Waterproofing my raincoat

I have a long thick lined cotton trench-coat that used to be waterproof at one time (Navy surplus), but 30 years later it isn't anymore and just soaks through.
It poured down yesterday, so the kids put on their wellies and I put on mine, and we went for a long walk through the woods. I need to re-waterproof my raincoat (Imagine a belted dark navy blue raincoat that schoolkids used to wear in the 50s & 60s).
I've seen sprays for wax type waterproofing and also silicon type. I don't want to end up with a waxed cotton type thing as it's a nice raincoat, but I don't know enough about these things to choose the right spray.
I know you lot will know.
Original Post
Before applying the Nikwax "Wash-in" waterproofing (if that's what you've bought) you need to wash the coat in either Nikwax's own washing soap or an equivalent. It's really important not to allow any contamination with detergent because it'll stop the wax from penetrating properly. And you'll get wet!
Originally posted by roger poll:
Ive used a Nik-wax product to reproof a Goretex jacket, and it worked a treat. Obtainable from from any good outdoor shop.

I thought Goretex was a membrane type of waterproof, and if so, if it leaks its due to the membrane having worn through. I suppose that reproofing the whole jacket might solve the problem, but is it still going to be breathable?

What happens with Gore-tex is that even of the membrane is intact, the water-repellancy of the fabric surface (which makes the water bead on the surface) fades with time so the surface gets saturated. This has two effects, one is that the wet surface no-longer breathes so you get damp with sweat, and two is that Goretex isn't totally impermeaable to water anyway, so if the fabric is saturated, some will sneak through. The Nik-Wax (an excellent product) restores the beading so the outer fabric stays dry and can breathe - although the Nik-Wax likely reduces the breathability a bit by blocking the micro-pores.

Nik-Wax is really good for non-Goretex stuff, too.

Washing, rinsing really, really, really well (detergent stops the beading - that's what it is designed to do) and then tumble drying (or even ironing) also helps restore the water repellancy that is important. The heat seems to do something But please check the care instructions on expensive garments.

The good news is that new nano-technology can now make fabrics that bead water due to structural nano-textures, not chemical coatings. These promise to be more durable w.r.t. to water repellancy. Watch for the absurdly priced products in an adventure store near you!
I don't think Ewan Eye's coat is Goretex. Nikwax works well on other fabrics but unlike Goretex you need to reproof it often - at least annually.

The best items of outdoor gear I've got are Paramo. They rely on regular Nikwax treatment for water repellance but they breath superbly and they don't have that rather stiff, clammy feel to them that Goretex stuff has. I've a Paramo waterproof fleece which is lovely and soft and yet when it rains the water instantly runs off its surface.
No my coat isn't Goretex, it's gabardine, which is the word I was searching for yesterday, but I'm learning lots from you guys, so don't stop. It's an old gabardine trench coat.
It's a bugger that I've got to wash it first, but I don't think it's ever been washed with detergent before, only dry-cleaned.
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