Molding & Finishes

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   In its most basic form molding a bikes frame consists of adding body filler around the welded tube intersections, brackets, various mounts and tab connections creating somewhat small radius 'blends' into the adjoining tube runs. How much filler one needs to accomplish this task is dependent on the quality of the tube fitment, the quality of the welds and one's personal taste. A frame having really good Tig welds usually doesn't even need any molding to look almost monolithic unless you're trying to build a showpiece. Molding isn’t something that’s necessary for a custom bike. Many people actually prefer to see the weld patterns under the paint and would never consider molding in the joints, so it all comes down to your personal preferences and the intended use of the bike.

In this section of the article, we’re only going to discuss the limited type of molding that average builders perform on a typical bike and not the extremes of full frame and tank molding seen on some exotic show bikes. There are plenty of write-ups describing that type of work on the Internet.

I’ll be writing here about using polyester based filler materials and enamel or lacquer-based primers and finishes so if you’ll be using epoxy-based products just make a mental adjustment as you’re reading. The only difference in the instructions is that fillers are applied over epoxy primers and not directly to bare steel like polyester fillers.

Before we go much further it must be understood that any type of molding material, including lead, and brazing overlays, might eventually crack and may even fall off in chucks leaving horrible looking gaps in your handiwork. How long the molding job lasts is largely dependent on how much care you take in preparation and how thick the material is applied. Filler applied much thicker than an eighth of an inch in depth will probably fail at some point in time so try to keep areas filled with putty as thin as possible. I’ve had the opportunity to work on bikes I built over twenty years ago and, in every case, my original molding work is still solid so I’m pretty confident that I won’t lead you down the wrong path with respect to this facet of frame detailing.

The mistake most first-timers make is to attempt to create a large fillet radius using the filler material to completely hide any and all welds which will only lead to premature filler cracking. The goal is to just barely hide the roughness of the weld itself which brings us to the really sticky question of grinding down welds that we touched on earlier.

Before we get into this really deep, we have to have an elementary understanding of weld beads to begin with and while I'm no expert welder I've run enough bead myself with a variety of equipment to make some relatively educated observations that are pertinent to a discussion about molding. First of all, almost all 'good' weld beads will be relatively uniform in both height and width except at the points where the bead is 'broken', either at the beginning or end of a run or where the direction has to be changed. At these 'transition' points you will usually see a small 'hill' of bead piled up a little higher than the surrounding material. These hills can be ground down to match the height of the surrounding bead without much worry about weakening the weld.

When I speak of grinding, I mean using a small Die-grinder mounted with a flexible oxide disc or flapper wheel and not a rigid grinding wheel which will only produce gouges in the metal. If you use the flexible disc or wheels with care, you will only be 'blending' the high spots down in a 'sanding' action as opposed to a 'grinding' action. There is a difference, but it can only be learned through experience. The key is to 'break in' the disc on some scrap metal until the edge starts to form a curl that wraps up backwards from the main disc surface creating a convex sanding 'edge'.

Always remember, that to be on the safe side, only dress up a weld where there is an obvious 'high' spot that is conspicuous compared to the surrounding weld material and never attempt to 'smooth' down the normal irregularities of a good weld bead.

After you've dressed up the welds, assuming that you had to, it's time to prepare the tubing prior to applying the filler material. All filler requires that the base strata be clean and relatively 'rough' or have a little' tooth' so that the filler material has something to adhere to and more importantly something to anchor it in place after it has hardened. Most tubing, fresh from the factory is very smooth and has a very thin coat of milling slag called 'mill finish' and sometimes a coating of light grease on the surface. This surface finish and film has to be removed either by sanding, sandblasting or acid etching.

Others may have other suggestions, but we sandblast the entire frame, so the primer has something to grab and then wash it down with Acetone to remove any oils (including fingerprints). You’ll often hear people recommend Lacquer Thinner as a good cleaner, but it can leave a film on the surface of steel. After the Acetone wash, we usually swab the tubes down with 'Metal-Prep', a body shop acid wash, to finely etch the surfaces. The entire frame is then washed in very hot soapy water (using Dawn Liquid detergent) to remove all traces of the acid and then thoroughly rinsed. Even though the Metal-Prep is an acid it takes longer to dissolve grease and fingerprints than it does to etch bare steel so don't rely on it to clean the tubing. In fact, if you haven't washed the frame the acid will highlight places where your hands have touched the tubing. As the acid eats into the clean metal it starts to turn whitish while areas contaminated with body oil show up as rusty splotches. Using cotton gloves, we move the frame back inside the shop and deliberately 'scuff up' the weld areas with a course file and/or 36-grit sandpaper rolls creating some very fine 'ridges' for the filler material to hook into.

