This plaster slab is about 5 years old. I have used it to dewater many raw clays that contain significant soluble salts. Over time they sealed the surface with a hard scum. That not only made the table slower to dewater slurries but it also significantly slowed down the time it took for water to evaporate out of it. Using this carpenter's plane I removed about half a millimetre. The blade self-sharpened. It took some experimentation to set it at a depth that would effectively remove the hard layer. I thought it would produce grooves and unevenness in the surface, but it did not. Sanding was not necessary. And the first slurry stiffened quickly, like a freshly-poured slab, and there were no bits of plaster in it.