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TOPIC: PRESERVATIVE-TREATED PLYWOOD FOR BOAT APPLICATIONS
PRESERVATIVE-TREATED PLYWOOD FOR BOAT APPLICATIONS 9 years 9 months ago #13318
I found this on the web... www.glen-l.com/wood-plywood/boatbuilding-plywood.html .....Mike
The plywood industry consists of over a hundred mills in North America utilizing dozens of wood species for manufacturing. Since the major application for plywood has been for building construction, the standards and plywood specifications have been primarily geared to providing grades and layups that are optimized for construction applications.
However, structural plywood also has a proven track record in boat manufacturing. With the current grades, specifications and treatments available, it is the best structural material to meet many of the boat manufacturers' needs. From the widespread use in PT boats during World War II to today's modern composite hulls, plywood has been a preferred structural element due to its high strength-to-weight ratio, machinability and excellent fastener holding capabilities.
Given the unique requirements of the boating industry, APA has developed specific recommendations that best address the needs of the boat manufacturer. Combined with readily available preservative treatments, plywood can provide long-term structural performance as boat components. This guide provides specification details for best performance and provides reference to a vast information base on plywood.
Plywood Standards and Specifications
Voluntary Product Standard PS-1 for Plywood
Plywood grade and workmanship quality are defined in Voluntary Product Standard PS-1. The standard defines the following panel attributes that are important for the marine industry.
Wood Species. Over 60 wood species may be used in the structural plywood industry. Coniferous species are the dominant and preferred species for boat manufacturing applications. The most popular of such species is Douglas-fir. Other species include southern pine, western larch and western firs.
Veneer Grades. Veneer grading is based on the size and frequency of natural growth characteristics such as knots, knot holes and splits. The common veneer grades for plywood are A, B, C, C-plugged and D. The plywood panel itself is defined by the grade of the face and back veneers (e.g., A-B or C-D).
Bond Requirements. Virtually all structural plywood made today uses waterproof phenolic resins which maintain the bond during moisture exposure.
APA Industrial Specifiers Guide
Today, manufacturers of industrial grades of plywood have very tight controls over how plywood is made. Current technology allows for production of specialty plywood with fewer core voids and gaps, which results in "tighter" panel construction. Such technology improves upon the prescribed combinations in PS 1 by considering exactly what attributes are needed by the industrial customer.
In order to fine tune the plywood grading system to more precisely meet the needs of certain manufacturing industries, APA developed an Industrial Panel Selection Guide. The grading system considers the following panel attributes in a four-number ranking known as the Industrial Category Index, or ICI number. The four-digit ICI number consists of the following:
Face Veneer Quality Ranking. A numerical scale indicating the solidness and smoothness quality of the face veneer.
Back Veneer Quality Ranking. Similar to the face veneer, the ranking addresses the back veneer quality required for the specific application.
Inner ply veneer under the face. These veneers are often important for applications with heightened fastener holding demands, and where panels are going to be cut into smaller parts.
Other inner pies. Similar to the veneer under the face, these are assessed for solidness.
A copy of the APA's Industrial Panel Selection Guide can be ordered by calling or writing APA at the address listed at the bottom.
APA recommends the following minimum grade specifications for most boat construction applications*:
APA C-C Plugged, PS-1, Group 1, EXTERIOR
the panel should meet an ICI Number of 7-3-3-3.
Plywood 1/4" to 1-1/8" thick is available, with the most common thicknesses being 15/32", 19/32" and 23/32".
* The best grade will vary depending on the application. Some boat manufacturers use treated panels with ICI number 4-3-3-3 for applications such as seats.