This is a closeup of the axle plate which is a good example of the overall condition of the entire frame when we started the prep work. Notice the sharp edges along the perimeter of the plate and the un-chamfered bolt hole and axle slot.

The photo below shows what we ended up with after only one 30-minute acid wash.

There’s still some stubborn rust remaining so we’ll do a second wash after some localized sanding and wire brushing in critical areas. We need completely rust-free bare metal before we move on to doing a little molding work.

Fillers

There are dozens of brands of Fillers on the market but almost all of them are polyester resin based. In other words, they're the same material as polyester fiberglass resin except pumped full of 'solids' in the form of microscopic, dried resin particles, styrene, talc, calcium carbonate, glass dust, clay, chalk and in some cases metallic material. Being resins they require a catalyst to cure and harden. Buy a lot of extra tubes of the catalyst or hardener since if you're like me you'll always use more than the product directions call for. Even though epoxy resins are harder the polyesters are more flexible and are better suited to applications where there may be some flexures like on motorcycle frames.

Everything in these products is harmful to your health but to be quite frank I just love the smell of body filler. I think it might be addictive. You should wear a face mask when you're sanding this stuff, which I never did, and that's probably one reason I have trouble breathing anymore.

In our neck of the woods the most popular fillers are the 3M 'Bondo' brand and several of the 'Evercoat' products but there are literally dozens of brands sold across the country. Bondo also comes in several 'grades'. You'll find the better stuff being handled by automotive paint supply stores but in my opinion Bondo, despite its bad rep, is every bit as good as anything else you're likely to find. The more expensive products have a slightly higher proportion of resin to filler and the filler materials are a little lighter so the salesmen will tell you it bonds better, but I personally find this reasoning a little shaky. The biggest difference between entry level fillers and the so-called ‘premium’ fillers is that the very much more expensive fillers are processed and then sealed in a vacuum to eliminate trapped air that forms microscopic bubbles upon application.

I’ve used several different brands over the years on both bikes and cars and to be honest I can’t tell much difference unless you’re laying down really thin coats on sheet metal and here the more expensive grades do have advantages.

Ironically some of the ‘high-end’ fillers designed for custom car sheet metal work are a little to ‘hard’ for bike work where there is a lot of flexures in the frame.

If you're planning on having your frame powder-coated, you'll have to use one of the fillers that has a metallic base like 'Evercoat's Metal-2-Metal' or Alvin brand ‘Lab-Metal’ since the filler has to conduct electricity in order for the powder particles to adhere to it. I personally haven't ever had a frame If this is your plan, talk over the selection of the filler with your coater before you do any work. I don’t recommend powder and we’ll talk about that later in the article.

Every manufacturer will have some printed recommendations on how to use and store their paint and primer products but from my experience I've found first of all, that this stuff needs to be stored inside your house where it’s not exposed to temperature extremes. It should only be applied when the shop temperature is anything over 70 degrees, preferably warmer. Don't lay it down on cold tubing. The shop may seem warm, but chances are that the frame will about 10 to 15-degrees cooler than the surrounding air. Set the frame in the sun for an hour or so before you start to mold it or warm the tubing with a hair dryer or heat gun or sit it in front of a small electric heater. The secret is to keep the tubing at somewhere near 70 degrees until the resin starts to cure. Getting it hotter is not necessary and can actually cause problems. A powder coating thermometer can come in handy. Don’t use a heat gun in an attempt to accelerate cure times.

