Aluminum beam repaint. Sand in epoxy or use zinc chromate first?

[Franziska]

Hi,

I had a look at some of the threads here regarding this but I'm still not sure what will work better.
I have a forward beam which is not removable and a painted anodized mast section.
Hardware is mostly tied on with Dyneema.
Some areas have lost paint and I want to repaint the whole beam without spending ages on prep. I'm not after a high end finish, but want it to last.

I know that you can glue to aluminium very well if you sand the resin mix into the surface while it is still wet.

Here is what I plan to do.

1)
Remove all lose paint thoroughly, down to the anodized tube.
Leave any areas where paint still adheres well.
Sand the whole beam all over (painted and anodized areas) with 80grit.
Remove dust.
Wipe down with acetone.
Mix clear epoxy and sand it into the surface while still wet.
Before it's fully cured apply a thick coat of epoxy thickened by phenolic (the brown ones) microbaloons everywhere where there was no paint left.
Sand everything flat with 80-120grit.
Paint with epoxy primer.
Paint with brush to good workboat finish in white with 2pot PU paint.

2)
Now here is the question, instead of the sanded in clear epoxy I could go down the standart route with 2 layers of zinc chromate.
Lightly sand that and than paint that with thickened epoxy or epoxy primer before painting with PU paint.

What I like on method one is that I have a lot of epoxy available and that I could easily built up thickness where needed. As it's a chemical bond between the layers (all epoxy) it will entail less sanding too.

Thoughts?

Thanks for them.

[Bill O]

We've painted many aluminum pieces on our boat spars, bow sprit, windshield frame, etc. and have had excellent durable paint jobs using zinc chromate (zc).

While I've never done the clear epoxy under coat method, would think the zinc chromate "bites" in the aluminum better. Each would have the mechanical sanding of aluminum to expose fresh, but the zc is a self etching primer that acts more of a tie coat. IMO not certain if the epoxy would do as much as a zc conversion coat.

The zc product we used was a very simple application. Blasted/sanded to bright metal, blew away any sanding residue w/pressurized air and vacuuming, then applied only 1 coat of vc (per instructions). Could apply epoxy primer after 1 hr.

[Cheechako]

Are you sure it was anodized? DONT sand it! Leave it bare. Sanding the anodized finish is destroying the best aluminum protection scheme there is.
The standard acid wash, Zinc Chromate, etc is marginal at best even on mono masts..... much less a crossbeam that is wet a lot.
I had one done by pro's... cruising with a lot of salt spray, the bottom 6 feet lasted about 1-1.5 years before corroding again...
I've not heard of the epoxy method you mention, but if you do it you MUST paint over it because epoxy deteriorates very fast in the sun/UV making a mess.

The best results I had on a painted mast was 2 part Sterling paint, no chromate under.

[Franziska]

Hey guys, thanks, I guess I'll get some zinc chromate and follow up with epoxy primer after all.

While the beam is anodized, someone decided in the past to paint them.
I have about 75% of good paint left. Hence the decision to repaint.
I'll only key the anodized areas lightly (not to bare metal).

As I understand one does not need to sand the chromate before applying the epoxy primer. As long as the epoxy primer is applied within an hour. Correct?

Regarding epoxy I am well aware of the UV issue. Been using that stuff for ages :-)

Sand the open metal areas, de dust & immediately apply two light coats of zinc chromate, than apply EP primer shortly thereafter.

[Cheechako]

Originally Posted by Franziska

Hey guys, thanks, I guess I'll get some zinc chromate and follow up with epoxy primer after all.

While the beam is anodized, someone decided in the past to paint them.
I have about 75% of good paint left. Hence the decision to repaint.
I'll only key the anodized areas lightly (not to bare metal).

As I understand one does not need to sand the chromate before applying the epoxy primer. As long as the epoxy primer is applied within an hour. Correct?