Preservative Treatments for Plywood
Plywood has a long history of good service in the boating industry. However, as with all wood products, given extreme moisture conditions for a long period of time, plywood may be susceptible to some degree of fungal decay. In many boat applications, the risk of elevated moisture conditions is mitigated by coatings, laminates, encasement in fiberglass or other protective means that reduce the moisture pickup or provides sufficient drying rate in order to reduce the panel moisture content. For the ultimate assurance against the risk of decay, commercial pressure preservative treatments are available. Since preservative treatments render the wood an unsuitable substrate for decay fungi, treated plywood can be considered at the top level of performance with respect to longevity.
Treatments and Standards
Treated wood products are readily available and are often in used construction where high decay hazards exist. Unfortunately, much of the treated plywood found in retail lumber yards may not have been redried to the degree required for boat construction. The following recommendations are geared specifically for treated plywood for boat construction. For best performance, care must be taken to specify and purchase treated plywood in accordance with these recommendations.
First, make sure the plywood comes from a mill that is a member of APA - The Engineered Wood Association. That is your assurance that the mill is subject to APA's rigorous quality assurance program.
Treating is conducted as a secondary process following the commercial treating standards written by the American Wood Preservers Association (AWPA). The most common treatment and retention level for plywood used in boat construction is CCA (Chromated Copper Arsenate) at 0.40 pcf retention. Other treatments for boat use are ACA, ACZA and ACQ. AWPA Standard C9, "Plywood - Preservative Treatment by Pressure Process", specifies that the preservative-treated panels be redried to a moisture content of 18% or less, unless waived by the specifier. For use in boat manufacturing, the redrying of the treated plywood is essential to good performance when laminating with fiberglass. Treated plywood purchased from lumber yards is often used in construction applications and is not necessarily re-dried after treatment. It is essential for boat manufacturers to specify redrying.
Treated plywood is trademarked by a grading agency that monitors treating quality. The trademark should specify the AWPA standard, treatment and treating retention. Many suppliers of treated plywood for the boat industry offer limited lifetime warranties. Check with your panel supplier for warranty information.
For BEST performance of plywood in boat manufacturing, APA recommends the use of treated plywood according to the following specification.
Treated in accordance with AWPA Standard C9 with < CCA, ACQ, ACZA or ACA> to 0.40 pcf retention. Kiln dry after treating (KDAT) to 18% or less.
Laminating Fiberglass to Plywood
Many uses of plywood in boats involve laminating fiberglass over a plywood boat component. APA recently contracted with a marine testing laboratory to study the strength of fiberglass bond using commercial resins applied to treated and untreated plywood. The objective of the study was to assess the effect of preservative treatments and panel moisture content on the strength of the laminate bond.
The study assessed the laminating strength on treated and untreated plywood. To study the effect of moisture content, half of the panels were humidified to simulate the upper range of moisture content of what may be expected from treated panels after redrying or from panels stored at a boat manufacturer's facility.
The treated plywood developed bond strengths similar to the untreated plywood.
As expected, the moisture content of the plywood influenced the strength of the fiberglass bond. However, even at the highest moisture condition, the ultimate test failure mode in the vast majority of the cases was wood failure within the plywood itself, rather than at the laminate bond interface. The influence of plywood moisture content reinforces the need to specify drying after treating when using treated plywood.
Handling and Storing Plywood
Like all materials used in manufacturing, plywood should be properly stored and handled to assure proper performance. Protect the edges and ends of panels during handling. Place panels to be moved by forklift on pallets or bunks when received to avoid damage by fork tines.
Panels to be transported on open truck beds should be covered with tarpaulins. For open rail transport, use "lumber wrap" to avoid weather exposure.
For best performance, store panels indoors away from open doors to minimize moisture differentials along edges and ends. Make sure the panels are not exposed to water, solvents or other foreign matter that may interfere with establishing the fiberglass bond.
Stack panels on 4x4 stringers or other blocking. To help assure continued panel flatness, use at least three full-width stringers or bunks to avoid bending of the unit. Covering and weighing down the top of the bundles assists in keeping the panels flat.
