Useful tube for DIY mortar?

[stix]

An update on my efforts: I let it settle for about a day then gave it a good flush with water, then let dry out for another 2 days. There was still a bit of white loose powdered material (sodium chloride, if all worked properly), so I gently cleaned it out with steel wool, and then a final wipe with a damp cloth.

 

The final surface seems a lot harder than before coating. One thing that I wonder about is this statement in the original text (post #12):

 

 

... This hardens and binds the surface making it resistant to damage by abrasion and alkaline residues...

 

Nothing about making it more resistance to fire? - which is the reason I ever took note of this method and only "assumed" the fire retardant properties - but surely it is.

 

The other thing I was thinking is to leave the 1mm layer of shrink wrap on there - it may help with strength. Then I got to even more thinking - what about placing the tube in the oven?. The plastic will shrink tightly around the tube adding strength - or it could completely screw up my careful hours of work!!

 

Probably best to leave it as is. Overall it looks like it has worked. There is lots of experimenting that could be done regarding timing, ie. how long to leave it after the calcium chloride stage to ensure that it's soaked into the cardboard, then how long for the sodium silicate solution.

 

The only test that counts will be to actually use it for it's intended purpose! That is to launch small 1 3/4" (45mm) can shells which will be better than what I've achieved to this point. Satisfying enough for me though .

 

Cheers.

[Col]

Calcium silicate melts at 1540 deg C

[stix]

Calcium silicate melts at 1540 deg C

 

Thanks for the info Col, from what I remember 1540C should be more than adequate to deal with short bursts of heat.

 

I'm happy that I finally got around to trying it (thanks to deer). I had the materials, the written instructions and the time - it didn't cost me anything except for the materials which I already had at hand. Sometimes it's not about cost - doing it for yourself is an accomplishment worth more than just buying something - this was one of those for me.

[Mumbles]

With cardboard, it's the residues that tend to kill the mortars before the heat. I assume it will enhance the thermal properties too though. Glad to see someone actually try this with success. Myke Stanbridge is quite knowledgable, but it's always good to see it put into practical use.

 

Please keep us updated after the mortars get some use. It'd be nice to know how these babies are holding up down the line.

[rsambo]

Hopefully this may be of some use to you. I put a lot of effort in trying to replicate this method. I have done this now for around 50 tubes ranging from 2 inch to 5 inch. I had a lot of issues with a successful process but I can now get this to work fairly successfully. However, it's actually no better than my preferred method which works surprisingly well which I'll mention briefly at the end. For larger tubes 4 inch and above it's just not really practical or cost effective but for the smaller tubes does work. The biggest issue I had was using tubes wrapped with a plastic coating, if you do this they don't dry out well at all. After a few days they will look dry but the calcium chloride will continue to leach to the surface for many months which causes a problem with overcoating the outside of the tube - basically if you use genuine turps / boiled linseed oil mix it will just flake off continually. The sodium silicate also tends to seal in a lot of the moisture - again causing problems with drying and the ends around the plugs often go spongey if you don't dry them quickly enough. Also, if you get the tubes too wet they shrink on drying and you end up with a tube slightly narrower in diameter by the time you have applied your layer of silicate and then that can be an issue getting your shells to fit.

 

I spent several months faffing around and in the end i just settled on solvent based polyurethane substantially thinned with acetone by about 4:1, it's cheap, it soaks right into the tubes and seals all of the layers of the paper together, including binding in the polythene wrap. I also add some lampblack which seems to help make them even more resilient and they dry looking really nice. It's withstands the heat of shells and mines easily and is completely waterproof - some of my mortars treated this way have been fired 30 times +, I now use this method for all my cakes which use cardboard tubes - having moved away from the sodium silicate method.

 

I agree, it's all about the experimentation...

[FlaMtnBkr]

I guess I didn't make it real clear in my first post and used the wrong word probably do to my phone, but I treated a couple tubes this way quite a few years ago that have been used a bunch and are holding up well. Lots of black residue but haven't burnt or gotten soggy or torn apart and they are around ten years old.

 

It wasn't the best process but does seem to hold up well. Something that seems to work almost as well but might not be easy to apply or real economical for bigger 3"+ tubes, is wood glue. It leaves a durable coating that has held up well and also seems water proof enough and will seal the ends and glue down any flaps of loose paper as well as glue and seal the plug, along with screws. It's not too expensive in gallon jugs but not sure how easy it would be to apply to the bigger tubes or how many tubes you could coat but it might be worth trying for anyone thinking about doing this. I don't remember the process very well but the tubes are holding up.