Surface Prep for Painting

Goal

Prepare any surface so paint bonds properly + lasts. 80% of paint failures trace to prep shortcuts. The visible work is paint application; the durability is in prep.

The four prep steps (apply in order)

1. Clean - remove dirt, oil, mildew
2. Repair - fix holes, cracks, rot, peeling
3. Sand - break gloss, smooth surface
4. Prime - seal stains, bond to new substrates

Skip any one + you compromise paint life.

Step-by-step prep

Step 1: Cleaning

Indoor walls:

• Vacuum dust
• Wipe with damp cloth + TSP substitute for grease (kitchen, bath)
• Mildew: 1:4 bleach/water; rinse; dry

Outdoor surfaces:

• Pressure wash (1,500-3,500 PSI depending on substrate)
• Mildew: bleach solution, agitated with brush, rinsed
• Salt (coastal areas): fresh water rinse essential

Glossy surfaces:

• Wipe with degreaser; let dry
• Then SCUFF SAND with 220 grit
• Without sanding, paint won't bond (peels in months)

Step 2: Repairs

Nail holes + small dings:

• Lightweight spackle, applied with putty knife
• Sand smooth after 30-60 min
• Re-spackle if shrinks (some shrinkage is normal)

Cracks:

• Hairline cracks: caulk (paintable, 100% acrylic or siliconized acrylic)
• Wider cracks (1/16"+): caulk; for plaster, mesh tape + joint compound
• NEVER spackle a crack (spackle isn't flexible; crack returns)

Rot (wood):

• Small rot: dig out punky wood; fill with epoxy wood filler
• Major rot: cut out + replace board
• Don't paint over active rot - rot accelerates under paint

Peeling paint:

• Scrape to sound paint with stiff scraper
• Feather edges with 80-grit sandpaper
• Tap remaining paint with hammer - if sounds hollow, scrape that too

Stains (water, smoke, tannin, rust):

• Spot prime with appropriate primer
• Water: water/oil-blocking primer
• Smoke: shellac-based (BIN, KILZ Original)
• Tannin (cedar knots): oil or shellac primer
• Rust: rust-blocking metal primer

Wallpaper:

• Removal is usually the right answer (paint over wallpaper risks separation, visible seams)
• Remove with steamer + scraper, or chemical wallpaper remover
• Wash residual adhesive, repair drywall, sand, prime

Step 3: Sanding

Purpose:

• Break glossy sheens so paint bonds
• Smooth filled areas + transitions
• Remove minor surface defects

Grit progression:

• 80-grit: aggressive removal of peeling paint, rough wood
• 120-grit: general smoothing, broken drywall edges
• 150-180 grit: light prep on previously painted surfaces
• 220-grit: deglossing trim, between coats on smooth finishes
• 320+ grit: high-end finish work, cabinetry

Sanding tips:

• Always sand WITH the grain on wood
• Random-orbit sander leaves no swirl marks
• Hand-sand corners + tight spots
• Vacuum / wipe dust completely before paint

Step 4: Priming

When primer is needed:

• New drywall (always; sealing)
• Bare wood
• Stains (spot prime)
• Going from dark to light color
• Repaired areas (spackle, caulk show through topcoat without primer)
• Glossy surfaces being painted (bond primer)
• Smoke or fire damage (shellac primer)
• New plaster (alkali-resistant primer)
• Metal (rust-inhibiting primer)

Primer types:

• Latex/acrylic primer: general-purpose, water cleanup
• Oil-based primer: penetrating, blocks stains, smells more
• Shellac primer (BIN): blocks worst stains, dries fast, alcohol cleanup
• Bonding primer: glossy or laminate surfaces
• Stain-blocking primer: water stains, tannins, smoke
• PVA primer: cheap drywall sealer (basic; no stain blocking)

Match primer chemistry to topcoat: oil primer → either oil or latex topcoat; latex primer → latex topcoat only.

Substrate-specific prep

New drywall:

1. Sand joints + screws smooth
2. Vacuum dust
3. PVA or general-purpose primer (full coat)
4. 2 coats topcoat

Previously painted drywall in good condition:

1. Clean
2. Spot-prime repairs only
3. 1-2 coats topcoat

Bare wood:

1. Sand smooth
2. Spot prime knots with shellac
3. Full primer coat
4. 2 coats topcoat

Plaster (older homes):

1. Wash + dry
2. Repair cracks (mesh tape + joint compound)
3. Alkali-resistant primer
4. 2 coats topcoat

Concrete / masonry:

1. Etch or pressure wash
2. Inspect for efflorescence (white salt crystals); remove + neutralize
3. Masonry primer
4. Masonry topcoat (breathable)

Metal:

1. Sand any rust to bright metal
2. Rust-inhibiting primer immediately (metal flash-rusts in hours)
3. 1-2 coats topcoat

Common mistakes

• Wet substrate: paint blisters within days
• Greasy/dirty surface: paint peels
• Glossy surface unsanded: paint peels
• Skipping primer on repairs: spackle + caulk show through (different absorption)
• Wrong primer: tannin shows through latex primer
• Painting cold (< 50°F latex): paint doesn't cure
• Inadequate cure time before topcoat: blistering, poor adhesion

Lead paint warning

Pre-1978 homes may have lead paint. Disturbing it (scraping, sanding) releases lead dust.

• RRP certification required for contractors painting these homes
• Contain work area: plastic sheeting, HEPA vacuum
• Wet-sanding instead of dry-sanding when possible
• Cleanup: HEPA vacuum + wet wipe
• Disposal: special handling

Fines for non-compliance.

References

• PCA prep standards
• Paint manufacturer prep guides
• EPA RRP rule (lead paint)
• Manuall internal: Interior Painting Process SOP, Exterior Painting Process SOP