Building and Preparing and Aluminum Composite Panel for Oil Painting
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Several years ago I posted a step by step guide to stretching, sizing and priming a linen canvas for oil painting. Around the beginning of 2014, I switched from painting on linen canvas to painting on aluminum composite panel. The following is a step-by-step process for archivally preparing an aluminum composite panel (ACP) for oil painting.
Why the Switch?
Linen stretched on a wooden frame, sized with rabbit skin glue, and primed with white lead in oil is a traditional painting support that is about as archivally sound as a stretched canvas can be. But it has a few drawbacks. First, it is relatively fragile and can easily be punctured or dented. Second, it is flexible, and as it flexes, the paint layers adhered to it flex as well leading to cracking over time. Third, it is dimensionally unstable and can change size, and therefore tension, dramatically with changes in temperature and humidity which, again, subjects the paint layers to mechanical stresses that eventually lead to cracking. This can also lead to wrinkles in the corners of the painting which necessitate adjusting the wooden frame, a process which also applies a mechanical stress to the paint layers. Finally, even a very well prepared linen canvas will eventually deteriorate and, assuming the painting is valued enough and the paint layers are intact enough, have to be carefully removed and replaced. This is an incredibly delicate and expensive procedure.Painting on wooden panels solves or limits the puncture problem, but wooden panels have their own set of issues with warping, cracking, and dimensional stability. They also can rot or deteriorate, but unlike canvas, they cannot be removed from the paint layers and replaced.Aluminum composite panels solve all of these problems. ACP is essentially two extremely thin layers of aluminum sheeting with a core of ABS plastic sandwiched between them. The panels are perfectly flat, dimensionally stable, and very tough. They don’t warp or crack with exposure to moisture or changes in temperature. They don’t rot or corrode over time necessitating removal and replacement.Incidentally, it turns out that ACPs are actually cheaper to build than a traditional, stretched linen canvas. For example, based on one cut list, I can get two 24 inch by 40 inch panels, four 18 inch by 30 inch panels, and one 18 inch by 24 inch panel out of one 48 inch by 96 inch sheet of aluminum composite (85 per full sheet). That’s seven panels! The aluminum frame for the back of these seven panels (see below) requires eight 96 inch lengths of ¾ inch aluminum L-channel bar stock ($16.50 each). Assembling the panels will use roughly four packages of epoxy (again, see below/$5 each). The total cost for all the materials to build these seven panels comes to roughly $250.00 after UT sales tax. Just for fun, I decided to price just the wooden stretcher bars to build seven linen panels in these sizes. At $7.20 for each 18 inch bar, $9.35 for each 24 inch bar, $12.45 for each 30 inch bar and $17.80 for each 40 inch bar, the cost for the stretcher bars comes in at $298.90 before tax. Considering the linen would add at least another $100 (that would be a screaming deal), that makes building these seven panels roughly 70% as expensive to build as seven similarly sized, stretched linen canvasses.The type of ACP I am using is manufactured by 3M and is branded DiBond or e-panel. It is roughly 1/8 of an inch thick with a 3 mil sheet of aluminum on both the front and the back. On one side, the aluminum is lightly coated with a clear coat to prevent oxidation and on the business side, a baked on polyester coating has been applied both locking out moisture and smoothing the panel. It comes in 4 x 8 foot, 4 x 10 foot and 5 x 10 foot sizes and, where I live, I can get a 4 x 8 foot sheet for roughly $85 (sounds expensive, but it’s cheaper than linen). It can be cut to size on a table saw, and the supplier I use will cut it for me if I supply a cut list. Depending on the dimensions, I can get 2-3 large (32 x 40-ish) painting panels and 6-10 small (9 x 12-ish) painting panels, or 7 medium sized panels (24 x 30-ish) out of one sheet. 
