Exploring the Natural World

Understanding Hiking Boot Sole Delamination

While cleaning and conditioning my leather hiking boots, I discovered the Vibram sole “peeling apart” on one side of the left boot. Because I paid $250 for the pair, no more than half a decade ago, my heart sank with disappointment. I was completely surprised. How could it be possible to purchase quality boots from a reputable dealer then find the bottoms falling off? I’d been planning to hike the treads down to slicks before replacing the soles. Instead, I felt cheated by the manufacturer for using cheap or defective glue. My previous pair (a different brand) had rock-solid soles that never failed. I set my mind to figuring out the current issue, and realized I had considerable learning to do. The last thing I wanted to do was throw them away and buy a new pair without understanding what went wrong and why. Maybe I’d caused the problem myself by using the wrong conditioning product. Furthermore, the leather uppers and boot interiors remained in fantastic shape.

My left hiking boot sole “peeling apart” on the right side.

Okay, so I begin by flipping over the boot and studying the situation more closely. I find the opposite side of the sole is also coming apart, but even more so. For kicks and curiosity, I pull gently on the loose flap of sole, and the damn thing all but comes clean off. The failed glue appears flaky and disintegrated.

Gentle pulling opens the separation further.

I decided against ripping it completely off, in case re-gluing it proved a possibility. But I needed a crash course in boot manufacturing to feel confident before attempting any repairs. (On a lark, I did try slathering in some Elmer’s rubber cement, which worked about as well as if I’d smeared in a couple of boogers.)

DOES NOT WORK (to repair boot soles)

To understand the manufacturing process and technology of high quality boots, I first studied Asolo’s website. On their site, Boot Sole Separation (Hydrolysis) is thoroughly explained. However, after careful study of that topic, I concluded that my issue is slightly different. My hiking boots consist of three main assembled parts, including:

  • Leather Upper
  • Polyurethane Midsole
  • Rubber Outsole

Polyurethane midsoles are commonly used in high quality hiking boots, offering a more sturdy and durable construction than the less-expensive EVA foam alternative. With age, though—approximately six to seven years, as estimated by Asolo—polyurethane midsoles may begin to suffer from hydrolysis. Hydrolysis is a chemical breakdown of the polyurethane due to reaction with water. Basically, the polyurethane may deteriorate and crumble from the inside out, if kept in undesirable conditions. The cause is gradual moisture absorption, which results in hardening of the polyurethane. Boots kept in dry, well-ventilated conditions, however, (i.e. not in some hot, dank closet) tend to resist hydrolysis better.

My thanks to Josh’s YouTube video on Polyurethane versus EVA foam, and here is the link to Asolo’s hydrolysis information as well as a video on how Asolo boots are made.

Now, back to my boot issue…

The rubber outsole (the Vibram part) is the component of my boot that is “peeling apart” from the polyurethane midsole. The midsole itself, however, appears to be in excellent condition. There is no crumbling or disintegration. True, hydrolysis works from the inside out and cannot necessary be seen, but boot sole separation from hydrolysis would result in the polyurethane midsole crumbling away from the outsole and/or the leather upper. Here’s a video posted by Mike Miller showing midsole crumbling.

So my issue is a glue failure between the rubber outsole and PU midsole, which is generally called sole delamination. Old school boots were manufactured (and some still are) using a durable stitched on method, e.g. Goodyear Welting. A less expensive alternative to stitched on soles, and the most common today, is a cemented method. Why the glue failed is an important question, because I’d rather not have it happen again. I’ve identified four possibilities: 1) defective glue, 2) aged glue, 3) excessive heat, 4) chemical breakdown. Of those four, only the last two would be my fault, so those I’ll discuss.

Excessive heat would essentially melt the glue, causing delamination. This could be from propping boots too close to the campfire or leaving boots in a sauna-like environment, such as a car’s trunk. Since I don’t recall having done anything similar, my next question is chemical. According to Asolo’s care instructions, “Acids, petrol and manure impact the outsole materials and cements particularly hard.” So my first suspicion is that the Nikwax conditioner I typically use could be chemically breaking down the glue—but, alas, I verified with Asolo (via their website’s FAQ page) that “Asolo recommends Nikwax products for the proper cleaning and maintaining of your Asolo footwear.”

I feel confidently off the hook for any blame.

Now what?

Defective glue? Should I return the boots to the retailer?

