Coating Compatibility

Prior to beginning application of any ALEXSEAL system over a previously painted surface, the surface should be inspected and tested to ensure the existing coating is adhering to the substrate and will not be damaged by contact with a solvent.

This cross cutting test should meet standards that comply with ISO/DIN 2409. The result of the cross cutting test shows the adhesiveness of paint or coatings on the underlying coatings and surface, it indicates the adhesiveness of the individual layers among each other. During this test, the adhesiveness is determined by cutting into the previously painted surface in crosshatch pattern.

Blistering or delamination occuring under the current paint and fairing system because of corrosion or adhesion failure must be removed by grinding with 24-36 grit. Spot sand or grit blast to remove corrosion from steel surfaces and oxidation from pitting in aluminum. Sand down to a solid layer or to the substrate. The edges of any blisters or delaminating areas should be feathered back to a minimum of a 6:1 feather to thickness ration (30-45° angle). Bare metal should be prepared as per metal instructions described in „Substrate Preparation & Priming“. Use the following ALEXSEAL products to seal, fill, and fair in the damaged areas to prepare the surface for finish primer:

  • ALEXSEAL Protective Primer 161 or 135 (US onl) to seal metal
  • ALEXSEAL Fairing Compounds to fill voids caused by removing blisters and other surface defects
  • ALEXSEAL Super Build 302 for heavy surfacing

All surfaces should be cleaned using clean dry compressed air and clean rags to remove all dust before product applications throughout the system. Wipe down the surface with ALEXSEAL Wipe Down Solvent A9049 using the „Two Rag Cleaning Method“ and perform final dust removal with a tack rag before top coating.

In order to assure proper finish coat adhesion, substrates need to be prepared and conditioned to accept initial priming, fairing and surfacing prior to application of a finsih coat.

Crosshatch Adhesion Test

If there is any question of current system or underlying coating systems integrity on this substrate, a crosshatch adhesion test and a solvent test should be performed.

This is a destructive test and will require additional surface preparation in the area where the test is performed. 

Using a razor blade or knife, cut into the coatings systems currently on the substrate at a 90° angle. Create straight cuts approximately 5cm (2 inches) long. Cut perpendicularly across these cuts for approximately 5cm (2 inches) to create ≈ 6.35 mm (0.25 inches) boxes. Apply an adhesive-intense tape such as packing or sealing tape and push down firmly. Remove the tape by pulling quickly at a 90° angle. The coating should stay secure in the crosshatch boxes. If it does not, then all of the old coating should be removed until a stable surface is obtained.

Solvent Test

Saturate a cotton ball or a small folded piece of cloth with one of the ALEXSEAL Topcoat 501/X Reducers or from the Finish Primer 442 product range. Tape the saturated piece to the hull and also to the crosshatch test area if one was performed. Allow the saturated piece to remain taped to the surface for 15 minutes, then remove and inspect the surface. The old coating may soften, but should not wrinkle, melt or dissolve.

  • If the surface does not pass these tests, the coating or coatings should be completely removed and the surface prepared as described in „Substrate Preparation & Priming“.
  • If the surface does pass the tests, then repair the test areas and any other surface defects prior to the application of primer and topcoat.

Repairing the Test Areas

Thoroughly clean the surface using ALEXSEAL Surface Degreaser A9091 using the „Two Rag Cleaning Method“. Additional cleaning may be performed using a household cleanser and 3M Scotch-Brite pads to scrub the surface to be painted. When rinsing the surface with clean water, the water should sheet out indicating a clean surface. Any breaks in the water film can indicate release agents and or other contaminants present on the surface. Additional cleaning would be necessary if this condition occurs.

The current coating in the test area should be sanded with 100-150 grit. If break-through to metal substrate occurs, spot prime these areas with ALEXSEAL Protective Primer  (Protective Primer 161 or Cor Spec Primer 135 (US only)).

Dark Color Consideration

Due to the heat absorbing nature of dark pigments, yachts painted with dark colors can experience surface temperatures of over 93° C (200° F). While light colors reflect heat and only reach ambient air temperatures, dark colors absorb heat. To address the growing trend toward dark yacht finishes, several issues must be considered.

The increased temperatures of dark colors can cause a variety of effects on the yacht. One such effect is the air conditioners run longer and harder to keep the yacht cool. Higher surface temperatures will make increasingly difficult to touch exterior surfaces by hand (e.g. when washing the vessel) and surface inconsistencies are magnified.

High surface temperatures can often cause surface imperfections called print-through or post-cure. This occurs due to heat amplifying the natural expansion and contraction of the vessel – resulting in a visibly “printed” image in the finish of the underlying substrate – such as glass fiber, core patterns, welded seams, plank seams or underlying fasteners. Even when materials and fabrication practices are designed to deal with increased temperatures, a dark yacht’s surface will inevitably move more than another painted with a light color. Increased costs should be expected regarding additional materials, labor and production time for fairing and painting needed to decrease the effects of high temperatures on exterior surfaces. Extra surfacing and fairing steps are required to meet minimum quality levels in darker colors.

