[pianotech] Abrasions in polyester finish

[Overs Pianos]

Paul,

If the scratch is white, but is shallow enough not to go right 
through to the substrate, it can be cut out with a hard block (which 
has been sanded flat), going through the grades from the coarsest 
which is required, to 1200 grit for machine buffing and polishing, or 
2000 grit for hand finishing.

The most common problem I see with poly repairs which have been cut 
and polished is that the damaged area often is sanded without making 
it a wider blend with original surface level. This results in a 
depression at the repaired area which can look quite unsightly, 
particularly if the final finish quality is good. This is why I don't 
use a cork bock or other easily deformed block for the sanding grades 
prior to the final grade. It is OK to use a cork block for the final 
grade, but it should be used wet and without too much pressure. The 
cork block should also be cut flat each time it is used. This will 
only take a couple of seconds if the block is close to flat, as it 
should be if it is touched up regularly.

A 'hand glaze' won't have enough cut to use straight after the 1200 
grit. You'll need a heavy-cut compound, to be followed by an 
intermediate cut, then by your hand glaze. There are so many 
different makers of cutting compounds out there, but they are 
starting to publish their cut rate in their promotional literature, 
which finally is giving us real information as to the relative cut 
rate and courseness of the various products. I still use a stitched 
mop for the first two machine cuts. We currently use three grades of 
abrasive compounds from the 1200 final sanding to the final finish.

Menzerna Power Gloss is a very agressive cut which takes out 1200 
marks in short order, and will even cut out 600 marks if you haven't 
been paying attention during the cut stages. Megiars Diamond Cut 
Compound 2.0 is economical to buy by the US gallon, and it cuts out 
the Menzerna Marks easily while leaving the surface very nicely 
prepared for the final cut with a foam wheel using 3M Foam Polishing 
Pad Glaze (05995). Getting a good finish is something which takes 
experience and developed skill, but its not something to be 
frightened of, and can be a good skill to have to complement your 
other piano work.

Regards,
Ron O.


>A new client I tuned for yesterday has a small YC grand. I noticed 
>light/white-colored abrasions on the treble side of the black-polish 
>case, right on the outside curve.
>
>When I asked her about how they came to be, she told me that they'd 
>had it moved many times, so when they wanted it moved one MORE time, 
>they decided to do it themselves ("It looks so easy when the pros do 
>it"), and dragged it on a "soft carpet, only soft carpet".
>
>She's the first client I've ever known that had her own bottle of 
>Cory High Gloss Finish polish (which I always bring, too) though the 
>piano was quite dusty and well-smudged. As I cleaned, dusted, 
>vacuumed, and polished with the Cory, I noticed that the abrasions 
>seemed to be slightly reduced in intensity.
>
>It just occurred to me now that perhaps this could be buffed out? I 
>didn't consider that possibility and took no photos while I was 
>there. I just called the owner to ask if she could take a photo or 
>two, but she cannot.
>
>Was the apparent reduction in abrasion likely my imagination? Or 
>would it be worthwhile to try something with a very mild abrasive? 
>I'm thinking something like "3M Imperial Hand Glaze 05990"
>
>And yeah, I know a photo would probably help a lot... sorry!
>
>Paul Bruesch
>Stillwater, MN


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