DETCO Product 3

Application of the STERLING system is perfectly appropriate for wood hulls and superstructures in good condition. If wood is moist, soft or dry rotted, STERLING is not advised, nor would any coating, until all such areas have been properly repaired with inlays or epoxy resin. Do not use polyester or body putty on wood, for this material chemically attracts water, contains solvent which evaporates, causing shrinkage and cracking and it does not demonstrate adhesion typical to epoxies. Blistering and adhesive failure may not occur for months after application.

Photo of High Build primer being sprayed

This old ketch was stripped, then sealed with epoxy and High Build primer was applied in several heavy passes to fill wood grain and sanding scratches, from the fairing process. Thoroughly sanded thereafter with flat boards, finish primer was then applied, followed by top coat.

It is most efficient to seal bare wood with two coats of epoxy resin, WEST™ or equivalent, allowing tack-free time between. When fully cured, sand with 100-120 grit and fair surface as needed with STERLING U-4869 or U-4870 Fairing, or an epoxy resin filled with colloidal silica, microballoons or other hollow spheres. For more details, see DETCO’s Wooden Boat Bulletin.

U-4749 primer is appropriate for high build filling over bare wood or to prime wood surfaces sealed with epoxy resin and coarse sanded. Always wipe epoxy-coated surfaces with C-8762 after sanding and before priming to assure removal of contaminates. These primers may be rolled in several applications to develop needed fill, by allowing surface drying and a firm resistance to finger pressure to occur before recoating. High build primers are best applied by pressure or airless spray, for the fastest build. Thinning 15-25% with U-1289 reducer produces good flow via pressure pot, while with airless, minimal thinning produces quicker build and appropriate flow. Use more thinner for a smoother, lower build film where deep filling is not required and less reducer for heavier filling.

U-4749 LOW VOC primer is higher in solids, shrinks less and cures faster having the extra advantage of easier sandability.

After the initial application of high build primer, fairing and glazing with epoxy may be accomplished to fill remaining defects, whereafter such areas should be reprimed to provide good surface continuity. International Red Hand epoxy putty or equal is an excellent surface glaze for minor imperfection repair. Surfaces may then be sanded to a 120-150 grit profile and finish primed with U-1000 or 94U-1000.

The day prior to topcoat application and after finish primer is well sanded, grooved carvel seams, joints beneath cap rails, bulwarks, cabin sides, etc., may be sealed with a fillet of urethane caulk such as 3M No. 5200 while small cracks may be filleted with water-soluble Polyseamseal, over which urethane topcoat may be applied after overnight drying. Polyseamseal is far easier to use for nominal fillets, cleans up with water and dries very quickly but should be used to bridge only minor cracks and to form a small radius in corners that do not work substantially.

Polysulfide caulk such as DETCO GS1-301 is best for hull seam caulking below the water line while 3M 5200 in white, may be easier above the water line.

Roughly sanded or tooled surfaces may be brought up to excellent fairness with the use of U-4749 high build primer. Coarse sand the surfaces with 60-80 grit and remove all contaminants with STERLING C-8762 Surface Prep, using the two-rag method. High build primers are capable of filling very rough grind profiles in order to provide a surface appropriate for final primer, and should be used before fairing compound application.

After the surface has been cleaned, well sanded and dusted, high build is used to provide a water-proof barrier coat and a good anchor for fairing compound. Use either the spray or roller methods discussed under PRIMING BARE WOOD and apply as much high build as necessary to fill the grind and/or cloth pattern.

Coarse sand after complete curing of the high build primer. If additional subsurface filling is necessary, make up a putty with epoxy resin and low density filler or, better, use STERLING the new, easy-sanding U-4870 or U-4869 fairing compounds for maximum resistance to water and the best performance. When using either fairing product, take care to thoroughly mix each component within its container before mixing together, particularly when using less than a full container, in order to assure proper chemical mixture. Mixing these products with a drill motor may be easier than doing it by hand. Do not add solvent.

After fairing compound has been thoroughly flatboard sanded to surface fairness, reapply high build primer, sand, glaze as needed, finish prime and apply topcoat.

The average fiberglass boat, laminated aircraft component or industrial surface which has molded or sprayed gel-coat, needs only finish sanding preparation and light primer application for appropriate topcoating. If the surface is fair and unweathered, a light sanding and topcoat application can produce excellent results without the need for priming but priming is certainly recommended for best results.

