From Oil to Latex: Converting Old Trim and Cabinets

Many older homes in East Tennessee have trim, doors, and cabinets finished with oil-based paints and varnishes. Before environmental regulations changed formulations in the late 1990s and 2000s, oil-based enamels were the standard for woodwork because of their durability and smooth finish. Now, when these surfaces need repainting, we face a challenge: modern waterborne paints do not always adhere well to cured oil finishes.

The solution is not complicated, but it does require the right products and process. Here is how we handle oil-to-latex conversions at Rock's Painting.

Why Adhesion Fails

Oil-based paints cure to a hard, smooth, non-porous surface. Waterborne paints rely on a degree of porosity to grip the substrate. When you apply latex paint directly over cured oil, the latex cannot penetrate or bond properly. The result is paint that peels, chips, or lifts, sometimes within months.

Sanding alone does not fully solve the problem. While scuffing creates some mechanical tooth, the fundamental chemistry incompatibility remains. You need an intermediate layer that bonds to the oil and accepts waterborne topcoats.

The Bridge Product: Zinsser Cover Stain

Zinsser Cover Stain is an oil-based primer that serves as the bridge between old oil finishes and modern waterborne paints. It adheres tenaciously to cured oil-based surfaces and provides an excellent foundation for latex or acrylic topcoats.

Why Cover Stain Works

• Oil-to-oil adhesion. Being oil-based itself, Cover Stain bonds chemically with existing oil finishes in a way that waterborne primers cannot.
• Accepts latex topcoats. Once cured, Cover Stain's surface readily accepts waterborne paints. The chemistry barrier is eliminated.
• Stain blocking. As a bonus, Cover Stain seals in tannin bleed, water stains, and discoloration that might otherwise show through the finish.
• Good sandability. It sands to a smooth foundation for your topcoat.

Our Conversion Process

Here is the step-by-step process we follow for oil-to-latex conversion on trim and cabinets:

Step 1: Clean Thoroughly

Old oil finishes often have decades of accumulated grease, grime, and cleaning product residue. We wash all surfaces with a TSP substitute or degreaser to remove contaminants that would interfere with adhesion. Rinse well and allow to dry completely.

Step 2: Scuff Sand

Sand all surfaces with 150 to 180 grit sandpaper. The goal is not to remove the old finish, just to degloss it and create mechanical tooth. Pay attention to edges, profiles, and any glossy areas. Vacuum and tack cloth to remove all dust.

Step 3: Apply Cover Stain

Apply Zinsser Cover Stain by brush, roller, or spray. We typically spray trim in place when possible for speed and smoothness, masking carefully to protect adjacent surfaces. One coat is usually sufficient for conversion purposes, though heavily stained surfaces may need two.

Allow Cover Stain to cure according to label directions, typically overnight. The primer needs to reach full hardness before sanding and topcoating.

Step 4: Sand the Primer

Once cured, sand the Cover Stain with 220 grit. This creates a smooth foundation and removes any brush texture or orange peel. Vacuum and tack cloth again.

Step 5: Apply Waterborne Topcoat

Now you can apply your choice of waterborne finish. For trim, we typically use Sherwin-Williams Emerald Urethane or PPG Breakthrough. For cabinets, PPG Breakthrough or Gallery Series. Apply two coats with light sanding between for the smoothest result.

Why PPG Breakthrough for the Topcoat

PPG Breakthrough is our preferred topcoat for conversion projects because of its exceptional adhesion and durability. It is formulated specifically for challenging surfaces and holds up to the demands of high-touch trim and cabinets.

The fast dry time is also valuable. On conversion projects, you are already investing significant time in preparation. Breakthrough's 30-minute recoat allows us to apply multiple coats in a day, keeping projects on schedule.

Common Mistakes to Avoid

Skipping the Oil-Based Primer

Some painters attempt to use only waterborne bonding primers like Benjamin Moore Stix on oil-based surfaces. While Stix is excellent for many applications, it does not bond as reliably to heavily cured oil finishes as an oil-based primer. For true oil-to-latex conversion, Cover Stain or similar oil primer is the safer choice.

Insufficient Cleaning

Old trim accumulates decades of hand oils, cooking grease, and cleaning product residue. Painting over this contamination leads to adhesion failure. Thorough cleaning is not optional.

Skipping the Scuff Sanding

Even with the right primer, some mechanical tooth helps. Sanding takes time, but it is essential for long-term adhesion.

Rushing Cure Times

Cover Stain needs time to cure before sanding and topcoating. Applying finish coats over uncured primer leads to problems. Follow the label directions, and when in doubt, wait longer.

When to Consider Stripping Instead

In some cases, the old finish is in such poor condition that conversion is not the best approach. Heavy chipping, multiple layers of alligatored paint, or severe damage may warrant chemical stripping or sanding down to bare wood. This adds significant labor but sometimes produces a better result.

During our estimate process, we evaluate the existing finish condition and recommend the most appropriate approach. Sometimes conversion is straightforward. Sometimes more extensive preparation is warranted.

The Results

When done correctly, converted trim and cabinets look excellent and perform well for years. The modern waterborne topcoats we use today, such as Emerald Urethane and Breakthrough, are more durable than the oil paints they replace. Yellowing is eliminated. Cleanup is easier. And the environmental impact is reduced.

At Rock's Painting, we regularly handle oil-to-latex conversions on interior trim and cabinet projects throughout the Tri-Cities. With 250+ completed projects, we have refined this process and can evaluate your specific situation during a free estimate.

If you have older trim or cabinets that need updating, we are happy to assess the existing finish and explain exactly what your project requires.