|
Painting Part II – My Thoughts Tim, Continuing on from Part I, I will try to express my thoughts on surface preparation and other stuff prior to applying any topcoat paint. I will also try to address the broad (not specific) issue of cost because most of us have to deal with compromises and cannot always afford “the very best”. I will repeat a worn phrase: surface preparation is 95% of the job. That’s true (probably more like 98%) and it’s where most of the hard work takes place and it takes the most time. IMHO, it is more important than selecting the type of paint for the topcoat. A relatively inexpensive brush alkyd job done over a carefully prepared surface can outlast and be “better” than the most expensive polyurethane topcoat applied over a poorly prepared surface. However, as with selecting the topcoat type, decisions have to be made concerning the goals of the owner, the budget for the job and, assuming a complete DIY project, the facilities and equipment available for use. I guess the first thing that pops up is sandblasting and dealing with rust. My personal experience is with automotive painting. However, a hood is a hood and rust is rust whether it is on a car or a tractor or whatever. The absolute best surface preparation is to sandblast to bright metal and start all over. This would be the route you would take if your goal was “the very best”, you were going to use a very expensive topcoat and cost was a minor consideration…if you did not have sandblast equipment, you would hire it done, including transporting the tractor and parts to and from wherever for this work. I believe that this approach is not always necessary...nor is it realistic in many cases. There are some lower cost alternatives that can do a very nice job, indeed. I have sandblast equipment. My current setup is a pressure blaster fed by a 17 scfm air compressor…arguably the high end for a home, general purpose, DIY shop. It replaces a small suction blaster and a 6 scfm compressor that I had used for over 20 years. I also have a tractor that needs paint…badly. It is a 1942 AC-B. It has spent the vast majority of its’ life outside all the time in the elements of New Hampshire. It has very little original paint left on it. It is all sound metal but is definitely “rusty” brown, not pumpkin orange! I am planning a paint job on this tractor. I also have a dump body on one of my trucks that is rusted very severely, especially on the underside. I will NOT be sandblasting either one of these things. Why not? Neither one of these projects will ever be for “show” purposes. They are, however, work vehicles that I use all the time. Like everyone else though, I want them to look “nice”, even though I may be the only one that sees them…I don’t care about pleasing others…and I want to halt further deterioration of the dump body. If you have ever used a small suction sand blaster you already know why I am not blasting them. That equipment is reasonable for only small touch up blasting…you would be there literally for days on end trying to do a whole tractor to bright metal! Plus you probably would burn out a couple of small air compressors (2hp) along the way! While my current equipment is faster and better than the old suction blaster, doing jobs of this magnitude is still a real strain on the equipment (and my time). All the blasting I do is done outside. The blast grit is, for the most part, not recoverable. I could see myself easily going through $200-$300 or more just for the grit. I believe that “play box” sand is not as effective as commercial grit (Black Beauty) and I simply don’t bother with that stuff. So I limit my sandblasting to relatively small projects, spot rust areas, a plow frame, a fender here and there, a lawnmower deck…single item stuff like that. Attempting entire tractors is several orders of magnitude beyond the realistic capability of any DIY, IMHO. For me, hiring a commercial firm to do the blasting is not a realistic option either. I know of no firm in my immediate area that is equipped with a blast booth and the necessary heavy-duty equipment to do whole tractor blasting, even on a piecemeal basis. There is also that problem of transportation. I don’t have a flatbed trailer so I would have to hire that out also…twice (at separate times) I might add. Plus all the wheels should be off the damned thing anyway, and it should be stripped down so that it is not even in a running condition! Sandblasted steel is in a very raw state and needs to be primed right away since rusting begins almost immediately just from the humidity in the air…so the firm that does the blast should do the bare metal prep and the prime. Still more $$$. You could always consider doing the thing a couple of square feet at a time…blast, prep, prime, blast, prep, prime, and so on…but that seems to me to be such a cluster-@%$# arrangement that it is not worth more than a passing thought. Are you discouraged yet? Good, because I think there are some less-than-perfect alternatives available that you should consider. I think you should start by reviewing the condition of any existing paint. Is it sound, no evidence of peeling, etc? I am of the opinion that decent sound paint should not be removed just for the sake of removal. You really don’t have to take the entire thing down to bare metal in many cases. If there are many coats of old paint buildup, with heavy, cracked and peeling chips though you should take everything off and start afresh. First step is removal of grease and dirt buildup over perhaps many years of use. I grease my belly mower pitman bearing quite profusely and the underside of the tractor torque tube is always covered with thrown grease spatter. The reality of a working tractor :o). The tractor, at this point should be disassembled to the maximum practicable extent…fenders, hood, radiator shrouding, etc. removed. It can still be runnable and movable at this point however. My suggestion would be to start with the old putty knife and scrape away by hand to get the major deposits off. After that, try a commercial degreaser such as GUNK, sold in automotive supply stores for degreasing engines and engine compartments. It won’t work well on heavy, caked-on deposits so don’t bypass the putty knife work. You