wooden, parquet, floor, working, varnishing, lacquer

How to Finish Plywood

Plywood products which are used for visible parts of furniture and cabinets need to be finished, just as any other wood pieces would. The finish improves the look of the piece, as well as providing the wood with needed protection from dirt and spills. Proper finish visibly enhances the finished piece, as well as helping it to last longer.

When we’re talking about “finishing plywood,” we’re normally talking about finishes that show off the grain in the face veneer of the wood product, or even the edge of the plywood on some products with a high veneer count. While paint meets the technical definition of being a finish, it is not common to call “painting plywood,” “finishing plywood.”

Normally, only hardwood or cabinet grade plywoods are finished in this manner, although some other specialty plywood products might be finished, such as Appleply, Baltic birch and even lauan, when used for cabinetry and other non-architectural applications. Both Appleply and Baltic birch have a high number of veneer layers in their construction, making for an attractive edge, when finished. But in all other cases, these finishes are avoided, because it doesn’t produce an attractive finished product.

In many of these cases, the face and back veneer of the plywood is not intended to provide for an attractive finish. Softwood plywood, for example, can have knotholes, voids and patches. Oriented strandboard is even worse, with the surface showing the chips of wood it is made of. Other plywood products, such as phenolic plywood already have a finished surface, which doesn’t show the wood grain.

Choosing a varnish or lacquer

Finishing plywood, like any solid wood, generally refers to the application of either varnish or lacquer. So the first question you need to ask yourself is: “Which one do you want to use?” Both appear similar, providing a clear or almost clear finish, although lacquer can be tinted and is often tinted to the point of being opaque. Both provide a nice luster, with lacquer able to be buffed to a higher shine. But the end results are very similar.

One factor to consider in making this decision is the sheen that you want to have on your finished project. If you are looking for a high gloss finish, then nothing can beat lacquer. However, lacquer can normally only provide high gloss and semi-gloss finishes. Although there are satin finish brushing lacquers, they do not come out the same as a satin finish done with varnish.

For most woodworkers, the answer to this question comes down to how they are able to apply the finish, although appearance is a factor. Lacquer is almost always sprayed on and varnish is usually brushed on. Herein lies the problem for most woodworkers. Spraying requires the right equipment, as well as a dust-free environment. So if your workshop doesn’t have a paint booth, you’re probably going to have to use varnish instead.

Varnish also works well over stained wood, something that is not often done with lacquer, due to the tinting of the finish itself. This also allows the addition of other factors in the finishing process, such as the use of paste wood filler on open-grain woods, such as oak.

A third finish option is resin; although this is not used with plywood projects. It is used almost exclusively with slab projects, where a large slab of some sort of exotic hardwood, with the outer edge of the wood, the “live edge,” and any splits left intact, is actually encased in the rosin, allowing the rosin to fill in the voids and provide a smooth, shiny finish, with a smooth edge.

Before You Start

You should decide how you are going to finish your project, before starting to build it. The finish may affect the way you construct the project and the materials you choose. More than anything, it may affect the order in which you assemble your project.

wooden, parquet, floor, working, varnishing, lacquer
Lacquering wooden parquet floor, Chris RD

One of the problems with finishing projects made of plywood is that if you use any sort of wood glue, the wood glue can prevent the wood from accepting the finish products, if it seeps out or gets smeared onto the surface, resulting in what appears to be a stain. What is actually happening in these cases is that the glue has soaked into the wood fibers and prevented the stain or varnish from doing so.

To prevent this, you may choose to stain and/or apply sanding sealer to the individual wood parts, before assembly. That way, any glue that seeps out of joints will be above the finish layer, where it can be wiped off with a damp cloth and without staining the plywood underneath.

Sanding

No finish is going to make up for a poorly prepared substrate. If your plywood’s surface is rough, then the finish will be rough as well. In order to get a good finish, it is necessary to have a well prepared, smooth surface.

Before applying any finish, the project should be finish sanded with 150 grit to 180 grit sandpaper. Always keep the sanding direction in line with the wood grain, to avoid creating visible scars across the grain. Be careful when sanding, especially when sanding with a power sander, as the finish veneer layer of any plywood is usually quite thin, so it’s easy to sand through into the lower layers before you realize what’s happening. When you are finished sanding, wipe up the dust with a damp cloth and then allow the workpiece to dry.

Never use a belt sander for finish sanding, but only a vibratory sander or hand sanding. Belt sanders are designed for removing a lot of material quickly. A quarter sheet or “mouse” detail sander is best; however a third sheet sander can be used as well. Keep in mind that the third sheet sander will take off more material than the quarter sheet sander, due to its more aggressive movement.

