Cherie,
Those small slabs of wood are about 1/4" thick. I made Joe cut me some slabs out of one of his MANY logs...LOL. Although, people have cut thicker slabs. The bark is really attached to the wood. You may have some small pieces that flake off but that shouldn't be a problem. They also have some stuff called wood hardener that you can soak the wood in if you wish. I do not use it but Joe has some in the shop for his pen blanks that are really soft.
Hope this helps and if you have any more questions just ask away...
Tonya