probably will have to apply it 2 or 3 times. If you have a pressure washer, so much the better, but a regular garden hose nozzle will work for the required water wash after application. I am told that oven cleaner works well also but that stuff removes paint too. If you have already decided you need to remove all the paint, fine. Otherwise hold off on the oven cleaner. After you get down to the existing paint all over you can make a better determination about the existing paint condition and whether or not you need to remove it all or just some of it. If you need to remove it all, your options involve hard work, hard work and hard work. You can start with any readily available commercial paint stripper or try the oven cleaner. This can take several applications. You can also use a power disc sander equipped with a 24 grit “paint buster” disc from 3M. I have also found that Porter Cable makes a neat 6” diameter tungsten carbide disc that is intended for removal of house siding paint. It is available in most woodworking supply outlets and does a very good job without clogging up. It has a 7/8” diameter center hole and will work with many disc sander/grinders. It only costs about $12 as I recall and is well worth it. I have also found that the 2” and 3” diameter ROLOC sanding discs by 3M work great in pneumatic die grinders for getting into tight places. If all you have is an electric drill though, I am afraid you are pretty much limited to the chemical strippers…the speed of drills is not high enough to be really effective in this type of operation. If you happen to have a small suction blaster, here is where you can put it to good use…in any nooks and crannies that you can’t get at otherwise. That’s also good for any heavy rust in those areas. You don’t have to take to bright metal…just “brush blast” the relatively loose stuff away. Make sure that no grit can get into any openings that might provide a path into the engine or other internal areas that could be damaged, such as around the gear shift lever…the stuff flies EVERYWHERE. Power wire brushing works good, especially on the cast areas for loose surface rust and/or old paint particles. A 2” or 3” wire cup brush in a right angle pneumatic die grinder works good as do the 4.5” electric grinders with a wire brush, cup or otherwise attached. Eye protection is mandatory here. Those wire bristles can come loose and fly out! Your approach from here should be different on the sheet steel parts than on the cast iron parts. You want to spend more effort on the sheet steel and less on the cast. The sheet steel, such as hood, fenders, radiator enclosure, etc. are the parts that are going to attract the eye. These are the parts that you want to get nice and smooth so the topcoat will have the maximum shine. The engine block, transmission and final drive housings, pto housing, etc are cast with a relatively rough natural surface, for the most part. You would be wasting your time (and money) trying to prepare these surfaces for any type of “mirror shine”. If you have dents and dings in the sheet metal, bang them out from the inside…but not enough to make any surface higher than the surrounding ones. Try to get everything to within about 1/8” of where it should finally be. You want to keep it lower for later filling with plastic filler. The purists will have a fit at mention of plastic filler. Don’t listen. If you want to mess around will dollies and body hammers (if you even have such specialized tools) or if you want to play with melting lead into the low spots, OK…but plastic filler works just fine, is cheap and is easy to use. You put the filler on AFTER you prime though. Repair work needed because of torn or missing metal is not covered here…that’s another subject altogether. If your sheet steel is now bright clean metal, either from sandblasting or from paint stripping, you should treat with phosphoric acid. This is a two part process that has an apply, scrub, wash, apply, scrub, wash work sequence. It should be fairly easy to do since you have all the sheet steel off the tractor in separate pieces. DuPont 5717S and 5718S are the products. PPG has the same as DX579 and DX520. The scrubbing part is best done with a Skotchbrite pad. Use rubber gloves. You do not absolutely have to do this step…it is kind of messy…and there are primers available called self-etching primers that are promoted to eliminate this messy step, but I have no personal experience with them. I just think it is good thing to do if you have the steel in this raw condition, plus the materials are not expensive. This should be done even if there is no visible rust present. This process is NOT a rust removal process but rather a metal conditioning process for improved corrosion protection. The first step can actually remove slight recent rusting that may have occurred, say if your part got rained on before you could get it primed or something like that. Don’t expect it to remove any serious rust though…it won’t. It is not a rust TREATMENT process either. Don’t use it if serious heavy rusting is present…that’s another situation altogether. At this point lets assume that your sheet steel is rusted and pitted quite heavily in some areas but in other areas on the same part the existing paint appears to be sound and you are not going to strip it. If the rusted areas are relatively small and you have rudimentary sandblast equipment, by all means blast what is needed and proceed as above with treatment of the blasted area. If, however, the rusted area is large…like on my B (most everything!), then I think you ought to consider treating the rust and then priming over it. Here again, the “restoration” purists will foam at the mouth at the very thought…but we are trying to be reasonably economical and practical here, right? I have tried two different products for this type of application: Rust-Mort by SEM Products, Inc. and Extend by Loctite/Permatex. I am not particularly impressed by Rust-Mort. It is a phosphoric acid-based product that is marketed as a “rust converter” and is to be applied over rust and then topcoated. The consistency is similar to water. The label instructions indicate that 3 to 4 thin coats should be applied with a brush. Have you ever tried to