I've had the best success by mixing the filler with slightly less catalyst than the instructions call for since it slows down the cure time and I think it retains a little more flexibility by doing it this way. The key to getting good adhesion, besides cleanliness, is to completely blend and mix the resin with the catalyst. I use pop-sickle sticks available at most hobby or craft stores as mixing sticks. A small putty knife also works well. For a palette I cut up corrugated cardboard box material into 3"x5" strips or use the flexible plastic container lids like the type that comes on coffee cans. Regardless of how you mix it, the putty and hardener must be completely amalgamated since any un-catalyzed resin that gets into your molding area will create a 'soft' spot that never sets-up.

The best 'applicator' I've ever found is my finger and after you've wasted a lot of time with pieces of plastic and strips of wood, you'll probably agree but if you do adopt the 'fingering' approach make sure to wash your hands in lacquer thinner to remove all of the oils first. The putty stuff cleans off with some acetone and paper towels pretty easily if you don't let it fully set-up on your skin. Sissy's can use some rubber gloves, but you lose the ‘feel’ that way.

The photo below shows a blob of putty prior to adding the catalyst. This looks like a lot but it’s way more than I’ll need to do the axle plates and some places on the rear wishbones.

Even if you mix the hardener on the lean side, you’ll only have about two to three minutes to get the putty applied before it starts to setup. Do not apply putty that is getting ‘stiff’ and starting to set-up. Just stop working and mix up a new batch.

Filler is just thick enough so that it won't naturally flow down into cracks and crevices on its own accord, so you have to 'work' it down into, and around, the weld being filled. It's better to put it down in several thinner layers than one big glob so it’s not necessary to try and cover all the major imperfections in the tube connections with one application. If you do need to use more than one coat let the first layer completely cure before adding another coat. Sand with 36-40 grit paper between each coat you apply. On the final coat you can rough sand it before its 100% cured which makes the final sanding much easier.

For final sanding use the same grits that you intend to use on the rest of the frame when applying primer. Pay particular attention to completely 'feathering' the edges of the filled areas back into bare metal. The correct way of creating a feathered edge is to move the sandpaper so you are sanding from areas of bare metal towards the area containing the filler which is just the opposite of what feels natural to do. Minor blemishes, pockets or burst air bubbles can be gone over with a light coat of glazing putty prior to final sanding. If you're painting the frame, you can use a one part 'glazing' putty over any imperfections but if you're using a metallic filler you need to use the 'skim-coat' method.

Just slather the putty in place pushing it down into the crevices. Don’t try to make it pretty or smooth it out with your fingers. Ninety-five percent of what you put down in the first coat will be sanded away to almost nothing.

I try to put down the first coat of filler at each area to be filled in a single work session, hitting all of the various joints and connections on the same day. Don’t bother adding filler in places that won’t be seen once the bike is completed. I generally let the first coat cure for a whole day before doing the initial rough shaping and sanding.

For shaping and sanding the filled areas I use a variety of tools. I’ll hit the large thick areas with a detail sander where I’ve deliberately ‘rolled’ the edges of the backer pad and paper until I’ve removed the bulk of the filler and then I switch over to hand-sanding. Do not contaminate the filler by touching it with your bare hands while you’re working on it, or the second coat and glazing putty won’t properly bond with the first coat. Use disposable cotton or latex gloves at this stage of the work.

The steering neck is usually the hardest area to work on and the one area where many people leave to much putty in place after sanding because it’s a difficult fitting to sand around.

This snapshot shows us at what I consider to be about the 65% stage of sanding. There is still a lot of putty that needs to come off.

For rough shaping by hand, I like to use medium tooth ‘rat-tail’ woodworkers' rasps. These come in diameters of 1/8” up to 1/2”, The ‘cut’ that’s best for working with putty is called ‘patternmakers’ grade. These rasps also come in ‘curved’ shapes. I also use a variety of short sections of wood dowel rods in various diameters, some that I’ve tapered. In use you just wrap sandpaper around them. I also use the thin flexible foam backed ‘sanding pads’ sold in most hardware stores instead of sandpaper. These wrap nicely around dowels of various diameters. Through experience making various shapes of dowels to use as backing rods for sandpaper I discovered by accident that artist paint brushes in various sizes have beautifully tapered and rounded shafts that worked far better than anything I could make by hand.

The photo below is an attempt to get a good closeup of a couple of different rasps. The teeth on the left-hand tool are equivalent to around 100-grit paper while the rasp on the right is closer to 60-grit. Notice the tips are broken off. These tools are ultra-high carbon steel and needless to say are extremely brittle so don’t drop them.

