Preparing Gesso Panels

Saturday, 16 November 2013, 1pm

This blog is about the preparation of gesso panels, written for information for my students.

The support for a charcoal drawing or subsequent painting or pastel is as important as the choice of drawing and painting material. A well prepared surface can really bring an artwork to life. I use flat gesso panels for many reasons, the main ones being that I can draw directly onto the surface with charcoal and I can use thin oil glazes, in both cases without interference from the weave of canvas. They’re also easy to transport. Gesso is the surface of choice for all painting.

There are many choices for the actual panel. Masonite and plywood are the oldest materials (plywood was used by the Romans to make shields, covered with stretched canvas and painted) and probably the strongest and safest. Plywood has the problem of grain pattern and will need more coats of gesso to get a smooth finish. I use Medium Density Fibreboard (MDF, ‘Craftwood’) of 3mm thickness, often using 600x900mm precut sheets. This size is about the maximum easily carried into the field and allows free and uncramped arm movement while drawing. MDF is easily damaged and care should be taken to protect the edges. If you’re using precut panels check the edges before purchase. If you’re cutting up large sheets, I recommend trimming the edges with a router. MDF can also be purchased with a white surface on one side, which can be used as the back of the panel and avoid the need for undercoating it.

The first step is sealing the panel. I use shellac, known as ‘the universal sealer’ before the days of plastics. You can buy this as flakes or premixed. If using flakes, cover the flakes with methylated spirits and leave to sit for at least 24 hours. This is the base stock. Fill an old shampoo bottle about 20% full with this and then top up with meths. This is what is used to seal the panel. Sealing cuts down on the amount of paint used (the paint soaks in less), strengthens the panel, helps to stop moisture getting into the wood and warping it and helps prevent outgassing of the glues used in the panels, which can damage pigments. Be generous with the shellac and allow 24 hours for it to dry.

Using a soft cloth to apply shellac

Next step is to paint all 6 surfaces of the panel. If the panel has a sticky label, scrape it off and mark this side as the back, as the surface is usually damaged by the removal of the label. I use two coats of a good quality interior/exterior undercoat/sealer and a good 5” roller with a fairly fine pile. Foam rollers work well, but don’t last as long.

It is unnecessary to wash out the roller between coats. Wrap the roller and tray in a plastic bag to prevent it drying out, which will last up to a week with no problems.

Roller and tray wrapped in shopping bag

I paint two coats of undercoat on the back and edges first, marking the back with a pencil when dry, to avoid confusion as to which side to use. The edges are painted before the main surface with a fairly dry roller (if painting many panels, don’t recharge the roller after the previous panel). If painting in hot weather, run the roller over the bead formed on the working side of the panel immediately, or it will dry off quickly and cause a lumpy edge. Don’t worry about the bead on the other (front) side. I usually put the second undercoat on about an hour after the first.

  

Bead formed when painting edge with roller

Lump in wet gesso picked out with finger. Lumps are more common in cheap gesso.

Now for the front surface. You can use five coats of gesso and no undercoat, or two coats of undercoat and two or three of gesso, just to extend the gesso, which is expensive. Before undercoating the front surface, sand the dried bead off the perimeter (left from painting the edges) and give the sealed surface a light sand. I use 240 grit Aluminium Oxide paper for all sanding. It has a more even grit size than common sandpaper, and won’t scratch the surface. 

Sanding materials

After undercoating the front, give it and the edges a light sand. The purpose of sanding is always just to knock off any lumps, not to make it completely smooth.  Be particularly careful when sanding close to the edges, it’s easy to rub through the coat. Sand up to the edges, not beyond them.

After giving the undercoat a day to dry I apply three coats of gesso (use minimum of two), allowing a day to dry between coats. I use the best quality acrylic gesso that I can get, diluting with 30 to 40% water. Cheap gesso can be a pain, with lots of lumps to pick out, and it can’t be diluted as much.

Diluted gesso and roller

Be aware with rollers that the pile has a ‘grain’, rolling in one direction will produce a rougher surface than the other.

Rougher surface on the left from running the roller the wrong way

The aim with applying gesso is to lay it on fairly thickly and as smooth as possible. I apply it quite wet, then smooth out with the roller in one direction, then at 90 degrees, using less pressure with each run.

Good, even wet surface

Sand the gesso lightly between coats and after the last coat. The bead that forms around the edge on the back of the panel can be problematic, sticking to adjacent panels when stacked. Either allow a couple of weeks to dry before stacking, or scrape or sand it off.

Panels drying on the back of the ute.

It’s a lot of work, but it’s worth the effort.