paint with water :o)? I found that you have to be very light on the brush…the stuff wants to run everywhere. It was not easy to get an even coat on a vertical surface and it dries very slowly. I am much more impressed with the Extend. Extend is marketed as a “rust treatment” and is some kind of polymer-based product that has a consistency similar to actual paint. It is applied by brush or spray in two coats and is fairly fast drying. It forms a relatively hard, black film. I used some of this stuff on the upper firewall and about half of the roof of one of my trucks that I painted last summer (I didn’t want to sandblast these areas). I would not recommend brushing it on in areas that you want a smooth surface, since it dries fairly fast, does not flow out that well and leaves significant brush strokes. Spraying works fine with light coats. Both products require wire brushing or some such method to remove any loose rust or flaking scale that is present prior to application. I do not have any long-term experience with how Extend works in this manner…ask me in 5 years. It does seem promising to me though and I intend on using it on the sheet metal of my own tractor and the dump body of my truck when I do those. It is available at NAPA and is not cheap at about $10 per pint ($80/gal). As I recall, the cost of the Rust-Mort is similar. For a technical data sheet on Extend, go here: http://www.loctite.com/datasheets/tds/Extend_Rust_Treatment.pdf There seems to be a number of people that don’t believe in using primers on bare metal. Maybe they think the paint companies are trying to rip them off by selling ‘em stuff they don’t need? Apparently they think they know more about paints than the paint manufacturer’s do. I have NEVER seen any topcoat paint from ANY manufacturer ever recommend NOT using a primer on bare metal. If you want to ignore the manufacturer’s instructions in this respect, you do so at your own risk. You should be aware of three products that fall into the general primer category: primers, primer-surfacers and putties. Primers are sometimes also called non-sanding primers and/or primer-sealers. This is the type of product you should use on SMOOTH and treated bare metal, including sandblasted metal AND existing paint, after you rough up the existing paint by hand with 320 grit paper. It is also the product you should use on the cast surfaces. Using it over existing paint “seals” the old surface to assure there are no solvent or adverse reactions between the old paint and the new topcoat. For these purposes I use PPG DPLF two part epoxi primer. This is an excellent non-sanding primer that does not contain isocyanates. The problem is that it is quite expensive at about $135/gal RTS (ready-to-spray, after mixing). You might want to consider any other similar product that is listed as an acceptable substrate on the technical data sheet for the particular topcoat you are using...any of them should work fine for you at a more reasonable price. Primer-surfacers are similar to primers but they are more heavily-bodied for a high film build and are fast drying. They are very easy to hand sand. They are used to fill in sandscratches and small surface imperfections, minor pitting included. This is the product you should generally use on the sheet metal under your topcoat. It may require two or more applications plus hand sanding with 220 grit between each to get the surface smooth. You MUST try and get these particular surfaces as smooth as possible. ANY imperfection in the surface will show through your topcoat…you want to minimize that…so spend the time here at this step. As with primers, you should carry the primer-surfacer over any existing paint and hand-sand everything with 320 grit or finer prior to applying any topcoat. A product I have had good luck with is DuPont’s 131S, “Fill ‘N Sand” acrylic primer-surfacer. I cannot recall what I spent for it the last time I bought any but it is not an awfully expensive product. Again, any primer-surfacer listed as an acceptable substrate on your topcoat tech data sheet should work well for you. Putties are even more heavily-bodied than primer-surfacers. They are not sprayed on at all but are applied in (hopefully) small, spot areas with a rubber squeegee. They are generally the consistency of toothpaste and come in a tube. They would be used on any pitting or other imperfections not filled in by the primer-surfacer. After using any putty, I always like to spray a thin coat of primer or primer-surfacer over those areas so as to have a uniform-appearing undercoat for the topcoat. Again, hand sand everything with 320 grit or finer. 3M is well known as a manufacturer of putties for this purpose and their products are carried in most autobody supply places. For an on-line check on one of these putties, go here: Link If the pitting is real deep and not taken care of by a couple of coats of putty, try using some plastic body filler (after removing the putty). Use the kind that does NOT contain fiberglass strands...I think it is smoother. Final step before applying the topcoat is to wash everything down with a solvent cleaner meant to remove any sanding dust and fingerprints from your carefully prepared surface. PPG’s DX-330, Acryli-Clean work’s good for this. Again, check for any recommendations on your topcoat data sheet. Tack-rag the remaining surfaces and apply your topcoat per the tech sheet application instructions. Then step back and admire your job as it dries! Technical Data Sheets for DuPont products can be obtained here: Link For access, click on the visitor login button. Technical Data Sheets for PPG products can be obtained here: Link This PPG site is hard to move around in. The info is there…you just have to find it by poking around. I hope the web page designers didn’t give up their day jobs :o). Here is an alternate site that is much easier for just the topcoat and primer products: Link If you haven’t sprayed any automotive topcoat before, I suggest you practice on a sheet of steel positioned so as to provide a vertical surface. You should get the feel for the application technique that is needed to stay between orangepeel and runs/sags before you put that final paint on your handiwork. Good luck and have fun. Rod
|
