What is finger jointed lumber?

We use quite a bit of finger jointed trim in our projects. Many people aren’t familiar with this product, so we often hear questions about it. Let us take this opportunity to explain what finger jointed lumber is.

Let’s start at the beginning.

How is lumber made?

It all starts with a tree. The tree is cut down and sawed into rectangular pieces called “boards”. The boards are dried, then they are run through a machine that will make their rough surface become smooth. If the finished boards will be flat, like 1x4s or 1x6s, the boards are run through a planer. If the finished boards will have a profile, like crown molding or door casing, they are run through a molding machine. 

What are the problems with wood products?

One of the biggest problems we face while processing or using lumber is that trees have knots. Knots effectively create a break in the strands of wood that make up the board (the wood “grain”), making a board weaker in the area where the knot is.

While knots affect the structural integrity of lumber, they are not a huge problem in larger boards, like 2x4s or 2x6s, because the affects of knots and other natural defects are understood and building techniques have been created to work within the limitations of this natural resource.

Where knots pose the biggest breakage problem is in very thin, or very small lumber, like crown molding, quarter round, or lattice strips. A knot in an already small and relatively weak board will almost surely cause the board to break and the carpenter to use bad language in response to the resulting inconvenience.

Knots also cause problems with finishes. First off, knots are very dense. This dense wood is very difficult to sand smooth. When a smooth finish is required, as is almost always required for a painted finish, knotty lumber requires a lot more work to sand and prepare than knot-free wood does.

Second, knots in many woods, like pine, have oils in them that will “bleed” through most paints, causing an ugly stain in an otherwise beautiful finish. Therefore, when knotty woods are painted, the knots need to be sealed with a shellac primer to keep the oils from bleeding through the paint. This adds another step to an already time-consuming process.

How do we solve the problems with wood products?

In order to avoid these problems, lumber mills use “clear”, knot-free lumber when they are making moldings or small trim boards. This allows them to manufacture thin and small wood products that won’t have an excessive amount of breakage. The use of knot-free lumber also allows the painters to avoid the problems knots pose in the finishing of these products.

The only problem with using clear lumber is that it comes at a premium price. Wood is a natural product, and it is normal for it to have knots. If a mill can only use perfectly clear, knot-free boards, they will have to pay a premium for them because those boards are relatively uncommon.

Is there a better alternative to clear trim boards?

What if we could take a common board that has knots and imperfections in it and we could cut it into short, knot-free pieces, throw the knots away, and put the board back together?! That would be great, wouldn’t it? A mill could then create beautiful moldings out of inexpensive, common lumber. Heck, if this were possible, they could even make good, usable lumber out of the waste lumber that was destined for the trash pile! That would be a “million dollar idea”, wouldn’t it? If only there was a way to do that…

Well, there is! Finger jointed lumber is essentially created in the way I just described!

A finger joint is a special type of wood joint that allows boards to be connected end-to-end. Lumber mills use this joint to connect short sections of good lumber that were taken from knotty or “defective” boards. The long boards that are created by connecting these shorter boards together can then be planed to make flat boards or molded to make profiled trims. Because these boards or moldings are made from less expensive lumber, they are less expensive to buy than clear boards or molding. 

What are the disadvantages of finger jointed lumber?

One downside to finger jointed boards is that they are more delicate than a knot-free solid-wood board. A finger joint is strong, much stronger than the wood around a knot. But, it isn’t as strong as a board that grew as one piece, in nature.

We have found that the finger joints in larger trims, like crown molding, base trim, or door & window casing, are very strong, and we don’t feel the need to treat these boards any more delicately than we would treat clear trim boards. We have, however, found that very small finger jointed trims, like quarter round, base shoe, or lattice strips, aren’t as strong as their clear counterparts, so we need to treat them with a little more care.

The other downside to finger jointed boards is that tend to have very erratic wood grain patterns because they are made from many short boards that are connected end-to-end.

When is finger jointed lumber a poor choice?

Due to the erratic woodgrain pattern of these products, finger jointed lumber are usually a poor choice for stain-grade applications. People that wish to have stained trim with visible, aesthetically pleasing woodgrain will usually be disappointed by the look of finger jointed trim. Homeowners that wish to have stained trim will generally find clear, solid wood boards to be a superior product for their application. 

When is finger jointed lumber a good choice?

While finger jointed trim may be a poor choice for stain-grade trim, it can be a great choice for projects that require a painted finish. The paint will conceal the wood grain, so the erratic woodgrain pattern will not be a problem. The finger jointed boards are knot-free and made of real wood, so they will take paint as well as clear boards will. Finger jointed boards also minimize waste at the mill, thereby saving money, and this cost savings is passed on to the homeowner! 

What are PFJ products?

Many lumber mills take the savings provided by finger jointed products a step farther by offering a factory-applied coat of primer on their finger jointed trim. These primed, fingerjoint (PFJ) products not only save cost by utilizing imperfect and/or waste wood, but they also reduce the amount of painting work that needs to be done on-site! The labor savings associated with using factory primed products has caused the primed variation of finger jointed trims to be incredibly popular, much more popular than unfinished finger jointed products. Because of their popularity, you can find PFJ products at most lumberyards and big box home improvement stores.

Why do we use finger jointed trim?

For the reasons we described above, we like using finger jointed trim on our paint-grade projects. Using these products reduces waste at the lumber mill, it saves us time on the job, and it saves our clients money! What’s not to love? 

Give some PFJ trim a try on your next project, we think you will love it, too!