Is it just my imagination or is my 'Kingspore' brand waterproof sand paper
leaving black marks on some of my work? Ok, I know you can't see it!
However, I've been working with white birch and it sure looks like it's
darker in spots after I've sanded it, both dry and with a blo/thinner mix.

How does the 'dark red aluminium oxide' waterproof paper perform and will it
leave a stain?

--
Tom in Qualicum Beach, BC

"Tom Storey" wrote in message
news:Lj4nf.95140$Gd6.22530@pd7tw3no...
Is it just my imagination or is my 'Kingspore' brand waterproof sand paper
leaving black marks on some of my work? Ok, I know you can't see it!
However, I've been working with white birch and it sure looks like it's
darker in spots after I've sanded it, both dry and with a blo/thinner mix.

How does the 'dark red aluminium oxide' waterproof paper perform and will
it leave a stain?

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

There doesn't seem to be any one area that attracts the stain, I just notice
a slight darkening here and there that I don't get it when I use 'normal'
sand paper. The birch I'm using is quite spalted and soft in spots and it
could be that some of the stain is from the spalting? I seem to get less
staining when I apply diluted shelec as a sanding sealer before sanding. The
following is a sample of what I'm dealing with. The tear-out is more evident
in the picture than it is in real time.
http://tinypic.com/view/?pic=igloi8

"robo hippy" wrote in message
ps.com...
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:

Is it just my imagination or is my 'Kingspore' brand waterproof sand paper
leaving black marks on some of my work? Ok, I know you can't see it!
However, I've been working with white birch and it sure looks like it's
darker in spots after I've sanded it, both dry and with a blo/thinner mix.

How does the 'dark red aluminium oxide' waterproof paper perform and will it
leave a stain?

Leo,

you wrote:
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.

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 van Aar" wrote in message
t.nl...
Leo,

you wrote:
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.

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.


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