I have a Winter Gear, Quasar, (1986) two man snow tent made in Wales (company change to Wild Country, now Terra Nova) that I only used for cross country skiing.
It didn't get a great deal of use. I have since removed the snow valance and seam tape from fly, and sealed the seams with aqua-seal which is bullet proof.
However, after testing with a hose the tent was still leaking and the roof fabric was holding moisture. On inspection, the PU coating was still in good condition and was not tacky. So I decided to reproof the fly sheet outer using dissolved silicon, I got advice from Franco and Moondog55 on the technique.
This is the method I used:
1) I washed the fly sheet with pure soap in the bath twice and then rinsed well, let dry.
2) The tent was setup in my garage on a plastic drop sheet, and guy lines were removed. (out of the wind and direct sun)
3) I Used sika 330ml pool sealant ($17 Bunnings) and
3) Dissolved the silicon with normal Turpentine.
4) A ratio of 15:1 solvent to silicon ( by weight?) was used.
5) Use digital scales tare a suitable container (I used a plastic Tupperware style container) weigh out 30 grams of silicon into the container.
6) Tare a second container and weight 450 grams of turpentine (30 x 15 = 450).
7) Add a small amount of the turpentine to the silicon and stir with a paddle pop stick. Then using a small paint stirrer ($6 at Bunnings) in a cordless drill mix for about 10 min until the silicon is dissolved completely.
I used a 100mm brush and started painting the tent bag first, then start on the roof and sides, paint briskly and make sure you cover fully, minimise runs.
9) Depending on the temperature it should be ready to re-coat after a hour.
Coat Two
10) Place container with remaining mix from first coat on scales and tare. Add 30 grams of silicon to container, place second container on scales weigh out 450 grams of turpentine. Then mix as number (7).
11) Apply second coat as above. "You May find Two coats is sufficient",
However, I put on a 3rd coat; but found the cloth was full and this caused the the solution to run down the tent as I was painting.
If you require a 3rd coat just make sure the brush is not loaded with too much silicon.
As my first two coats went on so well I was a bit slap harry with the third, hence a few run marks. But to be honest It looks fine and I am very pleased with the result. I have another tent I bought at the same time (1986) and will also re-seal using this method in the future.
When I did my 3rd coat I had fair bit of mix left from the second, so as described in 10) i only put 20 grams of silicon to 300 grams of turpentine (20 x 15=300).
While the tent is drying make sure flaps don't stick to each other. I used bull dog clips and string to separate guy flaps from tent. The curing times given on the silicon tube say 4 days plus.
The total amount of Silicon used was 30 + 30 + 20 = 80 grams and about 1.5 lt Turpentine.