Sealing with Wax Emulsions

by Steven D. Russell

Wax emulsion sealers are specifically formulated to control the rate of moisture loss in green timber, by forming a durable wax membrane between the exposed end/side grain and the surrounding ambient atmosphere. The goal is not to prevent moisture from moving through the wax coating, but instead to retard the rate of moisture evaporation, thereby reducing drying defects like end grain checking and warping.

Commercial Wax Emulsions

Two widely available commercial wax emulsion sealers are Anchorseal, by UC Coatings Corporation, and Mobil-Cer M, by ExxonMobil Oil Company. Anchorseal is paraffin based colloidal solution for logs and lumber. It contains paraffin, water and a surfactant and is milky-white in appearance. Mobil-Cer M is a microcrystalline wax based coating. It contains microcrystalline wax, water and a surfactant and is also milky-white in appearance. Winter formulations of these products may also contain anti-freeze agents.

In the woodturning workshop, wax emulsion sealers serve an important function by controlling the rapid loss of moisture through the end grain of logs, blanks, turning squares, or roughed out bowls. These sealers prevent the rapid onset of surface checking for a limited period of time, until the logs can be further processed into turning squares, or blanks. Few species of timber can successfully reach Equilibrium Moisture Content (EMC), when left in the full round log form, regardless of the type of end sealer used.

Turning squares, blanks and bowls of many species however, can be successfully air-dried by applying the wax emulsion sealer to exposed end grain surfaces and any high figured areas on the blank. Once the sealer has dried, the sealed pieces can be dried on wire racks in the open air. Several years ago this was my primary method for seasoning production salad bowls and turning squares in my studio.

How Wax Emulsions Work

Wax emulsions help to equalize the rate of evaporation from the surface of the wood, with the rate at which the interior moisture can travel to the surface. When this is achieved, many drying defects are eliminated and the maximum amount of timber can be utilized in every log. When the moisture inside the blank has reached equilibrium with the ambient moisture, the piece is said to have reached Equilibrium Moisture Content, or EMC.

Application Methods for Wax Emulsions

Wax emulsion sealers can be applied by various methods including brush-on, dip tank, roll-on, spray-on and vacuum assisted. The decision on which method to choose should be based on the quantity, size and location of the logs, or blanks to be processed. Correct application procedures are essential to obtain maximum protection from the wax coating.

TIP: Wax emulsions must be applied as soon as the log is cut for maximum protection. Application of the sealer to dried log surfaces will reduce the overall protection level achieved and may not stop the continued progression of any existing surface checks.

TIP: For best results, cut surfaces should be as smooth as possible. For very rough surfaces, spraying will generally produce a more uniform coating than brushing.

TIP: If the cut ends of logs have dried, or are already showing surface checking; a fresh cut should be made to eliminate surface checks, before application of the log sealer for best results.

Brush-On: Wax sealers can be easily brushed onto the exposed end grain, or side grain surfaces of logs, turning squares or bowl blanks. For an optimum surface coating, the cut surfaces should be as smooth as possible. If the exposed end grain is very rough, jagged, or dirty, a fresh crosscut should be made before applying the wax emulsion. Excess sawdust or debris should be brushed off before applying the sealer. In addition, if any checking is evident on the exposed end grain, the end should be cut back to a point past any surface checking.

Because even smooth surfaces cut on a chainsaw or bandsaw still have a ridged surface, you should brush the sealer on in a crosshatch pattern (first up and down, then back and forth) to insure uniform coverage. The sealer should be applied onto the end grain until it nearly runs off. Applying too thin a coating will reduce the protection level and may compromise the successful seasoning of the timber.

If any bubbles are present in the surface, brush across the area again until the bubbles are completely removed. Bubbles left in the wet film will burst when the coating dries, which may cause differential moisture gradients to form between thicker and thinner areas in the surface coating. These differential moisture gradients cause uneven drying zones across the face of the end grain and subsequent surface checking may develop.

TIP: If you wish to apply two coats to the surface, do not allow the first coat to fully dry before applying the second coat for best results.

TIP: For brush-on applications, simply decant a small portion of the sealer into a small bucket with a tight fitting lid. Cut the handle of an inexpensive brush to fit inside the bucket. When you have finished using the sealer, replace the brush in the bucket and secure the lid. There is no need to clean the brush! The tight fitting lid will prevent the remainder of the sealer from drying and the brush will remain ready for use.

When brushing the sealer on the end grain portion of resawn turning squares, or bowl blanks, also coat ½" to 1" of the exposed adjacent side grain. This insures a better coating on the area where the end grain and side grain areas meet. Brushing becomes inefficient when the logs are more than 12" in diameter. When applying the sealer to larger logs, it's far more efficient to roll the sealer on, or on very large logs, to spray it on.

