2 part clearcoat over bare magnesium - good idea?
 

I've removed the cooling fan as part of my altenator replacement. I cleaned it up, and one thing led to another; it is nice and shiney now.

I'm thinking of spraying it with 2 part polyurethane clearcoat. I this a good combination: 2 part on bare magnesium??

I used lacquer 7 years ago and it eventually flaked off as the metal oxidized under the lacquer and popped it off.

Same risk with the 2 part poly??

I don't know the answer first hand but I would say it would do the same thing as the metal oxidizes beneath the finish. I think I would treat it similarly as I would polished aluminum. Leave it bare, keep it clean it and from time to time I would give it a freshening up with some never dull wadding then a protective coating of Vaseline or a little collinite insulator wax.

most clears are of a urethane base and not of a polyurethane base .
the 2nd more popular used clear of today is of acrilic base .
non of them are good for going over any bare substraights .
you will need to buy a clear that is made for doing just what you are looking to do .
the clear we use in my shops for bare metal is diamond gloss clear for bare metals .
because i'm a shop owner i am able to get it from the maker but i think you can find it at places like eastwood .

most people that try to use it will get fisheyes . it's not the product it's all the user .
because it's acrylic based you have to make dam sure every thing you want it to be sprayed on is clean (real clean ) .
you have to wear vinyl gloves or a like right from the time you start to handle the part .
just the oil in your hand will cause fisheyes in using this type of clear .
then cleaning the parts is very important ! it has to be totally clean any bit of polish , oil , wax and so on will make it fisheye .
you want to use isopropyl alcohol to clean the parts . wipe it on with one clean soft cotton rag and before it drys wipe it off with another clean dry cotton rag . if it drys at all in the prat rewipe the part so that you know for a fact it's clean .
then tack the part off to remove any dust . only use a low tack type tack rag for this . most anti static tack rags are of low tack type .
if you do not use a low tack type tack rag the pine tar in the tack rags will give you fish eyes .
the reason why you have to go so nuts on cleaning the parts is unlike a substraight like paint and primers that will be a little forgiving because the things like oils from your skin can soak into them some what bare metals will not soak up any thing it just sits on top . also even if your hands are totaly oil free a finger print may show up when you clear that you could not see when the part is in bare metal .

the run of the mill type automotive clears will not work at all on bare metals !
you could get lucky and get them to last for a year or two but it's only luck they last even that long .

Thanks for the in depth answer. Wasn't sure about the bonding strength of the 2 part urethane clearcoats. Sound like i have some more work to do cleaning and getting the right clearcoat. Very helpful.

Zoops also makes a clear coat specifically for metals. I've gotten great results on polishes aluminum, so you might call them and see if it will also work on Mg.

magnesium is sooo porous. We tried polishing a fan, cleaning it with solvent, then getting it immediately clear powder coated. Looks great for a few months then spotty oxidation started under the coat.
It ended up looking mottled shiny and spotty. When you color powder coat fans, then you have to shave the anticipated thickness of the coating on the 11 blade fan blade edges. Think the fan ring and the fan coating thicknesses together when grinding or filing. Don't go too far as then your will get air spillage

I appreciate all the replies. Considering all of the negative experience with clear, I decided to just polish the fan. The housing inside surface is black paint. I figure i'll polish as needed and repaint the black every few years.

for many reasons i'm not a big fan of powder coating .
it has it's usages but most people tend to over powder coat things . if it's not use much at all by the auto makers then for what reasons do people want to use it in every thing they can think of on there cars ?

the reason why it wants to still oxidize is that powder coating is not chromated .
i would also bet the oxidation your seeing is the person was handing the parts with there bare hands .


i have cleared many magnesium parts along with god knows how many rims over the years with out any trouble at all . the only thing you have to do is keep your bare hands off the parts and clean them good .

Por 15 makes a clear coating for metal surfaces i have been waiting to try on something. Says its even for finished surfaces

GLISTEN PC-POR-15 Inc.