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Why Deck Railing Paint Fails

Painting wood deck spindles

Deck railing paint can fail prematurely - the following identifies some reasons and remedies.

1. Wood was wet when it was painted. (If only the surface of the wood is wet, then only one sunny day is usually needed for drying prior to painting. If the wood is saturated, several sunny or windy days are necessary).

2. Unfinished railings where exposed to several weeks of sunlight before painting.

Sunlight degrades the unfinished wood surface, thus it will never hold paint as well as fresh wood. If the unfinished wood was ex-posed more than a few days, lightly sand or power wash the surface to remove the thin layer of degraded wood before applying paint. If power washing, be careful not to get the wand to close to the railing as this can damage the spindles, handrails. Taping a stick on the wand will force you to maintain a safe distance and prevent otherwise easily caused damage. You also have to wait for the railing to dry, permitting more sun exposure.

Tests of wood painted, at least primed, before any exposure to sunlight show that the surface is not in need of repainting for at least 30 years. Duplicates exposed to sunlight facing south for 1 week prior to priming required repainting at 13 years. Wood exposed to 2 weeks of sun prior to priming required repainting at 10 years. Light sanding can remove the thin layer of damaged wood, and it is advised to prime immediately.

Although instructions on primer paint frequently indicate top coats should be applied soon, we found with a limited number of primers that 6 months of primer alone over the winter had no effect on topcoat life. A second primer can always be applied before top coating if it is suspected that the primer had been exposed for too long. When repainting, prime sanded wood as soon as possible after sanding. Test: Old paint that wipes onto a cloth or hand (chalk) should be cleaned. If paint still wipes off, repriming is necessary. If cleaning stops chalkiness, only cleaning is necessary before top coating.

3. Temperature was too cold when the wood was painted. Oil-based paints should be applied when the temperature is at least 40 degrees Fahrenheit or for latex paints, the temperature should be at least 50 degrees Fahrenheit and conditions should remain above these temperatures for 24 hours after painting. We do not know if paints formulated to be applied in even cooler temperatures perform as well as standard paints. When pretreating the wood with a paintable water-repellent preservative (a recommended practice), best results are achieved if it is applied when temperatures are greater than 70 degrees Fahrenheit.

4. Wood was too hot when it was painted or was heated soon after painting.

Do not paint when the temperature is greater than 90 degrees Fahrenheit. To prevent temperature blisters, avoid painting surfaces that will soon be heated. Painting with white paint on a white surface can be okay any time of day because white generally reflects the sun's heat. With colors, the best procedure is to "follow the sun" around the deck although this presents a problem on the west side. The east side of the railing should be painted late in the morning, the south side in the middle of the afternoon, and the west side late in the afternoon unless it gets full sun. Painting the west side in the morning would be a better choice if it receives full sun, you stop before noon, and there is little or no morning dew. The north side can be painted at any time during the day. However, at least 2 hours are needed for the fresh paint to dry before weather conditions cool to the point where dew forms. If blistering on the wood surface does occur, allow the paint to dry for a few days, scrape off the blisters, smooth the edges with sandpaper, and paint the area.

5. Weather was too humid when the surface was painted. When water-based paints cure, the water should evaporate as fast or faster than the solvents. After the water has evaporated, the paint will shrink to nearly its final shape. As the solvents evaporate the paint chemically reacts to form a hard material. When it is too humid, water cannot evaporate and the solvents may evaporate first, causing the paint to cure while still in a water-filled state. You cannot recover from this type of disaster. Oil-based paints may also fail if conditions are too humid.

Additional suggestions to prevent paint failure in this situation include the following:

1. Wood railing is dirty. If the railing is dirty, the surface of the railing should be power washed or cleaned with detergent and a stiff bristle or brass brush and rinsed well. Never use steel or iron, which causes iron stain and may glaze the surface.

2. Brown stains appear on the surface of the paint. Paint does not have to fall off to fail. Moisture traveling through wood pulls water-based extractives through the paint, leaving brown stains on the surface of the paint. If the wood is kept dry, the water-based extractives in the wood will not bleed through paint. Keeping all moisture out may be difficult. Oil-based primers usually block extractive stains better than do latex primers, and may be a better choice on redwood and cedar; however, oil paints can increase mildew. Compared with oil-based primers, latex primers produce a more flexible paint film with better durability. Extractives may bleed into latex stain-blocking primers, but if allowed to fully cure for 24 to 48 hours, they do not bleed into topcoats. In rare cases of high extractives, a second primer may be necessary although you won't know that until you have begun top coating. Multiple topcoats will not stop extractives.


3. Wood has decayed (rotted). Decayed wood can result if the wood has been wet for extended periods. If the wood is soft and spongy, it is degraded to the point that it will never hold paint and should be replaced. If there is only a small area of decay, it can be dug out. The remaining wood can be stabilized with a consolidate and the missing wood replaced with waterproof compounds. Be aware that wood shrinks when warmed because of loss of water and almost everything else expands-to be compatible, compounds must be and stay flexible.