APA maintains a vast library of literature regarding plywood. A selection of titles follows:
APA Technical Note: Fastener Loads for Plywood - Screws, Form E830
APA Plywood Design Specification, Form Y510
Consumer Information Sheet - Inorganic Arsenical Pressure-Treated Wood
APA Data File: Preservative-Treated Plywood, Form Q220
EWS Technical Note: Controlling Decay in Wood Construction, Form R495
Industrial Panel Selection Guide, Form T200
APA - The Engineered Wood Association is a nonprofit trade association whose members produce 70 percent of the structural wood panels made in North America.
APA has three main functions: 1) quality inspection and testing; 2) product and systems research; 3) promotion.
APA's Field Services Division is a national network of representatives with regional offices in major market centers across North America. APA Field Representatives help users, specifiers and distributors market, design, and apply APA and APA EWS trademarked products for countless end uses.
Most importantly, APA Field Representatives are available to help you. If you have questions about structural wood panels or engineered wood products please call the APA representative in your area.
Technical Services Division
©1998 APA - The Engineered Wood Association
7011 South 19th Street . P.O. Box 11700 . Tacoma, WA 98411-0700
Telephone (253) 565-6600 . Fax Number (253) 565-7265
EDIT EDIT EDIT EDIT::::::::::::::;From here down was added later and readers most likely havent seen this
Tip's For Painting A Fiber Glass Boat by David Pascoe
One of the most frequent questions that a marine surveyor is asked is whether it is worthwhile to paint a fiberglass boat. The answer is a qualified yes, so long as the owner fully understands the extent of the work and cost involved. Fortunately, there are some very clear advantages in doing so.
Most boats still use gelcoat for the exterior finish. Gelcoat is basically a resin with very high pigmentation content that gives it it's color. But gelcoat is used for another reason, and that is as a mold release agent that helps prevent the fiberglass part from bonding to the mold at the time it is laid up. Unfortunately, most gel coats have relatively poor resistance to sunlight and other environmental factors, despite claims to the contrary. Thus, we see the apparently never ending problem of boat finishes fading and chalking after only a few years time.
There are very high quality gel coats available that can hold up over the years, but very few builders use them because they are quite expensive. Bertram, for example, has always used a top quality gelcoat that, even after decades of aging, could be successfully buffed out and polished. But if you wax your boat and only a few months later it turns dull again, you've got a low quality gelcoat that won't hold a luster.
For boats using average or poor quality gel coats that begin to oxidize and chalk early on, painting is the only practical solution. Unfortunately, painting is expensive, but when done properly results in a finish that can last for a decade or more. In fact, with only annual cleaning and waxing, urethane finishes have been know to last for 15 years or more, even under the harsh Florida sun. Before making a decision, here are some important factors that you should consider.
Selecting a Painter Whether you use a yard or a jobber, beware that the price should not be the only factor in choosing a painter. The lowest cost will usually translate to the lowest quality of work. Jobbers tend to come and go with frequency because painting boats is a rough and difficult business. The ones who do the best work are usually more than happy to give you references of prior customers. It will be more than worth your while to investigate and actually go look at examples of their work.
As a rule, yards generally do higher quality work because they have a reputation to maintain. But it will cost more because they have higher overhead, and because they're probably paying higher labor rates. On the other hand, jobbers tend to be rather transient and their work can be inconsistent and unreliable. Be sure that they have a good track record and that they're likely to be around for while longer should they fail to perform to your satisfaction. If you're going to use a jobber, you'd be wise to get them to post a performance bond.
Not only are sprayers of urethane paints required by law to have an enclosed spray booth for environmental considerations, but it is not possible to achieve a good result when spraying in the open atmosphere. Be wary of any painter that does not have a covered paint shed.
