chromate conversion coating
Alodine (chromic acid, a carcinogen) is the 'bad sister' conversion coating. It is the wash treatment of choice. Some details in the posts above here.
All the reading I've done shows everybody uses it in conjunction with the phosphoric acid etch.
We may be having a problem here with the word PRIMER.
The two WASH & RINSE treatments are not primers in the sense of a coating - altho the chromate wash leaves a film behind. That film is supposedly THE corrosion protector. But its main claim is that it bonds to aluminum and paints bond to it. And bonding is corrosion protection.
It so far looks like epoxy paint primers with chromate used over the corrosion treatment are extra insurance in the eyes of the guy who's using it. There might be no need for them.
Can a chromated epoxy primer be used as a corrosion blocker on acid washed (Alumiprep 33) aluminum? Without using the 'traditional' conversion (Alodine) coat? www.aircraftfinishing.com Stewart makes only waterborne primers and paint. They have a one part non-catalysed non chromated epoxy primer that one guy anyway on vansairforce.net forums says can do just that. Go on bare scuffed aluminum............ayeduno.
If we sand with nothing coarser than 80grit on the mast, and nothing coarser than 180grit for any subsequent sanding before the first chromate conversion coat, it has been said we are more likely to make a technical transition from prep to coating stage. Coarser grit sanding "imbeds impurities" that will come back later to screw up paint integrity. Sanding a more uniform surface without deep scratches allows the film more uniform coating.
The insurance of including chromated epoxy primers is for some painters unavoidable because of aggresive or not sure sanding prep. Or on the mast I'm in charge of, a surface of 1000s of unknown tips and crannies.
A 45 year old mast has porosity issues that thin guage furniture or hotrod aluminum sheet (that is going to be painted) doesn't have.
litlgull's mast has countless visible scars with corrosion in them. Time,neglect, and sodium chloride have left an aluminumscape of unseen pin holes and mini fissures everywhere on its surface. Can't sand away old age.
Ben, I cannot find provenace for not including the Alodine film treatment. I don't want to use it.
The first epoxy primer always seems to be a corrosion blocker.
To be a useful as a corrosion proof coating, the epoxy primer has to be water thin so that it migrates/penetrates into the smallest imperfections on the mast surface.
SherwinWilliams supplies paint to the USNavy. They also have a specific epoxy chromated primer that is meant to go over a chromated conversion film. BUT
On the SW website we can find out what was used to renovate the USS Yorktown, now a "coastal Landmark". SW's schedule for renovating the coatings on the WWII aircraft carrier consisted removing most of the old and then a prime coat of organic zinc at 3.5 to 5 mils. An intermediate coat of Macropoxy 646 at 5 to 10 mils. A topcfoat of High Solids Polyurethane at 3 to 4 mils. They used "automotive-type body filler" (bondo) and caulk where ever there were rust streaks! Intended life of 'system' is 20 to 25 years. Painting a gigantic tourist/historical attraction isn't like mast preservation for sure. But no conversion coatings were used!!
The normal "coatings specs for an aircraft carrier really is as thick as a phone book."
The system was designed to coat rusty steel, galvanized iron and aluminum.
There is available from AirCraftSpruce a plain zinc primer. Don't know about "organic."
Glisando Triton 381. TimLackey used Alumiprep 33 and Alodine 1201.
He left the mast's top and bottom cast aluminum fittings in place.
And also did not remove the sail track.
He went Awlgrip and used the 30-Y-94 "yellow anti-corrosive primer" on top of the conversion film. It is a two-part strontium chromated epoxy in a soup of solvents. Awlgrip LPU requires an epoxy base.
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Simple Green scrubbing of litlgull's mast revealed
crevis corrosion in every (104) mast-track screw holes. Seriously, almost every hole has starlike crevises emanating from the hole. Every screw that came out did so with a little bit of white powder.
In the dozen or so holes below the track in the flat where a short piece of aluminum track was attached with fine thread s.s. screws there was nearly no corrosion or white. DFO's did some mangling here that caused corrosion.
My advice is to bite the bullet and remove EVERYTHING from your mast when renovating. Even if you are not going to paint it!
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I thought SimpleGreen was an environmental product.
Seems many people do. On my now almost empty qt spray bottle it says, "non-toxic and biodegradable."
When trying to find the msds the maker won't reveal ingredients in the formula 'to protect it from piracy'.
The Environmental Working Group, a consumer watchdog takes exception to that. It evidently didn't take industrial espionage for EWG to get an analysis of the cleaner that found 2-butoxyethenol, a carcinogen,
and 66 OTHER CHEMICALS IN SIMPLEGREEN including formaldehyde. Listed on their website.
What's in your detergent?
mast wash prime fill paint schedule
Hey Ben, don't take any of this as disrespectful.
