Painting aluminium?

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nimrod1230

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Both steering pedestals are bubbling and cracking. The base material is aluminium and the finish is flaking off showing very little sign of a primer. The builders are very careful to skirt round the responsibily issue though the boat is only 5 years old. They are saying the pedestals are finished with gel coat and quote numbers which don.t relate to any standard paint references. So, two questions. What sort of prep/paint finish should I be aiming for? How to identify a colour match for this finish. With both showing similar signs and being fairly major to remove I wonder if patching would be possible.
 
What were the reference numbers which the builders gave you? They may mean something to somebody here.

You need an acid etch primer on aluminium. Personally I think that trying to patch repairs to paintwork is rarely satisfactory unless you are a very skilled.
Colour matching is even more skillfull.
 
RM, not what I wanted to hear but what I know is true though stripping the steering both sides with electrics etc is a major undertaking. The numbers quoted are "White 10503" and ref 974131. Google brings up a German site referencing gel coat I think, my German is nil.
 
That number is a part number for Jenneau http://www.sv-zanshin.com/manuals/jeanneaugelcoatcolors.pdf
You could order it from them.......but painting aluminium with gel coat seems to be a bit odd. In any event, as the boat is five years old the colour, will have faded/yellowed a bit

What make are the pedestals? I thought that they were normally painted by the manufacturer and just bolted into place by the builders.
Why not repaint them in situ?
 
Wow, you lot certainly know your onions, or gel coat in this case. Yes, Jeanneau. The pedestals are relatively simple angular, slab sided affairs and could be cast or fabricated as I guess a very small production run for this model. The wheel lock has a Lewmar logo but no idea if Lewmar would have been involved originally. Now that the season is over for us I can take off the inspection covers and explore. Still going to struggle with a colour match. Some boats have stark white standard pedestals with slightly cream/white gel coat and look OK so that might offer a solution. Painting in situ might be possible with carefull masking. Thanks for your comments.
 
Before you start painting I would want to know the cause of the problem.

Pictures below are a three year old pedestal. The problems were probably caused by stray electrical currents. We improved the bonding and nothing got any worse.

file-10.jpg

file-9.jpg

file-8.jpg
 
Oh dear, I am not alone! How did you probe for stray currents and pin down the cause. There are lights in the binnacle compass housings which untill I changed their connections were on with the cabin light circuits. I have no expertise in electrics so be gentle with me please.
 
A word of caution. You can't just put gelcoat on as if it is paint....it won't dry. It is possible to use additives so that it does cure but I've never done it so I can't help.

Personally, I would be thinking of using a two pack paint and accept that the colour match won't necessarily be perfect. Odds are that in a couple of years, time and a bit of UV will ensure that you don't really notice it. Acid etch primer, followed by a couple of coats of undercoat then the top coat and it will be better than new!
 
Rigger Mortice said:
What were the reference numbers which the builders gave you? They may mean something to somebody here.

You need an acid etch primer on aluminium. Personally I think that trying to patch repairs to paintwork is rarely satisfactory unless you are a very skilled.
Colour matching is even more skillfull.
Click to expand...

To be honest even a self guided DIY book still would be difficult to walk through.
 
if you are going to try and patch the coating, before you put any new primer or even resin, you must get rid of any salts on the surface.

Very simple to do, just use boiling water. A few rinses will disole anything.. I used a zink chromate primer from an aerospace supplier, only £12 for a med size tin,

Good luck
 
Thanks all. Your collective suggestions have helped formulate a plan. No idea how easy/or not getting the old coating off may prove though where the coating has cracked I can pick it off with my finger nail as it seems to have very little grip on the base metal. Have not tackled it yet as still using the boat until last weekend and trying to keep it intact. Most of the damage has not ruptured so not exposed the under surface. Will now plan etch primer and suitable topcoat though when the weather gods will allow this is anyones guess. Thanks again folks, Terry.
 
