How to waterproof canvas

This is not so much a post about cooking or gardening, as it is about our preparations for a large event we sell at every year called Pennsic.  Every year, we and 10-20 thousand other crazy people who are members of the Society for Creative Anachronism (SCA), descend on the town of Butler PA and specifically a campground called Coopers Lake for a 2 week camping event. It’s the dirty middle ages lite for most of us. Yes, it’s camping, but there’s hot showers and ice cream. How can you go wrong there?

Last year, after a couple of false starts with a group we were (ahem) supposed to be camping with, we ended up at the merchant booth with a new to us canvas marquee tent top, purchased from the neighbors into the space in back of the booth, and borrowed sides and poles, courtesy of the nice neighbors who actually *gasp* wanted us and all four kids to be there. It worked and it was recovery from the two false camping starts we’d had. It was a better solution than being out in a camp anyway, and what I’d wanted to do for several years, but das husband’s booth was just too small. We even had space to put up our cook tent and a laundry line. There was a water hookup. There was an electrical hookup. Like manna in the desert! And, if you are reading this wondering what he does, go here for a look.

This spring, we’d been talking about getting new tent sides, but das husband says “I think I junked some last year…lemme go find them.” They turned up about two weeks ago (we’re leaving for the event on 7/19). They were so mildewey, dirty & smelly that I spent a week washing and drying them in the sun – I honestly think they went thru the washer about 7-8 times each. But, then thinks us; Um…what about water proofing? Well, to be fair, we couldn’t have used them as is – they were just too far gone. So I did some research & here’s what I came up with.

Aluminum sulfate (get it at your local garden store)
Plus washing soda (available in the laundry section at the grocery or orderable from your hardware)
Plus soap
Plus fabric=
Aluminum Sterate, a water repellant

Here’s how it works:
Take some hot water, enough to cover your fabric and stir in a 1-10 mixture of Aluminum Sulfate (I went with 1 lb. per 10 gallons of water) – mix the water and the sulfate first.


You will need to stir to disolve the solids before you add the fabric.  But, once you’ve done, put it right in!


After saturation, pull your cloth out (alternatively, do this in the tub and simply drain it…I got smart after I burnt my fingers heating water on the grill…)


OUCH!!!  (Don’t touch the lid without a hot-pot holder!!!)

Grind up your soap in a food processor – you need a good fat content here, because the fat in the soap is what’s going to convert into the sterate – I used a home-made Crisco soap. Again, it’s a 1-10 for both the washing soda and the soap. I ground up two bars of soap and added 2 cups of washing soda.


Mix and add your fabric back in.


Looks like this, kinda yellow…


Pull your fabric out.


The liquid will look cloudy with a solid in suspension; should look like this.



Mine got rained on, so you could put a rinse in there if you wanted to and still have it work, but it doesn’t require it.

I’m also “setting” the sterate in the dryer.  I read on one of these articles that ironing helped the process to become more waterproof and am thinking that it’s the heat, so am taking all of my stuff and tossing it in the dryer after it’s dry just for the “set” of it all.  🙂

When it’s done, water initially beads on the fabric, then sheets, allowing the inside to stay dry, though the fabric will appear wet.

Please note: This worked really well on the canvas, and the tighter the weave was, the better it worked. It did NOT work so well on the upholstery fabric we tried next. That said, it didn’t work badly on that either. Now, I’m working on a smaller tent we’re going to rob for its sides!

About catfeet1

Mom, canner, reader, sci-fi geek, she who loves car seats
This entry was posted in Household, Prepping and tagged , , , , , , , , , , , , , , . Bookmark the permalink.

3 Responses to How to waterproof canvas

  1. Dee Dee Barton says:

    I don’t know what the “Crisco soap” is… what else can I use that I can buy? Thank you.

  2. Na Na says:

    How very frugal. Cool.

    • catfeet1 says:

      And, WAY cost effective for large projects like this. I spent $13 on the aluminum sulfate; in the past, at this event, I’ve spent up to $50 on spray cans of “waterproofer” that didn’t actually, y’know, waterproof… Between the natural water shedding ability of canvas and this water repellent, it should do the trick.

Tell me what you think!

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s