Why Spray It Like New uses Shellac Based Primer vs a Waterborne Primer over Oil Based Lacquer

Most kitchen cabinets constructed from the 1960s to 2015 are finished with an oil-based lacquer. When considering refinishing or recoating these cabinets, it's important to choose a primer that adheres well to oil-based products. Using a water-based primer over oil-based lacquer is not advisable.

Alcohol-based (or shellac-based) primers adhere more effectively to oil-based nitrocellulose lacquers than water-based primers. Shellac is commonly used by woodworkers to prevent wood tannins and oil-based stains from seeping through a waterborne topcoat. Shellac-based primers are the preferred choice for effectively blocking knot stains on wood.

Why Alcohol-Based/Shellac Primer is Superior

• Chemical Compatibility: Alcohol-based products like shellac establish a strong mechanical and chemical bond with aged or cured nitrocellulose lacquers. Wood alcohol, the solvent in shellac primers, slightly penetrates the lacquer surface, creating a robust bond.

• Universal Binder: Professional wood finishers often use dewaxed shellac as a reliable barrier or tie-coat between different finish layers due to its strong grip on lacquer.

• Fast Evaporation: The alcohol solvent evaporates quickly, preventing it from sitting on the lacquer long enough to cause significant wrinkling or lifting.

  
  

The Problem with Water-Based Primer

• Adhesion Failure: Water-based primers struggle to adhere to slick, non-porous, solvent-based lacquer surfaces, posing a high risk of peeling. Even with fine sanding, the grain valleys, especially in oak wood, remain unsanded, affecting adhesion.

• Surface Tension: Water doesn't penetrate or slightly dissolve a lacquer layer like solvent or alcohol-based mediums, resulting in poorer adhesion compared to alcohol-based primers.

• An alcohol-based primer (such as pigmented shellac) adheres much better to oil-based nitrocellulose lacquer than a water-based urethane primer. Although specialty high-bonding water-based urethane primers are designed for excellent adhesion, alcohol-based primers are structurally superior for this application.

A strong bonding primer is essential for chip resistance as it creates a robust chemical and physical bridge between a smooth substrate and the topcoat. Without it, paint relies solely on surface tension, making it prone to peeling and flaking during the expansion and contraction of solid woods due to temperature and humidity changes. This makes a good bonding alcohol primer superior to waterborne primers.

How Bonding Primers Prevent Chipping

• Maximizes Mechanical Adhesion: Bonding primers are designed to fuse with the top layer of oil-based lacquer for maximum adhesion.

• Creates a Uniform Anchor: It cures into a tight, microscopic textured film that sands smoothly, providing a high-friction surface for the topcoat to adhere to.

• Absorbs Impact Energy: High-quality primers remain slightly flexible after curing, allowing them to absorb and distribute impact forces, preventing fracturing and chipping.