Random orbital sanders are fine for sanding between coats, on a finish where a lot of coats of finish will be used. However, if only a sealing coat and two coats of finish are to be applied, then you’re best off hand sanding, to avoid taking off too much finish. The random orbital sander will remove finish faster than hand sanding does.

Staining

Wood stains are often applied to plywood, before the finish is applied. Stains allow you to change the color of the wood, giving it the appearance of other types of wood. In this way, they allow less expensive hardwood plywood to look like more expensive woods or woods for which it is hard to find hardwood plywood. They also serve to bring the grain of the wood out more, making it more pronounced and attractive.

A project made of oak plywood may have golden oak stain applied to it, as the first stage of the finishing process. This would change the color of the wood veneer only slightly, while causing the grain to stand out more. Instead of a golden oil stain, summer oak or red oak stains might be used, darkening the wood, as well as bringing out the grain.

Stain can also be used to equalize the natural colors of the wood. Your project may combine a hardwood plywood, with pieces of that same hardwood. Since they didn’t come from the same tree, there is a good chance that there will be a variance in the color of the two pieces. Staining them allows you to darken the lighter piece, making it more closely match the darker one.

Some people use this trick to mix a lower cost hardwood plywood with darker solid wood components. They might be trying to make a project with dark walnut, but be unable to find walnut hardwood plywood in their area. In that case, they may choose to combine walnut solid wood pieces with birch hardwood plywood, which has a similar appearing grain. In this case, they would stain the plywood parts darker, while applying minimal stain to the hardwood pieces.

How to stain

Staining can be even trickier than applying the finish to a piece of wood, due to variances in how the stain affects the natural color of the wood being stained. It is always recommended to test the staining process out on a scrap piece of the same plywood used in the project.

Stain will continue to darken the wood it is applied to, from the time it is applied, to the time it is either removed or dried. In most cases, you will want to remove excess stain, once the desired color is reached, rather than allowing it to dry.

Apply the stain to the piece with a natural bristle paintbrush, using long strokes, in the direction of the grain. Always use a wet brush, dipping it into the stain for more, as needed. The idea is to cover the workpiece entirely with wet stain, not to work the stain into the wood with the brush. Be sure not to leave any bare spots, no matter how small. Also, watch for drips and runs on other sides of the workpiece, as they can cause discoloration and uneven staining.

Once you have allowed the stain to soak into the wood, wipe off the excess stain with rags or paper towels, wiping in the direction of the grain. Be sure to wipe off all extra stain, not leaving any in cracks, seams and corners.

If the first application of stain doesn’t make the workpiece as dark as you desire, additional applications of stain can be made. The need for this should be determined through your testing with the scrap piece of plywood, before staining the actual project.

It may be that you determine that the stain will need to dry on the project, in order to stain it as dark as you want. In that case, you will still need to wipe the project down, to remove excess residue, after the stain has had sufficient time to dry. Stain residue left on the project can break loose when varnish is applied, causing spots or other discolorations in the finished product.

Paste wood filler

Paste wood filler is a special finishing product, used to fill the pores of the grain in open grain woods like oak, walnut and mahogany. It is a thick-bodied product, which is spread onto the wood, allowing it to dry in the open pores of the grain. Once dry, the excess is removed, leaving a smooth surface.

Paste wood filler can be used either before or after staining, as you choose. The results will look different in either case, so you will probably want to do a test sample, before deciding what order you want to apply these finishing steps. Basically, if it is applied before, the stain will darken the paste wood filler, which is a light tan color. This will allow for a greater contrast between the color of the closed grain (light) and open grain (dark) parts of the wood. But if you apply the stain first, and then the paste wood filler, it will tend to lighten the normally dark parts of the grain.

One thing that most people don’t realize is that paste wood filler can be tinted with the same sorts of tints that are used to color paint. This provides for the opportunity to add different colors, like red, white, black or purple into the open grain part of the wood, creating totally new effects. The entire area of the open grain won’t turn that color, only the open pores that are being filled by the filler.

Applying paste wood filler

Paste wood filler can be painted onto the project or spread on with a plastic putty knife, depending on how thick your paste wood filler is. Some people prefer using it straight out of the can, which is rather thick. In these cases, it makes more sense to spread it on with a putty knife. You typically have to water it down some, in order to apply it with a paint brush. Some woodworkers even like using a plastic scrub pad to apply it.

Once applied, the workpiece should be left to dry most of the way. You don’t want to get to the point where the paste wood filler is hard; but you do want it dry enough that it doesn’t smear. With it at that point, you can either scrape off excess paste wood filler, leaving the remaining filler flush with the surface of the wood or you can rub it with burlap to do the same. Plastic scrub pads can also be used.

