I found a nice cheap, colourful, lightweight poncho today at a second-hand store but it's polyester and doesn't appear to be waterproof. Any suggestions about how best to make it so?

Liquid silicone. Any decent camping store, and even mass retailers like Canadian Tire and (I think) Wally World carry liquid silicone in small or large paint cans somewhere in the camping aisle. Give any fabric a coat or two and it's pretty tight. Repeat with a light coat for each subsequent season. (Avoid the spray-on equivalents, since you get 1/3 the mileage for the same price.)

But: (after dissing spray-on products), I can say that I've also had good luck with ScotchGuard, the 3M product. My experience is with the original formula, no longer in production; I used it on clothing, boots, and tents with good results. I can't give info on the current formulae, though it's from a solid company.

Hope this helps,
-Doug

Thanks Doug!! I appreciate it! Guess I'll HAVE to go to Canadian Tire again. Oh darn!

Make sure the product is suitable for polyester, as some things don't stick to it.

And there are these products from NIKWAX. On the right side of their site, use the 'Which product do I use?' resource, and two products will come up for polyester clothing.

Sue

Thanks Sue!! I don't want to ruin inthe process either. I'll check it out.

Waterproof with recoating sealer applied to the interior surface of the cloth. This is usually a thinner version of urethane based seam sealer. Paint/spray it on, and let dry. You can then seal the seams with the thicker stuff.

This makes the fabric waterproof but still allows the outer surface to get soaked, sag and cling. Which makes wearing it a miserable experience. To prevent this you want a water repellant. For everyday/job use I use spray silicone because it can be spot treated and touched up quickly and easily and after a few complete coatings the silicone saturates the fabric and can compete with the higher end stuff for durability.

Essentially you spray and let hang outside to dry. At the first sign of loss of repellency I touch up the high wear spots like the shoulders and tops of the arms.

There are other repellants. The best are termed DWR, Durable Water Repellants, and they can last for months of daily use and even some washing. But these treatments are more involved to apply initially, usually you need to wash to clean, rewash with special soap to prep the fabric, wash in or spray on the treatment and, usually, air dry, and then dry in a hot drier to activate it. Some types can't be spot recoated so you have to process and retreat the entire piece.

Hint: Follow the companies directions to the letter. Slight variations and shortcuts can cripple performance.

Thanks so much Art!

Slightly off topic but please don't ban me.

All this talk of coatings reminds me that I think we had a thread a while back with a video showing someone doing a do-it-yourself silnylon tarp. IIRC, they took the nylon fabric they had purchased, had the silicon waiting in a bucket, and slowly put the nylon into the bucket to be literally soaked in the silicon. He then pulled it out and hung it to dry. Perhaps a similar process may work with the polyester poncho, though the other suggestions from doug and art sound a whole lot simpler and easier. And I am wondering if the simpler processes might work to make your own silnylon as well.

So much research, so little time.

LOL @ Mark! It sounds like it might be a good idea. Maybe an experiment is in order. We could link it with the Scientific Method thread!

I'm in the bush with the Cub Scouts this weekend so have no time for it. I'm taking my good 'ol rain poncho with me instead.

CT has silicone waterproofing 25% off this week, remember to get the one for synthetic not canvas.