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Canvas impregnation with alum (tutorial)

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Forest Turtle:
This is traditional tutorial how to make canvas goods waterproof. It fits on everything with high content of cotton (or linen, I think). Tutorial wasn't invented by myself, it's traditional for Czechoslovak scouts, outdoorsmen of old etc. In contrast with modern impregnation sprays this is not protection  for only top surface of canvas but it's soaked through.  Waterproof effect lasts for  say, several rainy days (I mean rain dawn to nightfall), then you have to repeat impregnation process.

Basic brew is 3 litres, for tarps and big items is needed double brew (6 l or more). Please note, solution is a chemical, so keep safety principles. Open window during work, if you can.

For 3 l of solution is needed:

-   10g bicarbonate (baking soda is possible too)
-   21g alum (aluminium potassium sulphate ? I'm not chemist, is it right in English?)
-   350ml vinegar
-   2650ml hot water (not boiling)
-   Classic soap (for washing laundry, no parfum)
-   Rubber gloves
-   Old pot or bowl and large container for canvas soaking

1)   At first, get together bicarbonate with alum in old pot. Chemic reaction starts immediately. Carefully add an vinegar and wait until fizzing stops. Be really carefull and add vinegar in small brews.

2)   Then put the mixture into large container and pour hot water in it. Be aware of steam! Steam can cause chemical burns on your mucous membranes. Get rubber gloves and put dry canvas into solution. You have to really squeeze the canvas, until it's perfectly soaked.

3)   Remove canvas out of solution and squeeze (not wring!!) again to remove most of liquid from it.

4)   Make halfhearted soapy water and rinse canvas in it. Afterwards squeeze liquid off again.

5)   At last, rinse canvas in clear cold water. It removes remains of soap.

6)   Now, get canvas out and let it dry slowly.

7)   Now you have to well iron it, which increase waterproof effect.

If you were successfull, water makes pools and drops on your tarp! ;-)

I hope it was helpful and understandable. If you didn't understand anything, ask me. I'll try to explain.

Thank you very much Forest Turtle!  This looks like something I can do!   

Like I've mentioned before, I have had a canvas bag in mind to do this with.  If it works and I do it right, we have a bigger canvas cover for a boat I'd like to give this a try on.

I appreciate you taking the time to type this one out.



Very cool post.  Thanks for the info

If I can get all of the ingredients, I am going to try this.  Thanks!

That is neat how the water just beads up on the surface! Thanks for the post.


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