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Removing scratches from marble


#1

I’m hoping a lapidiary here will jump in and answer: otherwise
perhaps someone would tell me where I can find a lapidary forum.

I’d like to polish out scratches that are on the surface of some
flat, highly polished dark marble. I know I will need to go through
several different grits, but am not sure where to start or finish,
or what kind of abrasive to buy. For polishing tools my options aRe:
by hand, by flex shaft, or I can buy a vibratory palm sander or
something comparable. Scratches are about 4 inches long, and in
parallel “clusters”, so the flex shaft might not be my best option.
If I can avoid making big dips in the pieces I’d prefer it, even if
that means just making the scratches less visible or even coating
them in the end with some kind of “scratch filler” if such a thing
exists.

Thanks!


#2

Hello linlahlum,

I’m not a lapidary, but have you talked to a monument company about
your problem? They are accustomed to polishing large stone surfaces
and doing repairs on cemetary headstones. Perhaps they can help.

Just a thought,
Judy in Kansas, who now has 120 gladiolas to plant and is busily
harvesting asparagus. The strawberries are blooming… hope to have a
good crop in a few weeks.


#3

In the beginning, just treat it like really hard wood. Use
carborundum sandpaper, starting with at least 220 grit. You might
want to go 180 or even 120, but you’re going to have to get rid of
the scratches down the line. If 220 will do it, even if it takes
twice as long, it’s better. You want to use the biggest tool you can
i.e. not a flexshaft for 4" scratches. If it can be held, I might
start with a belt sander (carefully, of course). when it seems to be
uniformly sanded, sand it some more. Then go to 400, doing the same,
then to 600. For polish, probably something like a car wax buffer
would do it, and some sort of paste like silver polish. A lapidary
might use tin oxide, but marble is so soft that something like silver
polish will do. You could even make a paste - I’d suggest ZAM. Two
tips - marble really wants to be sanded wet, but you can’t do that
with power tools. Whenever you can, though, keep it wet (water).
Related to that is the dust. It’s not toxic, but it will plug up your
lungs and nose, and there’ll be lot’s of it. Second, as with wood but
more so, every step must be complete. 600 grit will not remove 220
grit scratches. Likely, on a large surface, as you start with 400,
you’ll clean up the surface and see 180 scratches underneath. Instead
of taking a day trying to get them with 400, just backtrack and touch
it up, and then move on.


#4

i would start with 600 wet and dry paper moving through 800,
1200,then finishing with 2000 grit clean between changes finish with
the 2000 by burishing with the back of the paper over the slurry that
has builtup. you can acid polish with oxalic acid crystals applied to
damp towel burnish with moderate pressure and clean immediatly with
soft soap to neutralize acid.

David Mcleod

Anne Jackman & David McLeod
34 Merchiston Street
Andersons Bay
Dunedin
New Zealand
http://www.dmcleod.co.nz


#5

Hi

Polishing scratches in dark marble, scratches are about 4 inches
long
  1. 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.

  2. 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


#6

The 3M micron graded abrasive sheets will not leave uneven gouges so
you’ll have a much smoother move between grits.

You should be able to do this by hand with some elbow grease and
time.

They are available on a strong backing (Imperial?) for wet/dry
application that could be cut and adapted for use on a radial power
sander. You might want to feather or soften the edges of the cut
circle to lessen the chance of the edges leaving circular
"footprints".

I think I recently saw some of these available at a higher price as
PSA sheets, probably in Rio’s catalog.

HTH
Pam Chott
www.songofthephoenix.com