Fixing Paint that ‘Alligators’: Causes, Patch Strategy, and When to Strip

Alligator cracking refers to a surface that pucker-cracks in a pattern like reptile skin. It starts as tight, shallow fissures that track across the coating. Over time, those cracks link up and the paint film begins to delaminate or peel away in sheets.

This problem isn’t simply a cosmetic issue; it signals the coating has lost its edge adhesion and moisture control. Understanding the progression helps you decide if you can spot-repair or if cutting back to sound material is needed. Check the product label or manufacturer instructions for guidance on repair limits and timing.

Visual characteristics and stages

Alligatoring, also known as crocodile cracking, is a paint defect that resembles the scales of an alligator’s skin. It starts small but worsens over time.

Early stage: You’ll notice fine cracks, barely visible from a distance, forming tiny squares or rectangles on your painted surface. This is when you can still easily repair it.

Moderate stage: Cracks deepen and widen, becoming more noticeable. Some paint may start to flake off. Repairing becomes trickier but still manageable.

Advanced stage: Large sections of the paint peel away, exposing the substrate underneath. The surface looks severely damaged. At this point, full stripping and repainting might be necessary.

Underlying physical mechanisms

Alligatoring happens due to issues at the coating level. Here’s what’s going on:

The paint loses its elasticity. Over time, and especially with temperature changes, it can’t flex with the surface anymore. Instead, it cracks.

The paint fails to adhere properly to the surface. This could be due to poor preparation or incompatible materials. As a result, the paint lifts off in large pieces when cracked.

There’s too much film thickness. Applying too many coats or using high-build paints can lead to excessive film thickness. The paint can’t dry properly and forms a weak, brittle layer that cracks easily.

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The most frequent culprits are improper surface prep and incompatible coatings. Skipping cleaning or using a primer not suited to the substrate invites trouble. Application too thick or in unsuitable conditions also invites alligator cracking.

Material incompatibility between old and new coatings can trap moisture and cause failure. Operator errors, such as recoating too soon or overworking a fresh layer, also play a big role. When diagnosing, compare the current layer to the manufacturer specs and local rules before proceeding.

Improper surface preparation and contaminants

Before you start painting, it’s crucial to prep the surface right. Dirt, oil, or soluble salts can prevent paint from sticking properly, leading to alligatoring later on.

Check for dirt: Use a damp cloth to wipe the surface. If it comes off dirty, clean it thoroughly with soap and water, then rinse and let it dry.

Test for oil: Dab some denatured alcohol onto the surface. If it beads up or leaves an oily residue, you’ve got oil to deal with. Clean it with a suitable solvent like mineral spirits.

Soluble salts can also cause problems. They’re not as common but can be present in some concrete or plaster surfaces. A simple water test can help identify them: if the surface turns white after wetting, you might have soluble salts. If so, treat the surface with a suitable primer or sealant before painting.

Overcoating and incompatible systems

Applying new coats of paint over old, brittle layers is asking for trouble. The new paint can’t stick properly to the weak underlying layer, leading to cracking.

Check your primer and paint: Make sure they’re compatible with each other and suitable for the surface you’re painting. Different paints have different bases – oil-based, latex, etc. – and they don’t always play nice together.

If you’re unsure about the existing paint, it’s better to strip it off completely before applying a new coat. This might seem like more work, but it’ll save you from having to deal with alligatoring in the future.

Also, be mindful of how many coats you’re applying. Too many layers can lead to brittleness and cracking. Stick to the recommended number of coats for your paint type.

Environmental and substrate issues

Moisture, temperature changes, substrate movement, and UV exposure can all contribute to or worsen alligator cracking. Here’s how:

Moisture: Paint doesn’t like water. If moisture gets trapped under the paint film, it can cause lifting and cracking. Make sure your surface is dry before painting and use a suitable primer to seal out any remaining moisture.

Temperature changes: Paint expands and contracts with temperature changes. If these movements are too extreme or happen too quickly, they can cause the paint to crack. Use paints that are designed for your climate’s temperature range.

Substrate movement: Concrete and other substrates can move over time due to settling, expansion, or contraction. This movement can cause the paint on top to crack. To mitigate this, use a flexible paint that can move with the substrate.

UV exposure: Prolonged exposure to sunlight can break down the paint’s binder, leading to brittleness and cracking. Use paints with good UV resistance for exterior surfaces.

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Begin with a visual and tactile inspection of cracks, edges, and delamination. Tap the surface gently to hear hollow spots that indicate deeper separation. If sound and feel are solid, spot repair may be possible.

If you find widespread cracking with loose areas, plan for partial replacement or a full strip depending on sound substrate. Baseline the decision on adhesion tests and the extent of coating damage. Always verify repair criteria against the product data sheet and local requirements before moving forward.

Simple adhesion and flex tests to perform

Before you decide on a repair, do some quick field checks. These help you understand the severity of the ‘alligatoring’ and what’s causing it.

Cross-Cut Test: Use a utility knife to cut through the paint at an angle. If the paint flakes off easily, adhesion is poor. This indicates a full strip might be needed.

