Aluminum mast/boom - how important is the anodizing?

[Orchidius]

Hi there,

So My mast and boom are down atm for rerigging, and while we're at it I figured it'd be a good time to give them a thorough clean. They're 30 years old and look the part...

The boom fit in the car, so I took that home and got to work with 600 grit wet-sanding paper. It did the trick and got most of the grime off (not all of it though), and while reading up on the matter of how to remove the alst 20% of the dirt, I bumped into the whole "don't use abrasives, it'll ruin the protective anodizing!-deal".

Last I heard was that bare aluminum doesn't corrode, but if I was to believe most discussions I read about the anodizing my entire boom will be corroded away within 5 years because I stripped it of its anodizing...

What's your take on this? How to properly clean the mast/boom? No, I don't want to paint it. How vital is the anodizing and how much have I ruined it by using 600 grit wet sandpaper?

[neilpride]

Bare aluminium dont need any special treatment,just leave it like that, if you sand the boom, leave it like that to, sure dont look pretty but in few months the alu start to oxidize and can look better, there is few products to clean aluminium, kind of acid wash and rinse , thats it, if you sand the boom with 600 grit and dont reach bare aluminium , you can polish the anodizing and see if is worth to keep it,

[Orchidius]

After a bit of a wet sand with the 600 grit, it still looks shiny 'n smooth 'n all. Not at all like my spinnaker boom, which looked dull grey after sandblasting it.

[Orchidius]

This sounds legit, and while it might be true, I still have no better understanding of the matter at all...

It is less corrosion resistant, what does that mean? I have never, ever seen aluminium structurally corrode other than under galvanic corrosion. How would it corrode, what would it look like and when would it become dangerous?

I haven't touched the spar itself yet, and I'm not getting the boom re-anodized (no way in life I can find some place that does it cheaper than a "new" second hand boom).

EDIT: Right, this post was supposed to be a reply to somebody else's post on this topic. I think something went wrong though, as the post I wanted to comment on seems to have disappeared...

[Delancey]

Originally Posted by Orchidius

What's your take on this? How to properly clean the mast/boom? No, I don't want to paint it. How vital is the anodizing and how much have I ruined it by using 600 grit wet sandpaper?

The best aluminum alloy for saltwater corrosion resistance is 5086, unfortunately your mast and boom are either 6061 or 6063 alloys, which have better strength than corrosion resistance. This is the reason they were anodized, to protect the metal.

Anodizing is an electro-chemical process that coverts the surface layer of aluminum into a specific structured oxide which electrically non-conductive and significantly harder than the base metal. Aluminum oxide is so hard in fact, it is commonly used as an abrasive media (think aluminum oxide sandpaper)

Quality of anodized coatings is generally determined by the depth of penetration. Generally, I have seen far better quality anodizing on sailboat spars than in most architectural applications. The last step in the anodizing process is the application of a fluoroploymer sealer which fills in the micro porosity of the surface resultant from the acid baths used in the anodizing process.

Given the fact that you likely used an aluminum oxide sandpaper of comparable hardness to the anodizing, it is possible you haven't ruined your spar. It is possible you have just polished off the sealer and part of the anodizing.

I suggest you try to test for conductivity with a multimeter to determine how badly you have messed things up. If it is still non-conductive you might be okay. You're probably okay anyway as long as you keep an eye on it. I'd be more worried if you told me you stripped the interior of the tube, where corrosion could occur that you couldn't see.

As far as what you are looking for if you want to see corrosion, it's the same flaky white powder associated with galvanic corrosion seen where stainless fasteners have been installed in aluminum or when you see a pitted corroded outdrive. The concern with spars is that they tend to have as thin a wall section as possible, which typically isn't so much to begin with.

As far as cost to re-anodize goes, only one way to find out. I know a guy who I would probably do it for fifty bucks. That doesn't help you much, point being make a couple calls, you might get lucky.

Cheers

[roverhi]

Aluminum corrodes. It starts immediately after it's been cleaned to bright metal. The oxidation acts as a protection for the underlying metal. Unlike steel, the corrosion doesn't exfoliate constantly exposing new metal to corrosion rapidly resulting in pukas in unprotected surfaces. There can be problems with corrosion in aluminum especially if there is dissimilar metal in contact with the aluminum like SS fasteners and/or the metal is constantly in salt water like the butt of a keel stepped mast.

The oxidation that protects the metals surface is not a particularly hard surface so easily abraided and can be quite rough and unsightly. An anodized spar may/will develop stains and unsightly appearance but won't have the rough finish of unanodized oxidated aluminum. Unfortunately, thanks to our friends at the State EPA in California, there are no anodizing tanks large enough to do masts there. That's why the masts out of LeFiell and other west coast mast suppliers were painted. Painting just creates a major problem down the line if you want a yacht quality appearance or even just a decent appearance of your mast down the line. To get paint to adhere to aluminum, you have to take the surface down to oxidation free bright metal then immediately do a multipart treatment system to ensure the paint will stick. The prep done right for painting a previously painted aluminum mast can make painting the topsides seem like a minor operation.

