# Alligatoring (crocodiling)

Source: https://coatmentor.com/defects/alligatoring/ · Updated 2026-10-14

Wide, deep cracks that divide the top coat into islands, like the hide of an alligator.

*Figure: Alligatoring (crocodiling): the surface as you see it, and a schematic cross-section.*

## Causes

- A hard, rigid coat over a softer, more flexible coat.
- A top coat applied before the coat below has dried.
- Ageing of oil-based or bituminous coatings under temperature cycling.

## Prevention

- Use compatible coats with the flexibility in the right order.
- Respect the drying and recoat times.

## How it is assessed

Visual. Note whether the cracks stop at the top coat or reach the substrate; cracking ratings follow ISO 4628-4.

## Telling it apart

- **[Checking](https://coatmentor.com/defects/checking/):** Checking is fine, shallow breaks in the top layer. Alligatoring is wide and deep, and splits the coat into separate islands.
- **[Mud cracking](https://coatmentor.com/defects/mud-cracking/):** Mud-cracking is a network of cracks in a coat applied far too thick, typical of zinc silicate. Alligatoring comes from a hard coat over a softer one, or from ageing.
- **[Cracking](https://coatmentor.com/defects/cracking/):** Cracking is the general term: rate its density, size and depth under ISO 4628-4.

## Repair

Remove the affected coats, usually to the substrate, and apply a compatible system. The specification and the coating manufacturer have the final word on the repair procedure.

## Related

- **Concepts:** [Drying, curing and recoat windows](https://coatmentor.com/learn/cure-and-recoat/) · [Protective coating types](https://coatmentor.com/learn/coating-types/)
- **Standards:** [ISO 4628](https://coatmentor.com/standards/iso-4628/)

## About this page

Written from coating practice and the published rating standards, in our own words; the drawing is schematic. Checked on 2026-10-14; errors go in the [corrections log](https://coatmentor.com/method/). CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.