Tape Test: Apply painter’s tape over the affected area and pull it off quickly. If the paint comes off with the tape, it’s not well-adhered and needs attention.

Flex Test: Try to bend or flex the surface gently. If the paint cracks further or peels, it’s too weak for spot repairs and a full strip is likely required.

When spot repair is appropriate vs full strip

Spot repairs can save time and money, but they’re not always the best solution. Here’s when to patch versus strip completely.

Spot Repair: If ‘alligatoring’ is limited to a small area (<10 sq ft), the substrate is in good condition, and there’s no history of recurring issues, spot repair might be enough. Just ensure you address the underlying cause to prevent further damage.

Full Strip: When ‘alligatoring’ covers a large area (>20 sq ft), the substrate shows signs of deterioration, or you’ve had similar problems before, it’s time for a full strip. This ensures you’re addressing all affected areas and preventing future issues.

Put on PPE: eye protection, glove, and a respirator or dust mask as needed. Have hand tools like scrapers and putty knives ready, plus a rigid squeegee for smoothing. Bring power tools such as a drill with a whisk or a variable-speed sander for feathering edges.

Stock abrasives appropriate for the substrate and repair stage, along with compatible primers, fillers, and topcoats. Keep clean rags and a bucket for wash water, plus masking materials for containment. Always cross-check the product label or manufacturer instructions to confirm compatibility and cure guidance.

Start with a thorough cleaning to remove dirt, oil, and loose paint. Rinse and allow to dry completely before inspecting for damage. Remove all obviously failed coating in areas that will be repaired.

Feather edges with a light abrasive to create a uniform transition zone. Vacuum up dust, then wipe with a compatible cleaner. Prime or treat bare or porous zones per the product data sheet instructions before applying patch material.

Contaminant removal and cleaning methods

Effective cleaning is crucial for durable paint adhesion. Here’s how to remove common contaminants without damaging your substrate.

Degreasing: Use a degreaser suitable for your surface type (e.g., TSP or a commercial degreaser). Apply, let it sit, then scrub and rinse. Be sure to follow the manufacturer’s instructions.

Rinsing: Rinse thoroughly with clean water after degreasing. Allow the surface to dry completely before proceeding.

Removing soluble salts or mildew: For salt efflorescence, use a wire brush or acid wash (follow safety guidelines). For mildew, apply a solution of bleach and water (1 part bleach to 3 parts water), let it sit, then scrub and rinse.

Mechanical removal: feathering, sanding, and profiling

Remove loose paint, create a smooth transition, and establish the correct surface profile for your coating system.

Removing loose paint: Use scrapers or power tools to remove any flaking or peeling paint. Be careful not to damage the substrate.

Feathering edges: Sand or scrape along the edge of the repair, gradually reducing the amount of material removed until you reach the existing surface. This creates a smooth transition between the repaired area and the original surface.

Profiling: Use sandpaper to create the desired surface profile for your chosen coating system. This could be light (e.g., for gloss paints) or heavy (e.g., for textured coatings). Always follow the manufacturer’s recommendations.

For small damaged areas, clean, dry, and apply a compatible filler or patching compound. Smooth and feather into the surrounding coating, then prime and topcoat to match. Follow manufacturer cure times for best adhesion.

Medium repairs require lifting and re-bonding effective substrate sections. Use appropriate patch materials and dress the edges before priming. Large areas may demand a cut-back and selective replacement of the coating system, with full-coverage priming and re-coating according to the instructions.

Small-area spot repair workflow

For small damaged areas, follow these steps for a seamless repair:

Step 1: Lightly sand the area with fine-grit sandpaper to create ‘tooth’ and remove any loose paint. Be careful not to sand too aggressively as it may cause more damage.

Step 2: Feather the edges using a flexible abrasive or sanding sponge to blend the repair into the surrounding area. This helps prevent visible lines between the repaired area and the rest of the wall.

Step 3: Apply a primer specifically designed for your paint type. Priming seals the surface, improves adhesion, and helps achieve an even finish. Allow it to dry according to the manufacturer’s instructions.

Step 4: Fill any small holes or cracks using a lightweight spackling compound or paintable caulk. For larger gaps, use a flexible filler. Apply in thin layers, allowing each to dry before sanding lightly and applying the next.

Once filled, apply a topcoat of paint matching your existing wall color. Blend the edges using a technique called ‘tack rag’ – lightly touch up the area with paint, then immediately wipe off any excess with a clean cloth. This helps create a smooth transition between the repaired area and the rest of the wall.

Large-area patching and blending techniques

For larger damaged areas, follow these strategies for an effective repair:

Step 1: Stagger your feathering. Instead of a single, wide feather edge, create multiple, narrower ones. This helps distribute the transition over a larger area, making it less noticeable.

Step 2: Match texture and sheen. If your wall has a specific texture or sheen level, try to match it as closely as possible during the repair process. For textured walls, use a flexible filler that can be sanded to match the existing texture. For sheen, choose a paint with the same gloss level as your existing paint.

