Coating a backpack with urethane sealant: CamelBak rebuild- Mtbr.com
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  1. #1
    JXG
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    Coating a backpack with urethane sealant: CamelBak rebuild

    In 2014, I bought a CamelBak H.A.W.G. N.V. Hydration Pack, 2011 model. This has a capacity of 1120 cubic inches (18 liters) per 2011 Camelbak H.A.W.G. NV Review - Pinkbike I got it on closeout for about $95.

    The ergonomics are good, especially how it transfers weight to the hips and the breathability of the mesh back panel.

    Early on, holes started to develop in the mesh back at the bottom, where the pack contacts my back and the ground when Iím not wearing it. Using a Speedy Stitcher awl, I sewed a piece of 3-inch webbing across the hip area:


    After a few hundred hours in the high desert sun the red fabric had faded badly. I thought this was excessive because a cheap cotton bandana attached to the back of my helmet to protect my neck had faded very little.

    Then, a rip appeared in the back of the pack. This was not a good thing considering I had expected the pack to last for many years.

    Trying to adopt the disposable mindset, I looked at the currently available model: 22 x 11.5 x 2.5 in, Total Capacity: 17L (1037 cu in) + 3L Reservoir CamelBak | HAWG NV 3L Hydration Pack All Weather Mountain Biking

    So the current model is a liter less than my 2011. And it costs $159.

    Given that the 18 liters of the 2011 model is barely enough for extra liquid and exposure gear, I decided to rebuild and transform my pack using urethane coating.

    McNett makes two urethane sealants that I have used in the past for wetsuit and caving gear repair.

    Aqua Seal is primarily for wetsuit repair. It is thick like honey and cannot be painted on with a brush. It runs and drips until it cures, often causing a big mess.

    Seam Grip is primarily for coating seams. It is thinner and is almost paintable with a small stiff brush.

    Outdoor Wilderness Fabrics has 8 oz sizes: Outdoor Hardware - Buckles, Zippers & More - Outdoor Wilderness Fabrics (OWF)

    McNett Aqua Seal and Seam Grip are unusual products that go beyond Goop, ShoeGoo, etc. because they use toluene solvent. This is a very nasty chlorinated solvent that causes genetic and nerve damage.

    I always wear a full-face respirator and disposable gloves when working with either product in a well-ventilated area: respirators link --> Robot Check

    At a minimum, use a dual charcoal cartridge rated for paints / solvents. A good investment to protect your health. Sometimes you can get good deals on respirators on eBay.

    These sealants do not come off of anything so masking and covering with newspaper is essential.

    The first step was to fix the rip, so I loosely stitched it back together:


    Then I cut out a piece of Cordura pack cloth and put it on with the contact cement technique.

    In other words, I coated the patch and the patching area with Aqua Seal, let each dry for about 30 minutes, then pressed them together.

    For coating the rest of the pack, I decided to try thinning Seam Grip to make it more brushable and hopefully reduce running.

    This might seem counterintuitive but I had a feeling that a thinner coating would stick tighter to fabric because of surface tension. I could not find toluene locally (chlorinated neurotoxic carcinogenic solvents are out of fashion) so I got a quart from Amazon.

    I cut open an 8 oz tube of Seam Grip and squeezed it into a glass pickle jar. I then diluted it with 4 oz of toluene. This seemed like just the right consistency. (To prevent curing in the tube or jar, store in the freezer.)

    Stuffing the pack with newspaper and packing bubbles was the most work. It needed to be completely full and bulging because the coating would lock everything into position.

    I masked all the zippers with Nashua aluminum duct tape folded into thirds and then cut with scissors. "HVAC aluminum foil tape" is great for masking because it is easy to work with, impermeable to liquids, and easy to remove.

    Cordura patch in place (bottom) and everything masked with aluminum tape:


    The diluted Seam Grip painted on nicely with a 1-inch brush. As I had hoped, there was almost no running at all.

    As soon as the Seam Grip was set firmly, I removed all the masking to check for runs.

    Once the Seam Grip was completely cured, I sprayed all the zippers with B'laster silicone spray. This made them much easier to slide.


    This project took several hours work but I now have a pack that will last for a very long time:


    Other advantages:

    + Pack stands up better when being loaded and accessed
    + Now tough enough that I can put it down on abrasive surfaces more freely
    + Much more waterproof, so I only have to pull out the rain cover for heavy rain

    The final thing I need to do do is cover the back mesh with shadecloth to keep more holes from developing. This is an open-weave fabric used for awnings and greenhouse covers.

    Hope these project notes give other riders ideas for what can be done with urethane.
    Last edited by JXG; 01-30-2016 at 11:43 AM.

  2. #2
    Don't worry, be happy!
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    Impressive, lots of work. I've got a couple of comments.

