# Why is my paint cracking?

Canonical: https://colorswatchlab.com/guides/why-is-paint-cracking/
Author: Color Swatch Lab Editorial Team
Published: 2026-11-02
Updated: 2026-11-02
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> The pattern of the cracks tells you the cause. Fine hairline cracks that later flake usually mean the paint lost flexibility: it was spread too thin, it was a low-quality paint, it went onto bare wood with no primer, or it is old and brittle. Deep, irregular cracks that look like dried mud, often in corners, mean the paint went on too thick or dried too fast. A pattern like reptile scales (alligatoring) comes from old oil paint aging, a hard coat over a softer one, or a coat applied before the one under it had dried. A crack running along a caulked joint usually means the caulk was not paintable or was painted before it dried. Never paint over cracked paint. Scrape off everything loose, sand the edges smooth, prime bare spots and repaint at the spreading rate on the label. If the cracks go down to bare wood, remove as much of the old paint as you can first.

## Read the crack pattern first

Cracks are a sign that the paint film can no longer stretch with what is under it, or that it shrank while it dried. Sherwin-Williams defines cracking as the splitting of a dry paint film through at least one coat, and says that in its early stages it shows as hairline cracks and in later stages it flakes. Benjamin Moore’s troubleshooting page describes the same progression: hairline cracks first, then larger pieces chipping off if the cause is not fixed. The shape and depth of the cracks narrow down the cause, and the cause decides how much paint has to come off.

| What you see | Likely cause | What fixes it |
| --- | --- | --- |
| Fine hairline cracks, later small flakes | Paint spread too thin or over-thinned, low-quality paint, bare wood not primed, or old paint gone brittle | Scrape and sand to a sound edge, prime bare spots, repaint at the label’s spreading rate |
| Deep, irregular cracks like dried mud, worst in corners | Paint applied too thick, allowed to pool, or dried too fast in very dry conditions | Scrape or sand smooth, prime if needed, repaint in normal coats |
| A pattern like alligator or reptile scales | Aging oil paint, a hard coat over a softer one, a coat over an undried coat, or paint over gloss | Remove the cracked paint, wash, sand gloss dull, prime, repaint |
| Cracks running along a caulked joint | Non-paintable caulk, paint over caulk that had not dried, cold application, or a joint too wide | Cut out failed caulk, prime, recaulk with paintable caulk, let it dry before painting |
| Long cracks across the grain on old, many-times-painted wood | Too many layers of paint (cross-grain cracking) | Remove the old paint down to wood and start a new paint system |

## Hairline cracks and flaking

Sherwin-Williams lists four causes for ordinary cracking: a paint with lower adhesion and flexibility, over-thinning or over-spreading the paint, poor surface preparation or painting bare wood without primer, and paint that has hardened and become brittle with age, so it can no longer expand and contract with temperature and humidity. Benjamin Moore gives nearly the same list, including “spreading paint too thin.” Over-spreading is easy to do without noticing. Trying to make one gallon cover a wall it was not meant to cover leaves a thin film that cracks. The spreading rate on the label is the guide. Our [paint quantity guide](https://colorswatchlab.com/guides/how-much-paint-do-i-need/) explains how to work it out before you buy.

Both manufacturers give the same repair. Remove loose and flaking paint with a scraper or wire brush, sand so the edges feather into the sound paint, prime any bare wood or plaster, and repaint. Sherwin-Williams adds two practical steps. First, test the paint 6 to 12 inches around each damaged area to make sure it is still well attached. Second, if the flaking runs through several layers, use a spackling compound to level the surface so the edges do not telegraph through the new coat. Benjamin Moore’s rule for prevention is short: never paint over cracked paint, and let each coat dry thoroughly before the next.

## Mud cracking: the coat was too thick

Mud cracking looks like a dry riverbed: deep, irregular cracks, often in inside corners, around trim, or where primer or paint was laid on heavily to hide a patch. Sherwin-Williams lists three causes: paint applied too thick, paint allowed to build up in corners, and a surface that was not cleaned. Benjamin Moore calls it a less common kind of cracking that happens while the paint dries, because the coat was too thick or the conditions were extremely dry. A thick film dries at the surface first, and as the rest shrinks it pulls the surface apart.

