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CharlieCobra · 03-12-2010, 08:02

Ok, I spent years painting aircraft and corrosion control is paramount in aviation. These were our procedures.

1. Chemically strip all old paint and primer.
2. Address any corrosion with brass brushes, media blasting etc. (DO NOT USE STEEL)
3. Acid etch the cleaned AL and scrub lightly with Maroon Scotchbright pads. Rinse very thoroughly.
4. Alodine the AL. Rinse thoroughly.
5. Apply anti-corrosion primer i.e. zinc chromate, Super Koropan, Epoxy. Note*, Super Koropan was the toughest primer I ever encountered. It was impervious to Hydraulic Fluid, diesel, phenolic strippers, acid strippers, media blasting.
6. Apply an Epoxy Filler primer for fairing.
7. Apply US Paint's Alumigrip or similar Polyester Urethane.

This process was good enough for heavy jets flying through rain at mach .85 so it should work just fine for a boat sailing along at 8-9 knots.

Cheechako · 03-12-2010, 12:06

I've seen a lot of masts which are unpainted and un anodized. It seems for years there must not have been an anodizing tank big enough or something! It's more common to anodize now. Based on what I've just visually seen...I think an unpainted mast is likely to last better than a painted one. The lower 6 ft of a painted mast just seems to go ugly real fast...once it starts around a SS fitting or screw it corrodes in deep. For some reason the unpainted ones dont seem to do this as bad (generally) This might be due to the large exposed area rather than a quarter sized anode to focus the corrosion....? I wouldnt hesitate to leave it bare. If your doing cruising, plentiful fresh water rinsing may not be an option. In Annapolis I had the Mast on my Passport 47 completely rebuilt, stripped, acid washed, Zinc Chromate primed and pro painted. In less than a year the lower 6 ft looked like a bad case of acne. Huge waste of money. In the Carribean you will see a lot of French boats completely unpainted...low maintenance. That's what aluminum does...builds it's own oxide layer... It aint pretty though!

akio.kanemoto · 03-12-2010, 12:15

Thank you for your replies, greatly appreciated.

I'm leaning very heavily towards unpainted and perhaps coated with something I've read in other threads called "Tectyl 506" (wipe on corrosion inhibitor which leaves a waxy film), but again, I'd love to see some photos. All the masts at the dock here and moorings etc are all painted/anodized - everybody says "unpainted is ugly"... but how ugly is ugly?

I will be having the mast professionally soda blasted and will use Alumiprep etc per the recommendations here - but I don't know how much pitting/corrosion I have until the paint is stripped. With the paint still on - at some locations, there is SERIOUS bubbling of the paint and when you crack it with your nail, there's an ooze inside.. so I'm quite worried.

I'm thinking that if the pitting is not bad, I'll leave it bare, otherwise, fill/paint etc..

But any pics of unpainted masts would be GREATLY appreciated. Especially those with Tectyl 506 if anybody has heard of it.

Cheechako · 03-12-2010, 13:13

The unpainted masts I've seen end up being a dark silver /gray. When you wipe your hand acrross the finish it feels a little rough...like salt crystals on the surface or something. Your hand may be left with a black residue...Aluminum oxide. Most I've seen are on 30 ft and under. Take a look at the older boats in that size range in your marina. I guess the up side is a couple years down the road you can lightly sand the lower 10 ft to make it look good again without a bunch paint prep etc. However, if you mast is corroded / oozing as you say...you may have some ugly pits. I suppose you could fill them with an sluminum based filler...or better yet weld them up. The weld will be darker than the surrounding metal though.
I took my 30 footer to Mexico for 2 years in '85. It had a bare mast. The one thing on the boat that was never an issue was the mast! We had no watermakers or hose down available the whole time. Rain though!

akio.kanemoto · 03-12-2010, 13:30

Quote:

Originally Posted by Cheechako

The unpainted masts I've seen end up being a dark silver /gray. When you wipe your hand acrross the finish it feels a little rough...like salt crystals on the surface or something. Your hand may be left with a black residue...Aluminum oxide. Most I've seen are on 30 ft and under. Take a look at the older boats in that size range in your marina. I guess the up side is a couple years down the road you can lightly sand the lower 10 ft to make it look good again without a bunch paint prep etc. However, if you mast is corroded / oozing as you say...you may have some ugly pits. I suppose you could fill them with an sluminum based filler...or better yet weld them up. The weld will be darker than the surrounding metal though.
I took my 30 footer to Mexico for 2 years in '85. It had a bare mast. The one thing on the boat that was never an issue was the mast! We had no watermakers or hose down available the whole time. Rain though!

On the black stains - can you remember whether the spreaders etc left dirty black stains on your sails and whether everytime it rained, you had a tonne of black water on your decks from the rigging rubbing against the mast etc?

Cheechako · 03-12-2010, 14:49

It's amazing how dirty the spreaders etc get on a boat...painted or not, I got stains from my spreaders. However if you live away from a metropolis...you may not get much. ...I think a lot of it is rubber dust from the roads. I never noticed any black water off the mast at all.

perchance · 03-12-2010, 15:43

If you look at all the aluminium commercial fishing boats running up and down the left coast there's not a lick of paint on any of them. If it works for them it works for me.

