory, and then burn the cardboard out, releasing the concrete plug?
Those things are made to stay pretty round in response to pressure from the inside.
Grab your roll of cling wrap from the kitchen.
Karacticus said:
Just spitballing an idea— fill the tube with concrete first, pour your refractory, and then burn the cardboard out, releasing the concrete plug?
Those things are made to stay pretty round in response to pressure from the inside.
Don't need concrete, sand would probably work just as well and be easier to deal with.
So if I understand correctly you're using the tube as the void in the center and pouring the outside between the tube and the keg wall?
I'd brace the inside and coat the outside heavily with a spray waterproofed for outdoor gear, like Kiwi Camp Dry or something similar. Several coats are probably a good idea. Those use silicone based formulations that will soak into the cardboard and keep the water out. It should also act as a mold release. The liquid rubber would also work well but might be a problem to get out. Burning it would suck.
buy a big block of beeswax and wax the tube.
here is what I would do. As these things are not as smooth as you think. Coat with bondo and sand smooth, fairing as necessary to get it super smooth. Fill with sand as Keith mentioned, tamping it down nicely to get it packed nicely. Then pour your Kastolite around as needed. Once it is all hardened up, you can pull the tube, dump the sand, and have minimal clean up for a smooth refractory with little to no faults.
Good idears guys, the tube form is 48" so I could test several coatings vs water.
Gonna cut cardboard discs on a circle gasket cutter for reinforcing the inside of the form to hold the diameter top to bottom. Gasket punch center of discs for 3/4" pipe to hold on center of keg. Hot glue gun discs inside.
Sand is good idea but I'll most likely have to weight from the top w/ the cardboard discs installed, barbell weights probably.
These gasket cutters are very accurate, been using them for decades. Cardboard should be no problem and crank 'em out in short order.
5 gallon plastic bucket should be the easy button, waterproof, even has draft. 10-1/4" at bottom to 11-1/2" top but still a struggle to remove, usually has to be cut out. Cardboard form will need cut out too but much easier than plastic.
Robbie said:
'Secretly' Grab your 'wifes' roll of cling wrap from the kitchen.
Forgiveness is easier than permission. 
If you use sand, you won't need the cardboard reinforcements. Just fill the tube. Done.
I like the saran wrap idea for waterproofing. It's not like you're building a dock with this form, just keeping the wet material from dissolving it for a short period.