Dark Colors A current trend is to use dark colors, especially black, to change the appearance, such as painting the space between windows black, or wide feature stripes. Because dark colors absorb much more heat, painting large areas in dark colors can result in damage or distortion to the surfaces being painted. Remember that fiberglass boats are plastic and somewhat heat sensitive. Because these plastics are thermosetting, a dark surface heats up under the sun and then the plastic continues to cure. This often results in shrinkage that can seriously distort the surface, resulting in permanent damage. The most serious damage occurs with cored laminates, particularly foam. You may have noticed some boats have a checkerboard pattern within these painted surfaces. This is caused by a secondary cure resulting from painting a cored laminate black that leads to shrinkage and the core showing through.
Preparation The three most important factors in getting a good result are preparation, preparation, and preparation. Seventy-five percent of the cost of painting involves preparation. Any paint job is only as good as the preparation that precedes it, and the skill of the people doing the work. Improper preparation can only result in dissatisfaction and a failed paint job.
Old gel coats are often porous and may have absorbed years worth of waxes and oils, a condition that reduces the ability of new paint to adhere to the surface. Thorough dewaxing and sanding is needed to make sure that contaminates are removed. This is followed by special primer coats that improve adhesive properties. All surface irregularities must be smoothed out, old holes and scratches filled and carefully faired out. There's nothing like a fresh, glossy coat of new paint to show up surface defects. Unless this work is carefully accomplished, all existing surface defects will be magnified and you will not be happy with the result.
Before signing a work order, you should go over the entire boat with the painter. Review all of the areas that need repair or special work. Have the painter tell you what needs to be done to achieve the best possible job, then decide if you're willing to foot the bill. Don't leave it up to the painter to make your decisions for you. Make it a point to ask about potential problems.
Removing Hardware If you've ever seen a boat that was painted by masking around hardware and painting over aluminum widow frames and other aluminum or plastic parts, you know what a bad paint job looks like. To achieve the best result, every possible piece of hardware should be removed. Yes, this is time-consuming and costly, but a good quality result cannot be had without doing so.
When hardware and other fastened-on parts are masked, this usually results in the paint bridging between the part and the mounting surface. The paint will eventually crack at this point, and when it does, water will them begin to migrate under the paint, resulting in flaking and peeling. This is true for virtually any kind of part mounted on the boat. That's why its always best to remove the part if at all possible.
Aluminum window frames and sliding doors should not be painted over for several reasons. First, because most frames are anodized and paint will not adhere well. Second, because the frames have stainless steel screws in them, the dissimilar metals cause galvanic corrosion. This why we see so many painted window frames with blistering and peeling paint. If the frames are anodized, don't paint them. Instead, the frames should be removed before painting. If the frames are in poor condition, they should be removed, stripped, sanded and repainted separately.
Plastic Parts should also be removed before painting, even if you are going to paint the plastic parts. The reason is that painting over the stainless screws will only result in corrosion and flaking.
Painting over caulked joints results in an unsightly mess. Caulking is soft and the paint is hard; therefore the paint will crack and begin flaking away wherever it is laid over caulking. For this reason, all caulking must be stripped off prior to painting, and recaulked afterwards.
Teak Trim All teak trim such as hand railings and covering boards must be removed before painting. The reason is that wood holds moisture that will eventually migrate under the paint and result in peeling. The entire area under the wood should be completely prepped and painted.
Difficult Areas Small, confined or enclosed areas such as up under eyebrows or tight spaces on flying bridges or cockpits are often not amenable to spray painting. The result is often heavy orange peel or unsightly over spray. Many times this is completely unavoidable and not the painter's fault. There are several alternatives to this problem, the first being not to paint the area if it is not really necessary. Carefully consider how it will look if you don't paint it. Another is to inquire if the painter has a skilled brush painter that can use a brush. Although some brush marks will be visible, really good brush painters can do a better job than a sprayer in these tight quarters.
