Considerations for Waterborne Finishes
Both Pine-Tique and Viking, a small wood-furniture finishing company in St. Joseph, had unique concerns when searching for suitable waterborne coatings. Below are some of their findings that should be considered by wood finishers when deciding to switch to a waterborne finish. Additionally, you may want to read MnTAP’s Source article, Working with Vendors to Change Wood Finishes, for more information.
Wood Species
Viking’s products are made primarily from pine while Pine-Tique’s products were made from six different types of hard and soft woods. Applying waterborne finishes to soft woods, such as pine, often causes problems with grain rise as these woods are more porous. An even, smooth-to-the-touch surface is an industry standard for wood furniture manufacturers.
Tip: If a complete waterborne finishing system is not working for your company, look at options such as using a solvent-borne sealer with waterborne stains and topcoats.
Color matching
Pine-Tique was concerned about matching the appearance of products already in showrooms and customers homes. Pine-Tique had been using nitrocellulose lacquers which have an amber tint. Waterborne finishes are water-clear so matching a nitrocellulose lacquer can be difficult. Also, walnut and cherry wood gain a deep, oiled finish with nitrocellulose lacquer which can also be difficult to match with a waterborne finish.
Pine-Tique’s desire was to find one finishing product that is suitable for a large variety of woods because mixing special tints for different woods adds labor costs, equipment costs and/or scheduling difficulties.
Tip: Find vendors that are willing to help with trouble shooting.
Finishing after assembly
A large percentage of Pine-Tique’s products were finished after assembly. These three-dimensional pieces need special attention to minimize overspray onto finished areas. Dry waterborne overspray does not blend into a finish as well as lacquer and could cause finishing defects like those caused by dust. The dry time of a topcoat should be slow enough to allow the wet edges to be blended together as the finisher completes the piece.
Tip: Your vendor may be able to supply a coating or additive with a slower dry time.
Dry time
Viking has a short dry time requirement. Because of shipping schedules and customer requirements, an eight-hour dry time is required for some products. This can be an obstacle for waterborne finishes which may not dry as quickly as solvent-borne finishes under certain conditions.
Tip: Allow a longer drying time or invest in equipment that will speed up the drying process. A climate controlled finishing/drying area may help.
Storage and transportation concerns
Storage of raw materials and coatings also becomes important when using waterborne finishes. Coatings should be stored in heated buildings to prevent freezing. Remember that eliminating solvents in coatings and cleaners reduces fire risk and helps meet building codes.
Because Viking has unheated warehouses, it tests for “cold cracking,” small finishing flaws shaped like spider webs that appear under cold stress. A finish is tested by placing a finished sample in a cooler with dry ice, then warming it to simulate the dramatic temperature changes the product could experience moving from unheated storage to trucks and then to showrooms or homes. The test is repeated several times.
Tip: Communicate the current method of storing finished products to your vendor and be open to change.
Sanding
Viking does not sand its product finely. This leaves more surface area open to absorb water which increases grain rising. Sanding at 60 grit is considered “rough” by many wood finishers, but Viking gets a satisfactory finish with this method and was not interested in investigating finer sanding methods. The finer grit paper would clog more often with pine pitch, resulting in increased material and labor costs.
Tip: Rough sanded wood may best be sealed with a high solids material or dried quickly with an oven or lamps to minimize grain raising.