Some damage could be from fasteners but also some in random places away from any potential mechanical damage to the coating. Even the inspection covers show the same signs. Pretty disappointing as the last boat was 29 years old and the pedestal was in better cosmetic condition. I suspect a small batch production poorly prepared and coated almost as a one off. Thinking about colour matching I may try using the blue hull colour and white covers though that may be a step too far?
 
Tomahawk said:
if you are going to try and patch the coating, before you put any new primer or even resin, you must get rid of any salts on the surface.

Very simple to do, just use boiling water. A few rinses will disole anything.. I used a zink chromate primer from an aerospace supplier, only £12 for a med size tin,

Good luck
Click to expand...

You want to put Zn near Al?

1) Don't they react to form aluminium zincate?

2) Doesn't painting Aluminium cause even more likelyhood of concentrated corrosion?
 
alant said:
You want to put Zn near Al?

1) Don't they react to form aluminium zincate?

2) Doesn't painting Aluminium cause even more likelyhood of concentrated corrosion?
Click to expand...

I suggest you Google 'zinc chromate primer'. Widely used for priming aluminium. I believe that about 30 years ago Duralac contained zinc chromate but it is now based upon barium chromate.

Painting keeps the water out. No water = no corrosion. There is a slight risk that with more noble fastenings, e.g. stainless steel, if the painted aluminium was damaged, then some concentrated corrosion could be developed at the bare points assuming that water bridged the two. In practice, painted aluminium is widely used and it isn't a big problem.
 
alant said:
You want to put Zn near Al?

1) Don't they react to form aluminium zincate?

2) Doesn't painting Aluminium cause even more likelyhood of concentrated corrosion?
Click to expand...
The "aerospace" primer like Duralac is actually a barium chromate compound.

Painting aluminium is almost impossible - hence the use of a gel-coat. Anodising aluminium is the most common means of producing a weather resistant coat of aluminium oxides, then further proofed with dye/corrosion inhibitors.

When attempting to paint aluminium it is usual to put on an etching primer after washing with hot water or a weak acid solution. Absolute cleanliness is essential before attempting painting and a 2-pot polyurethane is often suggested as the best finish.

How quickly the aluminium casting will corrode is very dependent on the alloy - I suspect that this is cast and will happily produce aluminium oxides and hydroxides in vast quantities (depending on the hydration of the salts they occupy x5 - x10 the space of the original metal.
IMHO the OP is faced with a Sisyphean task and would be well to ignore the problem which in essence is purely cosmetic.

Still on peut souffri pour la beauté.

PS In support of Vic's point, the most common final coat put on an anodised aluminium component is still zinc chromate
 
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vyv_cox said:
I suggest you Google 'zinc chromate primer'. Widely used for priming aluminium. I believe that about 30 years ago Duralac contained zinc chromate but it is now based upon barium chromate.

Painting keeps the water out. No water = no corrosion. There is a slight risk that with more noble fastenings, e.g. stainless steel, if the painted aluminium was damaged, then some concentrated corrosion could be developed at the bare points assuming that water bridged the two. In practice, painted aluminium is widely used and it isn't a big problem.
Click to expand...

+1
Also hammerite special metals primer will successfully prime aluminium. People on this forum tend to "go off on one" about hammerite but in my experience the primer stick like *hit to a blanket.
 
Halo said:
+1
Also hammerite special metals primer will successfully prime aluminium. People on this forum tend to "go off on one" about hammerite but in my experience the primer stick like *hit to a blanket.
Click to expand...

Yes, I have posted several times in agreement. The adaptor plate that I made to connect my radar scanner with its strut was painted in Hammerite primer and smooth paint well over ten years ago and remains in excellent condition.
 
charles_reed said:
Painting aluminium is almost impossible - hence the use of a gel-coat.
Click to expand...

I don't understand that.
If you put gel coat on it still needs adhesion if it is to remain in place. Putting gel coat onto aluminium is no different from using any other paint product. It's effectively the same as using a polyester, or epoxy, paint.
 
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