Step 1) Building the Panel
So what do you need to build an ACP worthy of your best artwork? Well, obviously, you need some Dibond or e-panel cut to the size you want your painting to be. Sweet! But hey: if you’re painting 18 x 30 inches or bigger, your panel is going to be a bit wobbly. Really wobbly if you’re pushing 30 x 50 inches or larger. You’re going to need to add a frame to the back to add rigidity. As a bonus, I like to take advantage of that frame to add a hanging wire to the back of the panel so I can keep it up off the floor until it’s in a frame.You could use wood, but then you’re back dealing with the dimensional instability/warping issues again. I like to use aluminum. Consistency! You can get extruded aluminum bars in a variety of shapes from most hardware stores these days. For the big 35 x 60 inch panel I built for ‘Terra Incognita’ (the first ACP I ever put together) I used one inch square aluminum tubing and even added a crossbar in the middle. This was probably overkill, but since the painting was a commission, I wanted to make sure the panel was as good as indestructible. For most moderately sized panels (the ones shown here are 36 x 40 inches, 40 x 32 inches and 48 x 24 inches) I use ¾ inch L-channel. It’s about an eighth of an inch thick, reasonable strong and light, and costs around $16.50 per 8 foot length. Again, this may sound expensive, but it’s cheaper than a good wooden stretcher bar. A chop saw with a general-purpose blade can cut these aluminum bars easily enough. Just go slow, and wear eye protection. Seriously, you’re an artist. Wear eye protection.
Here is my method. I cut the frame material to size with my trusty chop saw. I don’t miter the corners. Instead, I cut the pieces for the sides of the painting full length, and then cut the top and bottom pieces to fit in between. This works really well since in almost every situation you are only going to see the sides of the painting. And, of course, if you put a frame on it, you won’t see the edges at all. So, for example, for the 36 x 40 inch panel, I cut the sides 40 inches long (I really cut them 39-15/16 inches long because that is the actual size of the panel…) and the top and bottom pieces 34-1/2 inches long (add the ¾ inch thickness of the sides and you get the 36 inch width of the panel).Once the pieces are cut, I use a rasp to clean off the burrs and sharp bits left by the saw. I almost never cut myself.
Then I get all the parts together and make sure they fit. Shiny.
The first few panels I built were great, but they had one drawback. Until they were framed, they were really hard to hang on a wall. I came up with a neat little system for building a hanging wire into the panel that not only works great, but when the L-channel is used for the frame, also looks pretty cool when the panel is hanging on the wall (it looks like the panel is floating ¾ of an inch in front of the wall).Before building the panel, I make two marks a half inch apart and centered on the inside of the L-channel pieces that will be the left and right sides of the frame. I measure down about as far as I would if I were installing a hanging wire on a framed painting; in this case, about 8 inches. Notice I’ve marked the left and right side pieces so they are mirror images of each other! That’s important. Then I use a 3/16 inch drill bit make two holes. Aluminum is pretty soft, and my regular drill bits work just fine. The shavings are razor sharp though, so I’m careful brushing them off my work area. Then I put a ½ inch drill bit in the drill and with just a little pressure put a bevel on both sides of each hole so the hanging wire doesn’t get cut by the sharp edges.
Now I’ve got my panel and I’ve got my frame pieces. The panel goes face down (white printed side down, shiny aluminum side up) on the work surface. I leave the protective, white plastic in place at this point and make sure I’m not setting the panel on top of anything that might scratch what will eventually be the working surface of my painting (like…ummm…aluminum shavings from drilling holes…for example).
To fasten the frame to the back of the panel, I use a steel epoxy rated for aluminum called J-B Weld. I’ll get to that in a minute. In order for the epoxy to bond as permanently as possible, both the back of the panel and the side of the frame that butts up to it need to be sanded well with a rough grit (80-100 grit works great) sand paper. For the panel, the clear coat that protects the metal surface has to be sanded all the way through. You can tell when you’re down to the metal, because you’ll start making aluminum dust (black) and the paper will stop gumming up. I’ve done this by hand, but it takes a lot of work. I prefer to use a power sander. With the frame pieces, the top layer of the aluminum has to be completely removed. Aluminum oxidizes just like iron. Unlike iron, instead of flaking off, the aluminum oxide stays on the surface and protects the metal underneath from further oxidation. This is why aluminum doesn’t ‘rust’ like iron does. This is a nice feature for corrosion prevention, but the aluminum oxide layer won’t bond as well to the epoxy, so it’s got to go. I sand the side of the frame piece that will go against the back of the panel. I like to set all the pieces in place and on the frame and then label the size I’m going to sand just to be sure I get it right. I always sure I position the holes for the hanging wire correctly! Again, this can be done by hand, but a power sander is much easier. I’m not sure how bad for the lungs to breathe aluminum dust, but rather than find out the hard way, I just wear a dust mask. I do all this sanding immediately before I do the epoxy work. I don’t wait a day in between or a new layer of aluminum oxide will have started forming.