Non Skid Decks Decks that have a molded in non skid surface do not take well to painting. Not only can't the surface be sanded, but the high points of the texture will wear the paint away more rapidly and likely leave the surface looking more unsightly than it was before. Carefully consider whether high profile non skid surfaces should be painted. You may want to just paint around them. On the other hand, smooth decks with abrasive material added to the paint works very well. Less, rather than more texture is best. Very little abrasive material is needed to achieve skid resistance, and is much easier to keep clean.
When to Paint To achieve the best results, boats should be painted when the temperature is between 70 - 80oF and the humidity below 65%. In the north, the window of opportunity is rather short unless the painter has an indoor facility. To get the best price, consider doing the job toward the end of the season rather than at the beginning.
In the south, particularly Florida, avoid the rainy season, mid-May to early June and late August through October. Frequent rains and high humidity can not only ruin a paint job, but the frequent weather interruptions cause the job to take longer and cost more because of frequent delays. In Florida, the prime painting season is late November through April when there is little rain and low humidity. The peak painting season is January to May, so you'll likely get better prices in the summer and fall, although you risk getting lower quality. For bargains, look for a painter with an inside facility and schedule for late summer and fall.
Making a Work Order The objective of creating a good contract or work order is that both parties should know what they're agreeing to. Foremost is the nature of preparation to be done and a definition of the final result. We all know the difference between the $129.95 auto paint job and a good one that costs a thousand dollars. With yachts, its not quite that clear cut, but the end results are much the same. Remember that if you've driven a hard bargain for a price, but are not happy with the results, you won't have a leg to stand on if you haven't specified the quality of work to be done.
1. Take the time to specify the exact nature of all the preparation work to be done.
2. Specify the primers and finish coats to be used.
3. Specify the nature of the defects that you will or will not accept. These include fish eyes (caused by contamination), dust in finish, runs and sags, over spray and orange peel. Remember that the later are inevitable in all but the highest (and most expensive) quality of work.
4. Don't expect a warranty if you paint over aluminum hardware and trim.
5. Don't pay the full price up front. Pay half down in advance and half upon completion to your satisfaction.
Proper Care A good paint job should last for ten years or longer with proper care:
Don't use harsh detergents or abrasive cleansers for cleaning. Use only a very soft, natural bristle brush or mop. Never use plastic or stiff brushes that will scratch the paint. If you must use an abrasive such as on non skid, remember that chlorinated cleansers will damage the paint if allowed to remain in contact for more than a few minutes. Be sure to rise thoroughly, especially the point where the water runs down the hull side.
Keep the boat clean. Accumulated dirt and atmospheric fallout can result in acids forming on the surface of the paint and damaging it.
Wash down thoroughly to remove all salt after using, including the hull sides.
Wax the boat at least once per year, except for walking surfaces, or course.
Avoid ice damage; cover the boat during winter lay up.
Topside Painting - Rolling and Tipping
The difference between an amateur and a professional painter is preparation. The amateur focuses on painting. The professional puts most of his efforts into preparing for painting. It is a cliché, but it is also true, that 99 percent of a good paint job lies in the preparation. It does not matter if the boat is wood or fiberglass, preparation work still has to be done. However, remember, paint hides the underlying color, but not texture. The use of sanding surfacers, putties, sealers and sandpaper will have as much to do with the final result as how many coats, or what type of paint you use.
A professionally sprayed two-part urethane topside paint will last five to ten years, but the gloss gradually fades. To maintain a high gloss, a boat should be repainted every five years. If you do not worry about the gloss fading you can leave the paintwork for ten or twelve years. A two-part polyurethane will usually last 2 to 3 times the life of a single part paint.
Painting a boat is not difficult. By purchasing quality marine paints, you are assured of great results as long as you follow the manufacturer's instructions. There are a number of ways to apply paint:
Brush it (hard to get an even application of paint)
Roll it (Not bad with white. If done carefully roller marks are not too bad, finish ends up with a 'orange peel' texture, but may end up with many small bubbles too.)