I purchased these boots from REI, who has in the past maintained an outstanding return policy regarding manufacturer’s defect. So I called their flagship location in Minneapolis, connected with the boot department, confirmed I was a co-op member, and found out a few interesting facts:

First, the boots I purchased are still REI’s #1 recommended hiking boot—the Power Matic 200 GV. The boot rep I spoke with confirmed that these boots have thermal polyurethane (TPU) midsoles, which are expected to last 10 years. Second, I purchased these boots in 2008! (Wow, has time flown!) And so these boots are beyond the warranty period that REI would honor, only because the boot’s expected lifespan has been reached. (It’s worth noting that the rep also confirmed REI used to have a 100% satisfaction guarantee for any product purchased for the life of the original co-op member; however, that policy has been changed to a 1-year warranty.) Third, failing glue is a typical problem after 10 years.

The gentleman recommended two options for resoling the boots. First, he gave me the name and phone number of a guy in Seattle, Dave Page, who is currently REI’s go-to guy for boot repair. Second, he shared a rumor he’d heard, though unconfirmed, that Vibram operated a mobile unit, which currently roamed the country doing boot resoles, and that I might contact them to verify whether or not said rumor was true. I did a bit of quick research and found Vibram Sole Factor is a mail-in service, but I found no evidence of any mobile unit. (It may or may not exist.)

Beyond the re-soling option, I asked this boot rep if he felt re-gluing the rubber outsole might work, since my midsoles are still in great shape, to which he said “it might.”

That is what I shall attempt…

I have found a product called Freesole by Gear Aid (McNett), which gives me more confidence than any other glue I’ve researched. The product is made in the USA, and the tag-line is “Urethane Rubber Tough” (see the below photo). I’ve read many reviews via Amazon, as well as 50+ FAQs asked and answered by real people. The product “permanently reattaches soles,” among other things, according to the packaging. Here is a Youtube video by Gear Aid, which amounts to a promise, as far as my ears are concerned. Fortunately, I found this product at a local backpacking outfitter.

Freesole Shoe and Boot Repair by Gear Aid (McNett)

My next task will be to follow the instructions on Re-bonding Soles, which are listed on the back.

Freesole, backside of packaging for various uses and instructions.

Since my soles had not delaminated completely, my repair job required me to re-bond two crevices (rather than re-sandwich the entire soles). Step one in the directions called for cleaning both surfaces with isopropyl alcohol (aka rubbing alcohol). This proved a challenge, but I carefully spread the gap, manually blew out the tiny crumbs of old dried glue, and cleaned the gap as best I could using a fresh piece of alcohol-soaked purple cellulose sponge cloth.

Cleaning the gap with alcohol soaked cellulose sponge.

Included with my package of Freesole was a tube of ColorSync, which I decided against using. The idea is to blacken the glue so that, once dried and weathered, it is more eye-appealing than yellowed glue. I didn’t feel like messing with it for the sake of cosmetic improvement, especially since my glue job would stay hidden between the soles (hopefully).

A small brush for spreading the product was included. I supposed the idea is to paint the surfaces, and so I squeezed a glob of glue onto the clear plastic housing that had packaged the glue. The glue’s consistency compared to silicone caulk, proving too thick for the brush to manipulate. (Perhaps I should have warmed the product by carrying it in my pants pocket for an hour or so.)  In such a thick state, there was no hope of painting the glue into the gap using the little brush, and so I quickly resolved to squeeze the sticky goop out as best I could into the crevice, trying to lay down a switchback trail. (Again, had I warmed the tube, I’m guessing the glue would have been much easier to work with.)

Freesole is thick and difficult to squeeze out when cold. Warm in pocket first.

From there I used the small brush to spread the glue down deep into the crevices and onto both PU midsole and Rubber outsole, making sure to bring the glue clear to the edges of my sandwich. The brush, I believe, is only good for one session of gluing. Both sides of my left boot were delaminating, so I repaired both sides at the same time. While I tried cleaning the brush with alcohol afterwards, I was certain the bristles would harden and prove less useful for future repairs. I had about half a tube of Freesole left, and so, according to the instructions, I capped and stored the remains in the freezer.

Spread with included brush.