The fix is to smooth the cracked area by scraping or sanding, prime if needed, and repaint in normal coats. Sherwin-Williams also points to the roller. A 1/4 or 3/8 inch nap is usually enough on smooth surfaces, while textured ones need 3/4 inch or more. The wrong nap pushes people to load the roller and lay paint on too heavily. It also notes that quality paints hide well enough that you are less tempted to apply one thick coat. Two normal coats are better than one heavy one. Roller choice is covered in our [roller and roller cover guide](https://colorswatchlab.com/gear/paint-rollers-and-roller-covers-guide/).

## Alligatoring: reptile-scale cracks

Alligatoring is cracking in a pattern of connected scales. Sherwin-Williams says the cracks generally do not reach the surface underneath, and gives four causes. One is the natural aging of oil-based paint, as years of expanding and contracting with temperature cost the film its elasticity. Another is an extremely hard, rigid coating, such as an oil enamel, put over a softer, more flexible one. The last two are a topcoat applied before the primer or base coat had dried, and paint applied over a glossy finish without dulling it.

The National Park Service’s brief on exterior paint problems describes how it gets there on old houses. It starts as crazing, fine jagged breaks in the top layer when many layers of paint have become hard and brittle. Water then gets into the breaks, the wood swells, and the cracks deepen until they become alligatoring, which the brief says requires total paint removal once it reaches bare wood. If the cracking is only in the top layers, the brief says those can be scraped and sanded to the next sound layer and repainted. Sherwin-Williams’ repair for alligatoring is to remove the old paint by scraping, sanding, a chemical remover or a heat gun, wash and rinse, sand any glossy surface dull, and prime as needed before repainting. If the old paint is oil-based and you are switching to latex, [painting over oil-based paint](https://colorswatchlab.com/guides/painting-over-oil-based-paint/) covers the test and the bonding step.

## Too many coats: cross-grain cracking

On older houses that have been repainted many times, Purdue University’s extension bulletin on paint failures describes cross-grain cracking: the film gets so thick that it cracks, usually in the direction the paint was brushed. Purdue says that once this has happened, the only solution is to remove the old paint completely and apply a new paint system. Its prevention advice is to follow the manufacturer’s spreading rates and not to repaint sheltered areas, such as porch ceilings and roof overhangs, as often as the rest of the house. Purdue gives a target for the whole film, primer plus one or two topcoats: about 4 to 6 mils, roughly the thickness of a sheet of newspaper, gives the longest service life.

The National Park Service brief makes the same point about thickness. A thick buildup of paint is less able to tolerate the pull of a new coat as it dries, and it fails at its weakest bond, the oldest layers next to the wood. So adding another coat for a color change can be the coat that starts the cracking.

## Cracks along caulked joints

When the crack follows a joint, such as trim to wall, around a window or a corner bead, the caulk is usually the cause. Sherwin-Williams lists four. The caulk was not labeled paintable. The paint went over caulk that had not finished drying, so the caulk shrank under a paint skin that had already set. The caulk was applied below 40°F without being made for the cold. Or the joint was wider or deeper than 1/2 inch. Its fix is to prime first, caulk only when the air, the surface and the caulk are all above 40°F, and fill joints deeper than 1/2 inch with foam backer rod to within 1/2 inch of the surface before caulking. Caulk and prep supplies are in our [wall repair and surface prep supplies](https://colorswatchlab.com/gear/wall-repair-and-surface-prep-supplies/) guide, and the full prep sequence is in [how to prep walls before painting](https://colorswatchlab.com/guides/how-to-prep-walls-before-painting/).

## The repair, by depth

- **Check for lead first.** Scraping and sanding old paint makes dust. In homes built before 1978 that paint may contain lead. Test before you disturb it and follow [lead-safe painting](https://colorswatchlab.com/guides/lead-safe-painting/) practices.

