Hi
Polishing scratches in dark marble, scratches are about 4 inches
long
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There are polishes available for granite which will cover/conceal
light scratches. Do a web search for ‘granite polish’ or visit your
local granite store for a recommendation.
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The surface will have to be removed to the depth of the
scratches. If the piece can possibly be removed and taken to a
granite shop, I would try that, they will have the tools to keep the
surface flat.
Option 1 and 2 are not viable. Do not use the flex shaft, stones
which are a conglomerate have pieces with different hardness through
out its structure, some elements will cut faster and your surface
will be wavy. If you use a palm sander, find one with an inline
action. Place a hard piece of material on the bottom to backup the
wet-n-dry paper, remove the felt baking from your sander if at all
possible, if it is one of the high density foams or rubbers it may be
ok to use as is. The felt will be a great source of contamination to
your activities. Get a spray bottle to ‘mist’ your work area, it must
be kept damp to a light slurry, but not splashing, and wear rubber
gloves, not the kitchen kind, but ones for chemicals, the thicker
the better and keep them dry, you will have 120 volts in your hand.
The reason for the water is to keep the grit of the paper open. To
glue the paper to the sander, use 3M feathering disk adhesive. When
the cutting action slows down change the paper.
I would use silicon carbide wet-n-dry sheets. Start at around 320 or
400 and work up to 3000. Work the action at 90 degree angles to each
grit. Meaning if you work right to left with 320, work the 400 up and
down, then 600 right to left. The reason being, you continue to work
the grit until the marks from the last grit are gone it is easier to
see crossing lines. Make sure they are really gone, look at the
surface with a magnifying glass or what ever you have to see that
this is so. If you miss any, you would not believe how much longer it
will take you to remove the scratches caused by 320 with 600 grit if
you do not do this. Plan on having to clean very thoroughly between
each grit, you can’t even use the same towels from grit to grit on
clean up otherwise you may contaminate your work.
Start working at about 1.5 times the size of your scratched area
then with each higher grit work about 10% over this. The object of
this is to spread out the depression so it is not as noticeable. As
you are going through each grit size, check to see how the smoothing
is coming, you don’t want to remove any more material than you have
to. Keep your tool moving all the time, if it is not moving it should
not be on the surface and still running. When you think you are
close, clean and dry your surface and inspect to see all the
scratches are gone. If you have even a small one, keep going until it
is gone.
After this and you work your way up to 1500 or 3000 you should see
the polish you want. If you want to polish further, use the used 1500
or 3000, as the grit breaks down on the paper and stops cutting as
fast, it is also getting finer, the last session should be with the
worn pieces of 1500 or 3000.
The final action will be applying the granite sealer and polish.
If all the steps are followed, and each new grit is applied at the
proper time you should be done in about 2 hours, depending on how
deep the scratches are. Or it could take all afternoon if things go
poorly.
Terry