Ensure a Clean Surface

A clean, dry surface is essential to the success of any coatings application. ALEXSEAL provides effective products and guidance engineered to prepare all types of surfaces prior to application. It is critical to use appropriate products and procedures to prepare the surface in order to assure proper adhesion.

Be sure all contaminants have been removed before sanding!

Sanding can grind or fuse wax, grease, oils and residue into the surface making it impossible to obtain a clean surface. Follow the cleaning directions to avoid contaminants in the prepared surface.


It is recommended to remove surface contaminants before scraping or sanding. Clean the surface by scrubbing with a professional cleaner or powdered cleanser and an abrasive pad such as a 3M Scotch-Brite™. Monitoring the color and consistency of the rinse water is an effective way to determine if the surface is clean. Be sure to use a clean hose and / or change the rinse water regularly to avoid contaminating cleaned areas. Breaks, holes or beading of the rinse water indicates areas that may need additional preparation. It is important to use clean water and a hose that is not contaminated with oils or other foreign matter.

If you would not drink the water from the hose, then do not use it to wash or rinse the surface.

Some situations will prevent the use of water during the pre-washing procedure. These might include cleaning an interior space or a surface that is not sealed and would allow water to enter into an interior compartment. If this is the case, use the ALEXSEAL Surface Degreaser (A9091) with the “Two Rag Cleaning Method”.

ALEXSEAL Surface Degreaser (A9091)

ALEXSEAL Surface Degreaser (A9091) is a wax and grease remover used to remove wax and other contaminates from gelcoat, painted surfaces and metal prior to priming. This is important for new hulls, decks and components that have been released from a mold, or an older boat with considerable wax buildup. This initial removal prior to sanding can also be performed on metal to remove grease or other petroleum/paraffin contaminants.

DO NOT use ALEXSEAL Surface Degreaser (A9091) as a final cleaning solvent.
This product will melt the sand scratches and sanding pattern on fresh primer, resulting in poor adhesion

Prior to every product application, all surfaces should be cleaned using clean, dry compressed air and clean rags to remove all dust before product application. After applying High Build Surfacers such as ALEXSEAL Super Build 302 or ALEXSEAL Finish Primer 442, an additional solvent wipe down with ALEXSEAL Wipe Down Solvent (A9049) using the “Two Rag Cleaning Method” starting on page xx is recommended to ensure complete removal of surface contamination. A final dust removal with a high quality tack rag is recommended before top coating.

ALEXSEAL Wipe Down Solvent (A9049)

ALEXSEAL Wipe Down Solvent (A9049) is a mild solvent used for removing sanding dust and mild contaminants like fingerprints before applying finish primer or topcoat. This mild solvent may be used for final wipe down prior to any topcoat application or anytime a general cleaning is required.

Sanding The Surface

Prior to sanding, be sure the surface is clean and free of any wax, oil or other contaminants.

Assure proper ventilation and air circulation when performing sanding or grinding. A continuous flow of fresh air is necessary for both safety and keeping the surface being prepared free from additional contaminate particles. It is important to monitor the quality of the air for dust and other particulate matter as well as temperature and humidity.

Be sure the work area is free of tripping hazards and non-essential equipment and materials to prevent interference with an effective workflow and access to all areas of the work surface. Access to all areas of the work surface should be as simple as possible to get to.

ALWAYS wear protective clothing and safety gear to prevent sanding and grinding dust from coming in contact with skin or eyes.

DO NOT breathe sanding or grinding dust. Wear a commercially rated respirator outfitted with a new or clean cartridge or mechanical filter during sanding, grinding, and blowing operations. The respirator must have a good seal over the face to avoid particles from seeping in.

DO NOT allow other personnel in an area where sanding, grinding or blowing is occurring without proper safety equipment, clothing and training.

Proper sanding is crucial for adhesion of coatings. Sanding increases surface area when done correctly. This gives a coating additional surface area to bind to chemically and mechanically. Over-sanding or using too coarse of a grit for the application may result in a marred surface that will not take additional coatings well. Defects such as small holes or dimples in the surface, or scratches from sanding can occur and be too deep to be filled by the next product to be applied.