Cheechako · 04-12-2010, 09:16

Yep...Painting aluminum is definitely for those who dont mind spending a lot of time and money maintaining. I guess in some ways it's similar to varnishing teak. If you leave it unvarnished it doesnt look too bad (but not like a "yacht"), if you varnish it and let it go too long it looks terrible. Kind of an all or nothing thing. It seems some boats are electro neutral and others are pretty bad. My friends had an aluminum Perry designed 48. It needed paint when they got it. They had it painted in the US/FL by a big yacht expensive yard, it got stripped and painted again in Trinidad and it got painted again after that...in Columbia I believe...not sure.

**David M** · 04-12-2010, 09:26

Yes, leave the paint off if you can live with the ugly dull grey color. Aluminum oxide is the best anti-corrosive for aluminum that exists...and you don't even have to apply it!

akio.kanemoto · 07-02-2011, 14:26

Hello gentlefolk,

OK, I'm finally up to the point that I am about to start something - either I sodablast and leave it, or paint it.

Removing fittings doesn't look like it's much of an option - there are a lot of things fitted from the inside of the mast and thus removing/rebedding doesn't look like a winning solution.

I'm leaning heavily towards sodablasting and leaving unpainted.

Having said that - I've finally gotten around to taking some pics - please let me know what you think:

https://sites.google.com/site/mastcorrosion/pics

...the entire mast (except for right at the top) is covered in bubbling where not flaking... and as you can see, it's not pretty.

Thanks!

**atoll** · 07-02-2011, 14:47

with out removing the stainless hardware from the mast the bubbling will continue if you paint it,best option would be to find a new mast section,and re attach every thing correctly using plastic gaskets between the stainless and alloy.

to bring the existing section to a reasonable uniform finish i would sugest using a STAINLESS STEEL wire brush on a large grinder to remove the paint and most of the corrosion,paint stripper works also but not very nice to work with.

then treat with de greaser/engine cleaner.

then use mild phospheric acid solution,once bright wash off with fresh water.

then let normal oxidisation occur.

if you do chose to paint,use the same process,but once dry etch prime with an alumilium primer, then 2 coats epoxy primer, then 2 coats 2pack poyeurathane.

works on my un anodised 63 ft alloy yacht

akio.kanemoto · 07-02-2011, 14:58

Quote:

Originally Posted by atoll

with out removing the stainless hardware from the mast the bubbling will continue if you paint it,best option would be to find a new mast section,and re attach every thing correctly using plastic gaskets between the stainless and alloy.

to bring the existing section to a reasonable uniform finish i would sugest using a STAINLESS STEEL wire brush on a large grinder to remove the paint and most of the corrosion,paint stripper works also but not very nice to work with.

then treat with de greaser/engine cleaner.

then use mild phospheric acid solution,once bright wash off with fresh water.

then let normal oxidisation occur.

if you do chose to paint,use the same process,but once dry etch prime with an alumilium primer, then 2 coats epoxy primer, then 2 coats 2pack poyeurathane.

works on my un anodised 63 ft alloy yacht

I don't think removing the hardware is an option - there are some that I can remove, but some others like the spreader attachments which bend around the mast, I don't have the courage to do..

Just out of curiosity - is sodablasting (much more gentle than sandblasting) an option - instead of the wire brush? I believe that a sodablasting operator can get into all the nooks and crannies much better than I could with a wire brush. .. also sodablasting can't take off any of the metal itself, whereas I could potentially gouge holes in it etc with the brush.

Or do you think that blasting won't take off the corrosion?

Also - once cleaned up - since there won't be any paint on it - do you think that the nasty corrosion will return around the fittings if not rebedded - or since there won't be any paint left - it will just go a dull grey and that's it.. (no white stuff etc...)

**atoll** · 07-02-2011, 15:11

soda blasting i would think is fine,though i only have experiance with regular carbundium grit blasting on alloy,just check their no acid/alkali issues with the soda.

un fortunately the problems on your mast have probably been caused by in correct bedding of the stainless,so these will continue in close proximity to stainless fittings,though the rest of the mast should just go a dull grey,then stop corroding.

i also suspect this mast was never anodised,and relyed on paint to give it a barrier between the alloy and oxygen /atmosphere.

akio.kanemoto · 07-02-2011, 15:19

Quote:

Originally Posted by atoll

soda blasting i would think is fine,though i only have experiance with regular carbundium grit blasting on alloy,just check their no acid/alkali issues with the soda.

un fortunately the problems on your mast have probably been caused by in correct bedding of the stainless,so these will continue in close proximity to stainless fittings,though the rest of the mast should just go a dull grey,then stop corroding.

i also suspect this mast was never anodised,and relyed on paint to give it a barrier between the alloy and oxygen /atmosphere.

I might take a sample of the blast media and put it in a jar with some aluminium and water and see what happens. It's supposed to be very gentle though.

As for anodizing, no, I don't think it ever was.

So for the stainless fittings - what happens between raw aluminium and stainless - does it eventually stop as well - or keep producing white nasty al oxide until the aluminium loses and leaves a hole in the mast?