Hi, I’m Trusted House Painter. In this quick guide I’ll show how I prep a stucco chimney for painting by caulking its cracks before applying Sherwin‑Williams elastomeric paint (Loxon). The chimney had been power washed and was dry, but it still showed cracking and a bit of chipping—so I filled the gaps first to help the new coating hold up.
Why caulk stucco cracks before painting?
Elastomeric paints like Sherwin‑Williams Loxon are great at bridging hairline cracks, but they don’t always fill larger gaps or stabilize crumbling edges. Caulking first helps:
- bridge and seal hairline cracks more reliably,
- prevent existing cracks from spreading after you paint, and
- give a smoother, more durable surface for the elastomeric topcoat.
What caulking I use (and why)
I use Big Stretch (Sashco Big Stretch) on this job. It’s a flexible, paintable caulk that handles substrate movement better than many standard latex caulks. Color doesn’t matter much here since the chimney will be painted—what matters is flexibility and paintability.
Step-by-step: How I apply the caulk
- Make sure the stucco is dry. I washed this chimney 2–3 days earlier and let it fully dry before starting.
- Prep the crack area—remove any loose debris or easily crumbling material left from power washing.
- Load your caulk gun and apply a bead of Big Stretch along the crack. I run the bead directly into the hairline and into slightly larger chips along the edges.
- Wear gloves. After tooling the bead, I smear and smooth the caulk with a gloved finger to push it into the crack and feather the edges. (Trust me—do not use bare hands. You’ll end up sticky, and your fingerprints will be a mess.)
- Let the caulking cure/dry fully according to the manufacturer’s directions before applying any paint.
Tooling tips
- Use a consistent bead size—big enough to fill the gap but not so big it takes forever to cure.
- Feather the caulk into the surrounding stucco so the paint has a smooth transition.
- For larger gaps, consider using a backer rod before caulking, or re‑profile the area—caulk is best for cracks and small chips, not deep voids.
How this works with elastomeric paint
Elastomeric coatings stretch and bridge small hairline cracks, but they won’t fill bigger gaps or replace proper patching. By caulking first I’m giving the elastomeric topcoat a stable, sealed substrate so the finished coating can perform as intended.
Common questions and quick answers
- What kind of caulk should you use? Use a flexible, paintable caulk such as a high‑quality acrylic‑latex with added flexibility or a product labeled for masonry/stucco like Big Stretch. Ensure it’s paintable and compatible with your topcoat.
- Do you need gloves? Yes—wear gloves. Smearing caulk with your bare hands will get messy and irritating.
- Will elastomeric paint alone fix cracks? Elastomeric paints are good at bridging hairline cracks, but they don’t fill larger gaps. Caulk first for better long‑term results.
- When do you paint after caulking? Wait for the caulk to fully cure per the manufacturer’s instructions before applying elastomeric paint.
Final thoughts
On this chimney the stucco was in decent condition but slightly chalky and a bit chipped from power washing. Caulking the cracks with a flexible, paintable product stabilized the surface and minimized the chance of the cracking continuing after painting. Once the caulk cures, I’ll apply the Sherwin‑Williams elastomeric coating for a durable finish.
What caulking do you like to use? What stucco or elastomeric product would you choose for a chimney like this? Let me know—I’m always interested in hearing other pros’ or DIYers’ experiences.
