Proper prepping for house painting is essential.
Proper surface preparation is essential to a successful paint job, so don't skimp on time or elbow grease. Depending on the condition of the siding and trim, you may spend much more time preparing for painting than actually applying the paint.
The ideal surface for a good appearance is smooth yet slightly roughed up so the paint can adhere. In cases of severe damage or heavy paint buildup, you need the ultimate approach: Scrape and sand down to bare wood. A more moderate approach is usually enough: Sand the paint smooth and apply primer. If the existing surface is in good condition, you can get by with washing, spot-sanding, and priming.
Rotted areas can be hardened and holes filled, but if the area is large, you might want to simply replace the boards.
You can wash 300 square feet in 1 hour or less. Scraping down to bare wood may take weeks.
Pressure washer, paint scrapers, power paint remover, sanding blocks, power sander, heat gun, paintbrush, wire brush, steel wool, putty knife, abrasive pads, caulking gun, utility knife, ladders and/or scaffolding
Patient attention to detail
Protect plantings and lawn with drop cloths.
Sandpaper, liquid or paste paint remover, caulk, wood filler, wood hardener, epoxy filler, glazing putty
Many walls can be prepared simply by cleaning with a stiff brush (perhaps a push broom on a large area of siding). Use a mild detergent solution, then rinse thoroughly. Or use a pressure washer as shown. Spray with a fan nozzle, and avoid getting too close or you may damage the wood.
At corners and on molded trim, use a detail scraper, which comes with a selection of various-shape curved and pointed blades. If dry-scraping makes for slow progress, apply paste paint stripper according to instructions, wait for the paint to bubble, and scrape. Wear protective clothing when working with chemicals, and keep a bucket handy for collecting scrapings.
Scrape away any loose material, but you can leave soft, rotted wood in place. If the area is wet, dry it out before proceeding. Drill a series of holes wherever you suspect the wood may be rotted beneath the surface. Apply wood hardener to all the rotted wood.
If needed, tack on a rough form to hold the epoxy. Continue filling and pressing until the area is slightly overfilled. Use a putty knife or a scraping tool to roughly mold the filler to the shape of the surrounding wood. You may be able to cut a plastic scraper to the desired profile.