Spray (Due to extraordinary toxicity of sprayed poly paints, only to be done by professionals. No brush marks or roller marks of course. However, sprayed poly usually does not have the gloss of the roll and tip application.)
Roll and Tip (Apply paint by roller to get uniform coverage; tip off with brush to eliminate roller marks. If you develop the knack, this can produce a finish with NO roller or brush marks, and certainly no mistakes that can be seen from more than 18 inches away. Best gloss from this technique.)
Six Steps to Achieve Professional Results
1. Wash and de-wax the surface.
The first step is to wipe down the surface with a dewaxer. Wax removal is critical. Do not use acetone as it flashes too quickly and does not remove all the surface contaminants. If any silicone polishes (Star Brite, etc.) have ever been applied, be sure the solvent is blended to remove silicone. Use the remover generously so that you wipe the residue off and not just smear it around. Apply the dewaxer using a two-rag method: one rag to apply and one rag to remove.You will need plenty of clean rags and must change your rag often. Wiping a 2' x 2' section at a time is the best approach. Rotate the pad often to expose fresh cloth. A double de-waxing would not be overkill. Last, wash the area well with a strong detergent, including TSP (Tri-sodium-phosphate). Any good paint store should have it. This will help degrease the surface.
Products that could be used are:
Interlux 202 Solvent Wash
2. Fill any dents or gouges.
Fill any gouges with an epoxy fairing compound and follow with sanding. Let the putty stand "proud" above the surrounding surface so that it can be faired and smoothed by sanding. Epoxy filler is tough, so power sanding with a variable-speed, random-orbital sander is recommended. Rough sand the patch with 60 grit before switching to 120 grit to get the final contour.
Products that could be used are:
West System 105 / 205 epoxy
System Three - Phenolic Microballoons
West System - 407 Low Density Filler
3. Sand and prime.
Topside paints can be used on any surface (wood, metal, epoxy, Gelcoat) as long as the surface is prepared properly. If your boat has previously been painted and you are unsure if it was done with a two-part or single-part paint, use a single-part. Two-part paints are not compatible with single-part paints.
Preparing Wood (Unpainted)
Fasteners in wood hulls are always countersunk below the surface of the wood. It is necessary to fill these countersinks in order to achieve a completely smooth finish. The countersinks should be filled with plugs. Do not use epoxy or polyester putties for this job, precisely because they bond so well to wood. (Webmaster's note: This is a matter of opinion.) Should it ever become necessary to remove the wood for repair, it would be difficult to get to the fasteners under epoxy putty.
Bare wood should be sanded smooth with 80-grit paper before application of a filler type primer. The purpose of this primer is to fill in the grain of the wood. It has an unusually high amount of solid material. Allow the primer to dry for 24 hours before sanding with 220-grit paper. The goal is to sand to the thinnest possible paint film without sanding down to bare wood. Obviously, this cannot be done with just one application of primer. Some bare wood will inevitably show and require a second or third coat and sanding. Primer coats and sanding should be continued until the grain is completely filled and the surface is smooth.
Carvel planked boats require seam compound. Traditional seam compounds are never applied until after the hull has received its primer coat. They should never be applied to bare wood. The exact opposite is true of polysulfide seam compounds that must be applied only to bare wood. When polysulfide is used, it is put into the seam prior to applying the primer.
Preparing Wood (Previously Painted)
Paint in good condition should be sanded with 220-grit paper to knock off the gloss. Use a random orbital sander. This will invariably reveal some paint that is blistered or flaking and which needs to be scraped off the hull. In these spots, it may be necessary to sand down to bare wood. Such areas should receive a coat of filler type primer and be hand sanded to "feather" them into the rest of the existing paint.
Paint that has been sadly neglected must be completely removed. Power sanding is the only way. (Webmaster's note: Not true. If the paint is not a two-part urethane, it can be removed with a heat gun.) Paint remover is too costly and too time consuming. This process is affectionately known as "wooding". Once the old paint is gone, prepare the hull as if it were new bare wood.
