Learning Center · Exterior
Exterior Paint Prep: What a Good Job Includes
Most of what makes exterior paint last happens before the first coat goes on. This guide walks through the prep steps in order, so you can tell a thorough bid from one that skips the work.
Updated October 11, 2026
Read This First
The short version
- Prep decides how long exterior paint lasts, and it is the part cheap bids cut first.
- A good job washes, scrapes loose paint, repairs rotten wood, caulks open joints and primes bare spots before any topcoat.
- USDA research says a primer and two topcoats give the best service life on wood.
- Homes built before 1978 need lead rules followed before any scraping or sanding.
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Direct Answer
Why prep matters more than the paint
Paint only lasts as long as the surface under it, so prep is where a paint job is won or lost.
Paint sticks to what is under it
New paint cannot fix a bad surface. If it goes over chalk, dirt, loose paint or wet wood, it fails with that layer. Our pricing register notes that prep is 40 to 50 percent of the labor on an exterior job. When one bid comes in far below the others, prep is usually what is missing.
Process
The prep steps, in order
Wash, dry, scrape, repair wood, caulk joints, spot prime, then two topcoats.
1. Wash
Washing comes first. It removes chalk, dirt and mildew so paint can bond. Painted siding is washed at low pressure, because high pressure can force water behind siding and gouge soft wood. See our pressure washing page for how we wash a house.
2. Dry
The wall must dry before anything else. Wood and stucco soak up wash water. Painting too soon traps moisture under the new film.
3. Scrape and sand
Loose paint must come off. Scrape to a firm edge and feather the edges so they do not show through. In a home built before 1978, this step falls under federal lead rules, explained in our lead paint guide.
4. Repair wood
Rotten wood gets replaced, not painted. Soft trim at door bottoms, window sills and fascia under gutters is cut out and replaced, then primed right away. The USDA found that even one week of sun on bare wood before priming shortened paint life sharply.
5. Caulk
Open joints get sealed. Gaps at trim corners, window and door edges and siding butt joints are filled with a paintable sealant. The Painting Contractors Association has its own standard on painter’s caulk, because caulk is not a cure for every gap.
6. Prime, then two topcoats
Bare spots get primer. Then the walls get two topcoats where the plan calls for them. The USDA handbook names a primer and two topcoats, about 4 to 5 mils dry, as the system with the best service life.
Industry Standard
How much prep is enough?
The industry names levels of surface prep, so a bid can say which level it includes.
Ask which level is included
Prep comes in levels. The Painting Contractors Association publishes a standard called Levels of Surface Preparation for Repainting, and another called Inspection and Acceptance of Surfaces Prior to Painting. A written bid that names the prep steps, or the level, gives you something to hold the work to.
What you can check yourself
Walk the house before the topcoat. Look for scraped edges, new caulk at the joints you noticed, and primer on every bare spot and new board. If you cannot see prep, ask about it before the color goes on.
Watch For
Prep shortcuts to watch for
No wash, paint over chalk, caulk over rot and one coat on a color change are the common cuts.
The common ones
Some shortcuts are easy to spot. Watch for painting over heavy chalk with no wash, caulking over soft wood instead of replacing it, one topcoat on a color change, paint sprayed on rough siding with no back rolling to work it in, and painting walls in full afternoon sun. Our guide to reading a painting estimate shows how to catch these on paper.
Common Questions
Questions homeowners ask
How much of a paint job is prep?
On exterior work, prep is 40 to 50 percent of the labor in our own pricing. It is also the part a low bid most often leaves out.
Should a house be pressure washed before painting?
It should be washed. Painted siding is washed at low pressure so water is not forced behind the siding and soft wood is not gouged. Concrete and masonry can take more pressure.
Can you paint over peeling paint?
No. Loose paint must be scraped to a firm edge first, or the new paint peels with it. If peeling goes down to bare wood, look for a moisture source.
Do you need primer on a repaint?
Bare wood, new boards and repaired spots need primer. Sound painted surfaces in good condition often do not, but the paint maker’s data sheet decides.
Can caulk fix rotten wood?
No. Caulk seals a gap, it does not restore wood. Soft wood should be cut out and replaced, then primed.
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