My final step was to tape the soles together, for which I used duct tape. I made an effort to secure the tape only to the outsole and midsole components, not to the leather upper. While I doubt the leather would have been damaged, surely it would have become gummy, and having a gummy residue on my leather would have plagued me for some time. I made sure to close and seal the joints well and tape as tightly as possible. According to the directions, Freesole cures overnight. Here is a shot of my tape job…

Clamp or tape the soles together overnight. I used duct tape.

And so I left the glue to cure overnight, wondering how satisfied I’d be with the finished job by morning…

At 7 a.m., I discovered the duct tape had not held absolutely tight. (Because my work area in the basement stays somewhat cool in the winter, the tape was less sticky than it could have been in a warmer environment.) Removing the tape revealed a small unsealed gap still remained between the outsole and the midsole on both sides of the boot. Where the rubber outsole’s natural pliability wanted to pull away from the midsole, simply due to it’s pre-formed shape, the duct tape had not held tightly enough. On close inspection, the Freesole glue had yet to completely hardened in those places, and was in fact still tacky. Fortunately, when I pressed closed the gap, the tacky glue stuck, and so I decided to re-tape both sides, making especially sure to secure those gaps well. Then I left the glue to cure for another several hours.

By 3 p.m., the results looked better…

Outsole After Repair 1

The gaps now held tightly together on both sides…

Outsole After Repair 2

The final result will depend on time and field-testing. After one more day of curing (for good measure), I’ll wear the boots around the house for a day. If the soles hold together, I’ll take the boots outdoors for a cold winter hike on flat trail. I’ll see how long the fix lasts, and report back over the next several weeks (hopefully months). I’m especially curious to learn if the repaired areas hold longer than the original factory glue on the areas that have yet to fail. If ten years is truly the “expected lifespan” of the original glue, I should plan on more delamination and at-home repairs, and maybe a complete resole before too long. Most definitely, I’ll be overjoyed if Freesole turns out to be a long-lasting fix. Today is Feb 7th. I’ll append updates later.


Update 26 Feb 2018: Still holding. I’ve hiked several times in cold and snowy conditions, as well as in wet and mucky conditions. The seal remains very tight and shows no sign of failing.

Update 14 May 2018: Still holding. Not showing any sign of coming undone. I think this fix will last. I’ve hiked several times, getting the boots both wet and muddy.

Update 30 Oct 2018: The parts I glued with Freesole are still holding tight. Unfortunately, other parts of the soles are now beginning to come loose. I will thaw and use the remaining Freesole (which I have been storing in the freezer) to glue these new areas. At this point, I’m only using these boots for local hikes. I’ll probably have them resoled by spring, certainly before trusting them for any extended hike. That’s no dig against Freesole, it’s just that continued patching will become tedious. Besides, my treads are all but worn down now anyway.

About Bob Ward

In addition to nonfiction, Bob writes a fiction series featuring outdoor travel hero Kip Stone of Epic Adventures, Inc. For details, visit BobWardBooks.com.

4 Comments

  1. Trav on September 12, 2018 at 10:53 pm

    Nice post. I really appreciate the post-repair updates! Tells us it really worked for you. Thanks for writing it up.

  2. Dave on November 3, 2018 at 6:38 pm

    Great post! I’ll try this glue on my North Face hiking shoe soles. Like yours, it’s just the sides of the soles.

  3. Catharine Kolb on November 20, 2018 at 4:43 pm

    Gosh, thanks so much. I started up Tuckerman Ravine Trail recently and first one sole fell off my Merrill hiking boots , then further on the other did, leaving hard palstic for soles . I dreaded the descent . My spare pair ( EMS boots) also had partial delaminating, being my beloved boots I put them aside to send to Seattle to that guy the boot world seems to rely on. Now i am back up in the White Mountains with Danners and Vasques. All the boots had Vibram soles except for the Skywalker soles on the Vasques . I have many hundreds invested in these boots and ordered boot glue from Amazon . I hope it works per your careful instructions which are great.
    We had a hot summer but to have all those boots fail one after the other , each having had a different amount of usage , but all bought more than ten years ago , i think the glue longevity must be the real problem.
    Thank you so much for the thorough recounting of your efforts .

  4. Steve on January 16, 2019 at 10:18 pm

    Planned Obsolescence aka Engineered Point of Failure. This is a practice used by many companies to force consumers to buy new products. Yes, they intentionally design and manufacture boots (and many other products) so they don’t last as long as they used to.

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