Regarding epoxy I am well aware of the UV issue. Been using that stuff for ages :-)

Sand the open metal areas, de dust & immediately apply two light coats of zinc chromate, than apply EP primer shortly thereafter.

Be sure to get real 2 part Zinc Chromate primer. That one part stuff is a joke...

[Bill O]

Originally Posted by Franziska

Hey guys, thanks, I guess I'll get some zinc chromate and follow up with epoxy primer after all.

While the beam is anodized, someone decided in the past to paint them.
I have about 75% of good paint left. Hence the decision to repaint.
I'll only key the anodized areas lightly (not to bare metal).

As I understand one does not need to sand the chromate before applying the epoxy primer. As long as the epoxy primer is applied within an hour. Correct?

Regarding epoxy I am well aware of the UV issue. Been using that stuff for ages :-)

Sand the open metal areas, de dust & immediately apply two light coats of zinc chromate, than apply EP primer shortly thereafter.

In general, you will want follow the manufacturer's guidelines, but the 2 part instructions I was referring to wanted a min. of 1 hr to set up (temp. dependent) and up to 24 hrs. before you needed a new coat of zc.

All the paint work I did was on bare aluminum. Did paint an anodized spar section that I had re-welded into a new boom. Wasn't too bad to fully remove the anodized coating. Here is a link to an article that used common chemicals to remove anodized aluminum.

If I were going to put the time and materials to repaint, would want the surface as clean/uniform as possible before putting on the zc.

[Franziska]

As 75% of the paint is still adhering very good, I will not grind everything down to bare metal.

:-)

But I hear what you say and get a two pot zinc primer if I can find it over here...

[kryg]

I redid my mast as follows:. I would remove all the paint then burnish the beam D-wax and coat it with 3 clear coats of EverBright. No more failed paint issues - You will never have to repaint again. Just re-coat in 3 or 4 years time with a sponge or brush. Good luck with it.

Originally Posted by Franziska

Hi,

I had a look at some of the threads here regarding this but I'm still not sure what will work better.
I have a forward beam which is not removable and a painted anodized mast section.
Hardware is mostly tied on with Dyneema.
Some areas have lost paint and I want to repaint the whole beam without spending ages on prep. I'm not after a high end finish, but want it to last.

I know that you can glue to aluminium very well if you sand the resin mix into the surface while it is still wet.

Here is what I plan to do.

1)
Remove all lose paint thoroughly, down to the anodized tube.
Leave any areas where paint still adheres well.
Sand the whole beam all over (painted and anodized areas) with 80grit.
Remove dust.
Wipe down with acetone.
Mix clear epoxy and sand it into the surface while still wet.
Before it's fully cured apply a thick coat of epoxy thickened by phenolic (the brown ones) microbaloons everywhere where there was no paint left.
Sand everything flat with 80-120grit.
Paint with epoxy primer.
Paint with brush to good workboat finish in white with 2pot PU paint.

2)
Now here is the question, instead of the sanded in clear epoxy I could go down the standart route with 2 layers of zinc chromate.
Lightly sand that and than paint that with thickened epoxy or epoxy primer before painting with PU paint.

What I like on method one is that I have a lot of epoxy available and that I could easily built up thickness where needed. As it's a chemical bond between the layers (all epoxy) it will entail less sanding too.

Thoughts?

Thanks for them.

[s/v Jedi]

Check out Awlgrip Wash Primer CF. It’s their new system that doesn’t need ZC. It’s also compatible with epoxy primer as next coat.

About sanding epoxy in: I never did this with aluminium but did with West System on lead. Not 100% happy with it. Will try this with Interprotect 2000 next time.

Looking at painting my masts, I’m close to choosing the Wash Primer CF.

On Everbright: they claim 3-7 year lifespan so that’s not much...