During use they’ll start to clog up, so you’ll need to keep a file card handy, and I also use dental picks to remove any really stubborn putty that gets embedded in the teeth.

The objective when shaping and sanding is to keep sanding the filled areas until you start to see more ‘steel’ than ‘filler’. It’s hard to describe in words what a properly filled area looks like but you’ll know it when you see it. When you’re completely finished sanding, I can pretty much guarantee that you won’t have any areas where the filler is much over a sixteenth of an inch thick which is exactly what you want.

The photo above shows just about all of the tools I use when molding but the primary tool is usually just some sandpaper wrapped around my index finger.

Again, remember that as you’re sanding pay particular attention to areas where you aren’t seeing any small spots of raw steel starting to show through the filler. These are the areas where the filler is still too thick. Keep sanding, no matter how long it takes to start seeing a little steel becoming exposed.

Shaping and sanding the area of the neck gusset is probably the hardest work you’ll do and more often than not you’ll have to improvise some tools or backer rods to get into all the tight spots and this is where those flexible sanding pads really pay for themselves.

On most frames you’ll be working around four tube intersections, the two down-tubes, the backbone and the top brace tube. These all need to be blended in with the steering neck and then there are the welds around the neck gusset plate which are really hard to mold without building up too much putty.

It is not uncommon to spend several hours, even an entire day, hand working the neck area and the quality has to be high as this is the one area on the frame that everybody sees.

The snapshot below shows a typical homemade sanding setup I created by wrapping a flexible sanding pad around a dowel rod having a rounded ‘end’.

You can’t see the dowel since it’s hidden inside the pad with the end resting against my palm so I have leverage and can apply force against the filler.

To sand filler away on the flat gusset plate I’ve had good success using fingernail ‘emery-boards’ which are flexible enough to be pushed flat up against the steel with finger pressure.

Another tool you can improvise is to use the ‘burrs’ sold for die grinders that come in ’ball’ and ‘conical’ shapes. I don’t use them in a grinder but just as ‘backers’ for the flexible pads.

I can’t repeat it enough but always remember to keep sanding until you start to see the ‘gleam’ of the weld bead high spots beginning to show through the filler. At that point you’re finished. The high-build primer will cover any small imperfections from that point on.

Sometimes the filling gets complex when there are combinations of flat and round surfaces adjoining and it’s very easy to miss spots so after I sand down the first coat of filler, I’ll ‘mist’ the area with a very light coat of sandable primer as seen in the photo below.

Once the primer goes down any and all imperfections become easily discernable. I’ll spend several more hours working on the neck area. The primer comes off easily using one of the flexible pads.

Once you’ve shot the first coat of primer you might start to see some of the ‘fat edges’ we talked about. If you do, then it means you need to do more beveling or ‘radiusing’. Those fat and thin edges will not only ruin a good paint job they are also potential points of eventual cracking and then moisture intrusion.

At this point it’s worth mentioning that primer and paint will often fill-in your VIN number to where it’s almost unreadable. For this reason, I recommend that you mask the numbers off until you get the bike titled. It’s a pain to do a touch up job once the paperwork is secured but better safe than sorry. If you're working on an old frame, you’ve probably already got a title so ignore this suggestion.

Here's a snapshot of the axle plate molding in progress. This is the first layer of filler as the initial rough sanding is taking place. Notice that we’ve started to put a radiused chamfer around the perimeter of the plate and at the edges of the axle slots. The sissy bar mounting holes were also chamfered.

You need to resign yourself to the fact that no matter how good you are with molding there will be some welds in some areas on the frame that you simply can’t make invisible unless you make the filler way to thick, and this is almost guaranteed to eventually fail. There will be times where you’re sorely tempted to grind down a weld, but you have to exercise some discipline here and resist the temptation no matter how much it hurts.

I use 100-grit paper for the rough shaping/sanding and progress down to 150 and 180 to 220 for the final sanding before shooting a single coat of high build primer on the entire frame.

Glazing Putty

Glazing Putty is used to fill in minor imperfections and air bubbles in body filler. It goes on without a hardener and cures by evaporation of the solvents in the product. For this reason, it is relatively ‘soft’ when its dry. I seldom use it for this reason but sometimes you’ll have no alternative but use it sparingly and only when absolutely necessary.

