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Glue-in Bolts   

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Best Use: General route setting and rebolting
Rock Type: All rock
Pros: Reliable in soft rock compared to other bolt types; long-lasting
Cons: Expensive; difficult to set and remove

Glue-in bolts have gained recognition as the most durable bolts used in rock climbing today. Glue-ins are essentially a piece of high-grade bar stock glued into a drilled hole with construction grade epoxy. They vary slightly in shape, design and composition, but all have a ring on one end for clipping. With no metal on metal contact or moving parts and largely encased in a waterproof epoxy, modern glue-ins resist corrosion more than any other bolt. Unfortunately, they are perhaps the most difficult bolts to place. Skill, practice, and a couple of subtle tricks are needed in order to avoid making a mess when bolting with glue-ins.

Like any other bolting project, proper use of glue-ins begins with an understanding of the available equipment. Petzl, Wave Bolt, and Fixe are a few of the brands selling this product in the U.S. The sizes used in modern climbing applications include 3/8”, 10mm, 12mm, ½”, and 14mm. Like mechanical bolts, they also come in a variety of lengths, the shorter versions being better suited to hard rock and the longer ones to soft rock. Glue-in bolts are available in 304 and 316 stainless. Custom bolts for particularly corrosive environments have been manufactured with Ti64, but none are currently commercially available.

Rock Climbing Photo: ClimbTech wave glue in bolt

ClimbTech wave glue in bolt
Glue-ins are available in several configurations. Technically, any bolt glued into the hole qualifies. This would include hangerless rivets and threaded studs. However, these applications are rare and antiquated, as their corrosion resistant benefits over mechanical bolts are greatly reduced. Most modern glue-ins are either eye-bolts with a single stem or double stem U-bolts. Single stem glue-ins are available with a solid or twisted rod (known as the Buhler bolt) with a cast, welded or wire ring on one end. The bolt shaft may be centered or offset (i.e. “P” shaped). U-bolts require drilling two holes and, if the diameter of the hole is too large, can cause the bolt end carabineer to unclip if it twisted. This is problematic, since the dual holes need to be several inches apart in order to not weaken the rock. On the other hand, U-bolts are the easiest type of bolt to hand make, as they are essentially just a steel rod bent into the shape of a “U” with scoured ends.

Placement : Unlike mechanical and compression bolts, most glue-ins are placed in a hole drilled slightly larger (e.g. 2mm) than the diameter of the bolt itself. This allows room for the epoxy to encase the bolt and form a reliable bond with the rock. Because this bond is so critical, thoroughly cleaning the hole is extremely important when using glue-ins. Otherwise, the epoxy just bonds to the rock dust in the hole and can pull under low axial loads.
Experts still debate whether holes for glue-ins should be “troughed,” meaning reamed out at the surface in order to slightly recess the eye of the bolt below the surface of the rock. Troughing may help support the bolt by reducing torque under shear force.

Epoxy dries quickly, meaning that once mixed in the nozzle, the clock is ticking before it hardens in place between placements. For this reason, it is best to first drill all of the holes on projects requiring multiple glue-ins. The bolts can then all be placed with minimal delay, reducing the chance that the epoxy will dry in the nozzle before the line is complete.

To apply the epoxy, the mixing nozzle is inserted into the back of the drilled (and cleaned) hole. As the application trigger is pulled and the epoxy begins to fill the hole, slowly withdraw the nozzle until the hole is nearly filled. The goal is to avoid any potential air pockets. Leave enough room in the hole so that the epoxy does not ooze out too much when displaced by the bolt. Then slowly insert the bolt, rotating it as it is pushed to the back of the hole. Rotating the bolt helps reduce air pockets. Once in place, the epoxy must be given time to fully cure before the bolts can be used for climbing.

Due to the variation in glue-in bolts, the correct orientation in the hole will vary. For welded eye-bolts, the weld should usually be facing up. For “P” style eye bolts, the trought of the bolt will need to be on the bottom. Ultimately, follow the manufacturer’s instructions for the correct orientation.

Rock Climbing Photo: Petzl Collinox resin bolt

Petzl Collinox resin bolt
Glue-ins have a tendency to migrate out of their hole, especially in overhanging rock. The epoxy will also often try to seep from the hole. This can make a mess as well as create weak bolts. If epoxy spills from the hole, then there may not be total encapsulation of the bolt, reducing axial strength. If the bolt migrates out from the hole, shear strength can be reduced by the torqueing effect on the exposed shaft. The most popular solution to this is to place a piece of high strength tape (i.e. gorilla tape) over the drilled hole with a small cut in the center through which the epoxy and bolt can be inserted. Then, as soon as the bolt is in place, another piece of tape is placed over the bolt in order to hold it in the back of the hole. The tape can then be removed once the epoxy has dried and cured.

The Wave Bolt is a Buhler style glue-in bolt hybridized with a compression bolt. The Buhler style bolt is a single piece of twisted stainless wire engineered to be hammered into a ½” or 5/8” hole (depending on model). The shaft is shaped so that it is slightly larger than the hole, requiring it to be hammered into the epoxy filled hole. This helps prevent migration from the hole on overhanging rock and may increase overall axial strength.

Removal: Glue-ins can be removed by heating the bolt and melting the epoxy enough to where the bolt can be pulled. However, it is difficult to heat many bolts such that the whole shaft becomes hot enough to melt the epoxy at the very back of the hole since the metal may not conduct heat very efficiently. The most practical way to remove a glue-in bolt is to break or cut it and patch. Glue-ins resist corrosion very well so perhaps a new technique for removal will be devised before wholesale replacement becomes necessary. The goal should always be to reuse existing holes.

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