- **Find the depth.** If the cracks are only in the top layers, you can scrape and sand back to sound paint. If they reach bare wood, plan on removing as much of the old paint as possible, as Benjamin Moore and the National Park Service both advise.

- **Scrape and feather.** Remove everything loose, then sand the edges so there is no ridge. Test the paint around each spot, 6 to 12 inches out.

- **Level and clean.** Skim deep steps with spackling compound, sand smooth, wash off dust and grime, and sand any remaining gloss dull.

- **Prime bare areas.** Bare wood or plaster gets primer before the topcoat. Which primer to use is covered in [when to prime before painting](https://colorswatchlab.com/guides/when-to-prime-before-painting/).

- **Repaint in normal coats.** Use a quality paint at the spreading rate on the label, with the right roller nap, and wait the full recoat time between coats. [Dry time versus cure time](https://colorswatchlab.com/guides/paint-dry-time-vs-cure-time/) explains why touch-dry is not ready.

If the paint is lifting in sheets rather than cracking, see [why paint peels](https://colorswatchlab.com/guides/why-is-paint-peeling/). If it is lifting in bubbles, see [why paint bubbles](https://colorswatchlab.com/guides/why-is-paint-bubbling/).


## FAQ

### Can I paint over cracked paint?

No. Benjamin Moore says never to paint over cracked paint, because the new coat cracks with it. Scrape off everything loose, sand the edges smooth, prime bare spots, then repaint.

### What causes hairline cracks in paint?

Sherwin-Williams lists paint with low adhesion and flexibility, over-thinning or over-spreading the paint, painting bare wood without primer or other poor preparation, and old paint that has become brittle with age.

### What is mud cracking?

Deep, irregular cracks that look like dried mud. Sherwin-Williams says it comes from paint applied too thick or built up in corners, or from a dirty surface. Benjamin Moore adds extremely dry drying conditions.

### Does alligatoring mean I have to strip the paint?

If the cracking reaches bare wood, yes. The National Park Service says advanced cracking and alligatoring call for removing the paint. If only the top layers are cracked, scrape and sand to the next sound layer and repaint.

### Why does paint crack over caulk?

Usually the caulk was not paintable, or it was painted before it dried and shrank under the paint. Sherwin-Williams also lists caulk applied below 40°F and joints more than 1/2 inch wide or deep.

## Sources

- [Cracking, problem solver (Sherwin-Williams)](https://www.sherwin-williams.com/homeowners/how-to/problem-solver/peeling-cracking/cracking)
- [Cracking and Flaking Paint (Benjamin Moore)](https://www.benjaminmoore.com/en-us/contractors/job-solutions/troubleshooting/cracking-flaking-paint)
- [Mudcracking, problem solver (Sherwin-Williams)](https://www.sherwin-williams.com/architects-specifiers-designers/paint-coatings-exterior/resources/SW-ARTICLE-PRO-MUDCRACKING)
- [How to Fix Alligatoring Paint, problem solver (Sherwin-Williams)](https://www.sherwin-williams.com/homeowners/how-to/problem-solver/peeling-cracking/alligatoring)
- [Caulk: Paint Cracking or Crawling, problem solver (Sherwin-Williams)](https://www.sherwin-williams.com/homeowners/how-to/problem-solver/sagging-wrinkling/caulk-paint-cracking-or-crawling)
- [Paint Failure Problems and Their Cure, NCR-133 (Purdue University Cooperative Extension)](https://www.extension.purdue.edu/extmedia/ncr/NCR-133.html)
- [Preservation Brief 10: Exterior Paint Problems on Historic Woodwork (National Park Service, PDF)](https://nps.gov/orgs/1739/upload/preservation-brief-10-paint-problems-exterior-woodwork.pdf)
- [Reduce the Risk of Lead Exposure at Home (US EPA)](https://www.epa.gov/lead/protect-your-family-exposures-lead)