That ‘yellow’ sanding pad in the background is the ‘fine grit’ version. It behaves about like 220 paper. The black pad is the ‘medium’ grit, about like 150. There is a course pad, around a 100-grit but it’s also black.

Since Glazing putty dries by evaporation, I found out the hard way many years ago to let it cure in ‘still air’ inside the shop. If a good breeze is blowing through the doors the material will dry to quickly and start to form small shrinkage cracks. Same holds for sunlight, as the putty will dry too quickly.

The ‘experts’ say that you can leave a molded frame sitting bare for up to two weeks after filler application, but I think this is wildly optimistic. Polyester fillers breath so they’ll start attracting moisture almost immediately. For this reason, especially since I live in a high humidity region, I try my best to get all filler applied, sanded and the first coat of primer down within five days, six if I absolutely can’t get the job done faster.

Ideally this work needs to be done in the summer when temps are high but that’s riding season so most of us try to this work during the winter. If you go this route, it’s imperative that you have a good heated, but well-ventilated place to work. Watch out for high humidity build up.

When you're satisfied with the finish in the filled areas go ahead and primer. You'll probably notice that the filler tends to absorb the primer where the surrounding steel doesn't, so you'll need to do several coats of primer, sanded between coats, over the filled areas before they blend invisibly into the adjacent primer. Be sure to mask off the machined surfaces on the motor and tranny mounts as these should be free of primer or paints. Same applies to the neck cup seats in the steering neck. Be sure to plug any and all threaded holes.

Here are the plates after the first light coat of high-fill primer. I think they look pretty good compared to what we started with and there is hardly any filler under that primer, probably less than a tablespoon if we could measure it.

This primer will be hand-sanded, pretty much down to bare metal with 320-grit since it’s intended to only fill in any minor imperfections in both the molding and the raw steel. After that we’ll switch to conventional primer in two to three thin coats sanding down with 400-grit. No need to go any finer on a frame and in fact a lot of builders’ ends at 220.

It should take you about three or four full days to do a really good job of molding, shaping and sanding on a typical cycle frame (about 20 welds) before its finished and ready for primer. If I'm charging for the work, I usually estimate 45 minutes per weld so you can see why a good cycle paint shop gets the money they do. It's all in the prep. If you do this job yourself and do it right, you can save some serious money. If you don’t do it right your painter will double his estimate right off the bat.

To close out this section of the article keep in mind that Polyester resins, unlike epoxy resins, actually ‘breath’ and as a result they are not waterproof in the broad sense of the word, but moisture penetration is so slow as to almost be imperceptible and it can be completely stopped by a good coating of paint. So long as the filler is covered with paint, you’ll never have a problem with it and for this reason it’s good practice to build up a little thicker coat over filled area.

Also bear in mind in mind that you never want any filler applied to steel where another part is to be bolted on like where the sissy bar mounts are or where the top motor mount sits. Don’t apply filler around thin mounting brackets that you know are subject to vibrations like exhaust pipe mounting tabs or fender mounting points.

Mies van der Rohe is famous for saying that “Less is More” and in the case of body fillers this statement is certainly accurate.

Riders Vs Show Bikes

The bike being shown in this article is intended to be what most of us call a ‘Rider’. That’s a bike intended for everyday use, in all seasons and in all types of weather.

The opposite of a ‘Rider’ is a ‘Show’ bike that is intended to be a showpiece and seldom if ever actually ridden on the street. A good 85% of bikes seen in the various magazines are in this class even though the article usually mentions how much the bike in question is ridden every day which we all know isn’t true.

In between these two extremes are what could best be described as ‘Semi-Show’ bikes. This group is represented by a lot of rides where the builders have gone way beyond the normal things done to a ‘Rider’ but stopped just short of what could be called a full ‘Show’ quality finish. These bikes usually are ridden but not as a daily commuter or in bad weather. For most these are basically nice ‘bar-hoppers’. Sometimes they’re old show bikes that have seen better times in the past.

You have to determine what grade of overall fit and finished you’ll want on your particular project but owning a full-blown show bike isn’t really very much fun unless you just enjoy the competition at bike shows.

