Treating Cardboard Mortars
One of the problems faced by pyrotechnicians is getting a reasonable life span out of their cardboard mortars. Myke Stanbridge documented this treatment which he claims will make cardboard tubes last 25 years or more. I'll report back in 2022 on whether it worked that well for me!
Perhaps the cheapest, easiest and most effective treatment for paper mortar tubes is the following:
- Clean out any debris, cobwebs, etc. Use PVA adhesive to stick down any 'flapping' edges.
- Rinse each tube internally with a strong solution of calcium chloride in water. Allow your tubes to stand until they are just damp. Calcium chloride is rather hygroscopic and will not dry past remaining damp.
- Using a 25% w/w solution of sodium silicate in water rinse each tube internally. Pour out the excess into your bucket and let the tubes dry open end up. There is a chemical reaction that produces tough insoluble calcium silicate in the structure of the paper. This hardens and binds the surface making it resistant to damage by abrasion and alkaline residues. When dried give the tube a fresh water rinse to remove residual sodium chloride produced in the reaction and let dry open end up in a warm location.
- Coat your tubes externally with a mixture of spirits of turpentine 1 part (pine spirit NOT mineral turps) and boiled linseed oil 3 parts. Add 15% lampblack to the mixture if you want black tubes. Leave the tubes to dry for about two weeks, open end up... Omit this step if the tubes are for immediate use or will form elements of a boxed mortar block...
Note: I'm still using tubes prepared like this around 25 years ago, and they still function perfectly! The method of treatment is very quick and cheap once you've got set up... You can treat a hundred tubes in an hour or so for around 10 cents per tube. Painting costs around a dollar per tube and is not as effective.