Now I make sure I’ve got all my supplies at arm’s reach. Acetone to clean any oils from my hands that might interfere with the bonding off of the aluminum pieces, plenty of J-B Weld (it’s a two part epoxy…so I need both tubes!), paper towels for clean-up, sturdy rubber gloves both to keep the epoxy off my hands (it’s hard to get off later) and to keep oils and sweat from my skin off the aluminum, a good, flat, sturdy putty knife for mixing and applying the epoxy, and a whole bunch of 1 inch spring clamps. Hooray for spring clamps!
I put on my gloves and wipe down all the aluminum parts with acetone. I use a small scrap piece of DiBond as a mixing surface for the epoxy. The instructions for mixing the epoxy are on the package and the tube, but it’s really simple. I squeeze out equal parts epoxy and hardener. For a panel this size (36 x 40 inches) I have found it’s easiest to use the whole package of epoxy rather than trying to be a miser… so I squeeze out about ¼ of each tube. Why not mix the whole thing at one, you ask? Well, this stuff tacks up pretty fast. In fact, I have to move quickly to get it mixed and applied to just one frame piece before it gets too tacky to spread easily. So I do one edge of the frame at a time. I use the putty knife to mix the epoxy components together thoroughly. It’s just like mixing paint. Spread it out… scrape it up and flip it over…repeat. Then I spread a nice even coat over the entire surface of the frame piece that will be up against the panel. This is the side I sanded (hopefully). I start with one of the side pieces! The top and bottom pieces will butt up against it next. I move fast, but not so fast that I’m sloppy or get an uneven, patchy coat of epoxy. (Incidentally, this stuff will not come out of your clothes/carpet/concrete/etc. if it sets up there. Ever. Take the necessary precautions.)
I gently set the frame piece (one of the side pieces, yes?) on the panel so that the flange that sticks up is toward the inside and the other edge is flush with the edge of the panel. I get it as perfectly flush as I can all along the edge and at both ends. Then I clamp it down one clamp at a time starting at the ends, then the middle, then the middle of each remaining section, etc. I have to carefully adjust the clamps as I place them because the frame piece has a tendency to drift in or out under the force of the clamp as it settles into position. I keep adjusting the clamp until the frame stays put flush with the edge of the panel, and come back to check the clamps I’ve already placed as I’m placing the new ones. Once I’ve got all the clamps in place and am sure the frame piece is not moving, I use the putty knife to clean up the area where the top and bottom frame sections are going to butt up against the piece I just placed. I clean the putty knife immediately, and check to make sure I haven’t gotten epoxy anywhere I don’t want it.The epoxy tacks up fast. 5-10 minutes depending on the temperature. It will dry to the touch in a couple of hours and be hard enough to remove the clamps in 5-6 hours. I try not to put the joint under any serious stress for 24 hours.If you only have a few clamps, you’ll have to wait until the epoxy has set for a few hours before you can move on to the next piece of the frame. I have a lot of clamps, so I move on to the top and bottom pieces right away. They go on just like the first piece, except they butt up against it instead of being flush with the panel edge at the ends. I like to put a little epoxy in the joint. If I measured correctly, there should be exactly enough room left at the remaining edge of the panel for the other side piece.Once I get the last piece of the frame in place, I let the whole thing set for at least five hours before removing the clamps (I usually give it overnight) and then let it harden completely for 24 hours before moving on to the next step.Once the epoxy is fully set and the clamps are off, I clean up the edges of the panel and the joints on the back of the frame with rough-grit sandpaper.
Before I get around to preparing the painting surface, it’s time to install the hanging wire. This way, in theory, the painting should never have to be set face down again.
Step 2) Priming the panel
Ok. The panel is built, now its surface just needs to be prepared for oil paint. This is a good time to peel away the protective plastic from the business side.The first step is a very light scuff sanding to increase the adhesion of the primer. I use fine grit sandpaper (at least 320). The first few times I did this, I just went right at the panel with the sand paper, but ended up getting super-fine white dust everywhere which was a real pain to clean up. Then I had to wipe the panel down with a wet paper towel to get all the remaining dust off before priming. I’ve found it’s actually much easier to wet-sand the panel, so I use paper that is made for it. The sanding goes faster, the paper doesn’t clog up, and there is no dust. Sweet.A word of caution: It’s really easy to sand all the way through the polyester coating. This is a bad thing. Don’t do it. Just lightly scuff up the surface (it should be just a little more matte than it was when it was new, but it will still feel as smooth as silk) but do not expose the aluminum.Once the sanding is done and the panel is clean (I try not to touch it with my hands) and dry, it’s primer time. I should mention that I have been told that it is safe at this point to jump straight to an oil paint primer coat. However, the company that manufactures the panels (3M) recommends a thin coat of DTM primer first. It is formulated to bond to the polyester coating on the panel and provide a surface that will take the oil primer better. This DTM primer is not cheap. This one gallon can cost around $120. But, it should prime a lot of panels. A lot. Again, if you compare it to the cost of sizing a bunch of linen canvases with rabbit skin glue, it’s as cheap if not cheaper in the long run… and it’s far easier to work with. One light coat is sufficient.
