108: Preparing Laser Cut Wood for Paint

Scott at work!  Mixing the green wash (there is a touch of gel medium in the glass too)

Scott at work! Mixing the green wash with our trusty note taking and testing plate.  

This month I thought it would be fun to add a new skill: properly preparing a wood surface for painting.  I have painted laser cut wood in the past (Week 64 is a notable example), but honestly, the preparation and finished result is not what I’d consider fine art.   So, with the help of Scott Sherwood, Fine Art Conservator, we will learn some basic first steps to preparing unfinished laser cut plywood shapes for paint.

week 108

Supplies you will need:

  • Laser cut wood shapes
  • Grain filler (I picked up DAP Plastic Wood from the local DIY store)
  • Scraper or palette knife (we used a metal spatula!)
  • Gesso (Liquitex is Scott’s favorite, easily attainable brand)
  • Water
  • Paper Towel
  • Brushes
  • Foam roller
  • Sandpaper (240 or 400)

Step 1:  Cut your shapes

Our professional work surface

Our professional work surface. Apologies for the poor photos – I was not using my own camera, and we hopped from natural light to fluorescent light too much.  Another lesson learned!

For ease, I precut some plywood into shapes I had on file – a bird, the whale and a couple different quatrefoil examples.  I also had a couple plywood circles left over from an earlier project and threw them in the mix.  Cutting first means the edges will get some over paint and need to be finished at the end – if that is a problem or you have a particularly intricate shape, I’d suggest preparing the surface and possibly even applying the background color before cutting.

Step 2: Determine whether you have open grain wood or closed grain wood

Closed grain on the left, open grain on the right

Closed grain on the left, open grain on the right

Raking the light across the surface makes uneveness pop right out

Raking the light across the surface makes uneveness pop right out.  The ampersand wasn’t cut for this project, but something I had laying around.

Some wood simply has more prominent grain than others.  Oak is a prime example of open grain wood.  The shapes I specifically cut for this project were on closed grain (I believe it’s birch ply), but the circles were open grain oak ply.

Like buttercream frosting :)

Like buttercream frosting 🙂

Post filled and sanded disks. They are amazingly smooth!

Post filled and sanded disks. They are amazingly smooth!  The lighter spots are the fill.

Side angle on the sanded disks to better show texture.

Side angle on the sanded disks to better show texture.

Open grain needs to be filled in order to achieve a smooth surface, and that is where the DAP grain filler comes into play.  I purchased it in a tube, and it comes out like a putty almost.  We slathered it on against the grain, making sure it got into the pores of the wood.  Scott said “fill it proud!”  Well, we definitely did – it looked like we frosted cupcakes when we were done.  In retrospect, we make have over filled, and I would probably have thinned the paste a touch with water to make it easier to work with.  Live an learn!  Wait for it to dry (it was thick, so we waited 24 hours) and then sand off the excess.  You sand enough that you want to see the prominent grains, but it will be smooth as glass.

Picking up a closed grained wood allows you to skip this step, which I would recommend unless you wanted to look of oak or a specific open grain wood on the back.

Step 3: Acrylic Gesso Wash

Gesso, for those that do not know, is a priming paint.  There are versions for painting with oil paints and for acrylic paints.  Oil paint *can* go over acrylic gesso, so, for versatility’s sake, we used acrylic gesso.  It is made with white pigment, chalk, an acrylic binder (to make it a liquid) and a smattering of other chemically stable elements.

Why prime your wood with gesso?

  • It creates a uniform,  layer under the paint
  • It gives you surface a nice “tooth” to hold paint
  • It keeps paint from soaking into the material underneath
  • It protects the paint from chemical changes on the board underneath – wood is organic, and the process they use to create plywood is not exactly archival.
It's hard to see in the photo, but the gesso wash is pretty frothy!

It’s hard to see in the photo, but the gesso wash is pretty frothy!