Frame Paints and Finishes

Unless you have a need for an exotic paint scheme on your frame there is no reason why the average homebuilder can’t paint their own frame but before we talk about paint, we need to look at Primers.

Today it’s almost standard practice to use the so-called ‘etching’ primers but if you’ve done the proper preparation of the frame there is no reason to go this route. Etching primers were developed to make up for shortcomings in metal preparation so that painting could be done faster. It’s as simple as that. Etching primer contains a good amount of phosphoric acid and zinc that reacts with bare metal exactly the same as acid washing does but because of these additives the primer can cause problems with topcoats. Regular old sanding primer is just as tenacious with respect to forming a good bond to properly prepared steel as is etching primer but without any potential drawbacks.

One of the biggest problems with etching primer is that it’s not supposed to be sanded prior to the application of regular sanding primers. If you do have to sand it for ‘spot’ repairs or to remove blemishes on the substrate you’ll find that the application of a second coat might cause lifting, wrinkling, bubbling or peeling in some instances.

Contrary to the myth that etching primer is epoxy based and hence waterproof this type of primer is very porous and unless it’s sealed with sanding primer rust will still begin to form under the initial coating within a few days of application depending upon humidity. There is an epoxy based etching primer for use under 2K products, but this shouldn’t be confused with a single stage primer.

Another problem is that etching primers are not compatible with some paints or coatings and the claim that they dry fast is a myth. In fact, most manufacturers recommend a de-gassing period of 24-hours minimum if you read the fine print on the instructions.

Another myth is that etching primer can withstand higher temperatures than conventional primers, but this is just another misconception as both types will fail at anything much over 200-degrees. Some etches begin to fail at only 170-degrees.

Although I’ve never personally experienced a problem with applying etching primer over body filler many of my friends who run auto body shops told me years ago that etching primers will soften fillers over time, so they always stop their spray at the edges of panels that have been filled and then proceed with their sanding primer. I quit using etching primers a long time ago as a result of these conversations, but I decided to do some research when writing this section. I found that this is indeed the general consensus among body men, but the paint manufacturer sites disagree and say it’s okay. I’ll stick to my guns on this issue and still recommend that you never use etch primers over filled areas.

Keep in mind that painters got along for decades without etching primers and the use of such primer has not made paint jobs any better today than they were in the past.

Paints

When it comes to frame paints, you’ll find more disagreements on the boards by far than you’ll read when it comes to painting tins. The reasons are many but almost all involve making compromises in one way or another.

One group of builders will advocate using high-temperature paint. Another will push for epoxy-based products while yet another holds to using conventional acrylic enamels and yet another faction supports ‘engine’ paints.

Each group will post dozens of threads putting forth the pros and cons of any particular product or application, but you’ll never find a cohesive consensus anywhere you look and in fact almost all of the proposed ‘solutions’ have certain downsides and disadvantages. In the end most of us are left to find the products with the least number of potential long-range problems.

Let’s look at the ‘high temp’ paints first. These products, such as VHT are used by many but if you’ve ever used the coatings on BBQ pits you’ve no doubt seen the rust streaks begin to appear in the first season. The big problem with such products is that they are almost all designed for application directly on bare metal with no primer underneath. Some have a companion high-heat primer but even this stuff does little to prevent rust formation in the long run. Another problem with these types of coatings is that gasoline will leave whitish-grey streaks where it comes in contact with the coating.

Next down the list are the ‘engine’ enamels since most are formulated to resist oil, gasoline and temperatures up to 500-degrees but again these products are intended to be applied to raw metal. Dupli color does offer a primer which I’ve used on a small block Chevy but as far as I could tell it was just a ‘grey’ version of the basic paint they offer. Like most of the high-temp products these enamels do little to stop rust from forming under the paint but are far better than the VHT type of coatings first listed for cycle work.

The primary reason most high-temp paints fail over the long run is due to a lack of undercoat primer. Primers are intended to serve two functions. The first and most important is to seal the substrate from moisture by forming a chemical bond with the underlaying metal. Secondly primer forms a foundation for the subsequent layers of paint by another bond that is both chemical and physical. Without a primer even the best paint in the world will still permit rust to form beneath it eventually.

