Treating Cotton To Withstand Water

Maybe you have recently asked yourself, "Hey! How do I make a piece of cotton fabric stand against the winter rains? Maybe even cover my -insert item-, so it is kept dry and clean." So here it is.

Things You'll Need
Waterproofing Spray

Instructions

1. • 1
     Clean the cotton fabric before applying the waterproofing spray. If you are going to apply the waterproofing spray to a cotton trench coat or overcoat, have it dry cleaned first.
   • 2
     Hang the coat outside in an open area or lay it flat on a clean table outside. Apply the spray in an even back and forth motion to fully cover the material. If the coat is laying on a table, make sure to allow the spray to dry on one side before turning it over to apply to the other side.
   • 3
     Reapply the waterproofing spray following the same steps as above once you find that the coat has begun to lose its ability to keep the water from seeping through.
     
     Quoted from eHow.com after scanning around for an easy solution. Second best is something awkward, like hardcore oldstyle ways, for example our friend StigOfTheDump shares:
     

     Horace Kepharts book Camping and Woodcraft contains a recipe as follows:
     
     Waterproofing Cloth at Home. — If one has 
     home facilities, there is no reason why he should not 
     make a good job of waterproofing for himself. 
     
     Paraffine Process. — The cheapest, simplest, and, in 
     some respects, the most satisfactory way is to get a cake 
     or two of paraffine or cerasine, lay the tent on a table 
     rub the outer side with the wax until it has a good coat- 
     ing evenly distributed, then iron the cloth with a medium- 
     hot flatiron, which melts the wax and runs it into every 
     pore of the cloth. The more closely woven the cloth, the 
     less wax and less total weight. 
     
     Some prefer to treat the tent with a solution of paraffine. 
     In this case, cut the wax into shavings so it will dis- 
     solve readily. Put 2 lbs. of the wax in 2 gallons of tur- 
     pentine (for a 7x9 tent or thereabouts). Place the ves- 
     sel in a tub of hot water until solution is completed. 
     Meantime set up the tent true and taut. Then paint it 
     with the hot solution, working rapidly, and using a stiff 
     brush. Do this on a sunny morning and let tent stand 
     until quite dry. The turpentine adds a certain elasticity 
     to the wax; benzine does not. 
     
     For tents to be used in cold weather before an 
     open fire, the following process is better: 
     
     Alum and Sugar of Lead. — First soak the tent over- 
     night in water to rid it of sizing, and hang up to dry. 
     Then get enough soft water to make the solutions (rain- 
     water is best; some city waters will do, others are too 
     hard). Have two tubs or wash-boilers big enough for 
     the purpose. In one, dissolve alum in hot soft water, 
     in the proportion of 34 Jt). to the gallon. In the other, 
     with the same amount of hot water, dissolve sugar of 
     lead (lead acetate — a poison) in the same proportion. 
     Let the solutions stand until clear; then add the sugar 
     of lead solution to the alum liquor. Let stand about four 
     hours, or until all the lead sulphate has precipitated. 
     Then pour off the clear liquor from the dregs into the 
     other tub, thoroughly work the tent in it with the hands 
     until every part is quite penetrated, and let soak over- 
     night. In the morning, rinse well, stretch, and hang up 
     to dry. 
     
     A closely woven cloth should be used. 
     
     This treatment fixes acetate of alumina in the fibers of 
     the cloth. The final rinsing is to cleanse the fabric from 
     the useless white powder of sulphate of lead that is de- 
     posited on it. Failures are usually due to using hard 
     water, or a less proportion of alum than here recom- 
     mended, or to not dissolving the chemicals separately and 
     decanting off the clear liquor. When directions are fol- 
     lowed, the cloth will be rain-proof and practically spark- 
     proof, but not damp-proof if you use it as a ground-sheet 
     to lie on, or if exposed to friction. After a good deal of 
     use, the tent will need treating over again, as the mineral 
     deposit gradually washes out. 
     
     Remember that cotton goods shrink considerably when 
     first soaked. 
     
     Alum and Soap. — Shave up about a pound of laundry 
     soap and dissolve it in 2 gallons of hot water. Soak the 
     cloth in it, dry out thoroughly, and then soak in an alum 
     solution as above, and dry again. 
     
     I have had no success with the alum and lime 
     method mentioned by " Nessmuk." 
     
     Good waterproofing compounds can be purchased 
     teady-made from some tent-makers. 
     
     The following recipes, although not suitable for 
     tents, are useful for other articles of equipment, and 
     are included here while on the subject of water- 
     proofing cloth: 
     
     Oiled Cloth. — For groupd-sheets to use under bedding: 
     get some of the best grade of boiled linseed oil of a 
     reputable paint dealer. One quart will cover five or six 
     square yards of heavy sheeting. Pour it into a pan big 
     ■enough to dip your hand into. Lay out the cloth and rub 
     the oil into it between your palms, using just enough oil 
     at a time to soak the cloth through, filling the pores, but 
     leaving no surplus. Then stretch it in a barn or garret, 
     or other dry shady place, for one week. Finish drying by 
     hanging in the sunlight three or four days, fi .st one side 
     up, then the other. 
     
     Apologies for wierd spelling mistakes as its taken from an OCR scan of the book that is free online and in the public domain here:
     http://openlibrary.org/works/OL49656..._and_woodcraft