Ditto on a gallon of Thompson's, apply to both sides and let hang in a garage on clothsline with clothes pin.
Make sure you coat both sides, but do a small corner or older similar map first, let it dry and test with some water, before using it on the good maps. It will not completely waterproof them, but will make them extremely water resistant.
I honest;y beleive that nothing will really truly protect your map if it is not tyvek, when using all day long on a wet rainy day, folding and unfolding it, unless you either:
- use 2-gallon freezer bags and fold your map so that you can maximize looking at both sides of the map before you have to open and refold.
- Use think of one of the larger heavy duty map cases that kayakers use and just roll it up and keep it in your jacket.
FWIW, Walmart now sells 2-5 gallon ziplock bags - I beleive a whole map folded in half is veiwable through the bag. I saw them about a month ago over in the camping section.
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This courtesy of Gorp.com
http://gorp.away.com/gorp/publishers/ics/cam_rtes.htm
"....Finally, waterproof your maps with a chemical preparation. I've had good luck with"Storm proof," (write the Martensen Co., P.O. Box 261, Williamsburg, VA 23185), and "Thompson's Water Seal"-an industrial strength compound that's used for sealing concrete block. You'll find Thompson's Water Seal on the shelves of most hardware stores in aerosol cans and tins. I buy it by the quart and apply it to maps and journals with a polyurethane foam varnish brush. The product also does a fine job of waterproofing hats and clothing. Water-resistant maps should be further protected by sealing them inside a plastic map case. "
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