Alligatoring Paint: What It Means and When You Need to Strip

Alligatoring is a paint failure that shows up as a network of irregular cracks on the surface. The cracks resemble an alligator’s skin, which is where the name comes from. It signals the coating film is losing integrity and cannot flex with the substrate.

This pattern is different from simple peeling or blistering because the cracks run across the surface while some intact areas remain beneath. Understanding the pattern helps you diagnose whether the problem is adhesion, film structure, or substrate movement.

Visual characteristics and how to recognize it

Alligatoring paint has a distinctive, scaled appearance. It looks like the skin of an alligator – hence the name. You’ll see cracks forming tiny, irregular shapes, often resembling diamonds or hexagons.

The scale of these cracks can vary. Some might be barely visible, while others could be large enough to feel with your fingertips. If you run a finger over the surface, it should feel rough and bumpy.

Active alligatoring will show signs of deep cracking. The paint may flake off in small pieces when gently scraped with a nail or a coin. Cosmetic alligatoring might look similar but won’t show these signs of active failure.

How alligatoring differs from crazing, peeling, and checking

Alligatoring is different from other paint failures. Here’s how to tell them apart:

Crazing – Cracks are fine and hairline, like a spider web. They don’t affect the film integrity, just the surface.

Peeling – Paint lifts off in large sheets or strips. You’ll see edges lifting away from the surface.

Checking – Cracks are long and straight, often running parallel to each other. They don’t form patterns like alligatoring.

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The primary culprits are poor adhesion between coats, or coatings that don’t work well together. Incompatible products often fail when a new layer is applied over an old one. Over-thinning can also weaken film formation and durability.

Underlying substrate movement and improper surface preparation contribute as well. In reality, several factors can collide to create alligatoring, so look for multiple signs rather than a single culprit.

Coating incompatibility and application errors

Steer clear of these common mistakes to prevent alligatoring.

• Hard over soft: Applying a hard coating over a softer one creates tension, leading to alligatoring. Stick to compatible coatings.
• Improper recoating: Recoating too soon or too late can cause problems. Follow the manufacturer’s recommended recoat window.
• Over-thinning: Thinning paint too much reduces its ability to adhere and form a proper film, leading to alligatoring. Avoid over-thinning.
• Incorrect application: Rolling or brushing on paint too thickly can cause it to sag and run, leading to issues later on. Apply evenly and smoothly.

Remember, these are common pitfalls. With careful planning and execution, you can avoid them.

Substrate and environmental contributors

Underlying issues with the substrate or environment can contribute to alligatoring. Here’s what to watch out for:

Substrate movement: Wood expands and contracts with humidity changes, while metal can rust and move. Ensure your substrate is stable before painting.

Moisture issues: Paint doesn’t like water. Keep the surface dry during application and allow it to cure properly.

Extreme temperatures/humidity: Painting in extreme conditions can lead to problems. Aim for moderate temperatures and humidity when possible.

Age and UV/weathering effects

Over time, even the best paint systems can succumb to alligatoring due to age and weathering.

Long-term degradation: Paint breaks down over time. This is normal, but it increases the risk of alligatoring.

Loss of flexibility: As paint ages, it loses its ability to stretch and bend with the substrate. This lack of flexibility can lead to cracking and alligatoring.

Repeated cycling: Temperature changes cause substrates to expand and contract. Over time, this can cause even a sound paint system to alligator.

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Use a practical framework that weighs adhesion, extent of cracking, and what you see on the surface. Spot repairs may be enough if the damage is limited and the substrate is solid. Widespread cracking usually points to more extensive removal and re-coating.

Run simple checks like probing a small area for looseness and listening for a hollow feel behind the coating. Observe the substrate condition after moisture exposure and note any gaps or soft spots that could affect long-term results.

Simple tests to evaluate adhesion and depth

Before you decide how much paint to strip, do some quick checks. These help you understand if the problem is just surface deep or if it goes all the way down.

Scrape/Tap Test: Use a scraper or even a coin to gently scrape the paint. If it comes off easily and in large flakes, that’s a sign of poor adhesion. Tap the area with a hammer. If it sounds hollow, there might be substrate damage.

Tape Pull: Apply painter’s tape over the alligatoring, press down firmly, then pull it off quickly. If paint comes off with it, that means the top layers aren’t adhering well to each other or the underlying layer.

Probing: Use a screwdriver or awl to probe the cracks. If it goes in easily and hits something soft or hollow, you’ve got substrate damage that needs addressing.

Surface area and pattern considerations

The size and spread of alligatoring can tell you a lot about how much stripping is needed. Small, isolated patches might just need spot repairs.

Check the visual characteristics earlier in this guide to see what patterns you’re dealing with. If it’s a few small, disconnected areas, you could get away with spot repairs. But if it’s large, interconnected patterns, full stripping is likely your best bet.

Remember, alligatoring is like a disease – it spreads. Even if it looks contained now, it might not stay that way. It’s often better to bite the bullet and do the job right the first time.

When underlying substrate damage mandates full stripping

Sometimes, alligatoring is just a symptom of a bigger problem – damage to your substrate. If that’s the case, you’ll need to strip down to bare substrate before making any repairs.

Look for signs like rot, rust, or efflorescence. These could indicate moisture issues that need addressing. Also, check for structural movement – cracks in the wall or warping of the surface.

If you find any of these issues, don’t just paint over them. That’s like putting a band-aid on a broken bone. You’ll need to strip all the paint, fix the underlying problem, and then repaint.

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Wood requires attention to grain movement and existing coatings; sometimes stripping reveals a fresh surface that accepts new coatings better. Metal surfaces need rust control and compatible primers to prevent future bonding issues. Masonry can hold moisture that drives alligatoring, so it may need drying and proper vapor-permeable coatings.

