How do I waterproofing a tent

IMHO, it's a loosing battle– take it back. If the fly smells bad or the coating on the inside of the fly is sticky or cloudy, get rid of it. If not, it may be that the fly was never seam sealed. You can also buy sprays like Gear Proof to treat the outside surface. All the sealers will cost you more than the tent.

I assume that you really want a family tent that large.

First of all, you want to establish where the leak actually is. If the leak is in one seam, then a fraction of a tube of silicone seam sealer should fix it up. On the other hand, if there are multiple leaks from all over, then trying to seal it might become a lost battle.

I have one camp tent that I purchased about twenty years ago, and I had sealed the seams when it was new. Then recently it was out in a rainstorm and a little rain came in. Upon investigation, I discovered that I had originally sealed about 97% of the seams, but I had skipped one near the top of the rain fly. About a third of a tube of silicone sealer and then some DWR spray fixed it up.

–B.G.–

Ive never done this, but I've read nothing but success. This will also work for Silnylon, this is assuming you're needing to recoat whole surface.

http://dzjow.com/2011/04/11/applying-a-new-silicone-coating-to-the-tarp/

As for just a seam, I'd recommend using masking tape to the sides of seam to have a "clean finish". Just like paint, after applying thin coat, remove tape within a few minutes so that it doesn't harden and pull chunks of finished work afterwards.

I think they assume the bigger tents for car camping are going to be used when it doesn't rain. Most of them I assume are only 500mm – almost not even water resistant – based on the few that I've been able to find such specs for. Most backpacking tents are rated around 1300-1500 or so – my Lightheart tent is about 1300 and withstood pouring rain for an hour and a half without a leak. Consequently, when I was given a six person big enough to park my car in, I treated the fly with silicon spray and crossed my fingers. The floor is completely porous and water will come up through it in no time. The sides don't even feel like they have any PU on them. So if there is no "barf" smell or peeling PU coating, and it doesn't feel like the inside has any treatment at all (should feel plasticy and have taped seams if it's PU coated) it might be possible to get a bunch of cans of silicon spray and have at it.

Jack you are in CA, just throw a tarp over the top for when it does actually rain. How much time and effort do you want to add to your $14 purchase that it doesn't sound like you needed anyway? Re-donate

Sorry for the miss spelling of the original title.

The reason I posted this was to try and find a cheap and easy way to re-waterproof it.
I most likely will give it to a nice family I know that doesn't have a tent this size to accomidate all of them, and they can't afford one of the new ones for $300.00-$500.00 so I thought if I could re-coat it for a reasonal price no great loss on my part.

The tent is not delaminating, has a faint smell but not that bad, and I have a sensitive nose, most of the leakage looks to be coming from the side walls, not the rain fly, almost like it is misting through, there are little beadlets of water on the inside.

Thanks for all the feed back everyone, Jack

Well, you didn't say the material, not that it really matters. Ripstop silnylon can be re-coated with mineral spirits/silicone caulk. Roughly, the ratio is about a quarter to one sixth tube of caulk to one quart of solvent(~15-20:1, lighter for ripstop that has been coated, heavier for plain nylon.) It will usually seal seams, but use two coats, inside and outside.

Use a GOOD grade of caulk, 100% pure silicone, clear. GE is often cited as the best but I had good results with other brands, too. It should add about .2-.4oz/yd…that is thin. Otherwise it can form a coating that will peel rather than saturate the fabric.

Use a GOOD grade of mineral spirits, no eco-friendly products and no cheaper grades of mineral spirits that can contain kerosene. You need the mineral spirits to evaporate *before* the caulk sets. Kerosene does not do this. KleenStrip is a good brand. If the temp is below 60F(15C) use white gas(Coleman Fuel) instead of mineral spirits. You want it to evaporate quickly, but not so fast it sticks to the brush or leaves a sticky coating between brush strokes. Mix in a little more mineral spirits.

Use two brushes if you are doing the whole tent. Usually only the fly and sidewalls will need it, ie, those areas that are exposed to rain. Use a 1/2" foam hobby brush to do all the seams on the inside, first. Then a 4" bristle brush that holds a lot of mineral spirits. If the floor needs it, do this first. Then do the outside. 24 hours later (and likely a new batch of ms/caulk,) do the other side of the floor if it doesn't already have a PU coating. If the coating is thin enough it will require about 3 days to cure fully. It doesn't matter if it gets rained on after 24 hours (it uses the water to cure) but it should be dry when you touch it (often within 3-5 hours.) Some guys use a light dusting of unscented talc to break any stickiness, but this means you likely coated things too heavily. Shine in areas usually indicates too thick of a mix and can stick. After a few days, you can break the tent down and roll it up, do this a few times (once per day) to make sure nothing sticks. Once you get a little use on it or dust, it will be fine.

You cannot save any extra. It will harden right in the bucket after a few days forming a jelly like glop. The brush will be ruined for anything else, even if you clean it out with mineral spirits a few times. Silicone will react badly with varnish/oil based finishes if you happen to use it for this. (Spray lubricants containing silicone used on your table saw and other tools will also do that.) The foam brush will be ruined. Plan on that.

I've done a bunch of tarps and tents like this, including a couple large 12×18 and 10×16 family tents for car camping. It really helped them in rain storms as they got older. (One from BassPro leaked out of the box.)

"Misting" on the inside may not be a leak, it my just be condensation.

I too scored a big friggen tent from a thrift store a couple years back. It is a Coleman 3 room monster. It was $13. There was one broken pole. A simple $6 kit from Wally Mart fixed it right up. Now I am trained to go right back to that spot in the store to see if there are any other goodies.

They didn't use silnylon in 1976. They don't use silnylon in huge car camp tents now. So silicone caulk won't stick well to urethane coated nylon.

The side walls are probably uncoated DWR. You could try DWR spray on them.

Get a big cheap plastic blue tarp (or other color) and set it over your tent and out front to make an awning for sun and rain protection.

Thanks everyone, I donated the tent to a friend that has kids and won't use it in bad weather, more for his kids to play in at home, instant fort!