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How to Prep Exterior Window Trim for Painting (So the Paint Lasts)

Nashville Window Trim Pros · Exterior Trim Guides

Exterior paint fails for one of two reasons: bad paint or bad prep. Bad paint is rare; bad prep is everywhere. If your last trim paint job started peeling after a season or two, it almost certainly wasn't the can — it was the prep underneath. Here's the prep order we use on Nashville-area trim work.

1. Wash everything first

Paint won't bond to pollen, mildew, or dust. Start by washing the trim with a mild detergent solution and rinsing thoroughly. A garden hose and a soft brush usually do it. Skip the pressure washer on aging wood — it drives water into joints you'll wish you'd left alone.

Let everything dry for at least a full sunny day before going further.

2. Scrape, scrape, scrape

Use a sharp pull scraper to remove every bit of loose or flaking paint. The test is to drag the scraper across the surface; if more paint comes off, keep scraping. This is the step most homeowners cut short, and it's the step that determines how long the new paint lasts.

3. Probe for rot

While you have the scraper out, press it into corners, joints, and the underside of sills. If the wood is soft, paint won't fix it — you need to repair or replace the damaged section before going any further. Painting over rot just hides it for a season.

4. Sand to a feathered edge

Where bare wood meets old paint, the edge will telegraph through your new finish. Sand those edges smooth with 80- to 120-grit so the transition disappears. Sand all bare wood lightly to give the primer a tooth.

5. Spot-prime every bare spot

Any bare wood needs primer before topcoat. Use a high-quality exterior primer — oil-based or modern bonding primers both work. Don't skip this on small spots; bare wood under topcoat is where the next round of peeling begins.

6. Caulk last, not first

Once primer is dry, run fresh caulk on every joint that should be sealed: where trim meets siding, where trim meets brick, where casing meets the window frame. Use a quality exterior sealant rated for paint, and tool the bead smooth. Caulking before priming wastes caulk and leaves it stuck to old paint that's already on its way off.

7. Two finish coats — really

One coat almost never gives you the film thickness exterior paint needs to last. Two thin, properly applied coats outlast one thick coat every time. Let the first coat dry per the label before recoating.

8. Don't paint in the wrong weather

Avoid painting in direct hot sun, in high humidity, or when rain is forecast in the next several hours. Tennessee summers can make this hard; early mornings on shaded sides of the house are the sweet spot.

The shortcut that isn't

The biggest paint-prep shortcut homeowners take is skipping the scrape and sand because it's tedious. Of every premature paint failure we see, that's the cause. If you only do one thing well, do that.

If your trim already has rot or extensive paint failure, prep alone won't fix it. That's the right time to bring in a pro to scope the repair before the painting starts.