DIY waterproof map- Give them the silicone rubber treatment

Making a waterproof map using DIY impregnation with diluted TRV silicone rubber.

Introduction to a DIY waterproof map

With bushwalking maps, it is nice to have them protected from water and mechanical damage for the duration of a trip. It is even better if the map can survive for more trips in the same area if it becomes a favourite.

Paper map lamination has been the standard protection method for many years, particularly for large formally printed and published maps. Now, with the wonderful developments of customized map printing, making a specialised map or series of maps for a walk is possible.

The map used as the example for this post came from a wonderful free downloadable series that was prepared by Martin for the 2022Federation walks. “Thanks to Martin.”

I have been exploring the varied uses of RTV silicone rubber for DIY backpacking gear for some time. Paper impregnation was just another application that I thought would make maps tough and water-resistant for bushwalking in wet weather. “It was time to put the idea into action”.

Making a DIY waterproof map

Preparing dilute silicone rubber. I dilute about 5g of clear acetic cure RTV silicone (sold as bathroom sealant) with about 15g of clean mineral turpentine or mineral spirits. The quantities are not critical, but the liquid must be thin enough so that it can penetrate throughout the paper fibres.

I have made lots of thinned silicone rubber for tent seam sealing and made the mistake of mixing the thick silicone rubber into the thin turpentine with what I thought was an ingenious micro-whipper-snipper thing for my Dremel tool.

While the wizzer worked a treat. I later discovered that such mixing introduces air and moisture into the silicone and quickly catalyses the polymerization of the silicone rubber and makes the thin liquid go ‘goopy’ and useless far too quickly.

Now, I use a small ziplock bag to do the mixing after squeezing out most of the air. I massage the outside of the sealed bag to mix the two components together. In a laboratory such a mixing process can aptly be called a stomacher.

The impregnation of the paper map. I start the impregnation of the map by laying it face down on a clean sheet of polyethylene (plastic bag material). The massaging of the impregnation liquid can be done over the map so any leakage will simply start the impregnation process.

When the liquid has an even consistency, I pour a portion of it onto the back of the map and use a brush or a flexible and tapered stainless steel artist spatula to squeegee and spread the liquid over and into the paper. The brushing or squeegeeing back and forth will make the liquid permeate through the paper so that it will come out on the printed side against the backing sheet. Here is a little video of the brushing process.

In this way, the paper becomes a silicone rubber composite. When the solvent evaporates, it will become a tough waterproof map that still behaves like normal paper.

The post impregnation clean-up. When I see that the liquid has permeated through to the printed side I wipe off the excess liquid from the paper and the backing sheet with a piece of shirt cotton. I use pieces of silicone impregnated cotton for many of my projects. Consequently, I make use of the cleaned-up silicone in this way and also use up the excess liquid from the mixing bag.

Field testing of the waterproof map

I took the map on a three-day return walk to the Wonnagatta Valley. It survived the usual folding and stuffing into a jacket pocket for the trip, river crossings and even a diversion of some hours of walking up a river while fishing. The weather (and fishing) was good and I failed to fall in on many possible occasions that were on offer. The waterproof map came home slightly ‘dog-eared’ but very intact and useable without the usual decaying fold lines. However, the map’s waterproofness was never put to the test. Consequently, when I got home I plunged the map into a wheelbarrow load of rainwater for its real baptism in water.

The next photo better indicates the strong water repellency of the map’s surface

Discussion and conclusion

For a first try, I was delighted with the simple silicone impregnation process and the way it turned paper into a very waterproof map that did not lose its strength when damp or wet. The map will be perfectly serviceable for more walks in that lovely area.

There was a little bit of smudging of the printing in some parts of the map that happened at the time of impregnation. From this, I learned that it is best to work the liquid through only from the unprinted side and have minimal contact with the other side until the map has dried.

Tim