Cutting and Handling ACM Panels
The panels come with a protective film that is pretty tough. I can load them into the back of a pickup without worry of them being scratched.
The panels can be cut a number of ways, but the best way I've found is on a table saw with a common 32 tooth carbide blade. The Aluminum isn't that much of a challenge for a saw blade as the aluminum is only about as thick as ones thumbnail. This method leaves a nice edge that can be sanded easily with a few passes with 150 grit paper.
Other methods, such as cutting with a box knife, leave the edge with a bit of a ridge that is much harder to sand down.
Applying Gesso to ACM Panels
In preparation for priming I sand with a 150 grit Garnet sand paper. The polyester paint sands quite nicely, making a free sanding dust without gumming up, like chewing gum, on the sandpaper. The objective here is to sand the surface thoroughly, without sanding through the paint and into the aluminum. I use an electric sander and am careful to sand the surface thoroughly making sure there are no glossy spots yet not sand through to metal. My best results were with an open grit Garnet paper.
I then take the panels to the kitchen sink and wash them free of the sanding dust and dry them and set them up to be primed. Just before I prime them I give each a squirt (from a plant mister) of rubbing alcohol to clear any surface oils and they are ready to prime.
I use DTM Bonding Primer B66 A 50 by Sherwin Williams. It's a water based Distributed Acrylic Base which provides strong adhesion and is especially designed for priming over pre-finished metal siding such as the polyester polymers used on Dibond. the B66 A 50 includes a small amount of marble dust that provides a nice tooth for adherence of Gesso coats to follow.
Especially note that there are two kinds of DTM primers that Sherwin Williams sells. Be sure to buy the Bonding Primer B66 A 50 which is intended to be painted over and leaves a very nice toothy surface for the Gesso to adhere to.
The DTM primer provides a very strong bond to the ACM panel's polyester coating and is the primer recommended by Golden and several technical sources I've found.
DTM Primer Application
I apply the primer with a 6" white, high density, micro foam roller that I buy from Lowes. It's the one that they recommend for painting doors and cabinets. I apply 4 thin coats of primer to get complete coverage. No sanding is required between coats. The application method and technique is the same as described for applying Gesso below so you can skip forward and pick up some of the more subtle tips. Roller clean up with water is easy.
Using Liquitex Gesso I squirt out a little onto a large tile palette. I thin it only slightly with a squirt of water from a plant mister and very thoroughly distribute the gesso into the roller, so it will apply evenly. I very lightly load the roller.
I use Liquitex only for the reason that it is less messy to get out of the container and onto the palette, but Golden Gesso also works well. Golden is a little thicker and requires a bit more water when thinning.
I apply 4 thin coats which provides quite a smooth surface that requires no sanding between coats. If you want more of a textured surface just load your roller a little more until you find the texture you prefer.
To get a smooth surface I keep a plant mister by the palette and thin the gesso on the palette with a few mist squirts of water. I don't load the roller with too much paint so I can keep the application of each coat pretty thin.
When the first coat of gesso is applied the appearance is thin and a bit transparent. Even though the first coat is thin there will be a lot of meringue like peaks that betray a smooth surface. Those will dissipate a bit in the first few minutes but not completely. After the first coat has dried for about 2 min then go back over with the roller (mostly dry not loaded). With no pressure on the roller, lightly roll the surface again breaking down the roughness and smoothing the surface.
I use four coats to get a smooth surface that covers completely. And the best part; no sanding is required between coats or after the last coat. The only sanding I do is when I sand the panel in preparation for the primer. The thickness of the application of course determines the drying time between coats but it dries pretty fast.
Thicker paint and a heavier loaded roller loading will make a heavier texture, so vary the misting and the amount of paint on your roller to suit the finish you desire.
Clean up..... If I'm gessoing or priming several times in a day, or even the next day I wrap my roller in a plastic WalMart sack to keep it from drying out between uses. My coats are pretty thin, I wait about 1-1/2 hours between coats. I do not pour out any gesso on the panel. I work the gesso into the roller on the palette then roll the next coat on. Pouring the gesso on the panel will soften and lift previous layers .
After much review with various Technical Departments and experienced ACM users as well as other "Best Practices" sources, I'm pretty comfortable with this system. It makes a surface similar to expensive quadruple primed surfaces that are smooth with a very slightly pebbled texture.
Applying Oil Ground to ACM Panels
For those wanting to paint on an Oil Ground surface the following method applies.
