Why surface inspection comes first
Most paint failures are not “bad paint” problems—they are surface, moisture, or contamination problems that were painted over. Surface inspection is the step where you decide what you are actually painting (sound substrate vs. failing coating), what is actively changing (moisture movement, salts, biological growth), and what must be corrected before any sanding or coating. The goal is to match the defect to its cause, fix the cause, and then choose a primer/paint system that can bond and breathe appropriately.
Tools for diagnosis (quick kit)
- Bright flashlight or headlamp (raking light reveals texture and cracking)
- Moisture meter (pin or pinless) and/or plastic-sheet test materials
- Painter’s multi-tool or putty knife (for probing and scrape tests)
- Adhesive tape (cross-hatch adhesion check)
- Spray bottle with water, mild detergent, and a small brush
- Bleach-free mildew cleaner or exterior biocide (for verification/cleanup)
- pH test strips (masonry/efflorescence context)
- Marker and masking tape (to label problem zones)
Moisture first: when to delay painting
If moisture is present or recurring, paint is a temporary bandage. Diagnose moisture pathways before you diagnose coating chemistry.
Step-by-step moisture check (exterior and interior)
- Look for water paths above the defect. Stains and peeling often start at the highest leak point and travel down. Inspect roof edges, kick-out flashing, window/door head flashing, and penetrations.
- Check gutters and downspouts. Overflowing gutters, missing downspout extensions, and clogged leaders dump water onto siding and trim. Look for “wash lines” and algae stripes below the gutter line.
- Inspect grading and splashback. Soil should slope away from the house. Hard surfaces should not pitch water toward the foundation. Splashback from bare soil can keep lower siding wet and dirty.
- Probe caulk joints. Failed caulk at trim-to-siding joints, window casings, and corner boards lets water behind paint. Look for gaps, brittleness, and separation.
- Check interior moisture sources. Bathrooms and kitchens need venting to the exterior. Verify bath fans exhaust outdoors (not into an attic). Look for condensation on windows and peeling near ceilings.
- Measure moisture content. Use a moisture meter on wood near defects and compare to a “known dry” area. If readings are elevated or vary widely, find and fix the source before coating.
- Use a plastic-sheet test when needed. Tape a clear plastic square tightly to the surface for 24 hours. Condensation under the plastic suggests moisture moving out of the substrate; condensation on the outside suggests room humidity/condensation issues.
Delay painting when
- Active leaks are present (roof, flashing, plumbing, window/door failures).
- Wood moisture is elevated or rising compared to nearby areas.
- Masonry shows active efflorescence (salts continuing to migrate).
- Mildew returns quickly after cleaning (indicates persistent moisture).
- Surfaces are cold/damp and cannot dry within the coating window (common in shaded north walls).
Decision tree: symptom → likely cause → required remedy → compatible primer/paint system
Use the tree below by starting with what you see. Confirm with simple tests before choosing a remedy.
1) Chalking (powdery residue)
Photo-style description: When you rub the surface with a finger, it leaves a dusty, colored powder on your skin. The wall looks faded and “dry,” especially on sun-exposed elevations.
| Symptom | Likely cause | Required remedy | Compatible primer/paint system |
|---|---|---|---|
| Powder transfers to hand/cloth; paint looks faded | UV degradation of older paint (often low-quality or aged latex); oxidation of binder; sometimes over-thinned paint | Wash thoroughly (detergent + rinse). If heavy chalk remains, scrub more or pressure wash carefully. After dry, do a tape test: if powder still releases, you must remove more chalk or use a binding primer. |
|
2) Mildew (black/green spotting)
Photo-style description: Pepper-like black dots or green smears, often on shaded walls, under eaves, behind shrubs, or in bathrooms near ceilings. It may look like dirt but smears when scrubbed.