During application, special attention must be given to film thickness and coverage, as surface imperfections are magnified in darker colors.

The following steps should be considered to reduce the imperfections commonly amplified when using dark exterior finishes.

The resulting costs could double or triple over a typical light color finish for this type of application. Even when these steps are followed visible surface imperfections may still occur.

Tips to Decrease Imperfections in Dark Colors

  1. Use heat resistant resins and core materials during the lay-up and building process.
  2. Elevate the surface temperature of the vessel by using any of the following practices:
    (A) use of heat lamps,
    (B) applying a temporary dark color and exposing it to the sun,
    (C) building an enclosed structure to cure the boat with heaters. The resin and core manufacturer must be consulted for advice on what temperatures and curing schedules are recommended for these processes.
  3. Fair the surface with ALEXSEAL Fairing Compound. The fairing should be finish sanded with fine sandpaper to minimize sand scratch print-through in the topcoat.
  4. Apply ALEXSEAL Fine Filler 303 and/or Super Build 302 and then block sand to remove imperfections.
  5. Apply ALEXSEAL442 Finish Primer, Dark Gray and finish sand with 320 - 400 grit. Spot prime any sand-through areas so the primed surface is one consistent color.
  6. Apply three coats of ALEXSEAL Topcoat as a “Show Coat”. After confirming acceptability of the fairing and surfacing quality, sand the surface with 320 - 400 grit and thoroughly clean to prepare for a final topcoat application. Spot coat any sand-through areas to achieve one consistent color.
  7. Apply 2 - 3 coats of the final ALEXSEAL Topcoat dark color.

Dark finishes may show scratches and damages more easily. Extra care should be taken when choosing wash-down equipment and in the placement of fenders and lines. Additional wash-down care and maintenance procedures are needed, especially when removing dried and sunbaked salt residue.

Dissimilar Metals

Whenever two dissimilar metals are placed in an electrolyte solution, such as sea water, they are prone to galvanic corrosion, also known as electrolysis. Galvanic corrosion is the process in which one metal ionizes or gives up small particles to another metal that favors it. This process occurs with propellers, rudders, keels, trim tabs and skegs that are common components of most watercraft. Over time, if not properly protected, these materials corrode with oxidation and pitting, often to the point of mechanical failure.

If severe electrolysis damage is present, a certified marine surveyor should be consulted and the underlying problem corrected.

When assembling or mounting parts together, it is highly recommended to use an insulating material or isolating compounds (such as nylon washers, plastic sleeves or uninterrupted layers of caulk or sealant) between dissimilar metal parts to help prevent electrolysis or galvanic corrosion.

ALEXSEAL Protective Primers create exceptional barriers to help inhibit galvanic corrosion. Prior to application of a Protective Primer or other coating, the surface must be abraded with special attention paid to removing any remnants of oxidation. On large surfaces, fairing or surfacing may be required to repair deformities created over time by corrosion of this type.

Surface preparation for an aluminum or copper surface may not be the same as for steel. Each is susceptible to anodizing to other types of metals that it is in contact with – either in the water or by common grounding. Refer to the appropriate section for the type of metal substrate you are working with for instructions on preparation, surfacing and finishing.

Below Waterline Considerations

ALEXSEAL epoxy primers, surfacers and fairing compounds may be used below the waterline prior to the application of an antifouling system. When painting the bottom of a boat it is common to have an overlap area where there are ALEXSEAL materials on the hull sides or bottom, and an anti-fouling system will be applied over the top. Follow the manufacturer’s recommendations for the anti-fouling product to prepare the existing ALEXSEAL coatings before over coating with another product.

It is not recommended to apply polyurethane topcoats below the waterline or in areas where they will be in constant contact with water. The chemistry of a polyurethane topcoat may allow water to migrate through the topcoat and become trapped, causing blisters to form in the topcoat.

Curing and Drying of Polyurethane Topcoats

There are three stages of polyurethane curing:

  1. When it is dust free
  2. When it is “tape dry”
  3. When it is safe to launch the vessel

These stages are referenced with temperature variation within each of “Technical Data Sheets”. Pot life, as well as re-coat and overcoat times are also listed. Careful attention must be paid to these times to avoid introducing defects into a surface that could result in the need to resand and/or reapply. To clarify, “Re-coat” is when a second coat of the same product may be applied without sanding. “Overcoat” describes when a different product can be applied. Please refer to the appropriate “Technical Data Sheets” for tape dry times with and without accelerators, and other variables.

Use the “Paint Application Protocol” to document your application process, equipment settings and environmental conditions for future reference.