Catalyzed Varnish (Part 2) 1/17/2012 3:04:00 PM
Catalyzed varnish provides a durable finish that is relatively easy to apply. The reason it does this is the specific chemistry that goes into it. When the formulation and use are correct an excellent finish results. The part finishers have control over is the use of the catalyzed varnish. Many variables in using catalyzed varnish can affect the final results.
Catalyzed varnish has become the standard when durability and ease of use are both required. Catalyzed varnish tends to be more durable than lacquers, pre-catalyzed and post-catalyzed lacquers. It is also easier to use than 2K polyurethane and plural component polyester and does not require the extensive curing equipment UV does. Catalyzed varnish has found its place from large furniture and cabinet manufacturers using extensive application and curing equipment to small finishers, some applying the coating to woodwork at the construction site where only basic spray equipment and no curing equipment are used.
The catalyst and how it is added is one such variable. Adding acid catalyst to catalyzed varnish needs to be performed with attention to detail.
- First, make sure to use the correct acid recommended for the varnish. There are many acids and blends of acids for different varnishes. Just because one catalyst works in one coating does not mean it will work in other coatings. The correct acid will have been tested to not only provide the initial desired properties, but to also provide the long term durability desired.
- Next, use the recommended amount of catalyst for the amount of varnish being catalyzed. An accurate measurement of the catalyst is critical to the results both short term and long term. Purchase a measuring cup that allows you to measure exact amounts. See your supplier for assistance to identify how accurate the measurement needs to be and the material of which the cup needs to be made. Too much catalyst will shorten pot-life and cause the finish to become brittle over time. Also, finished products can develop an “acid bloom” which is the excess acid rising to the surface over time. Inconsistent sheen is possible and “starburst” cracks. Starburst cracks are cracks that develop from a single point and run in multiple directions. Too little catalyst will not allow the coating to reach its needed hardness and chemical resistance.
- Add the catalyst slowly while stirring the varnish well. This allows the acid to be evenly distributed and prevents small “pockets” of acid/varnish blend that are over catalyzed. Catalyst that is added without being stirred immediately in allows the acid to stay in one area, and at the interface between the acid and varnish the ratio of acid to varnish is 50-50, way over catalyzed. This can result in specs or chunks of reacted varnish to form, making the varnish trashy and possibly even clog the spray tip. It can also mean too much acid is over reacted with the varnish at the interface and there will not be enough acid left to react properly with the remaining varnish.
- Catalyzed varnishes may need to sit for 10 to 20 minutes, after the catalyst is mixed in well, before it is applied. This may be referred to as “induction time” or “sweat in time.” Not allowing for this time may result in a partially or non-cured finish.
Catalyzed varnishes are affected by many variables at application and during curing.
- The temperature of the varnish, substrate and air will all affect the flow, leveling, dry time, cure time and the durability of the final finish. Remember that temperature can be a catalyst, and that raising the temperature is like adding more catalyst. Some varnishes may be designed to be cured with an oven and need a certain temperature to reach the correct final cure and other varnishes may be designed for use at room temperature and too much temperature may over catalyze the varnish. Also, too low of a temperature can result in an under catalyzed varnish. This can show up as a soft finish, multiple coats of improperly cured varnish can also cause cracking (even though the varnish is not fully cured). Check with your supplier to find the optimum temperature range for proper cure.
- Air flow rates also affect the drying of the solvents from the film. The solvents need to be removed, after the varnish has flowed out, to allow for a proper cure of the resins. Too much air flow and the varnish will dry too quickly and not flow out evenly. Not enough air flow will slow the dry rate, thereby slowing the cure rate.
- The amount applied per coat of catalyzed varnish will also affect its properties. Too thin a coat may not flow out well and not provide the coverage necessary to protect the wood substrate. Too thick a coat will lead to excessive dry times and can leave solvent trapped deep inside the coating, not allowing for proper cross linking. This can cause poor resistance properties and cracking.
Catalyzed varnishes are subject to a certain pot-life after catalyzing. Pot-life is the amount of time the varnish is fit to use after the catalyst is added. The pot-life may vary from hours to days and even weeks. Each formulation of varnish will be different based on the particular resins, solvents and acid catalyst used. Catalyzed varnishes often increase in viscosity over time, after the catalyst is added. An increase in viscosity usually means the varnish is nearing the end or past its pot-life. Do not use catalyzed varnish after the end of the recommended pot-life. Even if the varnish will spray and flow out, it will lose its long-term durability past the recommended pot-life. Pot-life recommendations are typically based on the catalyzed varnish being stored at 77F in a closed container. Higher temperatures will shorten the pot-life; also containers that are not sealed well will shorten the pot-life.