Roll-On: Standard 9" paint rollers make excellent applicators for medium to large sized logs and blanks. My favorite roller is the type sold for painting in tight areas. It is approximately 4" long and works exceptionally well for any but the largest of logs. Rollers can apply the coating much faster and more uniformly than hand brushing. In addition, because the nap on the roller is available in different sizes, rough or uneven cut log surfaces can be more easily and uniformly covered.

TIP: To eliminate cleanup of the roller, leave the roller submerged in a small amount of the wax sealer after each use. As long as the application bucket has a tight fitting lid, the sealer will not evaporate and the roller will remain ready for use at all times.

Dip Tanks: When processing large amounts of smaller blanks, turning squares, or pen blanks, dip tanks are simple, economical and efficient. Almost any shallow container can be used for making a dip tank. Old pie pans work well, as do small plastic bowls. Simply decant a small amount of the sealer into the tank and dip each end of the blank into the sealer. The level of the sealer inside the dip tank should be adequate enough to coat the end grain and the small amount of adjacent side grain, in one step.

When using this method, it's quite easy to process several hundred squares per hour. To insure proper drying of the coated blanks, stack the wet blanks in an alternating crosshatch pattern. This allows maximum airflow around the blanks, whilst insuring a stable drying stack. To speed the drying of the coating and increase overall throughput, a high velocity fan can be directed towards the drying stack. Adding forced air circulation to the application protocol is particularly useful when processing blanks on days with high humidity.

Spray-On: If you will be processing a large amount of squares or logs, or you are working with very large diameter (2' to 6' diameter) logs consider spraying the sealer. Many types of spray rigs are available in electrically powered, petrol powered and manually powered with sizes and price's to fit any budget.

Because most of my timber harvesting is done during the hot and humid summer months in remote field locations, I prefer to spray the logs before transporting them to my studio. Spraying the logs in the field insures the end grain will be protected during transport back to the studio and is the fastest and most efficient method of applying the sealer on large logs.

Manual sprayers are excellent for spraying in remote locations that do not offer electrical service. Trombone type slide sprayers are available that draw directly from 5 gallon buckets of sealer. In addition, backpack type sprayers are also available that are manually pumped. However, I have found that simple pump-up garden sprayers available in most garden, or home centres, work very well and are much easier to use after a long day chainsawing logs, than trombone or backpack style sprayers.

Vacuum Assisted Application

When sealing high figured, unstable burrs, or crotch figured pen blanks, vacuum assisted impregnation of the surface is useful. This method applies sealer to the side grain and end grain simultaneously, producing a well sealed outer surface. My use of this method is limited to pen blanks, but it can be adapted to larger turning squares quite easily.

The pen blanks are loaded into a Mason style jar and the sealer is added until it covers the blanks. Using a special adapter that fits the top of the jar, a vacuum is pulled on the jar. The blanks are allowed to remain under vacuum for a few minutes, then, they are removed and allowed to drain on a wire grate inside a closed bucket. When the excess sealer has drained off, the blanks are transferred to another wire grate and allowed to dry in the open air. This method is particularly useful with unstable timbers, as it produces a very uniform and well-sealed surface.

Storage and Handling Considerations

These sealers must be kept in containers with tight fitting lids to prevent evaporation, or crusting. In addition, unless the particular formula was ordered with and anti-freeze agent, the sealer should be protected from freezing temperatures. When using wax sealers in your studio, care should be taken to clean up any spills on the floor. When dried, these sealers produce a nearly clear, waxy coating that is quite slippery.

Soap and water is used to clean any undried sealer. Fully dried sealer requires a chemical solvent, or steam cleaning. When spraying these sealers, or when working with heated emulsions, consult the manufacturers MSDS sheets in the U.S.A, or COSHH sheets in the U.K. for full safety and handling instructions. Avoid prolonged skin contact, or wear impervious gloves. Eye and respiratory protection is required under certain conditions, consult material safety sheets for full information.

If you wish to dilute the sealer, always add the water to the wax emulsion, never emulsion to the water. Dilution water generally should not exceed 100 ppm CaC03, or the wax may separate from the emulsion. Avoid storage areas that have abnormally high heat levels (such as near a radiator, or furnace), as this may cause separation of the product.

Buying in Bulk

Typically, these log sealers are available in 1 gallon, 5 gallon and 55 gallon drums. If you are a member of a turning club, consider having your club purchase a 55-gallon drum and divide the sealer among your club's members. When purchased this way, the cost is substantially reduced over the 1 and 5-gallon container sizes.