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| Symptom | Likely cause | Required remedy | Compatible primer/paint system |
|---|---|---|---|
| Dark spotting that grows back; musty odor indoors | Persistent moisture + organic food source (dust, chalk, soap film). Poor ventilation (bath fans), shade, clogged gutters, or water intrusion | Fix moisture source (venting, leaks, drainage). Clean with an appropriate mildew remover/biocide per label; rinse and allow to dry fully. Confirm removal: stains may remain even after organisms are dead—do not confuse staining with active growth. |
|
3) Efflorescence (white crystalline salts on masonry)
Photo-style description: White, crusty, sometimes sparkly deposits on brick, block, stucco, or concrete. It may appear in streaks or patches and can reappear after rain.
| Symptom | Likely cause | Required remedy | Compatible primer/paint system |
|---|---|---|---|
| White powder/crystals; paint blistering on masonry | Moisture moving through masonry dissolves salts; salts deposit on surface as water evaporates. Can be from poor drainage, missing flashing, or unsealed capillary paths. | Correct moisture source (grading, downspouts, flashing, capillary breaks). Dry the wall. Remove salts by dry brushing and rinsing; repeat as needed. Do not trap moisture with a non-breathable coating. |
|
4) Peeling/flaking (loss of adhesion)
Photo-style description: Edges curl up; chips come off in sheets or flakes. Often starts at joints, end grain, or where water sits (bottom edges of trim).
| Symptom | Likely cause | Required remedy | Compatible primer/paint system |
|---|---|---|---|
| Paint lifts to bare substrate or to a previous layer | Moisture intrusion; poor surface prep; painting over dirt/chalk; incompatible layers (e.g., latex over glossy oil without deglossing); end-grain water uptake; failed caulk joints | Identify where it starts (top edge, joint, bottom edge) and fix water entry. Scrape to sound edges; feather transitions. Clean. Spot-prime bare areas and any suspect edges. Consider full prime if widespread. |
|
5) Bubbling/blistering
Photo-style description: Rounded bubbles under the paint film. Some pop and reveal damp wood or a powdery layer; others reveal bare substrate. Often clustered on sun-facing walls after rain.
| Symptom | Likely cause | Required remedy | Compatible primer/paint system |
|---|---|---|---|
| Soft blisters; may contain moisture | Moisture vapor pressure pushing paint off (water behind film); painting over damp substrate; trapped solvent; non-breathable coating on a damp wall | Pop a blister and inspect: if substrate is damp, stop and fix moisture source. Allow thorough drying. Remove loose paint; sand/feather. Recoat with a system that matches the substrate’s need to breathe. |
|
6) Checking/crazing (fine cracking network)
Photo-style description: A spiderweb of fine cracks, often in older paint. It may look like dried mud cracks or tiny rectangles. Usually no bare substrate visible at first.
| Symptom | Likely cause | Required remedy | Compatible primer/paint system |
|---|---|---|---|
| Fine cracks in top layers; brittle feel | Old, thick, brittle paint layers; thermal movement; aging oil/alkyd films; too many coats; inadequate flexibility | Scrape any loose areas. Sand to smooth and remove brittle edges. If checking is widespread, consider more aggressive removal to stable layers. Prime to unify porosity and improve adhesion. |
|
7) Tannin bleed (brown/yellow staining from wood)
Photo-style description: Brownish or tea-colored streaks bleeding through paint, often at knots, cedar/redwood boards, or where water ran down. Stains can appear even through fresh paint.
| Symptom | Likely cause | Required remedy | Compatible primer/paint system |
|---|---|---|---|
| Brown/yellow stains reappear after repaint | Water-soluble tannins in cedar/redwood or knots; moisture accelerates bleed; using non-blocking primer | Fix moisture source first. Clean and dry. Spot-prime stained areas with a true stain-blocking primer; allow proper dry time. Recoat. |
|
8) Rust staining (orange/brown streaks)
Photo-style description: Orange-brown drips below nail heads, metal brackets, railings, or cracks in stucco where metal lath is near the surface. Often appears after rain.
| Symptom | Likely cause | Required remedy | Compatible primer/paint system |
|---|---|---|---|
| Rust streaks bleeding through paint | Corroding fasteners/metal; water exposure; inadequate metal primer; galvanic corrosion (mixed metals) | Stop water contact where possible. Replace with corrosion-resistant fasteners if feasible. Remove rust (wire brush/sand) to sound metal. Clean. Prime promptly to prevent flash rust. |
|
9) Glossy contamination / poor adhesion on slick surfaces
Photo-style description: New paint scratches off with a fingernail, especially on glossy trim, factory-primed slick surfaces, laminate, or previously oil-enamel doors. The surface may look clean but feels “hard and shiny.”
