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Some Notes on Fiberglass Antenna Painting
By Dave Fortenberry NA6DF, Mike Perryman K5JMP, Ralph Mowery KU4PT, and Mike Morris WA6ILQ
Compiled and HTML'd by Mike Morris WA6ILQ
At 02:58 PM 03/22/06, Dave Fortenberry NA6DF wrote on the Repeater-Builder yahoogroup:
>I have a shiny new Antennex FG1440 2 meter repeater antenna, and I >thought that before we install it on the tower, maybe I should put an >additional protective coating on over the fiberglass. Looking for >something that would not get brittle and crack off any time soon. Any >ideas? Urethane maybe? I once used some urethane designed as a >marine finish with great results, but I'm open to suggestions.. > >Thanks, >Dave NA6DF
Mike WA6ILQ responded:
One local guy is using a double layer of white heat shrink. It went up about 3-4 months ago. I don't how it's going to stand up to to summer sunlight and ultraviolet. He pointed out that black heat shrink seems to hold up as a cover for the connectors on the Heliax jumpers, white should hold up as a coating on an antenna radome. And since heat-shrink is designed to shrink down on whatever substrate is under it then it will be watertight to the antenna radome and there should be no capilary action to retain rainwater between the outer heatshrink and the radome.
(one year later followup - he got transferred out of state, the antenna went with him, so I don't know how the heat shrink stood up to the sunlight)
The outside gelcoat is what gives fiberglass its watertight properties. Too many antennas have "died" after the fiberglass allowed rain water ingress. Once the gell coat is gone the microcracks that are created by flexing in the wind don't help either as rain water is held in the cracks by capilary action. If your area has an ice and snow problem in the wintertime then the water freezes and the expanding ice enlarges the cracks. Each thaw and freeze makes the damage worse. You really don't want to wait until the gell coat is completely gone before you replace it by recoating the antenna radome.
Be very careful that whatever coating you use is either clear or has a NON-METALLIC pigment. For example, many white paints get the color from titanium dioxide, a metal. A local urban legend comes to mind as I write this: a ham, never identified, uses white fiberglass boat paint on his short stationmaster antenna, then wonders where the signal went... finds out the white pigment is metallic... realizes that he just put a shielding coating on the radiating element and ends using the antenna as a very expensive plant stake.
If you have a body shop in your area that specializes in fiberglass work (look under "Corvette" in the yellow pages) I'd start there. If you live in a coastal or major river area, you can also look for boat shops that specialize in fiberglass.
A number of years ago Fred Deeg K6AEH/N6FD (now a silent key) took a super stationmaster that was shedding to a local body shop and they did a very good job of resurfacing it. He found the shop by an interesting method: one day he passed a very nicely restored late 1950s Corvette on the street and saw in his rear view mirror the 'vette pull into a fast food restaurant. He drove around the block and pulled in, then walked into the building. A few minutes of talking to the 'vette owner generated the name and location of a auto body repair shop that did good fiberglass work.
He just told the body shop manager that final cosmetics were not as important as something that was as good as the original coating... or better, and the cable and connector needed to be protected from having any fiberglass gel spilled on it. The antenna was too expensive to replace, was 15 years old and it needed to last another 15. The manager promised to do multiple coats and load up the fiberglass coating with lots of UV inhibitor, and protect the cable.
Despite the comments about cosmetics they did a beautiful job of resurfacing the radome, coating it and applying a couple of layers of nice clear gell coat to the antenna. Fred spent over $100 for the job (mid 1980s). Last I knew, that antenna has been coated again and is still in service.
Personally, I would use what Celwave recommends even though it's about US$150 a gallon, maybe more by now. This is a coating made by Sherwin Williams and is called "Polane Type HS 2.8 Plus Polyurethane", along with the appropriate catalyst. Just remember, no matter what the name, it's fiberglass and you get only one chance. You can't use a paint remover and start over. And you can't cap the can and use the rest later. Once you mix in the catalyst the clock starts ticking.
Any good Sherwin Williams paint store should be able to get the Polane, (or its current equivalent) for you. You can sometimes get quart samples for asking for them. If not, buy a quart (about US$40). If you work carefully and keep it on the antenna and not on the ground a quart will do one coat on two or three short Stationmaster-type antennas. Get any data sheets, painting procedure writeups, etc that you can.
If Polane is out of your price range, a good grade of urethane marine paint will probably work just fine. Just make sure it's not a metallic pigment (or get a clear-coat).
You might even want to buy a quart of cheap marine epoxy and coat a piece of PVC pipe just for the do-it-yourself training and experience. Or buy two quarts and do it on two sequential weekends - two sessions of training and experience.
No matter what coating you use, a "painters mitt" will help apply it evenly. Just wear old clothes and if you can get it, put the mitt on over a looooong rubber glove (talk to your vet or to a zookeeper to get one or two - and I'm talking a horse and cow vet, not a dog and cat vet). There are both elbow and shoulder length rubber gloves that are used when birthing calves, sheep or horses, when doing large animal surgery or any other situation where they have to "reach deep inside".
You will want to do the painting while wearing old (read "disposable afterwards") clothes, and on a day that doesn't require a jacket - which means that you want to do the painting fast enough to get the damn glove(s) off and let your skin on your arm(s) breathe...