Thoroughly wipe surfaces to be coated, using the two-rag method, with C-8762 Surface Prep and accomplish any fairing, damage repair or surface glazing as might be required, with epoxy putty. Acrylic glaze for very small defects is satisfactory but overnight drying should be allowed, followed by touch-up priming, for best results. Stick with epoxy for the very best performance.

Finish sand gel-coat to 150-180 grit profile if primer is being applied while, if primer is not used, sand surface to a 220 grit profile until gloss has been removed, then topcoat.

STERLING U-1000 and 94U-1000 (Low VOC) primers are the standards for spray and brush application, cure quicker than epoxies and have improved sanding characteristics and adhesion. Because these primers dry quickly to the touch, they may be over coated with several passes to gain film thickness, just as soon as the preceding surface is dry and firm.

For roller/brush application, 94U-1000 is preferred. Very little, if any, thinning is required but U-2965 Brushing Reducer may be used as needed. For spray application in temperatures above 65-70°F, use U-1014 Reducer and in cooler temperatures, U-1385. Nominal thinning on up to 25 or 30% will depend upon surface profile to be filled.

When cured, finish sand U-1000 and 94U-1000 surfaces to 220 grit profile before topcoating. For a more industrial surface, U-1000 may be recoated without sanding, because of its relatively smooth spray application characteristics, if thinned 30% or more. Topcoat within 24 hours after application if sanding is not undertaken. Some surface stipple is sure to print through, however, so sanding is much preferred for the best finish.

Surfaces previously painted with oil base or synthetic coatings must be carefully tested to make sure lifting will not occur from primer contact. Although there are numerous methods of testing compatibility, the best is testing the surface itself with the intended coating. Simply catalyze a small quantity of the primer, brush or spray an area where potential damage will not be of consequence, and observe the results.

If, by the time the primer has dried, no lifting or softening has occurred, it is generally a safe bet that the process can be completed without significant incident. There is always the possibility that isolated lifting will occur where the existing finish has been taken down into primer base for the latter is much more vulnerable to solvent intrusion than the enamel surface. If lifting occurs in such areas, simply scrape with a putty knife or scraper, glaze and re-prime these spots.

For the most part, STERLING U-1000 or 94U-1000 PRIMERS may be safely applied over a wide variety of acrylic enamels, oil base enamels and even some synthetic lacquers. If in doubt, it is always best to apply a very light coat, just enough to cover the surface and allow overnight drying before applying more primer, thus producing a more solvent-proof surface. Reapplication within 24 hours requires no further prep. This is particularly important when painting cars and trucks for there is such a wide variety of lacquers and enamels that can be encountered.

Caution: Existing one part enamel finishes can be softened with STERLING C-8762 Surface Prep, hence a detergent wash, followed by a water rinse and/or a wipe, using the two-rag method, with denatured alcohol is usually safer.

Surfaces in good condition and previously coated with linear polyurethane need only be sanded with 220 grit paper, glazed to eliminate surface imperfections and prepared with a solvent wipe, using STERLING C-8762 Surface Prep, following which topcoat gloss may be applied. If priming is necessary to repair surface defects, any of the STERLING primers are appropriate depending upon the surface profile to be covered.

(Request DETCO’s Aluminum Specification from us or your distributor for greater detail on this subject.) Exterior, exposed aluminum surfaces, particularly salt water exposures, should be carefully treated for maximal metallic protection and coating durability. Do not apply fairing compounds over bare metal. Do not use polyester or body putties at any time.

All heavy plate surfaces should be thoroughly solvent cleaned with C-8762, then ground with rigid discs, to a 24-36 grit profile. Sandblasting with clean silica or aluminum oxide abrasive may be undertaken but it is a less effective alternative, particularly when substantial quantities of fairing compound will likely be used and more stress will thereby be induced on the coating system/aluminum interface.

All weld beads should be ground to eliminate scale, and to expose pores, which should be re-welded and re-ground.

After all surfaces have been solvent cleaned to remove obvious grease and oil contamination, followed by coarse abrasion, acid etching and cleaning is accomplished with Alumiprep 33. Follow directions on the container. The metal should be thoroughly brightened during the etching process, best accomplished with a soft, plastic bristle brush. Continue treating all surfaces until thorough wetting is apparent and do not allow to dry.

Once metal has been brightened and complete wet-out is evident by the lack of beading, surfaces are thoroughly water-rinsed and while the metal is still wet, Alodine 1201 should be applied by low pressure mist spray, sponge or brush. Spray equipment should be plastic or stainless steel. Alodine is a conversion coating, greatly improving primer adhesion, corrosion resistance and corrosion creep when the coating film has been broken by impact or stress.