The idea here is twofold. On one hand, you want to remove the excess paste wood filler, so that there is none left sitting on the surface of the wood. At the same time, you want to press it down into the wood’s pores, ensuring that you didn’t inadvertently miss any. Rubbing it in a circular motion with the burlap works well to accomplish both of these objectives. Take extra care in corners, so as to not leave any excess paste wood filler on the surface of the wood.

Once completed, allow to dry fully before applying sanding sealer.

Sealing the wood surface

The first coat of finish, regardless of what finish you are using, should be a sanding sealer. This is a shellac or lacquer based product to seal the wood’s pores and raise up any “fuzz” from sanding, that is on the surface of the wood. It is the rough equivalent of using a primer coat when painting. Sanding sealers dry quickly, so you shouldn’t have to wait more than 20 minutes before sanding again. The dry sanding sealer should be sanded with 220 grit sandpaper.

You are actually sanding the finish this time, so it isn’t important whether or not you sand with the grain. Once again, avoid oversanding. When done, the surface should feel smooth and almost soapy. Wipe the surface once again, and allow it to dry.

Varnishing

Now you are ready for your varnish or lacquer. Although there are brushing lacquers on the market, for most purposes lacquer should be sprayed. You will get a smoother finish that will provide a higher shine when spraying. Varnish should be brushed on, staying with the grain, so that any unevenness in the finish thickness will look like part of the wood’s grain. Once this coat is dry, it can be sanded with 320 grit.

Continue applying coats of finish to your project, sanding with 320 grit sandpaper between them, until you are satisfied with the depth of the finish. Deep finishes provide a nice effect, magnifying the grain and making the project look rich. Always sand lightly between coats, to help ensure adhesion, but do not sand the final coat. If you are applying lacquer and the finish turns cloudy, it indicates that there is too much moisture in the air of your workshop. Find a drier area to work in and apply another coat the cloudiness should disappear.

High-build urethane finishes

You can achieve the same relative effect as applying many coats of varnish by using a “high-build urethane finish.” These products are usually thick, two-part products which are poured onto a table top and allowed to self-level and then dry. It may be necessary to use a paint brush to spread the product around, but it is not painted onto the workpiece in the typical manner.

When using these products, there are two common ways that edges are dealt with. One is to frame the tabletop so that it captures the finish and prevents any from running over the edge. This method is most commonly used when insetting objects into the finish, such as putting foreign coins onto a tabletop as part of the design. The outer frame may have the same finish brushed onto it or be finished with normal varnish.

The other way that edges are finished is to allow the finish to run over the edge, providing a slightly rounded top edge. The uneven finish on the sides of the tabletop are then sanded off, making them smooth. This method is most often used where a heavy finish is desired on a butcher-block style table.

Another place where the finish might be allowed to run off the edge is on a slab type table, where the “live edge” of the inner bark is left natural and not sanded smooth. In that case, the dripping excess is cut or sanded off to be flush with the bottom edge of the slab.

This sort of finish is not normally used on the sides of dresser cases or bookcases, but only on the top. It would only be possible to use it on the sides, by laying the assembled piece of furniture on its side and finishing one side at a time, leaving the top to be finished last.

Combination stain and varnish

The major stain and varnish manufactures have come out with a new product in recent years, which combines the finish qualities of both stain and varnish. Minwax “Polyshades” and Varathane “Stain + Poly” are the two most common brands of these products. In both cases, the products come in a variety of shades, just as stains do, in both semi-gloss and satin finishes.

These products have been developed to be an easier and more convenient means of finishing wood products. When properly applied, it is all but impossible to tell whether the project was finished with more traditional stain and varnish or with these products, without looking very closely.

While these products combine stain and varnish in one single application, they are a bit different than staining and varnishing. With normal stain, the stain soaks into the wood, changing its color. With these products, the stain is already mixed into the varnish and stays there. While the finished product may look the same, the lack of soaking in means that if the varnish wears or is scraped off, it will affect the coloration of the wood as well.

Some basic precautions should be taken for best results when using these products. Since the pigmentation is in the varnish, successive layers of the product darken the finish. This trait can cause problems if you have any drips or if you go over some parts of the finished project twice, in the finishing process. Care must be taken in planning and executing your finishing process, to prevent either of these from happening.

One place where there is a tendency to go over an area twice is when you have a large panel and are finishing it in stages, working from one end to the other, rather than long strokes that go the length of the panel. As long as the finish remains wet from the first section to the second, this isn’t much of an issue; but if it begins to dry, you’ll actually have two coats at that point. The same thing can happen when you have an edge piece, with a panel. Finishing the trim and then the panel or vice-versa can create a point of overlap.

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