Brushing is the cheapest performance gain in climbing. A clean hold has more friction than a dirty one. That is the whole story, and it is worth understanding why.
Chalk builds up in the texture of a hold. So does the rubber you leave behind from your shoes, plus skin, sweat, and dirt. That gunk fills the tiny pores and crystals that give a hold its grip. Brush it out and the surface bites again. Skip it and you are climbing on a polished, greasy version of the same move. This is true indoors and outdoors, but it matters most on real rock, where the consequences of bad habits last a lot longer.
Why brushing matters
Friction
The texture you grip is microscopic. Granite crystals, sandstone grains, limestone pockets: all of it works because the rock surface is rough at a small scale. Chalk and rubber smooth that roughness out. A well-brushed hold can feel like a different grade than the same hold caked in chalk. This is why you see strong climbers brushing between every burn on a hard boulder. They are not stalling. They are resetting the friction.
Etiquette
Brushing is also how you leave a problem the way you found it. Every time you climb, you leave chalk on the holds and chalk marks (tick marks) on the wall pointing to them. Indoors, that is mostly a friction problem. Outdoors, it is also a visual and ethical one. A boulder covered in white chalk smears and arrows is an eyesore for everyone who comes after you, and on some rock it accelerates wear. The rule is simple: clean up after yourself.
How to brush a hold
Brush with the texture, not against it
Brush in one direction, following the grain or texture of the hold, not back and forth like you are scrubbing a pan. Scrubbing back and forth grinds chalk deeper into the pores and can wear soft rock faster. One firm pass with the texture lifts the chalk off and carries it away. A few short, deliberate strokes beat a frantic scrub every time.
When to brush
- Between attempts on a hard move, especially anything crimpy or sloped where friction decides the send.
- Before you start, if the holds are caked from previous climbers.
- At the end of your session outdoors, to reset the rock for the next party.
Let the rock dry
If a hold is damp, do not brush it hard and do not climb on it. Wet rock is softer and far more prone to breaking, and brushing a wet hold just smears the chalk into mud. Wait for it to dry. This matters most on sandstone, which can stay fragile for a day or more after rain. When in doubt, leave it alone.
Bristle types
Boar bristle: the gold standard
Boar's hair (natural bristle) is the standard for a reason. It is stiff enough to clear chalk and rubber but soft enough that it will not polish or scratch the rock. For outdoor climbing, boar bristle is what you want. The Sesh Bouldering Chalk Brush uses boar bristle for exactly this reason.
Nylon: fine for the gym
Nylon bristles are firmer and more durable. They are fine on plastic gym holds, which are tougher than rock and do not care about polishing. Plenty of climbers keep a nylon brush for the gym and a boar brush for outside.
Never use a wire or metal brush on real rock
This is the one hard rule. A steel or wire brush will strip chalk fast, but it polishes and gouges the rock surface, permanently. It destroys the texture you are trying to clean and ruins the hold for everyone after you. Wire brushes have no place on natural rock. Ever.
Toothbrushes are too small to be useful
A toothbrush gets recommended as a budget option, but it is too small for real work. The head covers almost no surface area, and the bristles are too soft to move packed-in chalk. Use a real climbing brush. It is a cheap piece of gear that lasts.
Brush sizes
Match the brush to the hold. A compact brush gets into small edges, pockets, and crimps where a wide head cannot reach, and it clips easily onto a harness or rides in a pocket. The Sesh Climbing Chalk Brush is built compact for exactly this. Slopers, big features, and gym volumes have a lot of surface area, so a wide brush covers them in a few passes instead of twenty. Most climbers end up carrying both.
A brush you cannot reach is a brush you will not use. A chalk bucket with dedicated brush slots keeps both sizes within reach while you climb. The Bolder Chalk Bucket has slots built for this.
Outdoor etiquette: leave no trace
Brushing outdoors is not only about friction. It is about access. Climbers keep crags open by being good guests. Visible chalk is one of the most common complaints from land managers, and it has cost climbers access at more than one area. Before you leave a boulder or a route:
- Brush the excess chalk off the holds. Knock the heavy buildup down so the next person is not staring at a white smear.
- Brush off your tick marks. Those chalk arrows you drew to find holds are yours to erase. Take them with you.
- Use a soft brush and a light touch. You are removing chalk, not sanding the rock.
Two minutes of brushing at the end of a session keeps the rock looking like rock. The next climber should not be able to tell you were there.
FAQ
How often should I brush climbing holds? Brush between attempts on hard moves where friction matters, and brush off caked holds before you start. Outdoors, always brush off excess chalk and tick marks before you leave. For easy terrain you are flowing through, you do not need to brush every hold.
Can I use a wire brush to clean climbing holds? No. Never use a wire or metal brush on real rock. It polishes and gouges the surface permanently, destroying the texture and ruining the hold for everyone after you.
What is the best bristle for a climbing brush? Boar bristle (natural hair) is the gold standard. It is stiff enough to clear chalk and rubber but soft enough that it will not damage rock. Nylon is firmer and fine for plastic gym holds, but for outdoor rock, use boar bristle.
Should I brush with or against the texture? Brush in one direction, with the texture or grain of the hold, using a few firm strokes. Scrubbing back and forth grinds chalk deeper into the pores and wears soft rock faster.
Why does brushing a hold actually help? Holds grip because the surface is rough at a microscopic scale. Chalk, rubber, skin, and dirt fill that texture and smooth it out, which kills friction. Brushing clears the gunk so the surface bites again. A clean hold can feel a full grade easier than a dirty one.
Is a toothbrush good enough for climbing? Not really. A toothbrush head is too small to cover real surface area and the bristles are too soft to move packed-in chalk. A proper climbing brush is inexpensive, lasts a long time, and does the job in a fraction of the time.
A good brush is a few dollars of gear that makes every hold grip better and keeps the rock clean for the next party. The Sesh Bouldering Chalk Brush is boar bristle for outdoor rock, and the Sesh Climbing Chalk Brush is the compact one for crimps and easy carrying. Keep one in your chalk bucket and use it.