The 45 year old mast on my boat was anodized and has stood the test of time. It may not be pristine but looks just fine after a little cleanup with scotch brite pads and waxing. Wouldn't get too aggressive with trying to clean up a bare mast as you may grind through the anodizing. That will leave you with a blotchy finish and destroy the protection of the anodizing.

[Cheechako]

There are plenty of masts that aren't anodized when new. I wouldnt worry about it. Do you know it was anodized in the first place? If it is anodized I would limit cleaning the mast to non abrasives.... as anodizing is nice to have.
Bare aluminum protects itself, but it will get a little crusty sometimes.. sharp little "pimples" for lack of a better word. You can feel them as you run your hand over the aluminum. Bare aluminum also gets that grey powdery finish on it... it comes off on sails etc a bit.

[vientoman]

to the original poster,

coat it with this stuff and forget about it.

Marine – Uses and Benefits :: Nyalic®

[JPA Cate]

Orchidius,

I don't know if it's available in Belgium, but we finished our replacement mast on our first Insatiable by fine sanding, and wiping with clear Tectyl. We just touched it up after that, if the finish started looking less good. Our mast simply glowed. The trick is to sand in single strokes along the whole length of it, as if you were on an escalator. It will work on your boom, too.

Ann

Ann

[shipleft]

Anodizing is usually black or goldish in color so you should be able to tell how much or little anodizing you rubbed off,(if it was anodized to begin with). i have seen bare aluminum masts on older boats than yours that are fine, no corrosion problems at all, and I have seen lots of masts that have wear spots where the anodizing has been rubbed off by a halyard or some other line slapping against the mast constantly, they seem fine after years of use. That NYALIC spray coating is incredible stuff though, I have used it to re-coat aluminum motorcycle parts like engine cases and fork bottoms, where the original clearcoat has chipped or worn off, and to protect cast iron surfaces(tablesaws, jointers,etc.) from condensation rust and it does the job perfectly, at a reasonable price! It's some type of clear lacquer modified with a polyimer, seems to wear pretty well..

[ggray]

Thanks for this post.
I was just going to say that spar manufacturers pay a good amount of money to anodize spars, so it must be important. But your post gives a bit more information.
Earlier versions of my boat came with either a painted mast or an anodized mast made in two pieces spliced together because the tank had not been long enough. Sounds like a lot of trouble for something if it's not important.

Originally Posted by Delancey

The best aluminum alloy for saltwater corrosion resistance is 5086, unfortunately your mast and boom are either 6061 or 6063 alloys, which have better strength than corrosion resistance. This is the reason they were anodized, to protect the metal.

Anodizing is an electro-chemical process that coverts the surface layer of aluminum into a specific structured oxide which electrically non-conductive and significantly harder than the base metal. Aluminum oxide is so hard in fact, it is commonly used as an abrasive media (think aluminum oxide sandpaper)

Quality of anodized coatings is generally determined by the depth of penetration. Generally, I have seen far better quality anodizing on sailboat spars than in most architectural applications. The last step in the anodizing process is the application of a fluoroploymer sealer which fills in the micro porosity of the surface resultant from the acid baths used in the anodizing process.

Given the fact that you likely used an aluminum oxide sandpaper of comparable hardness to the anodizing, it is possible you haven't ruined your spar. It is possible you have just polished off the sealer and part of the anodizing.

I suggest you try to test for conductivity with a multimeter to determine how badly you have messed things up. If it is still non-conductive you might be okay. You're probably okay anyway as long as you keep an eye on it. I'd be more worried if you told me you stripped the interior of the tube, where corrosion could occur that you couldn't see.

As far as what you are looking for if you want to see corrosion, it's the same flaky white powder associated with galvanic corrosion seen where stainless fasteners have been installed in aluminum or when you see a pitted corroded outdrive. The concern with spars is that they tend to have as thin a wall section as possible, which typically isn't so much to begin with.

As far as cost to re-anodize goes, only one way to find out. I know a guy who I would probably do it for fifty bucks. That doesn't help you much, point being make a couple calls, you might get lucky.

Cheers

[sailersteve]

22 years ago i used mother mag polish (a lot of work & 15 small $6.00 jars) & a cheep 3/8 craftsman sander/polisher on my mast , 2 coats meguiar's wax . It still looked ok 12 years sailing & 10 years under a tree. ( Lake Erie ) Ohio. Now i've take in off rub rails & all metal that looked like crap , polished all with White Diamond Metal polish & sealant 2@ $19.99ea & very easy & looks great, like stainless & or chrome look. Polish/wax with ( Insulator wax ) Collinite # 845 Marine,Rv,Aeronautical & Industrial. XBEY UNDER $20.00. Said can't be washed off with detergent. Protects against adhesion of future surface corrosion caused by UV, Salt ,etc. I don't know about anyone else ,but i can't stand the look of a nasty looking mast , rub rails , etc. Make sure to wax same day as polishing .

[rognvald]

Orch,
I have been using Woody Wax's 2 part system on my mast and boom for the last 8 years. It is an outstanding product and provides great protection. It is applied with fine bronze wool and removed with a soft cloth and does not damage anodizing. Good luck and good sailing. www.woody-wax.com/