Linking Lumber Quality and Knot Proximity

The southeastern United States is home to millions of acres of southern yellow pine forests. These trees are worth billions of dollars when harvested and sold as lumber. Their value, however, is affected by their quality, and their quality can be affected by multiple knots in close proximity on a board. Continue reading

Every Cut Counts II : Lumber Lasers Illuminate Imperfections

Earlier, we looked at nondestructive evaluation (NDE) laser scanning as applied to logs prior to sawing, but the utility of laser technology extends to dimensional lumber as well.

A typical lumber mill will use two laser scanners which capture two distinct data types — profile scanning data, and tracheid effect data.

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A photo demonstrating the tracheid effect across six different samples of white pine. Notice how the shape of the laser changes depending on the defect present in the sample.

A profile scanning laser is aimed at the board in shallow angle, and is primarily used to detect wane (insufficient wood at a corner or along an edge, due to surface curvature) on the board’s edges as well as splits, cracks, and holes. It also yields accurate measurements of the amount of wane, which are used to automate the edging and trimming of the lumber.

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Sample laser profile image of a board. The lighter shades of grey show the wane of the wood. The jagged white abnormality in the upper left hand corner could indicate a defect.

Profile scans will yield grey-level images with the normal, level surface of the board shaded in dark gray. Slightly higher areas of the board are represented as darker shades of gray, and lower areas will be shown as lighter shades of gray. This additional information about the board’s surface helps industry professionals optimize the cutting processes and eliminate waste.

Diagram of a typical laser scanner used in a lumber mill. Notice how the laser on the right is angled for tracheid effect scanning.

A tracheid effect scanning laser, on the other hand, is aimed at the board at a sharper angle. When the beam strikes the surface of the wood, the beam is propagated along the board’s elongated cells, the tracheids, creating the titular effect. The angle of glow of the laser beam shows the angle of the wood grain, and by analyzing how the laser beam’s glow changes shape, researchers and industry professionals can predict a board’s strength or even reveal defects such as knots and pitch pockets.

This type of scanning technology was first used commercially to locate defects in hardwoods and softwoods for the production of furniture and mouldings, but has since expanded. Today, there are several manufactures producing commercial laser scanning equipment capable of tracheid effect scanning.

This blogpost was adapted from FPL’s publication Nondestructive Evaluation of Wood: Second Edition.

Improving Log Defect Detection

The location, type, and size of defects in hardwood logs affect the value of the resulting lumber, so knowing what’s going on inside the tree before it is sawn is valuable. Turns out, you don’t have to be a superhero with x-ray vision to see inside a tree. Several technologies have been developed to do just that, but they each have their limitations.

High-resolution laser scan image of a log with detected defect areas highlighted and acoustic waves passing through.

High-resolution laser scan image of a log with detected defect areas highlighted and acoustic waves passing through.

High-resolution laser surface scanning of hardwood logs can gather data relating to defects on the surface of the log, which can be used to generate maps of defects inside. However, surface inspection can miss unsound or rotten areas inside the log.

Acoustic evaluation, which involves measuring the speed of sound waves traveling through logs, is very accurate at determining soundness, but provides no data about the location of the defect.

Can combining these methods determine the soundness of a log as well as the location of the defects? FPL researchers are working to find out.

FPL Research Forest Products Technologist Xiping Wang, along with partners at the U.S. Forest Service’s Northern Research Station and the University of Minnesota Duluth Natural Resources Research Institute, are examining the technical feasibility of combining acoustic wave data with high-resolution laser scanning data.

Researchers are hoping to develop a combined scanning approach that uses these data to identify potentially unsound defects and facilitate sawing of each log to optimize value.

See this Research in Progress report for more background information and details on the specific approach of the study.

Butt and Fillet Joints

The Ins and Outs of Caulking defines butt sealant joints and fillet sealant joints. A butt sealant joint is a joint in which sealant is applied between two approximately parallel substrate surfaces that are either edge-to-edge or face-to-edge.

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Cross-sectional sketches of butt sealant joints.

A fillet sealant joint is a joint in which sealant is applied over (not into) the intersection between surfaces are approximately perpendicular to each other.

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Cross-sectional sketches of fillet sealant joints.

In a well-executed butt joint, the sealant does not adhere to any rigid material at the back of the joint nor does it adhere in the root of the joint. If sealant adhesion occurs at the back of a butt joint or in the root of a fillet joint, stress concentrations will occur in the sealant when there is differential movement between substrates. Joint failure will thus be likely, even when a high-performance sealant is used.

To prevent adhesion behind butt joints or in the roots of fillet joints, use non-rigid sealant backers or bond-breaker tapes. In commercial construction, caulking tradespersons are familiar with non-rigid sealant backers and bond-breaker tapes, and part of a tradesperson’s skill involves his or her ability to fit joints with backer or bond breaker (or both) before application of sealant. Unfortunately, residential construction contractors and home owners rarely pay attention to prevention of three-sided adhesion in butt joints or to sealant adhesion at the roots of fillet joints.

Hardware stores and home centers may sell sealant backer rods, but the variety of shapes and sizes is usually limited and virtually none of these retail businesses sell bond-breaker tape. An internet search will typically locate a handful of online merchants that market bond-breaker tapes to the general public. In retail home centers, backer rods are usually stocked with weatherstripping rather than with caulks and sealants.

No professional consensus exists on how long sealant joints in residential construction can be expected to remain functional. Professionals commonly believe, however, that the service life of residential sealant joints is usually shorter than 20 years. Manufacturers’ warranties of multiple decades of sealant joint performance only provide for replacement of the caulking material. Cost of application labor is not covered by the warranties, nor is the cost of repairing damage sustained as a result of a failed sealant joint.  

Sealant Adhesion: Don't Forget to Clean

woman caulking

Photo from Flickr Creative Commons

How best to get a firm seal on your substrate? The Ins and Outs of Caulking states that nothing adheres well to a dirty surface. In addition, new and apparently clean metal components may have oils in their surfaces left from manufacturing processes. Likewise, the extrusions of vinyl, vinyl-clad wood, and wood–plastic composite windows may have residual extrusion die lubricants on their surfaces.

Satisfactory sealant adhesion requires removal of such contaminants. Wiping with a clean rag moistened with mineral spirits is an effective method of removing surface oils and die lubricants. This can, however, pose health and fire risks if done carelessly, and residual mineral spirits that do not fully evaporate before caulk is applied may compromise adhesion. Substituting denatured alcohol for mineral spirits generally poses fewer health risks, and alcohol’s relatively rapid evaporation rate is more likely to leave a clean dry surface. Organic solvents, while generally effective at removing organic surface contaminants such as oils, may not be compatible with all substrates; this is an additional reason that justifies caution in their use. Surfaces contaminated with dirt, airborne dust, and mud usually are most effectively cleaned with a well-rinsed water-wetted rag. Rinsing the rag in a detergent solution can aid in surface cleaning, but if this is done, residual detergent left on surfaces will interfere with caulk adhesion.

If you decide that using detergent solution is necessary to obtain adequate surface cleaning, you must follow the cleaning with a thorough rinsing with a water-wetted rag. It can be difficult to ascertain if the rinsing was adequate; therefore try water and a non-abrasive nylon cleaning pad before resorting to use of detergent solution. Because porous surfaces are generally absorptive and thus difficult to adequately rinse, use of detergent solution on them as in preparation for caulking is not recommended. At application, surfaces must also be free of ice or frost. At below-freezing temperatures, frost may accumulate on surfaces from an applicator’s breath; this is among the reasons that manufacturers commonly restrict application temperature.