Fiberglass gel coat is not an ideal surface for paint. It is so slick and has such low porosity that paint has a hard time adhering. A primer coat that chemically softens the gel coat and bonds to it should be used prior to applying the first finish coat of paint. Special fiberglass primers are made just for this purpose.
According to International Paint (Interlux), the use of this type of primer results in better adhesion of the finish coat than can be obtained by sanding the gel coat with 80-grit paper. Always choose a primer that is compatible with the finish coat paint. If sanding is chosen instead of a primer coat, the goal should be to remove all gloss and establish a good anchor pattern for the paint.
Primer can be applied with a brush or a roller. Using a roller speeds up the work and provides a more even film thickness.Do not worry too much about looks at this point. Just be sure that the entire surface is given a thin even coat with no skips. To understand how a fiberglass primer works, think of flypaper that is sticky on both sides. The primer softens and bonds to the gel coat on one side. On the other, it provides a chemically compatible base for the first coat of finish paint. Professionals often refer to this type of primer as a "tie coat". The chemical bonding to the finish paint works best when the primer is still quite fresh.
Apply two coats of epoxy primer, sanding in between coats. The next step is to sand the entire surface with 220-grit sandpaper, depending on the hardness of the surface. When power sanding, a variable-speed random orbital sander with a circular foam pad works best. Hold the sander perfectly flush on the surface or you will create dips and swirl marks. Avoid the temptation of tilting the sander from the flat position when sanding areas where filler was used.
When hand sanding, always use a sanding block (rigid or foam) to ensure that you do not add any dips in the surface that may appear in the finished surface.The next day wet sand the entire area with 220-grit paper and lots of water. Then do a thorough water wash and a full wipe down with thinner, rotating and throwing out the rags every couple of feet. Then paint it again. Be sure not to touch the surface after cleaning or you will spread contaminants that can affect the cure.
Products that could be used are:
Interlux Pre-Kote Primer
West System 800 Foam Roller Cover
West Marine has 1/8" nap foam roller with a phenolic core>/li>
Do not use 3M fine line masking tape, unless you like retaping every day; while a terrific product, it is not designed to stay on for more than a day or two and will leave residue if left on longer, especially outside. In addition, the thin tape may be more difficult to remove with a thick Awlgrip on top of it. Use 3M #225 tape it works flawlessly and removal is easy with no residue even after more than 3 weeks on the boat.
It is no longer possible for do-it-yourself application of many two-part urethanes popular for refinishing fiberglass boats. These paints use isocyanates and other dangerous chemicals in their formulations. Under current OSHA and EPA regulations, they can only be sprayed by professionals using supplied-air respirators. Less durable formulae are available for most two-part urethanes. These do not use the regulated chemicals, so can be used for do-it-yourself application. Even so, chemical respirator masks, protective clothing and eyewear are essential. Many people prefer to use the single part polyurethane. The two part gives a harder more durable finish. However, you have to mix the two parts and fiddle with the ratio to get it to be runny enough to level itself out, but not so thin it runs.
Unless you are an expert with spray equipment, the best way to apply paint is the "roll and tip" method. One person rolls a thin coat of paint. The second person follows the roller with a brush. The brush removes the "stipple" created by the roller and produces the smooth finish.
Rolling paint is the best way to get the desired great gloss thin finish coat. Use a solvent resistant (phenolic core), high density/closed cell foam roller with a 1/8" nap. This will minimize the formation of bubbles in the surface that can occur with mohair and large cell foam rollers. A thick coat with a regular roller will run or sag and may not adhere as well to the substrate.
One word of caution: check that both the roller covers and the brushes you plan to use are compatible with the paint before your start the job. Many brushes and roller covers will fall apart in the solvents used with these paints.