| Symptom | Likely cause | Required remedy | Compatible primer/paint system |
|---|---|---|---|
| Topcoat scratches/peels easily; tape pulls paint | Glossy surface not deglossed; silicone residue (from polishes/caulks); grease/hand oils; inadequate primer choice | Clean with degreaser; rinse well. Test for silicone: water beads strongly and refuses to sheet—repeat cleaning. Dull the gloss by sanding or liquid deglosser (per label). Apply bonding primer before topcoat. |
|
Field tests to confirm your diagnosis
Rub test (chalking)
Rub a dark cloth or your hand across the surface. If pigment powder transfers heavily, cleaning alone may not be enough; plan for a chalk-binding primer after thorough washing.
Tape pull test (adhesion)
- Cut a small cross-hatch grid through the coating with a sharp blade (light pressure—do not gouge deeply into substrate).
- Press painter’s tape firmly over the grid and pull back sharply.
- If multiple squares lift, adhesion is poor. Expand prep (degloss, remove weak layers) and use a bonding primer.
Blister autopsy (moisture vs. heat/solvent)
Slice a blister and inspect immediately. Damp substrate points to moisture movement. Dry, powdery layer can indicate chalking under the film. Strong solvent odor (more common in certain coatings) suggests trapped solvent or recoating too soon.
Mildew verification
Apply a small amount of mildew cleaner to a test spot. If the dark area lightens quickly, it is likely biological. If it does not change, it may be dirt, staining, or tannin/rust bleed.
Photo-style defect gallery (what you’d see on a walkthrough)
- Chalking: “Your fingertips look like you touched sidewalk chalk; the siding color is faded and dusty, especially on the south wall.”
- Mildew: “Black freckles clustered under the porch roof; when scrubbed, the spot smears and the rinse water looks gray-green.”
- Efflorescence: “White crystalline bloom along the bottom third of the block wall; after rain it reappears in the same map-like pattern.”
- Peeling: “Paint is lifting in sheets from the bottom edge of the window sill; bare wood is visible and the edge curls like a potato chip.”
- Bubbling: “Quarter-sized domes on sun-facing clapboards; popping one reveals damp wood and a musty smell.”
- Checking: “A tight spiderweb of cracks across old trim paint; it looks like cracked porcelain glaze.”
- Tannin bleed: “Amber streaks under cedar knots; the stain outlines the grain and returns after repainting.”
- Rust staining: “Orange tears below nail heads on fascia; the metal feels rough and pitted.”
- Glossy contamination: “Fresh paint on a door scratches off in ribbons; the underlying surface is shiny and slick like glass.”
Stop-and-fix checklist (prevent failure before prep and paint)
Water management (fix before anything else)
- Repair leaking gutters, add downspout extensions, and clear clogs.
- Verify kick-out flashing where roof meets wall; repair missing/damaged flashing.
- Seal failed joints with appropriate exterior sealant after surfaces are dry and clean.
- Correct grading/splashback issues; keep soil and mulch below siding clearance.
- Confirm bath fans vent outdoors; address condensation sources.
Substrate stability
- Scrape until remaining paint is firmly bonded (no edge lift under a putty knife).
- Probe wood for softness; replace or repair deteriorated sections rather than “priming over rot.”
- On masonry, remove efflorescence and confirm moisture is controlled before coating.
Contamination control
- Wash off chalk, dirt, and pollutants; rinse thoroughly and allow full dry time.
- Remove mildew and treat with a biocide where appropriate; do not encapsulate active growth.
- Degrease glossy trim/doors; remove silicone residues that cause fisheyes and adhesion loss.
Primer selection checkpoints
- Stains (tannin/rust): use a true stain-blocking or rust-inhibitive primer matched to the stain source.
- Chalky surfaces: use a chalk-binding/bonding primer after cleaning.
- Glossy or oil-enamel surfaces: degloss + bonding primer.
- Masonry with moisture history: prioritize breathable masonry systems; avoid trapping vapor.
Go/no-go decision
- No-go: active leaks, recurring efflorescence, wet substrate, or mildew returning quickly after cleaning.
- Go: moisture sources corrected, surface clean and dry, weak coatings removed, and primer system chosen based on the verified defect.