Even cheap rattle-can sanding primer contains a good amount of zinc phosphate and it is this chemical, not found in paints, that forms the rust inhibiting bond with bare metal.

Most of the builders I know, me included, who paint their own frames tend to use either’ Dupli-Color’ or ‘Rust-Oleum’ acrylic Enamels on frames. Both paints have a long track record of success, are very affordable and can be gun-sprayed or shot from a rattle-can with excellent results.

If you have a spray gun at home, you might want to consider House of Color Acrylic Enamels as they are mixed with a ‘hardener’ that results in a very tough finish. Their chassis satin looks really nice. The downside is needing a spray apparatus, respirators, protective clothing and a clean room even if it’s a temporary homemade setup. It’s also relatively expensive if that’s a consideration for your project.

Powder Coating and Epoxy Finishes

I used to have the rear legs of my springers powder-coated with the fronts done in chrome. I had heard the stories about rust forming under the coating but really didn’t put much stock in it until one day I decided to use a fork I had sitting in the shop for about a year. The coater had accidentally coated over the bearing shoulders on the steering stem, so I started to work on these areas with a chemical stripper. Much to my surprise there was significant rust under the coating. That’s all it took for me to become a believer so the last thing I’ll ever do is powder coat a frame.

Epoxy paints and coating have similar problems with rust formation starting under the surface in the interstitial spaces between the coating and the raw metal.

Both powder coating and epoxy finish systems work just fine so long as the monolithic outer surface of the finish remains monolithic but once the coatings are ‘broken’ from cracks, chips, gouges, dents or at the edges of bolt holes things can start to go wrong very quickly.

The biggest problem with epoxy is that it isn’t flexible like a polyester resin so hairline cracks can easily form due to vibration and flexure of the frame. In this respect powder coating is actually better since it is quite flexible.

Best Compromise

The best compromise made by most homebuilders is to use either ‘Dupli-Color’ or ‘Rust-Oleum’ acrylic enamels covered with ‘SprayMAX’ 2K clear coats. SprayMAX is catalyzed acrylic resin, so it remains flexible, unlike epoxy clears, but it still has excellent resistance to oils and gasoline and is perfect for bike frames.

I still haven’t decided on what we’ll use on the ‘Project’ bike frame so I’ll do what most people do and buy a can of ‘everything’ and do some testing on pieces of sheet metal that are available at all box stores and hardware outlets. There’s way too much work in a frame to trust to luck.

Since I wrote the paragraph above about a month ago, I’ve had time to do some paint ‘tests’ with both Dupli-Color and Rust-Oleum on some scrap tubing and I preferred the Rust-Oleum. I did all of the test, outside in the shade when the ambient temperature varied from 72 to 76-degrees during the day. I applied the paints per the instructions on the cans over three coats of (same brand) sanded primer on sections of 1.5-inch diameter DOM tubing. I used ‘satin’ sheen in both brands as it matches factory paint almost perfectly.

I found that the Rust-Oleum was slightly more viscous than the Dupli-Color and didn’t want to run or sag as much and it seemed to surface film and dry faster. The thickness of the ‘coats’ was visibly thicker on the Rust-Oleum samples. The Dupli-Color however might be better for Tins where you deliberately want thinner coats. On the Dupli-Color I had ‘orange peel’ even on the initial ‘mist’ coat and all subsequent coats so I didn’t do any more testing with this product.

On the Rust-Oleum I had to really force myself to do heavy second and third coats in an attempt to get some sags and only when I really ‘soaked’ it did I get one large sag. Much to my surprise the next day I had a hard time finding the spot since it had shrunk so much during the cure period. On inspection with a magnifying glass, I found that I could have put down much thicker coats from the start but the finish in my opinion is as close to factory as you’ll probably get and the application is very forgiving, almost fool-proof for us amateurs.

The can says that the product is dry enough for use after 48-hours but the car guys I know who use a lot of this paint for chassis work tell me it really takes five to seven days before it’s fully set so keep that in mind.

Summary

About the only thing I can say about this stage of frame preparation is that I wish you success with your particular project. With respect to the molding phase I doubt that you’ll be too keen on doing another frame right away. It’s a lot of work but worth it on a nice bike. If you come up with a good painting process, drop me a line and let me know what worked for you.