My desk is stacked with downloads, Vansairforce.net forums most prevalent.
I make copies so I can sit on the couch and take notes, rather than at the monitor.
Latest one here is a three pager on what the guys think of PreKote.
Guys building airplanes and hotrodders like the rest of us are interested in less toxic materials - therefore PreKote as an alternative to Alodine.
From his description of its application to his RV7 one guy makes it sound like a description of an application of Alumiprep. But for me peeking in, it's all guys who know what they are talking about talking with each other. I'm really unable to extract info that really works for my general yet very specific interest. There's never a single track to a reasoned conclusion. PreKote seems to be softer and more difficult to apply.
An RV7 isn't a Winnebago.
But here's one for you, Ben, quote:
(dated 9-15-2010) from dedgemon, (titled) scuff, clean, epoxy
" I've painted two RV's now and have talked to countless other builders about this. The traditional method of etch, alodine, prime does work, but it is NOT necessary. Modern automotive (such as PPG DP) epoxy primers are designed for adhesion on scuffed aluminum.
I've been happy with the following. Use soapy water and scuff with a gray (or red) scotchbrite pad to a totally satin finish. Then clean and DRY thoroughly with compressed air. I use rubbing alcohol and lots of paper towels to produce a totally clean surface. Then shoot the epoxy and whatever topcoats you want.
Another friend of mine did this exact thing on his '6 about 12 years ago. Still looks great with no adhesion issues. "
Well OK, mon, no toxics at all, except for the epoxies and the urethane.
Then the next guy comes along and says:
"....try baby bath - no salt, no wax. Then, when dry, or if you don't need to wash - scuff the whole surface with red Scotchbrite - please get the real stuff, not the cheapo brand. 3M products just do it correctly. Then go over the whole aeroplane with Alumiprep from Spruce - a mild acid brightner - you really see the surface clean up.
Swill off with water, let dry in the sun, then spray on 2 part etch prime, build prime and sand, shoot colour, stand back, admire!"
This is followed by a newbie (R4LIFER) about to build a '4 uncertain from reading the posts whether he should prime at all. And how much weight all the primer and paints will add to his airplane....
"please be as complete with your answers as you have time for. THANKS!!!"
And that is the problem - because we are faced with unsubstantiated opinions and no continuity.
The PreKote thread just peters away into other subjects, and very little is revealed. If something peaks your interest it usually is one man's opinion, who writes with a little more authority than usual.
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Ben, thanks for the blueline, haven't seen that product before.
It is a polyester based 2-part fairing compound. Assume it is a squeezable 'traditional' bondo, which is a neat idea. I don't think of polyesters as glue.
This 'glazing compound' would have to go on scuffed/sanded bare metal which might be OK, but my own limited/peculiar/misinformed experience tells me not to use it like that. This whole wash&chromate business is to get aluminum to accept foreign stuff - which it really doesn't want!
In the old mast's case using the polyester material on bare sanded/etched I'd describe as "imbedding" the surface of the aluminum. But will the compound bond to it?
If the glazing is used on treated aluminum (acid etched and conversion coated) I'd guess there would be even less tooth for the polyester to stick to altho Alodine's other job is as a next coat adhesion enhancer. So maybe that would be the time to use this glazing compound.
But if applied after etching before alodine, I would be uncertain about the alodine treatment which 'traditionally' is applied to bare aluminum.
A series of unknowns, not good for the immune system or stress level. Is there any literature that specifically addresses the Alodine issue?
Or is all info anecdotal: 'my friend painted his RV'007 with only epoxy 12 years ago and it looks just fine today.'
The next usual layering on of materials would mean I could go smooth after the first thin epoxy primer, WHATEVER THAT EPOXY COATING IS I HAVEN'T A CLUE YET? Concensus has the first primer as a strontium chromated epoxy. But there is obviously movement afoot to remove chromates from the process.
But I don't think it can be just ignored. YET.
I'd go next with my familiar SherwinWilliams ProLine sandable epoxy primer that I've used all over the boat inside and out.
- then next on to the fairing/smoothing of the whole spar.
In the past I've made a kind of alternate slurry fairing compound by mixing West System 407 dust into the ProLine primer and using that for fairing. (But a normal batch of 407 mixed with top-of-the-line (TAP) laminating epoxy would be just as good because its consistancy can also be thin or thick as you like it.) Worked for me and the paint still set up like epoxy. Was even more sandable.
Then a final ProLineprimer coat. Then topcoat.
Cheeeeze! sounds..... heavy!!!
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It is my unscientific opinion that any epoxy PRIMER ( solvent or waterborne / poisoned ones like chromated primers) can be overcoated with any type of enamel topcoat, solvent or waterborne, epoxy or urethane.
chemical resistant GLOVES
ALL DISPOSABLE GLOVES ARE PERMEABLE.