Step 3: Use glazing or scumble coats. After filling and sanding, apply a thin layer of glaze or scumble coat – a mixture of paint and clear glaze medium. This helps blend the repaired area into the surrounding wall by subtly altering the color and sheen.

Finally, apply a topcoat of matching paint. Remember, patience is key when repairing large areas. Take your time to ensure each step is done correctly to achieve a seamless finish.

Using flexible fillers and surfacers

Flexible fillers and surfacers are ideal for areas with movement or stress, such as corners, joints, or areas near windows and doors. Here’s how to use them:

When to select: Choose flexible products when you’re repairing an area that experiences frequent expansion and contraction due to temperature changes or structural movement.

How to apply: Apply flexible filler in thin layers, allowing each to dry before sanding lightly. This helps prevent the filler from cracking or peeling as it dries. Once filled, apply a surfacer – a primer with built-in filler – to seal the surface and improve adhesion for your topcoat.

How they help: Flexible fillers and surfacers accommodate substrate movement by flexing with the wall. This helps prevent recurrence of damage caused by stress or movement, extending the life of your repair.

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Strip when the base coat is compromised across a substantial area and adhesion tests show failure over most of the surface. If the substrate remains sound, full stripping may still be unnecessary, but check the data sheet for strip criteria.

Consider safe removal methods specified by the manufacturer and local rules, such as mechanical abrasion or chemical stripping. Ensure proper containment and disposal, then re-prime and re-coat according to the recommended system for your substrate and climate conditions.

Objective criteria forcing a full strip

Before you grab your stripping tools, step back and assess the situation. You’re looking for signs that tell you it’s time to strip down to bare substrate.

Widespread alligatoring – those deep, wide cracks in the paint – is a sure sign. It means the paint has lost its bond with the surface beneath.

Substrate deterioration, like crumbling drywall or rotting wood, also demands a full strip. You need to address these issues before applying new paint.

Multiple incompatible layers can cause problems too. Different types of paint or finishes can’t bond properly, leading to peeling and flaking. If you’ve got more than two coats of paint on top of each other, it might be time for a full strip.

Stripping methods, pros/cons, and safety notes

There are three main stripping methods: mechanical, chemical, and heat. Each has its pros, cons, and safety considerations.

Mechanical stripping, like sanding or scraping, is labor-intensive but effective. It’s good for small areas and doesn’t require harsh chemicals. But it creates a lot of dust and can damage the substrate if not done carefully.

Chemical strippers are fast-acting and easy to use. They dissolve old paint, making it easy to wipe off. However, they’re toxic, flammable, and emit strong fumes. Always use them in a well-ventilated area with proper PPE.

Heat stripping uses infrared or open-flame tools to soften the paint for removal. It’s efficient but poses fire risks. Never use it on surfaces near flammable materials or in poorly ventilated spaces.

Post-strip substrate prep and verification

After stripping, don’t rush into applying new paint. You need to prepare the surface properly and ensure it’s ready for coating.

First, clean the surface thoroughly. Remove any residue or dust that could interfere with adhesion. Use a damp cloth or sponge, but avoid soaking the substrate.

Inspect the surface for any signs of damage or deterioration. If you find issues, repair them before proceeding. You might need to sand down raised grain or fill in holes with a suitable filler.

Finally, prime the surface. This seals the substrate and provides a better bond for your new paint. Choose a primer that’s compatible with both your old substrate and the new paint you’ll be using.

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Choose a coating system compatible with the substrate and traffic level, and follow the label’s application guidelines. Stick to recommended cure times and avoid applying when conditions are outside the specified range. Regular inspections help catch early signs before they advance.

Maintain cleanliness and promptly address any standing moisture or surface damage. Use proper recoating windows and patch techniques that preserve edge adhesion. Document the product and batch details to verify future compatibility if you need to touch up later.

Selecting compatible coating systems and application best practices

When choosing a new paint system, match its flexibility to your substrate. Too rigid? It’ll crack again. Too flexible? It won’t stick.

Follow manufacturer’s drying and overcoating windows. Rushing it causes alligatoring. And don’t forget, proper film thickness control—too thick, it cracks; too thin, it peels.

Use quality application tools. Roller covers should match paint type. Spray guns need regular cleaning to prevent clogging.

Environmental and maintenance controls

Keep moisture in check. Seal any leaks before painting. Use primers that block moisture if you can’t fix the source.

UV protection’s key outdoors. Use paints with UV blockers, or apply a clear coat over top.

Inspect regularly. Spot repairs early to prevent small issues becoming big problems.

Clean dirt and mildew off surfaces before painting. It helps your new paint stick better and last longer.

Troubleshooting common post-repair issues

Blistering? Check for moisture trapped under the paint. Scrape off blisters, let it dry, then repaint.

Edge lifting? It’s usually a sign of poor adhesion. Sand, clean, and prime before repainting.

Sheen mismatch? You might’ve used different paints. Remove all old paint, prep, and start fresh.

If you see any issues early, address them right away. Ignoring them just makes them worse.

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