[Manateeman]

I’m stunned by all this prep work. On our bottom, we kinda went nuts and ran the disc grinder before slathering on layer after layer of epoxy. The only reason we paint the top half of the hull and the deck is to stop the heat from the sun.
We epoxied the deck to make it look smooth and yacht like.
I think I’ll try the Jedi system. The yellow zinc chromate is great stuff but don’t ever sand it...very toxic. I didn’t even use zinc chromate on the hull topsides...hold on to your hats...oil ...deck and floor paint... right from Home Depot or Lowe’s. Just a touch of color so it doesn’t look like Snow White owns the boat. Easier on your eyes too.
120 sandpaper, zinc chromate, oil deck and floor paint. That’s it for me.
I’m not out to impress the New York Yacht Club sailors .
Gloss lipstick is never worn by manatee girls. A smart straw hat with a ribbon...maybe, but nothing more than Chapstick on the lips.
Happy trails to you.
The manatee crew

[Franziska]

Thanks.

Looks like the days of Zinc Chromate are over in France (and probably in the whole of Europe)...

The yard here uses Interprotect directly.

As I can't get something as zinc chromate, I'll end up using Metapox by Nautix as base and follow that up with epoxy primer.

I'll wet sand the Metapox in and will progress sectionally, so it's covered with primer within the recommended time.

Originally Posted by Manateeman

I’m stunned by all this prep work. On our bottom, we kinda went nuts and ran the disc grinder before slathering on layer after layer of epoxy. The only reason we paint the top half of the hull and the deck is to stop the heat from the sun.
We epoxied the deck to make it look smooth and yacht like.
I think I’ll try the Jedi system. The yellow zinc chromate is great stuff but don’t ever sand it...very toxic. I didn’t even use zinc chromate on the hull topsides...hold on to your hats...oil ...deck and floor paint... right from Home Depot or Lowe’s. Just a touch of color so it doesn’t look like Snow White owns the boat. Easier on your eyes too.
120 sandpaper, zinc chromate, oil deck and floor paint. That’s it for me.
I’m not out to impress the New York Yacht Club sailors .
Gloss lipstick is never worn by manatee girls. A smart straw hat with a ribbon...maybe, but nothing more than Chapstick on the lips.
Happy trails to you.
The manatee crew

[Pauls]

Franziska - ANY sanding you do on the anodizing will damage it. It is a very thin layer. And as Cheechako said it is the best aluminum undercoat you will ever have. Please consider using a paint stripper to remove the failed paint. You can try this on a small area and see how it goes. There is nothing you can paint onto aluminum that is as good an undercoat as undamaged anodizing.

[s/v Jedi]

Originally Posted by Pauls

Franziska - ANY sanding you do on the anodizing will damage it. It is a very thin layer. And as Cheechako said it is the best aluminum undercoat you will ever have. Please consider using a paint stripper to remove the failed paint. You can try this on a small area and see how it goes. There is nothing you can paint onto aluminum that is as good an undercoat as undamaged anodizing.

The problem is that paint has a hard time sticking to anodized aluminium. It’s a shame they painted it. Normally you either paint or powder coat or anodize. With anodizing you use an ink that fills the pores to color the metal but this needs to happen during the anodizing process.

[AKA-None]

Originally Posted by s/v Jedi

The problem is that paint has a hard time sticking to anodized aluminium. It’s a shame they painted it. Normally you either paint or powder coat or anodize. With anodizing you use an ink that fills the pores to color the metal but this needs to happen during the anodizing process.

Kind of
Anodizing is a chemical application where you strip the metal with an acid or alkaline solution and plate via the application of electricity while the item is submerged in a chemical bath.
I did this as a job after high school and it’s very nasty stuff, not something normally done at home
Also not something you can easily touch up

[s/v Jedi]

Originally Posted by AKA-None

Kind of
Anodizing is a chemical application where you strip the metal with an acid or alkaline solution and plate via the application of electricity while the item is submerged in a chemical bath.
I did this as a job after high school and it’s very nasty stuff, not something normally done at home
Also not something you can easily touch up

Since the invention of anodizing, they started using inks to color the aluminium after the electroplating and before sealing. You can make it red, blue, black etc.