It is a game to ID a single all-purpose glove we could count on to guard hands from the whole gaggle of boat yard liquids & solvents.
Ketones degrade nitrile, pvc, viton.
Alcohols degrade pva (pva is also degraded by water ! ! )
Aromatic solvents degrade neoprene, pvc, latex and butyl.
So what to grab? There are a couple brands of chemical resistant 'disposable' gloves that say they can be used with all the usual hazardous suspects. 280 hazardous chems (list exists.)
BUT take this as opinion only - you should do your own research check - can't vouch for what the corporate world foists on us po' sailors.
North 4H SilverShield - quite thin at 2.7mil. 5-layer PE/EVAL/PE (polyethylene and ethylene vinyl alcohol) laminated FILM. Gloves are not dip molded over a three dimensional form but cut flat from sheet with an identical second piece edge bonded on top. Probably stampt out using a hot metal wire shape pressed thru two sheets of the 5 layer plastic laminate that also melt-bonds the hand shape together. Couldn't rate these sacks for dexterity. There are seams everywhere when on your hands. The thumbs don't really 'oppose the fingers'. These are finger bags.
Least pricey throw-away I've seen is from LSS - $51.10 bag of 10pr. Sizes up to 11.
Come in three lengths. Purely by chance got the 16" which gives the glove a decent cuff. 14.5" and 29" also available.
Mine came from Northern Safety & Industrial delivered for $66.28. Catalog price about $5.50pr.
McMasterCarr has them on pg 1770 - but only in sizes 7,8,9 - mil thickness 2.7 and similar lengths - so they probably are North Silver Shield.
You can buy a single pair for $6.60 or a 10pr bag for $6.14ea. Fastest delivery time on earth, and probably only vendor selling single pairs!
[MMC never mentions brand names - which allows them to provide generic and comparative descriptions of products without brand hype.]
These stamped out gloves are not handed, so you can replace a single glove.
Ansell is probably the best known glove maker. Their "280 chemical resistant" gloves are called
Ansell Barrier 2-100 - at 2.5mil, also 5 ply laminate of PE/PA/PE (polyethylene & polyamide) films - they are lined with Tyvek inside. Believe these are flat thumb but supposedly a 'second generation' Barrier version with opposed thumb is in the marketplace, which would make them easier to wear. Haven't found them. Don't have a spare sixty bucks to try them out just now.
Both these gloves are not built over a liner. They are thin films that probably could easily be punctured. Lit suggests an over glove or under glove be used.
Most of us won't be batheing in solvents, so a nitril or butyl glove could be pulled over the barrier glove to protect the expensive disposable for multiple use. But good luck holding on to anything. Immobilized hands get tired quickly.
Aromatic solvents (naptha, xylene) will also seriously degrade nitril if you soak the rubber, which will expand and fall apart. Desperation found that in a pinch nitril gloves can be doubled up (two ply!) and the outer glove sacrificed - if your exposure is short term, like maybe 2 minutes max.
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Coating mast with Aluthane:
Final wipedown prep immediately before each recoat, to remove dust*, is done with the coating's primary solvent on a soaked rag gripped in a SilverShield glove. Logic has it that any lurking solvent left on the last coating is recognized as family by the next coat being rolled on.
Logic also has it that this method is based on ignorant superstition & faith - because
De-dusting could just as thoroly be done with sponge & water & clean rags - smarter & safer in a number of ways. NEVER EVER use a tack rag.
(*Outdoor shade for mast work is provided by a couple poplar & liveoak trees, both of which drop, drip & ooze on hot days. Project manager assumes that xylene cuts and dissolves these natural resins better than the saner stuff.)
mast coating done, it's over!
I'd like to have a photo here - because litlgull's mast is now coating complete.
8 coats of Aluthane and 7 of System3 WR-LPU clear satin.
The mast, waiting for its attachments, looks like a normal galvanized spar.... blank.... but it GLOWS!
For the record, as I sanded each coat of the aluminum filled (25%) one part moisture cure urethane, it's single mat shade of gray strangely changed into uneven darker grays with lighter gray continental google-earth formations. Like a bad job of sanding.
Using 220, there isn't a significant amount of material coming off, but because the coating is so extremely thin, it is too easy to sand too deep. Very mild toothing still produces a cosmetically nasty looking surface - which is OK as long as it's only a mode in 'perfect prep.'
This paint officially requires no toothing or scotchbrite scouring to recoat. After fiveorsix coats of perfect prep between each, the last three rolled one on top of another without sanding. You wouldn't know it.
SYSTEM 3 WR-LPU CLEAR SATIN is a ridiculous water reducible, almost zero viscosity, polyurethane... that ebb hopes will mate with a completely crazy and - until now - virtually unknown and non-yachtsie rusty piling & barge paint.
