Painting and Stripping Old Wood Siding — Overview

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A. Peeling paint from moisture

B. Too many layers of old paint

C. Finished. Note the metal overhang on the window. This was caulked on the sides and the old metal overhang pried up a bit so the water wouldn't wick.

When we started to paint our house, we faced the problem of trying to decide what we could do to maximize the life of our paint job. Unfortunately, we kept finding contradictory information. Should we use a latex primer or and alkyd primer? Should we use a water repellent sealer before priming? Should we just scrape or totally remove the old paint?

Here is a summary of what we did. For full details). Go to our step-by-step page

Strip the old paint (Go to our paint stripping page) We decided to strip the paint to give us the best chance of producing the longest lasting paint job. Be sure to remove any caulk where the siding overlaps as old houses need to breathe.
Pull out loose nails and renail using stainless steel siding nails.
Fill any dents and holes with either a wood or epoxy filler.
Sand the surface.
Apply an epoxy consolidant to soft wood and coat the rest with a wood preservative. We used the paintable Wolmans WOODLIFE® Classic Clear Wood Preservative . We have also learned of Smith and Co's MultiWoodPrime that also is paintable.
Caulk cracks. We used GE XST Extreme Paintable Silicone II (We are now using GE Groov caulk ). Never caulk between the overlapping siding boards as this traps in moisture which will cause peeling.
Apply one coat primer. We are using ZINSSER 1-2-3 primer as it dries faster and looks like it has better properties than regular oil based primers.
Tip: Have the paint store tint the primer to the same color as the top coat.
Apply two coats of Behr exterior paint form Home Depot. When I buy paint, I try to use the top rated on in Consumer Reports figuring at least there is a test behind the paint. Recently, I've been able to get the #1 rated California paint.

The experts do not agree on the use of a water sealer/preservative before priming. The National Park Service recommends it as do some other top painters. We decided to use a sealer because our area is humid and gets regular rain during the Spring and Summer. Therefore, we wanted to seal the fresh stripped wood surface as soon as possible after using the infrared heat stripper. The process of infrared heat stripping dries out the wood and allows the sealer to readily penetrate. We applied the sealer, which cleans up with water, as small areas were stripped. Since the freshly striped siding was now protected, we could wait to prime larger areas on dry days, and by priming larger areas with the alkyd primer, we were more productive in priming setup and clean up.

Hints:

Never caulk between the overlapping siding boards. This traps in moisture. Moisture needs to flow between the inside and outside so your house can breath.
Don't caulk unpainted wood. Caulk after using the sealer. If you don't use the sealer, caulk after priming.
Wood that is gray or weathered will not hold paint. Sand down to fresh wood.
Unfinished siding exposed to several weeks of sunlight before painting needs to be sanded. Sunlight degrades the unfinished wood surface, thus it will never hold paint as well as fresh wood. If the unfinished wood was exposed more than 3 to 4 weeks, lightly sand the surface to remove the thin layer of degraded wood before applying paint.
Don't let the primer sit more than a few weeks before painting. Soap-like compounds can form on oil primers in as little as two weeks.
Use a brush when painting old siding. It allows the paint to be worked into the siding's imperfections more effectively than a roller or spray.
Don't prime or paint in direct sunshine, when it is dry and breezy, or is very hot (over 90 degrees F)
Paint should not be applied when the air temperature is below the stated figure for the product, nor if the temperature is forecasted to drop below that minimum during the next 36 hours, nor if the surface being painted is below that temperature.
Oil-based paints should be applied when the temperature is at least 40 F; for latex paints, the temperature should be at least 50 F. Conditions should remain above these temperatures for 24 hours after painting. 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 F.
Don't paint if it is too humid (between 20% and 80% is ideal). 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 will also fail if conditions are too humid.

Additional information:

Why is my paint peeling

Why exterior finishes fail

Proper siding preparation

How to paint old siding

Repairing old windows

Repairing old windows (National Park Service)

Exterior paint problems on historic woodwork (National Park Service)

Using a water sealer/preservative before priming

Painting pressure treated wood

Removing mildew from surfaces—Wet and Forget Commercial Product

Primers

Wolmans WOODLIFE® Classic Clear Wood Preservative

Smith and Co's MultiWoodPrime epoxy primer

Epoxy fillers and consolidants

Rot Doctor's Penetrating Epoxy and FILL-IT™ Epoxy Filler

Abatron's LiquidWood and WoodEpox
Only buy enough epoxy for a year as it doesn't keep well.