Horsetail equisetum

[Jay Higgs]

I cut mine green and glue them to small rubber squares. They last a long time. 

[David Beard]

I just put them aside until they air dry. To use them, I simply grab a few stalks and rub.

The point of using this is rather like pumice and cuttlebone.  These abrasives erode as you use them.  That is their great virtue

I don't want to glue them to a solid backing and make a very short lived file out of them.  That defeats the purpose.  Similarly, I don't want to glue them to clothe or similar flexible backing.  That's just using them a poor quality sandpaper.

 

The purpose of these eroding abrasives is that they behave differently.  They can clean up your sculpting without changing the purity of the carving.  

Files much more actively change the carving.  Sandpaper tends to make waves out of the irregularities of a carving.

Eroding abrasive behave in different ways that can be very helpful.

If you want that result, don't back your horse tail.   Have plenty on hand and use it wastefully for best results.   Just grab a bunch of stalks and rub.  Let the stalks erode as you work.  Toss them out as need.