Sticky Issue - The QT On 3M PMA

Back in the day advice was called 'QT' as in 'here's something to keep you in the QT'. Or maybe it was like being in 'the loop'. Whatever you call it, what follows is an update on PMA to add to your giclée zeitgeist.

If you've read my book, Giclée Prepress - The Art of Giclée (www.gicleeprepress.com / (ISBN 9780-9865-75112) you'll recall that after discussing PMA there was a caveat, that the jury is still out about the long-term bonding characteristics of Scotch® 658 Positionable Mounting Adhesive (http://solutions.3m.com/wps/portal/3M/en_US/Graphics/Scotchprint/Prod-Info/Catalog/?PC_7_RJH9U5230GE3E02LECIE20S7M3).

It's been almost a year and a half since we first used PMA to mount several 96X20-inch paper giclées onto Foamcore® board. The product is ideally suited for large-sized bonding because sprays are especially dangerous and unhealthy in such quantities and brush-on adhesives produce lumpy surfaces. Even though it is very fussy to work with, it is a dream if you know its foibles and how to deal with them. That is discussed in the book, along with some of Scotch's caveats. But as I said then, lets wait and see how long it holds.

Now I can report that if the Foamcore® is allowed to bow, the PMA will let go. The release problem was discovered when we went to rehang one of the 8-footers at a book signing event and show recently. The piece had been in storage, vertically leaning against a wall and had acquired a slight bow as vertically stored panoramas are wont to do. About 18-inches had released from the center of the picture. I should have known better.

A few years earlier I learned that any curved mounting should be done post bend if possible. In other words, bend the substrate and then mount the giclée onto it. If you mount the giclée while the substrate is flat and then bend it, the adhesive will let go somewhere in the bend. If the bend is concave it will let go in the middle. If the bend it convex, the bond will let go at the ends. So as I say, I should have known. However, the amount of bowing on the big Foamcore® was rather slight... possibly 2-3 inches over the 96-inch length. So I would have thought that the PMA would have held, but I am sorry to report that it did not. That said, the ones kept flat show no signs of release.

We'll stick with PMA at Vashon Island Imaging though. You could say we've 'bonded' with it.