Drywall is sensitive to moisture and pad-coated films; stripping must avoid exposing damaged paper or fiberglass. Tailor the repair and priming steps to each material, and address any underlying issues before repainting.

Wood surfaces

Alligatoring paint on wood surfaces can be a sign of rot or moisture damage. Inspect the area for any signs of decay.

Mechanical removal is usually the best method here, using tools like scrapers and wire brushes to gently remove the paint. Be careful not to damage the wood further.

If you find rot, replace the affected area before repainting. If it’s minor, you can repair with wood filler and sand smooth.

Always prep wood surfaces by sealing any exposed areas with a primer or sealer to prevent future moisture issues.

Metal surfaces

Rust is the enemy on metal surfaces. Remove all rust scales using a wire brush or sandpaper before stripping paint.

Mechanical stripping works well here, but beware of flash rusting. Wipe off any exposed metal with a damp cloth immediately after stripping.

Apply an appropriate primer to seal the metal and prevent rust recurrence. Use a rust-inhibitive primer if necessary.

If rust continues to form under the paint, you may need to treat the underlying rust or replace the metal altogether.

Masonry and stucco

Salt or efflorescence buildup can cause alligatoring on masonry surfaces. Remove any visible salt deposits with a wire brush or acid wash.

Check the mortar integrity. If it’s crumbling, repoint before painting. Rigid exterior coatings over porous masonry often lead to moisture trapping and further damage.

Full removal of the old paint is necessary here. Use a chemical stripper or mechanical method like sandblasting, ensuring you don’t damage the substrate.

After stripping, apply a breathable primer to allow moisture escape and prevent future alligatoring.

Interior drywall and plaster

Alligatoring inside often signals previous incompatible coatings or moisture issues. Inspect for any water damage or mold.

If the alligatoring is minor, you can skim coat with joint compound to smooth out the surface. For larger areas, consider replacing entire panels.

Spot-prime any bare spots before repainting to prevent future issues. If moisture is the culprit, find and fix the source before proceeding.

Always use a primer designed for your specific substrate and paint type to ensure compatibility.

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Chemical strippers offer thorough removal but require proper ventilation and disposal practices. Mechanical abrasion is effective on many surfaces but can damage softer substrates if not controlled. Heat-assisted methods can speed up removal but must be used with caution on flammable or sensitive materials.

Consider a combination approach when appropriate, and always follow local disposal rules for the removed material and used chemicals. Match the method to the substrate and the extent of alligatoring to reduce risk.

Chemical strippers and how to choose one

When it comes to chemical strippers, you’ve got three main types: solvent-based, caustic, and biobased. Each has its own strengths and weaknesses.

Solvent-based strippers are great for tough films like urethanes and enamels. They’re quick-acting but can be harsh on some substrates. You’ll need good ventilation with these.

Caustic strippers, like potassium hydroxide or sodium hydroxide, work well on latex paints. They’re less harmful to the environment but can damage certain surfaces if left on too long.

Biobased strippers use natural ingredients and are safer for you and the environment. They might take longer to work but are a good option when dealing with sensitive substrates or indoor projects.

Mechanical removal (sanding, scraping, media blasting)

For mechanical removal, you’ve got a few tools at your disposal. Hand and power sanding are great for small areas and fine details. Use coarse grits to remove paint quickly, then switch to finer grits for smoothing.

Scraping is another option. It’s labor-intensive but effective. Use a sharp scraper and work in small sections.

Media blasting is powerful but can cause surface damage if not done right. It’s best used on large, flat surfaces like concrete or metal. Always wear protective gear and contain the dust to keep your workspace clean.

Heat-assisted removal and cautions

Heat guns and infrared tools can make stripping a breeze by softening paint for easy scraping. They’re great for large areas and tough films.

But be careful. Heat methods can pose fire risks, especially on dry, flammable surfaces. Always keep a fire extinguisher nearby.

If your home has lead-based paint, heat methods are a big no-no. Heating lead paint releases toxic fumes. Opt for wet methods instead to minimize dust and reduce the risk of exposure.

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Start with a careful inspection to identify the extent of cracking and any moisture issues. Contain debris and protect surrounding areas before you begin work. Check compatibility of primers and topcoats before committing to a full repaint.

Proceed to test patches on small areas to confirm adhesion and finish. After stripping and repairing the substrate, apply appropriate priming and then the new coating in the recommended sequence. Verify that the coating system remains compatible across layers.

Inspection, Test Patch, and Method Selection

Before starting, use this checklist to inspect your surface and perform a small test removal.

• Check paint condition: Look for alligatoring, peeling, or flaking. Gently scrape with a putty knife to assess adhesion.
• Test strip area: Choose an inconspicuous spot and apply your chosen stripping method. If it works well, proceed; if not, try another method.
• Inspect substrate: After removing paint, check for any hidden damage or issues that need addressing.
• Avoid skipping this step: It helps prevent costly mistakes and ensures the best results.

Quick rule: Always perform a test patch before committing to a full strip. It’s your best bet for avoiding surprises.

Substrate Repair and Preparation After Removal

After stripping, clean the surface thoroughly to remove any residue. Use a wire brush or scraper if needed.

Treat rust: If you’re working on metal, treat any exposed rust with a suitable primer or converter before proceeding.

Repair and fill: Address any damage (rot, cracks, holes) using appropriate materials. Sand smooth for best paint adhesion.

Primer Selection, Compatibility, and Topcoat Planning

Choose a primer that’s compatible with your substrate and final coating type. Read manufacturer recommendations for best results.

Check compatibility: Ensure the primer is suitable for your surface and won’t interfere with paint adhesion or performance.

Plan topcoat: Consider your desired finish, color, and sheen. Check manufacturer guidelines for recoat conditions to avoid disappointment.

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