Finish Over Polyester?

[Overs Pianos]

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Hello Philip,

At 12:24 PM -0400 25/10/04, Philip Jamison wrote:
>

>I have a nice black lacquer Yamaha grand with a white
>polyester music desk! Obviously a replacement, I wonder if I
>can safely apply black lacquer over the polyester.

You certainly can. Repair any cracks or damage in the polyester 
first, then cut it back to 600 grade (wet is better, but don't get 
water in the screw holes or you'll ruin the flatness of the finished 
job, then light dry sand before applying the top coat). Never apply 
lacquer to a wet sanded substrate or you may get keying (adhesion) 
problems. If you cut it by hand using a cork block, make sure you 
sand the bottom surface of the block flat on a known flat surface 
(eg. the cast iron bed of one of your workshop machines). If the 
cutting block isn't flat you will not get the panel flat. I give my 
cork blocks a wipe with 150 grit paper on a flat surface every time I 
use them because the water from the previous use will cause the cork 
to swell and distort. The same applies to wooden blocks if you use 
them. Wooden or hard synthetic blocks are a must when repairing 
polyester damage - or the result won't be flat.

Lay up two or three medium-wet coats of lacquer, block sand to 1200 
wet (or 2000 if you have it), then buff and final polish with a foam 
pad at low speed (I use a speed control on a Makita polisher, with a 
custom handle made to lower the handle-height down to about 50 mm 
(2") higher than the pad surface for better control). As with 
buffing, always polish with the foam 'rubbing' from the flat area to 
the edges, and definitely not the other way round or you'll burn the 
edge. Lacquer won't be as hard as polyester but the finish standard 
can be every bit as good.

Yamaha use lacquer for some of their parts and polyester for others 
anyway (in the same piano). Make sure you are using a proper 
'jet-black' black, or your repair area will look smokey-grey against 
the original panels. A lot of the new automotive finishes use the 
proper black color. The current Mazda jet black is a perfect match 
for Yamaha. Furthermore, you can get it in a two pack material (if 
you have the proper respiration gear to avoid premature greyness from 
the cyanide content - not to mention an early death should you make a 
thorough job of inhalation). The two pack material would be much more 
durable for the music stand.

Ron O.

-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
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