Inside waterproof coating of backpack has become sticky

Question

I have a 50-liter backpack which I used very little and that afterwards was kept stored for more than 10 years.

Today I noticed that some parts inside, I think the waterproof coating, has become sticky. This is apparently a common problem (read here and here) due to the breaking down of the urethane coating.

What one can do to remove the stickiness? From what I've read, one should avoid machine washing, and some people solved the problem by rubbing the inside with talc powder. Are there any other solutions?

EDIT: similar question: What is this brown dust/powder inside my old pack? However, in my case the coating looks perfect and is not delaminating; it's just sticky at the touch.

Answer 1

Solution: Use Ethyl / Denatured Alcohol to dissolve it off. I've used this solution on two bags now and it had worked amazingly.

Bag 1 - Thermarest stuff sack: It was so sticky I had to peel it apart. I turned the bag inside out and put it in a jar with rubbing alcohol 91%, let it soak for about 24hrs then pulled it out of the jar & used a scrub brush on the sticky part. The old coating either went into solution or balled up and came off.

After a second soak/scrub, I threw it in the wash on hot/quick with laundry powder to help wash away the rest of the solution. After it air died, it was completely tack & odor-free.

Bag 2 - older Dana Design pack: A larger (60L) pack with many facets, with the same issue. First, I took off as many of the straps, foam & stiffeners as I could. I put it in a trash bag, then put that in a bin of water. This way, when I poured Denatured Alcohol into the trash bag with my pack inside, the pack would get soaked/saturated without needing 3 gallons of alcohol. The snap lid of the bin also helped hold the pack down, preventing it from floating on the surface of the water.

After it'd soaked for 24hrs, I put on rubber gloves & pulled the bag out for agitation. I used the lid of my bin as a tray outside, to capture as much of the alcohol as possible, so I could pour it back in the trash bag for round 2. I scrubbed the pieces of fabric against each other or used a stiff brush. When I was satisfied, I hosed it off, threw it in the wash & air died. It's completely tack free.

I opted for the denatured over rubbing alcohol because it's mostly ethanol (renewable). As a solvent they worked about the same. I didn't try diluting them. Hope this helps!

Answer 2

I had this problem with a favorite fanny pack (L.L. Bean) a few years ago. I turned the pack inside out and used a stiff brush on it to get it all out. I even tried a wire brush for tough spots. But, you have to be careful not to damage the pack itself. As a result, I now try to find/buy packs that don't have this coating. There are some with a plastic liner. Or, I get an unlined pack and use zip-lock bags or plastic containers. Using the bags and containers actually keeps things more organized.

Answer 3

I have temporarily solved the problem by rubbing the sticky part with talc. But this protection leaves a bit of talc around, and must be repeated every few days. Luckily I don't use the backpack for long trips.

This is far from being the best solution, but at least allows me to use the backpack (I don't want to throw it away).

Answer 4

I had a Deuter bagpack which had similar problem. I kept the bag in hot sun (covered in old cloth so that no fading happens) for few days and then washed it with detergent with a nice scrub on the sticky parts. Now its like new...

Answer 5

I have had this problem with several packs. One solution that has worked for me is to spray the insides with VALSPAR Premium Finish-Satin (in a very well ventilated area).

Answer 6

I had this same issue with a twenty-year-old CamelBak which hadn’t seen heavy outdoor use. I guess the coating just ages out over time and becomes sticky. I tried scrubbing it out with an old toothbrush, and then noticed that the silicone portion of the bristles was doing most of the work. Turned it around to use the mostly silicone toothbrush handle, and the sticky stuff started coming off in rolls. (I expect a silicone barbecue glove would have made this go even faster.) I was able to get most of it off and vacuumed out of the bag interior, but the surface if the fabric was still slightly tacky to the touch. I found that a 70% isopropyl alcohol pad (first-aid type) was able to remove the last of the tackiness. I tried using 100% ethanol and it seemed to smear the sticky stuff around.

Answer 7

I had this issue with the rubberized interior coating of my backpack, which was deteriorating and flaking. So I sprayed the interior with Dupli-Color Vinal & Fabric coating (bought at an auto parts store). Worked great!

Answer 8

I have had the problem on a Gregory Baltoro 65L. Lots of peeling. I did not use any solvents but I used a sponge I had bought at grocery store, can't remember names but they were light green, one side typical sponge other side was covered with small tiny nubs not abrasive or scratchy but removed the peeling stuff easily.

Answer 9

Sticky Coating
Yes, it's indeed a problem with the waterproofing. There are two main causes:

1. Bad storage
   Any outdoor gear must be bone dry before you store it. It also needs to be stored in a dark, dry, and ventilated place. If a tent, never store it in its stuff sack, instead use a dirty laundry mesh bag (for a small tent) or if a bigger tent, jacket, backpack, use a giant mesh bag for corn, beans, etc. You can get those free at your local grocery (pictures at the bottom). However, the best for a backpack is to hang it just like that.

2. Deterioration
   No matter what, the waterproofing coating (inside), and the exterior DWR will deteriorate over the years (DWR has a much faster deterioration rate)

DWR is NOT waterproofing
Many have that wrong, including several magazines... DWR stands for Durable Water Repellant. As you can see, it's Repellant and not Waterproofing. DWR is increasing the “contact angle” or “surface tension” created when water touches a textile. DWR will make water pearl and slide off instead of sticking to your gear/jacket. DWR is to be applied outside, and waterproofing on the inside.

Waterproofing
The most common waterproof coatings used in tents and backpack are: polyester urethane (PU), polyether urethane (PE), and silicone, and combinations thereof. You can read a very good article about that to help you choose between PU, PE, and silicone to re-waterproof your backpack: https://www.slingfin.com/blogs/the-beta/fabric-coatings-101-pu-vs-pe-vs-silicone

Step-by-step process for your backpack
a) Remove the old coating by using a sponge (or a rag) and rubbing alcohol
b) You need to make sure your backpack is 100% clean. So wash it but do NOT use any laundry detergent or anything like that because it will leave residues and the coating won't "stick" properly. There are three main products for that: Tech Wash (from Nikwax) and Tent+Gear Cleaner (from Grangers). And the third one is the good old Castile Soap (any brand will do).
c) For waterproofing, it's best to use the same coating as used by the manufacturer. However, this may be very hard to find in your case. You can choose between polyurethane or silicone. One of the best sealant for polyurethane treated fabrics is Gear Aid Seam Grip + TF Tent Fabric Sealant. Silicone treatment is a bit trickier so I suggest you go for the PU coating.
d) Sealing the seams: that part is often forgotten! For this, the best is to use Seam Grip WP (from Gear Aid) or Seam Grip FC (also from Gear Aid) if your backpack is treated with silicon.

DWR on the outside
The final touch is to add a DWR on the outside. For this, I suggest TX.DIRECT (from Nikwax). Just apply as indicated on the bottle.

In short
a) remove the old coating
b) apply the waterproofing coating inside the backpack
c) seal all seams
d) apply the DWR on the outside
e) no matter what, always use a plastic bag inside!
f) if you have a double zipper, never close with both at the top, always on the side.

Don't hesitate if you have any questions.