Guide Coats

Guide coats are sprayed or wiped on the surface of primers and surfacers to allow the person sanding to see where they have sanded and how much material has been removed. Quite often when sanding a white surface, the person(s) doing the work will become “snow blind” and will not be able to see if they missed an area. It is recommended to use a compatible dye, dry guide coat or spray-on coating that dries quickly without penetrating or softening the Super Build 302, Finish Primer 442 or topcoat (if sanding). The guide coat should not clog sandpaper or cause any adverse reaction to the topcoat or primer. Good mixture choices for a guide coat would be:

• Gray laquer-based primer reduced 200% with virgin lacquer thinner and sprayed on as a mist

• Machinist Dye reduced with virgin alcohol

• Water-diluted pigments with clean water

Sanding Methods

There are three basic types of sanding used when preparing a surface for ALEXSEAL products. Each may be accomplished by hand, with a block or using power equipment. The shape, area and overall quality determine the tool(s) best suited to carry out the sanding work. Always choose the grit of sandpaper by the process and product to be applied. For instance, if you are preparing for topcoat then choose a sandpaper grit that the topcoat will fill when it has dried. Hand-sanding creates deeper scratches than machine sanding so be aware that you should change grits depending on the method of sanding. It is recommended to use quality sandpaper and abrasives that have been certified and standardized to ensure that the cutting grit is accurate.

All references to grits in this application guide refer to “P” grit such as P320 or P220. The “P” designation indicates that the manufacturer is using best industry practices to consistently match the grit identified. It should be noted that different regions of the world have different grit designation systems.

Scratch Sanding

Scratch Sanding is the procedure of scuffing or scratching a smooth surface to create additional bonding surface area or a profile to improve adhesion of another coating. Scotch-Brite™ Pads or other abrasive sanding pads may be used to smooth stripe edges flush or to remove light primer overspray. Caution is recommended when considering sanding pads for scratch sanding between topcoats, because the scratch depth may not be adequate to create the surface needed for complete adhesion. Sandpaper with minimum grit of 320 - 400 is recommended for scratch sanding.

Smooth Sanding

Smooth Sanding makes the surface smooth of ripples or deformations such as orange peel or fine texture, and is usually done with small sanding blocks, a machine or hand sanding using relatively fine grits such as 120 - 400 depending on the material you are sanding. This creates a level surface but is not considered to be fairing.

Block Sanding

Block Sanding creates a level and aligned surface for fairing. The amount, as well as the depth and height of the high and low contours, combined with the width between them, determines the size of the block needed and the amount of filler/surface products needed to properly fair the surface. Block sanding to fair a surface is typically done with 40 - 100 grit depending on the material you are sanding.


Grinding is an aggressive process and should be carried out with care especially with gelcoat and wood substrates. Grinding is only used for the removal of material that cannot be removed with solvent or sanding. When grinding, consider course grits such as 24 - 36 - 60, which create a surface profile receptive to priming and finishing. Grinding is often used to clean oxidation from metal and to remove old or damaged gelcoat. Prior to any grinding, make sure that the surface does not contain any salt residue that could be ground into the surface.


Blasting as a method to remove old paint, debris or corrosion, can be destructive and should be done with great care.

Blasting typically should only be performed on steel or aluminum surfaces where fairing will be necessary. While effective at removing undesired material, blasting can result in extreme surface deformations. When considering blasting as a course of surface preparation, various media such as soda, glass, styrene beads, granite sand, or water should be considered as well as a standard media such as silica sand.

When Blasting Aluminum
To achieve optimum adhesion and performance, the aluminum should prepared to a 2 - 4 mil (50 - 100 micron) profile and a very clean, silver/white appearance.

When Blasting Steel
To achieve optimum adhesion and performance, steel should be prepared by blasting to near-white metal Sa 2.5 (SSPC-SP10-85) and/or to a 2 - 4 mil (50 - 100 micron) profile.