No doubt that there are a few other repeater owners around that need antennas coated - you might be able to split the cost of enough Polane to do all of them at once, and the other owners can be the helpers... Yes, helpers. Better to have a helper or two to help you manhandle the antennas, and a homebrew cradle to support them from the ends only. One "cradle" I saw was made by hole-sawing a clearance hole for the Stationmaster pipe base in one piece of 2x8 lumber and a smaller clearance hole for the metal tip in another, then sawing both pieces in half right down the middle of the holes. Each length was C-clamped to a sawhorse rail and the antennas laid horizontally into the half-holes.
Mike Perryman K5JMP made this comment on the Repeater-Builder yahoogroup back in 2003...
> If you use auto-body polyester resin, you will need to add a UV > inhibitor. If not, the surface will become very cloudy, and begin > to chalk within a month or two. In two years it will be just as > bad as before. > > Even a good quality gel-coat will begin to chalk fairly quickly if it > is used without the UV inhibitor. Also there are many different grades > of polyester resin... the grading affects flexibility / hardness... > and cost!! > > The auto-body grade is generally the bottom of the barrel, so to > speak. There are many reasons the that the correct paint is > expensive... first of all, it protects. Second it won't > affect the antenna. Third it will last for over 10 years. > > IMHO.. West Systems Epoxy would be the way to go. You can tint it > any color you want (being careful not use metallic pigment is a must!!). > Or, use their gel coat. You can also add a UV inhibitor for a few bucks > more. I have used this stuff many times in the past for with outstanding > results. It, however, costs more than the Polane. I used to work in a > "custom fiberglass shop" back when dino's roamed the earth. > We produced many fiberglass/carbon fiber bodies for race cars. TOO much > experience doing "hand-layup" of 'glass!!! We found that the better quality > stuff is just exactly that.... Better Quality! > > One other thought.. If I were to re-gel my stationmaster antenna, I > would want it to last for many years. Our radio site requires a bonded > rigger to satisfy insurance purposes. I can't afford a couple of > thousand dollars every two or three years to hire the tower crew. The > proper paint will save you money in the long run, and prevent damage > to the radome.
The above was followed by a posting from Ralph Mowery KU4PT which included
the following information from his files, with a 1998 date. The telephone
area code may have changed, and Mr. Stadalman may no longer be there.
Note that you can order Polane in white, grey or blue.
= = =
Antenna Painting Instructions
The following is courtesy Celwave and is what I received when I asked them for a recommendation of what to use in refinishing my 18 year old PD455.
> Celwave receives frequent requests for advice about refinishing weathered > antenna radomes or changing the radome color for aesthetic reasons. We do > not take a position on any manufacturer's paint. However, Sherwin-Williams > seems to make a product, which should be compatible with radomes and > not interfere with the antenna's electrical performance. The following > suggestions are not a substitute for detailed instructions and mix ratios > provided by the paint manufacturer. > > > RADOME MATERIAL (Standard Color) CELWAVE PRODUCT LINE > 1. Spun Epoxy Fiberglass (Blue) Penetrator Antennas (AxR, BxR Series) > 2. Polyester Impregnated Fiberglass (White) Stationmaster Antennas (PDxx Omni Series.) > 3. Polyester Impregnated Fiberglass (Grey) FR CELlite Panel Antennas (AP18, 19 Series) > 4. ASA (Grey) FR CELlite Panel Antennas (AP90 Series) > 5. AES/ABS (White or Grey) US Panel Antennas (Other APxx Models) > 6. Gel Coated Fiberglass Tubing (White) Marine Antennas (Cel-1, 3 etc.) > > Notes: > > FOR RADOME MATERIAL USE THIS FINISH #1, #2, #3 > Primer and Top Coat #4, #5 > Primer may be required > ---- > > (Top Coat retention may be tested with adhesive tape after paint dries) > > #6 Requires Pre-Treat (Acid Etch) to remove gloss, then Primer > and Top Coat > > SHERWIN-WILLIAMS PRODUCTS: > > Etch P60G2 "Wash Primer" > Primer D61H75 "Polane 2.8 Plus Spray Fil" > Top Coat Polane Type "HS 2.8 Plus Polyurethane" > > SURFACE PREPARATION: > > Removal of surface contamination is normally accomplished by using > an alcohol solvent, ethanol, propanol, isopropanol, or butanol. A > ten percent solution of methyl ethyl ketone in water can also be > used whenever stubborn oil or grease is encountered. > > APPLICATION PROCEDURES: > > Painting to be done indoors, as the uncured product is sensitive to > moisture. Apply one coat of Polane 2.8 Plus Spray Fil D61H75 Primer. > It is designed to fill and/or hide profile and surface imperfections > on metal castings, structural foam, plastic and wood. Apply one coat > of Polane HS 2.8 Plus Polyurethane Enamel Monochromatic Intermix > Color System F63 Series. > > FOR FURTHER S-W PRODUCT INFORMATION CONTACT: > > Ralph Stadalman - Product Finishing Representative > The Sherwin-Williams Company > Chemical Coating Facility > 3165 Tucker Road Bensalem, PA 19020 > Voice = (215) 638-0104 > Fax = (215) 638-1008= = =
At the time of this writing the current version of this same information was on a Celwave web page. RFS bought Celwave, and the material was moved to: http://www.rfsworld.com/index.php?p=276&l=1&listName=applicationnotes&indexVal=1. It's still a long URL.
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