Surfaces are kept wet by constant application of the Alodine solution for 3-5 minutes until metal turns a transparent watch-band gold color. The surface can be expected to look somewhat mottled but when the metal turns an amber-gold color, rinse thoroughly with water, allow to thoroughly dry. Use clean, uncontaminated air to blow welds, corners and crevices free of all water droplets. Primers should be applied within a maximum of several hours after Alodine treatment, the longer the wait the less effective the protection.

U-4747 HIGH BUILD EPOXY CHROMATE PRIMER is used as the moisture barrier over etched and converted aluminum. They may be applied by roller but improved results are obtained by the development of a 20-30 mil dry film through the application of either primer in two-three passes with pressure feed, conventional, HVLP or airless spray. Allow interim drying time between coats, to avoid solvent entrapment, waiting for recoating until surfaces are tack dry and firm to finger pressure. The strontium chromate epoxy primers are used for corrosion protection above or below the waterline and for proper functionality should not be penetrated as later coats are sanded and faired.

After last coat of chromate primer is applied, allow overnight drying, then apply an additional heavy pass of U-4749 primer to be used as a guide coat.

Following application of chromate primer, guide coat and the appropriate drying period, up to 4-5 days, all necessary fairing may be accomplished with STERLING U-4869 or U-4870 FAIRING COMPOUNDS after surfaces are sanded with 60-100 grit for mechanical adhesion. If substantial fairing is required it is best to fill all obvious low spots and then apply fairing compound to entire surface in a one-eighth to one-quarter inch film thickness so that flat board sanding to bring up low spots, does not result in coating break-through over highs. U-4749 primer is applied over last coat of chromate, serve as an excellent guide coat so that, when the off-white color shows beneath fairing compound, sanding ceases and more fairing is applied around the high. This prevents the integrity of the yellow chromate primer from being interrupted.

Following sanding of faired areas, STERLING U-4749 high build primer may be applied in necessary film thickness to fill porous, faired surface. Spot fairing and finish glazing are then undertaken, using only epoxy putties, followed by 150-180 sanding and the application of U-1000 or 94U-1000 finish primers. To avoid unwanted solvent absorption by the porous fairing compound, apply first coat of high build, up to 10 mils wet, followed by overnight wait before building further.

Areas in which bare metal has been exposed beneath the chromate film should be quickly spot primed with U-4747 in sufficient mil thickness to prevent the immediate formation of corrosive salts.

U-1201 primer or U-1201G chromate epoxy primers are best applied by spray over surfaces treated with Alumiprep 33 and Alodine 1201. Allow overnight drying before topcoating, unless temperatures remain at 75°F or more. Thin 25-40% with U-1289 Reducer. Wait until primer film is firm and becomes powder sandable, before topcoating, a minimum of 6 hours or so..

STERLING U-1201 and U1201G are applied unthinned for brush application to aluminum spars and components, preferably over surfaces etched and treated with Alumiprep 33 and Alodine 1201. U-1201G is preferred, for it brushes more efficiently. Several coats of chromate primer may be applied to develop adequate film build, simply allowing surface to become firm to finger pressure before recoating. Best results are achieved by overnight drying, followed by the application of U-1000 or 94U-1000 intermediate primer which may be fine sanded to a 220 grit profile when cured, before topcoating. This way the chromate film integrity is not affected in the sanding process.

(Request detailed steel specifications from DETCO or your distributor.) Ideally, the very best corrosion protection for steel in corrosive exposures is attained by sandblasting to near-white metal (SSPC 10), removing all rust, scale, surface contamination and old coatings in the process. After blasting, a quality inorganic zinc primer such as International’s Interzinc 351, should be applied to spec film thickness and allowed to dry according to manufacturer’s recoating recommendations. Thereafter it may be coated with at least 20-30 mils of U-4747 primer in 2-3 passes, allowing surface drying between coats.

Below the waterline, inorganic zinc primers are not recommended, hence the anti-corrosive primers may be applied direct to the blasted metal.

Above the waterline, following complete curing of the chromate epoxy primer, fairing compound may be applied after coarse abrasion, followed by flat board sanding, high build priming, finish priming if necessary and topcoating.

