Sand Paper Stains

Silicon Carbide (SiC) grit doesn't fracture like aluminum oxide, which is why it abrades as full grit from the glue into the raw wood sometimes Plus, it's normally mounted on thin paper, where creasing and flexing knock off even more. That's why I don't use it on raw wood. Once you have some finish between the paper and the pores it's easier to wash off the mix of cellulose and grit with a bit of solvent.

You can use the Klingspor gold cloth-backed stuff wet, so I'm told. I've never given it more than a few brief tries, but it seemed to hold and not color. Haven't encountered any red wet/dry, but if it had a more flexible backing, it would seem a better choice. Aluminum oxide is almost colorless in the mineral.

Tom. I am curious where the dark spots are. I have noticed that sometimes the end grain will finish out a different color than the flat grain. I have also had black spots show up on wood that is reaction from the powder left on my gouges from sharpening. If your wood is dry, it won't show up at first, but does after a while. robo hippy

Hi Tom

The water proof sandpaper is not designed for the rough treatment of sanding bare wood, but rather for the sanding of automotive finishes and other more delicate final finish treatments IMO.

And yes the abrasives will be ripped off of the paper backing in imbedded into the wood, and in light color wood you can get enough of that to be visible, other people have also reported this.

However I do not see a need to use more expensive water proof paper for sanding bare wood, there are better and less costly abrasives for that, and when sanding a finish on wood the loss of abrasive particles should not be a problem.

Have fun and take care Leo Van Der Loo

Tom Storey wrote:

I think dark red aluminium oxide waterproof is cost efficient on wet wood, because:

- you can clean it in water when it clogs up and re-use it

- you can store it in a damp place, such as my little barn with very high humidety (90%), without a loss of sanding ability

- only a fold will leave a red stain with high preasure in a tight spot I agree its not cheap, so if you know a better way or cheaper sandpaper for sanding wet and thin (2-4mm) wood, I'm very interested.

Dutchturner Chris

Chris, are you referring to aluminum oxide paper (or cloth) with red resin adhesive? From your description of breaking the adhesive by folding, I think you might be.

A German sandpaper manufacturer, Klingspor, makes a gold-colored cloth-backed paper with good moisture resistance in grits down to P400, though it is not designated as wet/dry. I have used it to wet sand finishes when I felt too lazy to go downstairs after the SiC paper.

Wet/dry SiC (black) papers, as people have told you, are designed to be used on non-porous materials, where the relatively weak adhesive merely creates a sharpening slurry when it sheds grit. Sort of like rubbing with pumice. If the grit embeds itself in the soft area of a spalted piece or an open-pored area in light wood, a shadow remains. You might choose to use pumice instead of sandpaper, as well. It becomes transparent when embedded in the finish.

I have heard and seen this issue with dark automotive waterproof sandpaper used on light colour woods. I follow a process I read in a posting somewhere. I clean the wood after using the paper. The colour is bits of the dark grit getting caught in the grain. Some people clean the wood with a cloth wet with alcohol, others blow the wood clean with compressed air. I wipe the wood down with a piece of very fine scotchbrite pad, first while it is turning, then I stop the lathe and wipe in the direction of the grain. I usually finish sanding with an extremely fine non-waterproof paper. Hope this helps, Brad HardingPens.com