    Seam Grip and Seam Seal are two different products. Which one did you use?

    Seam Grip, McNett, toulene based.
    Seam Seal, Couglan's, waterbased.

    You can get an accelerator for the Mcnett products that will cause it to cure faster and thins it out for better application.

    Impressive, lots of work.

    Regarding fading- UV causes fading, nylon is very susceptible. Level of fade will really depend on fabric treatment, type of dyes, and so on. Polypropelene has much better UV resistance. A product like "303 Protectant" applied regularly will prevent/slow down fading and UV degrading.

    I've repaired a lot of nylon Scott tents using your contact cement like application. The thing that will fail in the long run is that the glues will start to peel. The seam grip doesn't actually bond with the nylon; it's bonding with itself. The strongest glue applications come when the glue bonds with (chemically reacts with) the surface of what you are gluing. I have yet to come across anything that will truly bond with the nylon. Seam grip doesn't do this, but your repair will still probably last years.

    Cheers

  3. #3
    JXG
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    Thanks for catching the error: McNett Seam Grip. I edited the original post.

    McNett Cotol-240 is an accelerator, but it is expensive so that's why I used toluene to do the thinning. I could not find Cotol-240 in bulk any more.

    I have started using 303 Protectant on items that can't be coated like jackets.

    Agree, polymers are very inert so difficult to truly bond with. I have some PVC caving packs that were coated with McNett Aqua Seal up to 17 years ago. PVC is slick and it makes nylon look easy to bond to. The Aqua Seal is still clear, uncracked, and bonded. Goop tends to turn yellow and crack after about 5 years.

    Thanks for the comments.
    Last edited by JXG; 01-30-2016 at 11:55 AM. Reason: Clarify

  4. #4
    Don't worry, be happy!
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    Have you ever played with the spray on 303? we use it on life jackets. I've never tried it on packs, coats etc but why not? The worst that would happen is possible some discoloration.

    This is what I do, (shameless self promotion)
    Specialty Outdoors: Technical Sewing Specialist

  5. #5
    JXG
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    I use 303 Fabric Guard water repellent in a pump-spray bottle. Have not had any issues and it seems more environmentally friendly than ScotchGuard spray cans.

    Thanks for your business link and especially

    Tips for Sewing Your Own Outdoor Gear | Specialty Outdoors

    Lot of great info here!

  6. #6
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    WOW! That's serious goo there!
    I'll share my recent experience on the subject. Had a Hawg and a Mule for several years that faded just a little as expected and then I saw the 2015 Mule NV. They made it bigger in it's redesign, more like the old Hawg, and the pocket ergos and design are great as was the color similar to the OP's. I bought one from Backcountry.com for $138. No deals to be had anywhere for a new model and they shipped 2 day for free and no tax so that was the best I could do. After a few months (Jul/Aug/Sep), I noticed the Barbados Cranberry Red color was fading to a pink color only on the lower outside half of the pack. I thought that quite odd considering it was all immersed in the sun while on my back, maybe more so on the top half. I decided to ask about it thinking maybe there was an issue with the dye lot during manufacture. I queried Backcountry's customer service /Warranty Dept. The response was with concern but they said that was sort of beyond their control and would check on it with Camelbak and get back to me. A couple weeks went by and I hadn't heard anything so I shot an email back to the girl that was doing the leg work. She said Camelbak had not yet responded but she decided to take matters into her own hands and had me do a "field destruction" of the pack I had and send her pics showing the destruction and they would immediately 2 day a brand new one to me. I cut the straps about 3" below their upper attachment (so I can sew them back ) and got my new pack. Backcountry.com is awesome and GETS IT DONE even when the manufacturer drags it's feet! I have no clue how Camelbak responded to the issue, now. Anyone experiencing the same should pursue the matter because at $138, a pack should NOT be fading out like mine did.

    As soon as my new pack arrived, I cut the tags off and immediately, evenly saturated it with 303 Fabric Marine/RV. I buy it and 303 Protectant by the gallon, it works! I actually double coated the Mule NV after a day's drying and it's awesome. I've been riding in some areas with sloppy conditions due to our rains we're FINALLY getting here in CA and the pack gets spotted with muddy watery goop all the time. It dries quickly and the offending goop just brushes off the pack in seconds leaving it looking like new. I got caught in a hard rain one ride and I was in too much of a hurry to get back down the mountain and off the trails to take time and pull the rain guard out. The pack beaded the rain right off and was perfectly dry when I got to the truck at the trailhead.

    Well, that's my story. Hopefully it helps others in making the call to deal with early fading and YES, go with the 303 Fabric Guard!! I'm reminded now that I need to get my wife on the strap reconnection project with the old one! We'll see how that goes.

  7. #7
    JXG
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    Good story and thanks for sharing the info on 303.

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