When I apply my primer coats to panels, I like to finish with light brush strokes in random directions so there isn’t an obvious vertical or horizontal pattern that might be distracting if it shows through in the final painting. With a canvas support, the texture of the fabric conceals the brush strokes of the primer coats, but everything shows up on these super-smooth aluminum panels. The upper, left-hand image below shows the brush stroke texture of the panel after the light coat of DTM primer has dried for 24 hours.The final step in getting the panel ready to paint on is a few coats of a good oil primer. I cannot recommend Rublev Lead Oil Ground (manufactured and sold by Natural Pigments in California) highly enough. It is an absolute pleasure to paint on whether you are using panels or canvas. It’s as archival and traditional as it gets, dries to a hard, flexible film, and takes paint like a dream. Yes, it has lead in it. A lot of lead. So don’t drink it, don’t lick your freshly primed panel, and wear gloves when you apply it and clean your brushes. Not a big deal.I apply two thin coats straight out of the can allowing the primer to dry completely between coats. Then I finish with a coat I have tinted slightly with Ivory Black and Raw Umber so I don’t end up painting on a blinding white surface. The bottom, right-hand image below shows the texture of the fully primed panel.Note: I am currently experimenting to find out if my use of Raw Umber in tinting that final coat is increasing the problem of darker colors ‘sinking in’ when they dry. If you are an oil painter, you are familiar with this problem. If I find the Raw Umber is the culprit, I will update this post with a better practice.Update: My current experiments seem to indicate that the base ground used has more to do with the sinking in effect than any tinting pigment added to it, and that sinking in is mostly correlated with the pigments applied to the ground, not to the nature of the ground itself. So go ahead and use that burnt umber to tint your ground.
Step 3) Paint something awesome the panel!
The panel is finished! Well, almost. It’s a good idea to let the panels sit around for a few weeks to fully cure. I don’t always have the patience to do this, but if I’m planning my projects far enough in advance, I try to prime several panels at once for upcoming paintings while I’m still working on whatever is on the easel.The only step left is to put the beautiful, new, archivally sound panel to good use! The 36 x 40 inch panel shown in this post ended up as the support for ‘Saturn and Dione’.
After a couple of years of working on Aluminum Composite Panels, I am a big fan. They end up costing less to prepare than a traditional linen canvas. They are only the slightest bit heavier, and if the time is taken to incorporate a hanging wire, they are as easy to move around and hang. They are vastly superior archivally to their canvas alternatives. I do, occasionally, miss the springiness of a nice, tightly stretched canvas, and the subtle linen texture, but I’m very glad not to have to worry about punctures, tears, dents, wrinkles and stress cracks.
A Note on Logistical Considerations:
Stretched canvas is often thought of as the most traditional support for oil painting, but this is not exactly true. Painting on panel, even metal panels such as copper and gold, is a very traditional practice that predates the use of stretched canvas. Some of the oldest paintings that have survived with the least amount of damage were done on metal panel. However, if you want to paint big, panels become a more difficult proposal. Hiding seams and joints was historically and is today extremely difficult if not impossible. Transportation of large paintings done on panel is also an issue. Size and transportation considerations were leading factors in the rise of canvas as the most popular painting support.As I mentioned at the beginning of this post, Dibond, e-panel, and all the other brands of Aluminum Composite Panel of which I am aware are limited in size to 5 x 10 feet at the very biggest.I recently completed a commission painting designed to fit a specific space that ended up measuring 194 x 92 inches (roughly 16x8 feet). The clients were very interested in Aluminum Composite Panel as the support for the painting. I ended up collaborating with a local metal fabrication shop and frame maker and an expert on archival painting practices and materials to design and build a custom aluminum panel for the project. Logistics were a huge factor that had to be taken into consideration, including the fact that the painting would not fit through a standard door or make a turn in any standard hallway. The panel also weighed in at around 500 pounds which meant I couldn’t move it without help and it required some seriously beefy easels to support it while I painted on it. If you’re interested in the full story, you can find it here.