Clear poly repair

[Ron Overs]

At 7:45 AM -0800 30/12/02, Paul McCloud wrote:

>I read the article in the latest Journal.  It doesn't cover how to build
>a dam to hold the polyester on a vertical surface.  I would get the
>Konig polyester kit from Ruth Phillips.  I think it has the mylar sheet
>that you will need to make dams with.

Masking tape also makes an excellent 'dam' construction material.

>  Take a pocket knife and scrape
>each of the chipped areas so the edges of the repair are smooth and
>there is about a 45 degree angle into the damaged area.

Indeed, or another alternative if you plan to do a lot of poly' 
repairs is to get an old chisel and cut off say 1.5 inches (37mm) of 
the shank with a cut-off wheel, and epoxy it into a piece of 1" 
(25mm) dowel to make a suitable handle. The scraping surface is best 
ground to a convex curve, which makes the job of scraping the 
bevelled joint surface very much easier. The scraper must be very 
sharp to allow for the original poly' to be scraped away without 
disturbing the bonding of the finish with the veneer at the bottom of 
the scraped region. If the veneer/poly joint line is damaged an 
unsightly ring will become visible after the pour.

>   Cut a piece of
>mylar sheet and tape it over the area with clear tape.  Keep the top of
>the sheet open so you can drool the polester into the pocket.  Be sure
>the tape is tight on the other 3 sides so it doesn't leak.

Indeed, we have a wooden box for the kit which is leak-proofed at the 
corners with Titebond. We place this under the repair if we a doing a 
repair on the client's premises. It can save an awkward situation 
should the dam leak before the gel-time.

>   If your
>chips are close together, you can use 1 piece of mylar, otherwise cut
>more pieces and tape them too.  Cut your sheet just big enough to cover
>the damage.

Another procedure which makes the grind and scrape down of the cured 
poly' easier when finishing, is to cover the polished surface 
adjacent to the scraped area with masking tape prior to forming the 
dam. This protects the original surface against inadvertent damage 
when grinding and scraping the new material.

>Mix your poly and dribble it in with a stick.  You might have to hold
>the top edge slightly away from the surface so the poly will slide down
>and fill your pocket.  Mix the poly carefully so there will not be any
>bubbles.

Indeed, the partial breakdown of the MEKP which can release oxygen 
into the mix, is a common problem with poly' repairs. Different 
resins and catalysts can exhibit the problem to varying degrees. The 
problem can be helped by thinning the resin if it is a little thick, 
with up to 20% Styrene Monomer.

>   I usually tip the mixing cup and let the resin come up near
>the lip where I've put a small dab of hardener.  Then I use a stick to
>mash the hardener and resin together before I mix the whole thing
>together like a cement mixer (cup is still tipped).  Use the stick to
>scrape the sides of the cup and SLOWLY turn the cup, so you won't
>introduce any bubbles.  I've never had much luck getting rid of bubbles
>after they are in there.

Excellent advice.

>Next months' Journal article, part 2, is going to be how to sand and
>finish the repair.  If you get the poly kit from Ruth, there will be
>instructions with it how to do this.  It's not difficult.

Ron O.
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OVERS PIANOS - SYDNEY
Grand Piano Manufacturers

Web: http://overspianos.com.au
mailto:info@overspianos.com.au
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