As a second alternative and particularly where sandblasting cannot be accomplished, U-4747 high build primer may be applied directly over machine-cleaned bare steel, in 2-3 applications, to achieve a 10-15 mil dry film thickness, over which, for industrial coating quality, urethane topcoat may be applied after overnight drying. Corrosion protection is not as good without the inorganic zinc precursor.

Cast iron keels are often protected from corrosion after machine cleaning or blasting, by the application of multiple heavy coats of chromate epoxy high build primer, followed in turn by the application of anti-foulant.

All rust and corrosion must be removed prior to finishing, by grinding, sanding or blasting. Remove oil or grease contaminants with solvent and etch surface with Alumiprep 33 working with abrasive pads or a plastic bristle brush until surface is clean, free of contamination and thoroughly wetted. Scrub for several minutes then rinse with clean water, do not allow to dry.

Apply Galvaprep SC or Galvaprep #5 using plastic bristle brush, keeping surface thoroughly wet for several minutes, following with a thorough water rinse.

Allow surface to dry and immediately apply STERLING U-4747 primer to a 10-20 mil coating thickness, depending upon surface profile. Finish sand and topcoat or finish prime with U-1000 or 94U-1000 primer, followed by 220 grit sanding, for a fine topcoat finish.

After 180 grit sanding, solvent wipe with STERLING C-8762 Surface Prep using the two-rag method and prime with U-1000, 94U-1000 or high build primer, depending upon surface profile to be filled. Finish sand primed surface to 220 grit profile and apply topcoat by brush or spray.

Cement should be sandblasted and/or etched with muriatic acid (HCl), a 20-25% solution, and thereafter water-rinsed thoroughly. After thorough drying U-4747 high build chromate epoxy primer may be applied, to be followed by necessary fairing, repriming and topcoating. Some builders apply epoxy resin to the etched or blasted cement surface before using sanding primer, this method providing an excellent waterproof barrier coat, with which sufficient mil thickness may be achieved by brush or roller, when spraying is impractical.

Following application of the barrier coat and sanding primer, necessary fairing, repriming, finish priming and topcoating may be undertaken. Take care that any protruding portions of the steel reinforcement matrix are carefully de-rusted and thoroughly coated with corrosion-resistant primer, before applying epoxy resin, fairing compound and subsequent coatings.

Although the causes are myriad and yet to be universally explained, blisters in gel-coat below or even above the waterline are all too common. In severe cases, the glass/resin laminate may be adversely affected beneath the gel-coat by water which has wicked through the protective coating and penetrated along the fiber bundles. Gel-coat can fail from intrinsic causes when entrapped solvent within the laminate results in blistering. It may fail, more commonly, when water osmotically penetrates through the protective film, resulting in delaminating and wicking along the glass fibers, deep within. If allowed to persist, severe structural damage can occur. Whatever the cause, gel-coat and the laminate beneath must be protected from water exposure by something more than anti-foulant paint as boat builder and yard experiences have now verified for many years.

A new hull should be sanded below the waterline to a 100-120 grit profile and thoroughly solvent-wiped to remove all traces of mold release, wax or polish. The bottom should then be coated with 15-20 mils of STERLING U-4749 high build primer, best applied by spray in 2-3 heavy applications or rolled in multiple coats with tack-free time in between. The bottom paint may then be applied per manufacturer’s recommendations.

Older hulls with significant blistering should be allowed to remain out of the water until all traces of entrapped moisture are gone, verified by the lack of any wicking from exposed blister bases or better, favorable moisture meter readings interpreted by an expert. Sandblasting or shaving the gel-coat from the laminate may be the only alternative in severe cases, to remove the defective gel-coat, to expose the voids within the laminate and to permit close examination of the laminate for possible structural defects and required repair. Grinding the entire bottom of a severely affected vessel is another alternative and with just local blistering, local grinding to the base of the blisters may be all that is required.

Thereafter the isolated voids may be filled with epoxy putty and if large scale damage exists, the entire bottom may be re-glassed, then coated with 15-20 mils of STERLING high build primer, followed by fairing, if needed, with STERLING U-4869 or U-4870 and repriming with high build. After final sanding, bottom may be coated with anti-foulant, per manufacturer’s recommendations.

There is always the possibility that blisters may recur when the boat is placed in service, following epoxy coating of the bottom but the problem will certainly be minimized and the exposure reduced by following the above procedures. Epoxies are so water-resistant compared to gel-coat and so relatively impermeable to moisture transmission that the situation will have been substantially improved, if not corrected.

Last modified: November 12, 2004 Website Design: D. E. Templin & Associates, Inc. (800)-845-0023