Bigger is not better. A 9-inch roller loaded up really has enough paint on it for two or three, 3 square foot sections. If you roll more than 3 square feet at a time and then try to spread the excess paint, the paint will already be setting by the time you start tipping and the brush will drag and leave marks. You will get too much paint on the first section, just right in the second, and not enough in the third.
A good approach is to roll the paint on in about a 2' x 2' square area. Roll out the paint in a big W and then re-roll the area to distribute all the paint evenly in the 2 foot square area. Roll horizontally, then tip vertically with a good unloaded 3" bristle brush.
It takes a certain amount of trial and error to get the knack. Too much paint and it will run. Too little and the roller marks will not tip out or the brush will drag and leave brush stroke marks that do not level out. The proper amount of reducer is critical, and you will likely have to add more as you go along. If the brush drags even a little, add more reducer (in small increments).
Paint runs are a problem when rolling vertically then tipping horizontally. Instead roll horizontally and then tip vertically top to bottom. Then the last motion that touches the paint is downward and excess paint will be pulled down off the side of the boat to the bottom. The paint then levels out horizontally resulting in no roller marks, no runs, and no brush marks.
Clean the tipping brush with solvent every single time it is used. This keeps the brush from loading up and brush strokes in the paint unbelievably fine, hence they flow out and level as the paint sets.
You need to work and move quickly. If you move too slowly, the paint will already be setting and the brush strokes do not level out.
The next day wet sand the entire area with 220-grit paper and lots of water. Then do a thorough water wash followed by a full wipe down with thinner, rotating and throwing out the rags every couple of feet. Then paint it again.
Do two to three coats this way. You should find that with your nose 12 inches or less from the hull and the light at ANY angle there are not but a handful of tiny brush strokes to be seen, much less roller marks. The very small number of imperfections that sneak in are not visible from two or three feet away.
Products that could be used are:
Interlux Brightside single part polyurethane
West Marine 1/8" nap foam roller with a phenolic core
West System 800 Foam Roller Cover
West Marine 3" Flagship natural badger brush
Natural Badger brushes
Plain old mineral spirits from the hardware store or Interlux 333 Brushing Liquid
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Re:PRESERVATIVE-TREATED PLYWOOD FOR BOAT APPLICATIONS 9 years 9 months ago #13325
I was always told that fiberglass doesn't bond well to treated plywood. This article trends towards almost no difference in the "bond" between 'glass and plywood- and that the plywood itself will fail before the bond.
I did an experiment a few years ago- during the restoration of a 1965 Chevy Pickup. I looked for suitable coatings for the wooden bed.
There was an article I came across that tested many different coatings on wood bed-planks, both Oak and Pine. I posted the link here a couple years ago...
The consensus was that POR-15 sealed the wood better than anything else.. But it had to be top-coated, because it is not UV rated- and fades quickly.
I took a piece of 1"x12"x1/2" plywood and coated it with POR-15. Then I put it in a bucket of water- and left it for 3-days. I then cut it lengthwise and across. There was no discernable water intrusion. That was "good enough" for me..
I have been using POR-15 as a wood-sealer on my floors, stringers, transom, and splashwell...during the rebuild of my Fabuglas. That's what all the "black-stuff" is in the web-galleries. I thin the first coat 15% with urethane reducer, then go right back over that with a 2nd coat without thinning.
When I fiberglass (or finish-coat) over the POR-15, I sand it liberally with 80Grit until the gloss is dull. I don't worry too much about sanding through. I have had no adhesion-problems at all. For the finish-coats, I use an epoxy primer first- then top-coat with full-urethane finishes.
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Re:PRESERVATIVE-TREATED PLYWOOD FOR BOAT APPLICATIONS 9 years 9 months ago #13328
wow,mike and ray you both will get a thumbs up from me,i can only do 1 a day,but ill make sure you both get them,they are both great articals,and anyone reading this should click on the link that fabuglas put in.
and to the moderators ,i think imho,these and the link should be in the fg site ,maybe under research.john
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