Many catalyzed varnishes can be “de-catalyzed” to extend the pot-life. De-catalyze a varnish by adding un-catalyzed varnish. This is most commonly done with catalyzed varnish that has a pot-life of one day or less (e.g., one gallon of catalyzed varnish left at the end of a day). Extend the pot-life by add one gallon of un-catalyzed varnish to it and mix well. This usually extends the pot-life over night. The next day add the proper amount of catalyst for the one gallon of un-catalyzed varnish. This is possible with some catalyzed varnishes because the amount of acid is reduced enough to slow the chemical reactions that cause the short pot-life. Check with the catalyzed varnish supplier to find out if this is recommended with the particular varnish, the ratios of catalyzed to un-catalyzed needed and how long will it be good.
We have already learned that temperature can act as a catalyst for catalyzed varnish, therefore do not store the catalyzed varnish (even before catalyzing) at high temperatures. Even if the high temperatures do not cause the varnish to gel, the high temperatures will prematurely age it.
Lifting or wrinkling is a common problem when using catalyzed varnish. The most common cause of lifting is using two coats of catalyzed varnish over a non-catalyzed finish. The non-catalyzed finish may be a catalyzed coating that did not fully catalyze, a lacquer or vinyl sealer or even a wiping stain, glaze or toner applied too heavy.
The adhesion of catalyzed varnishes can be impacted by a variety of factors. Using sealers or washcoats not designed for the varnish and stains and glazes left on too heavy, over pigmented, or not of a recommended type are some common causes.
Final durability will be determined by the particular varnish formulation, what it was used on, other finishes it was used with, how it was catalyzed, application and curing conditions and how it was applied. Even the best coating cannot protect a substrate that is not coated properly.
Catalyzed varnishes are some of the most durable and easiest to apply wood coatings on the market. Learning more about them will help you get the best results possible.
Ed. Note: This is the second installment in a two-part series on Catalyzed Varnish. Read part one here.
Comment on this story
Re: Solvent Pop with Catalyzed and non Catalyzed finish
Created by David Jackson in 2/8/2012 1:43:40 PM
Thank you for the question.
Solvent pop and micro foam (very small air bubbles) can have the same appearance, but may have different causes.
Solvent pop can be caused by a previous coat not being dried enough before another coat is applied. You have allowed the stain to dry overnight which should eliminate it from being the cause of the defect you are seeing. Common causes include;
• Excessive wet film build – solvent can get trapped in heavy wet films. The surface flashes while solvent is trapped in the film. The solvent eventually evaporates and leaves voids in the finish.
• Not enough dry time between coats – not only the dry time of the stain but of all coats of finish applied. Just as with excessive wet film build solvent from a previous coat can be trapped under a fresh coat applied too soon. The solvent in the prior coat will eventually evaporate and leave voids in the finish.
• Excessive air movement as the coating dries – the excessive air movement will cause the surface of the film to flash dry while solvent is trapped below the surface. Again the trapped solvent will eventually evaporate and leave voids in the film.
• Ovens used too soon after application – this will flash the surface while trapping solvent in the film that will eventually evaporate and leave voids in the finish.
• Excessive heat used after application – the excessive heat will volatize the solvents in the film too fast causing solvent pop as it “boils” out of the finish.
Micro foam can appear similar to solvent pop, but may have different causes. Common causes include;
• Excessive fluid and or air pressure – this promotes air entrapment in a finish.
• Holding the spray gun too close to the substrate – this also promotes air entrapment.
• Excessive wet film build – the surface of the finish flashes dry before the entrained air can rise through the finish and exit. The entrained air is usually caused by improper pressures, application or equipment problem
Solvent Pop with Catalyzed and non Catalyzed finish
Created by Duane in 1/23/2012 11:21:15 AM
Too often I get solvent pop even after letting the stain dry overnight. I am using Gemini Gem Var Satin and usually try to apply an even wet first coat and sand thoroughly then apply the second coat. Most of the time the solvent pop as I call it ( bubbles rising to the surface and causing pin holes in the finish) occur in the first coat. Am I applying to thick of a coat? Thanks