Choosing a Primer
This topic is filled with many different opinions with many people recommending many different products and some recommending that "scuffing up" the surface is all that's needed! I tend to go first to the manufacturers and commercial users recommendations for advice. The fabrication Manual from Alcan/3A Composites says that the best direct adhesion occurs after lightly scuff-sanding the painted polyester surface, followed by wiping with isopropyl alcohol, and then application of properly selected paints/primers. They also caution not to sand through the coating to the aluminum surface. Acrylics are mentioned among the list of “suitable paints”. Oil based paints/primers are not on this Manufacturer's list of approved primers. There are paints and inks that are recommended for direct application. But these are inks and sign paints specificly made for sign painting. A broad majority of products recommended as primers are all posting Acrylic based primers citing adhesion to the polyester coating.
Two bonding primers seem to be mentioned most often in the users sites I've been on. Sherwin Williams DTM Bonding Primer and Rustolium UMA Bondin Primer both are commercially available primers. Both are designed to be primers for polyester coatings as found on ACM panels and are often used in other hard to coat surfaces. I've used DTM Bonding Primer, it has a history of many successful, interior AND EXTERIOR applications. This does not mean that other similar primers could not work as well, but these two have a successful track record for this kind of application.
See the following article from Golden Artists Paints
To apply, follow the Surface Preparation and Primer Application in the Gessoing Section above. Then apply the Oil Based Ground / Primer of your choice.
Bonding Canvas to ACM Panels
Bonding Canvas using Natural Pigments Beva Film
--- sand and wash the panel as described in the method above.
--- mist the panel with alcohol and wipe dry and clean from grease and dust
I"ve used Beva Film as my adhesive from Natural Pigments... it's a heat activated adhesive film that comes in a roll. It's a thin layer of adhesive applied to a clear plactic sheet and backed with another layer of opaque plastic.
I cut the film to the size of the panel plus about a quarter of an inch on each side. Leave just enough overhang so that you insure 100% coverage. But too much overhang will get messy when the glue melts in the press.
Then I peel the opaque plastic sheet off leaving the adhesive sticking to the clear plastic film. I lay the plastic film (glue side down) on to the panel and with a heated iron from a hobby store (a regular iron works fine) I touch the iron to the corners of the panel activating the glue. Now with the plastic sheet and glue is attached to the panel so it won't slide around. It's ready to for the dry press.
Dry Press Preparation
I use an old Commercial 200 Dry Mounting and Laminating Press made by Seal Inc. There are many kinds and models. I bought mine from Craigs list for 200$. It works ok but the temperature is a bit tricky to adjust since the knob with the pointer is missing.
To tune up the temperature control I use a kitchen oven thermometer... the kind that you stick in the turkey and it reads out on a digital display on the counter.
CRITICAL NOTE: Most ACM Panels have a max temperature limit.... above which the panel will warp. I try to keep the panel I'm using to a max of 160-165F.
Precautions: (1) Be aware of the temp limits the product you are using, (2) temperature test the heated press you are using for accuracy and (3) make several "dry runs" on a scrap piece of panel.
The bottom plate on my press is about 1/2 inch of felt and the top plate is metal so when I put the panel in I lay the ACM panel on the felt and then put a couple of sheets of craft paper on top of the panel.
To temperature test your heated dry mount unit put the oven temperature probe into the press, close the lid and adjust the temp knob so that the probe reads 160 to 165F. Wait at least 10-15 min for the system temp to stabilize so that you're confident it won't go above 165. The panel will warp if temps go much higher and the glue activates between 150 and 155F, so temperature accuracy is critical.
Once the Press is warmed up and temperature is controlled you are ready to proceed.
Just a note of caution... Don't believe the temperature read out on the press. Test it with the digital kitchen thermometer
Attaching the Adhesive to the Panel
First we attach the glue to the panel. The clear plastic sheet and glue "tacked" to the panel was prepped previously and is ready to go. So we open the press and insert the panel and place a couple of sheets of craft paper over the panel. This keeps the upper platten clean and free of glue.
I leave the panel in for about 60 to 90 seconds. Just enough to activate the glue so it will stick to the panel.
After removing the panel and while it's still warm I use a small brayer to roll over the plastic pressing the glue into the panel. Then I let it all cool for a few minutes.
After cooling the plastic can be removed leaving the glue attached to the panel.
Bonding the Canvas
Carefully lay the canvas over the panel making sure it is square and straight. Note the canvas should be cut so that it overlaps the edges about 1/4 to 1/2 inch. Carefully insert the panel back into the press, once again covering the panel with craft paper.
This time let the panel "cook" for about 4 or 5 minutes. Then remove and roll the canvas down with the brayer making sure the canvas is down securly and there are no bubbles.
Trim the panel with a razor blade and you are finished.