Tested using an Aluthane coated piece of aluminum tube with vertical paint tape separators - brushed some unthinned & uncrosslinked transparent coating onto three sections: 1. unprepared Aluthane, 2. (3M 7447 maroon very fine) Scotchbrite mesh scoured section , and a 220 grit sanded. The 220 with LPU still looked nasty and uply. The lightly scoured section had a slightly darker overall hue than the unprepared Aluthane BUT was even and UNBLOTCHED. Might have guessed that applying clear urethane on top of aluminum urethane would produce no changes in shade. LPU takes a couple weeks to completely cure, but it seemed bonded-as-one to each test strip and hard as nails the next day. Will it wrinkle, bubble, or squeek?
SO, a light tickling of the 8th metallic seal (which had cured on the mast a few days) with a new piece of maroon pad became the transitional prep. The aluminum coating out of the can isn't smooth like varnish when dry. There is a texture produced by the metal filler. A light going over made it slightly, shall we say, smoother. But aye knew it was going to be a number of LPU coats that would really get the mast looking visually and mechanically... smoother. That's what clear coat is all about.
WR-LPU
is not strictly a 2-part like they advertise. Part two is a crosslinker added at 8 drops to an ounce of first part. Ap guide suggests that normally it's added to the last couple coats of a session to leave a really hard abrasion resistant film. The drops aren't essential for part one to set.
Made up in turn three 4-ounce batches. This being the first time for quantities, it just worked out as an unintentional seven coats on the 30ft mast. Could have continued making batches! 17 total wet ounces with water thinner. No prep necessary between coats within the guide's 8hr window.
First batch, while there still was some cool cloud cover, 32 drops were added to 1oz of tap water, and then mixed in with the fab 4oz. Rolled on using the 4" Whizz premium foam roller with a half-sized plastic tray. Immediately tipped with a 2" foam Jen Polybrush. Second and third batches had 32 drops of linker added to 2oz of reducer, because the day heated up. The Whizz spreads evenly and leaves no ridges like a short-nap hard roller (that they recommend in their guide) on the curved surface of the spar. Spreads the coating beautifully, but wants tipping right now.
Open can is casually covered between stages, and the roller seranwrapped while breaking for lunch - one roller, one foam brush for the completed session. What's that?.... approx 38sqft of mast surface coated 7 times = 267sqft total. 12oz, of a 32oz $59QT. $3 in applicators.
Right!.... & my labor is cheap too!
Of course, with the coatings super-thinned, the resulting number of coats would be superthin also! Maybe that's OK on metal?
Has to be celebrated - this mild melon scented waterborne S3/WR-LPU is a delight to use. NO PETROLEUM SOLVENTS. What a relief! Worth every feeftynine dollar. Keep it off your skin, bonds to it very good.
[Silver Shield gloves - used with xylene to wash down the mast before Aluthane coatings - worth every $5.50pr, easy to slip on & off & use again.]
Tipping seemed easy, altho there was some tugging as the material immediately began setting. Armspan sections at a time - applied wet on dry and rolled into the previous wet edge. Second and third batches had two ounces each of water added as thinner. Those are 50% reductions! Twice the recomended 25% limit. Of course, coatings being super-thinned, rssulting total thickness super thin as well. LPU already is a thin paint.
Because the Whizz is so efficient spreading liquid evenly, application and tipping goes quickly. Had to: the coating is setting while tipping... it was bone dry at mast top - ready for the next coat - while still slopping it on wet at the heel. There seemed to be barely enough time for the application to flatten as it set up. Every batch was crosslinked so every coat is crosslinked.
Clear coating the lightly scrubbed aluminum paint in no way changed the gray color, first to last coat.
After seven coats of WR-LPU clear satin there is now a dolphin skin like glow to the stick. Every imperfection hoped to disappear is fully present. Yet the original filled & sanded ancient surface is under 15 coats of hi-tech can magic.
It's quite obvious both unrelated 'thanes like cooler surface and air temps to apply. [System3 formulated in Seattle. Aluthane in Alabama.]
Applied all LPU coats one right after the other at 70 to 85F (temp rising) - and 70 to 50 RH (humidity falling).
These numbers are within application guidelines - and the resulting roll and tip surface looks OK
- but imco the coating would have relaxed more AND the worker been more relaxed applying 25% thinned paint in cooler temp and higher humidity.
Time will tell. Next mast, I'll roll all those Aluthane coats one right on top the other NO prep, same as the System3.
But it's DONE. Looks seamless with no staggers, lap marks or ridges in coverage. Spar appears more sprayed than painted. But because it's aluminum colored you have to look twice to see that it is actually coated! If that's a grace.
A few runs. And all the prep booboos.... never went away.:o If not impeccable, it's righteous.
Hope this is useful!
Maybe post a pic.