Don’t Climb On Wet Sandstone

Boulders in Fontainebleau

I’m guilty of this myself. For years we’d go to Fontainebleau on rainy weekends and climb on rock that we judged “dry enough”. The problem is, that it really wasn’t. Sandstone takes a day or so to dry after heavy rain and tends to become brittle when wet. At the time we didn’t know any better but now we do.

If you climb on wet sandstone you contribute to erosion. Some popular sandstone problems have changed so much with climbing traffic over time that the grades have needed an update.

You’ll spot these changes easily if you look around in sandstone bouldering areas: footholds that seem to be gauged out of the rock, handholds that seem to grow deeper over the years.

In some areas climbing on wet rock is completely forbidden because the brittleness of wet sandstone makes gear placements dangerous. You’ll break off holds and rip out your gear in case of a fall.

Sandstone becomes really fragile when wet and because a sandstone boulder acts like a giant “sponge” sucking up all the moisture around it, it takes a while to dry from the inside out. That’s the reason why sandstone sometimes feels like it’s “sweating”. As a rule of thumb, leave the boulders alone on rainy days.

Another big contributor to erosion on sandstone is climbing with dirty climbing shoes, especially in sandy areas like Fontainebleau. There’s a reason locals have been carrying these little rags to wipe off their shoes for decades. Particles of dirt on your shoes act like sandpaper to the rock. Over time this hollows out the footholds and changes the boulder problem. The solution is to really wipe down your shoes before every climb. Clean shoes also means more friction an stronger climbing!

Photo by Alexandre Debiève