paint problem

[Birdseye]

I have spray painted an ally pole for my new windmill and find mthat the paint coating is so brittle you can scratch it off with a finger nail.

The ally was roughened with emery and then given a coating of epiphanes wash primer, something I have previously used with no problem. I then used a spraycan of etch primer before spraying with Aldi /lidl metal paint thinnned slightly with normal thinners from a car body paint supplier. It seems to be the top coat that is thin / brittle with the primer having better but still not brilliant adhesion.

the whole thing stirs a vague memory of once applying XM antifoul after thinning with cellulose only to find later on that it came away in sheets.

any ideas?

 

[KellysEye]

You need to apply Aluminiun etching primer before painting.

 

[vyv_cox]

I'm not quite sure of the function of the wash primer but it may be it has inhibited the etching mechanism of the etch primer? EP contains KOH (well it used to, at least) that etches the aluminium to provide good adherence for subsequent paint. I would have thinned in the same way - cellulose thinners is a pretty universal solvent and evaporates fast, so has little effect on most paint surfaces.

 

[Birdseye]

I suspect I might have thinned too much. the paint can says 3% max and I used maybe 15% - i'm a man. I dont do instructions - not until something goes wrong that is.

I dont think its the etching bit because most of the time the white topcoat is scratching off and leaving the primer still on. not all the time but mostly.

so could over thinning cause the dried paint to become brittle/ flakey with poor adhesion?

 

[SHUG]

I have used Hammerite Smooth Silver spray on spars without any priming. Its long lasting and matches the anodised finish very well.

 

[Steve C Cronin]

You can only paint raw aliminium and then only after it has been cleaned to bright metal and primed with two-pack zinc chromate. Anodised ally will need quite a lot of the surface removing first and would be substantially weaker as a result. The zinc chromate just doesn't work on anodised.

 

[VicS]

The zinc chromate just doesn't work on anodised.

But the Epiphanes wash primer does ... at least according to their literature

 

[Paddingtonbear]

It obviously does not :} , you need to get down to the base material and etch prime and use COMPATIBLE top coat. There could be a problem with the propellant/thinners which is why paint companies have 'systems' Good luck, a bit of a tricky one. What does wash primer do btw?

 

[Cloven]

Repainted the housing of my aero4gen about 3 seasons ago as original finish was flaking off. Scraped/sanded back to bare metal, treated with Hammerite special metals primer and then Hammerite smooth white paint. No problems and still looking good.

 

[30boat]

I read somewhere that etching primers for aluminium were not that effective and that it was better to abrade well and paint.I'm confused.

 

[vyv_cox]

I have had great success with Hammerite etch primer on aluminium.

 

[Steve C Cronin]

I read somewhere that etching primers for aluminium were not that effective and that it was better to abrade well and paint.I'm confused.

Tell OMC (Evinrude, Johnson) that. They always use zinc chromate primer on bare aluminium as do local authorities on lamp posts.

 

[Daydream believer]

Why not just paint straight on well sanded aluminium with trilux antifouling
It does not rub off like hull antifouling & sticks to my saildrive ok

& before any joker suggests it--- if you capsize you wont get any barnacles!!

 

[Birdseye]

It obviously does not :} , you need to get down to the base material and etch prime and use COMPATIBLE top coat. There could be a problem with the propellant/thinners which is why paint companies have 'systems' Good luck, a bit of a tricky one. What does wash primer do btw?

It does Paddington. A few years ago I stripped a mast of black anodising and painted it white using the Epifanes primer ( looks a bit like PVA adhesive), epoxy primer and twin pack poly topcoat. It worked well with no problems in the time I owned the boat. This current problem doesnt seem to be the bond between the undercoat and the ally, but a flakey topcoat. Anyway I've rubbed it down and re- sprayed the topcoat undiluted. The finish isnt great since the paint is too thick to spray, but it isnt flakey. So it looks as if my problem was either over dilution of the top coat or the wrong thinners.