Prime exterior wood before painting, otherwise your work will peel down to the bare wood. Priming exterior wood is your best bet the paint will adhere and last years. I learned that even when the best materials are used, poor procedures can make a job fail.
Primers come in many flavors and price ranges. I am of the old school that prefers an oil-based primer for bare wood. My last batch of windows received a coat of linseed oil, and then an oil primer designed for latex paint. The finish coat was a quality pure acrylic latex paint and after five-years I am still pleased with the results.
Try to determine why your old paint is peeling. A moisture problem usually causes the paint to peel down to the bare surface. An adhesion problem is when the paint peels down to the old paint. What do you see under the paint chips?
If the wood underneath is bare with no paint or primer showing, it is a sign of water entry behind the paint. When wood gets damp, the sun will pull moisture out of the wood and take the paint with it. Check above the area where the problem is for possible water entry.
Scrape and sand all loose paint to expose all the bare wood you can. Remove all loose caulking and check for damp wood while you are prepping. Once damp wood is encountered, all precautions must be taken to prevent water from getting to that area again.
To quote quality painters, “Perfect prior preparation prevents poor performance.” These are words to live by when painting exterior wood.
If there is paint underneath the chips, is it shiny, dirty or mildewed? It could require sanding, cleaning, or bleaching and then cleaning.
Before sanding and breathing dust, first check for lead in the paint. Sanding and scraping will contaminate both the air and the ground below, not to mention the workers breathing in the dust! If the old paint is suspected of containing lead, do not remove, or sand, the old paint. For guidance, contact the EPA at 1-800-424-LEAD.
Some of the tools of choice are scrapers, 3M Paint & Rust Stripper #9099, particle masks, eye protection, utility knife, draw scrapers and a sharp wood chisel. Heat guns are OK, but propane torches are out. It is too easy for them to start a fire.
Once the surface is cleaned and is dry, prime the surface and cracks before caulking. This will give the caulk a sound surface to bond to. It will also protect the wood underneath if the caulk ever fails. Us a good quality caulk, it is the backbone of your project.
Do not use inexpensive products for this job. Your time is far more valuable than saving three to five dollars on a gallon of paint. There is no sense in ruining all that work with inexpensive products when you are investing hours of labor you hope will last years.