Wiping away the gesso wash

Wiping away the gesso wash

You can slap the gesso on, undiluted, but it really doesn’t penetrate the wood very well.  We mixed up a gesso wash, which is gesso + water.  It may have been a 50/50 ratio, I should have been measuring!  But you want it nice and runny.  We put it on with a foam brush.  You can also use your fingers if you like a more tactile experience.  We really smushed it on, working it into the grain of the wood, which created a sort of foamy looking paint layer.  When we were satisfied with had penetrated well, we wiped off the excess paint with a paper towel.   Let dry thoroughly.

Step 4: Light Sanding

The gesso wash soaked in well, and caused some of the grains of wood to swell, and the dried surface was slightly uneven.  We hit it quick with some 400 sandpaper to smooth it out.  It’s not uncommon for artists to sand between each prep layer – it gives a nice even finished look.

Step 5: Full Strength Gesso

This is the step where the ground work you lay down has a stronger effect on the finished piece.  Scott suggested a couple different ways to incorporate texture with the gesso layer on the laser cut shapes:  with brushes, or with foam rollers.

Swirled whale texture

Swirled whale texture

Flowing bird texture

Flowing bird texture

Full strength gesso has the ability to hold some texture; it’s not self leveling as a more watery version would be.  We took brushes to the whale and the swallow.  I made swirls of gesso on the whale, trying to emulate a turbulent sea.  Scott chose to paint gesso on the bird with long, flowing brush strokes, to evoke the feeling of flight, or airiness.  The subtle peaks and valleys of the gesso will still be present behind whatever paint it will have in the end, adding a depth.

First layer of the foam roller texture

First layer of the foam roller texture

The more geometric shapes for the foam roller treatment.  Rolling on the full strength gesso created a fabulously fine pebble texture, almost like vinyl.  The first layer looks suspiciously like a popcorn ceiling treatment, but it calms down with repeated applications

We let all the pieces dry overnight.

Step 6: Repeat Step 5 as necessary

Everyone has different goals for their primer, and different levels of “done.”  We put a second coat on, and looking as I’m writing this post, I’m tempted to do a third.  As it dried (and sadly got got banged up a bit when I cleared off the table they were on) imperfections became clear – the brush lines weren’t exactly where I wanted them, or had areas where the vinyl-like texture was less pronounced.  If you want, you can also do a quick sanding between each coat of gesso – it’s up to you and the finish you want!

Step 7: Add art!

When you feel your board is primed properly – but that, I mean it has even coverage of gesso, a good texture and reminded me of a sheet of really nice paper that I was itching to put my pencil to – you are ready to add your art.  I didn’t intend for the project to go to the actual art stage, but Scott and I were experimenting, and I couldn’t resist picking up a tube of “sap green” acrylic when buying the gesso (colors are so PRETTY.)  Here are three different paint treatments you can do:

From left to right: Wash, glaze and tint. It's amazing these greens all came from the same tube of acrylic!

From left to right: Wash, glaze and tint. It’s amazing these greens all came from the same tube of acrylic!

Wash – We mixed the acrylic paint with water, which created a very flowing semi-transparent layer of paint.  It was very light in color and was very wet.  If we were using oil based paints, we would have used turpentine to thin it.

Glaze – Glazed are made when a color is added to a “transparent gel medium.”  I’m not 100% sure what the medium is made of, but the color was really vibrant.  Glaze is nice because it is translucent – light can penetrate the layer and make it really pop.

Rolling on the tint.

Rolling on the tint.

Tint – here we mixed white gesso with the acrylic and came up with a lovely minty green.  It is opaque.

The gesso base is also good for charcoal, pencils, pastels, oils, even mixed media or collages.  It’s a good standard base to build on.  Today, most painting is done on canvas, but it actually wasn’t until the 16th and 17th century canvas became popular.  By painting on panels, you are paying homage to an old tradition (even though the panel was cut with new technology!)

This post is in no way comprehensive (even though it is the longest one I’ve ever written!), and it’s one professional’s opinion.  Artists come to develop their own style and preparation methods they like – experiment!  And enjoy!



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