- - > Road Rash < - - Marine Grade

[Johnny]

the header is just to get your attention.

I have worked with many different types of metals for a good many years.
And, just recently learned something I did not know about aluminum and corrosion.
DaleH sort of discussed it in his adventure of manufacturing a new transom skin for his project.

The recent article I just wrote has been modified in paragraph #2 as to metalwork
preparation prior to priming and painting.

Aluminum Corrosion can be described as Road Rash . . . .
Think of it like this . . . . a person takes a hard tumble onto a dirt road.
Small bits of sand, gravel and dirt are embedded in the wound. (road rash).
Instead of having it surgically cleaned and the foreign stuff removed,
you apply some Neosporin, bandage over it and let it heal.
Only for it to become infected later on down the road with a more serious infection
that could be life threatening or the loss of a limb.
LOL not quite that drastic, but you get the point.

This is the same with aluminum corrosion. If the corrosion is not removed or 100% arrested,
when you go hammering on it to smooth out dents, dings and flatten out old rivet holes, etc,
what you are actually doing is forcing the corrosion fungus into the pores of the metal and
sealing it up. Then, with your wire brushing, acid washes and etching primer, the corrosion fungus
is still alive buried inside the metal - only to resurface later and create paint adhesion issues
as well as possible metal deterioration.

Read the article at https://www.tinboats.net/primer-and-paint-basics/ paragraph #2.
This is just my own "informed" opinion from information that I have gathered from reliable sources
on the World Wide Web.
You may agree or disagree...... all comments are welcome !!


.

 

[Skiffing]

Yup

See also: Mill Scale

Which also leads to crevice corrosion.

 

[DaleH]

Also explains why aluminum or SS propellers shouldn't be filed with a metal file to fix nicks. In this case the inclusions inhibit subsequent welding. I recommend the use of metal 'crocus cloth' on hardwood backers to smooth out nicks in propellers.

 

[sonny.barile]

Chromate conversion coating!!!! Alodine or Irridite. Protects aluminum from corrosion.

Anodizing also does, but it is expensive to do one part.

 

[PSG-1]

Unlike steel, aluminum is what I would consider to be a 'grainy' metal. No matter how nice the weld may appear, magnified cross sections of aluminum welds often look like a sponge. You can also see this where an aluminum weld breaks. Because it's like a sponge, this makes it far more susceptible to corrosion, especially from impurities such as dirt. After all, it begins life as dirt (bauxite) Due to these properties, it is a difficult material to weld if there is any kind of corrosion, as opposed to steel, where you can literally weld rust with a 6011 rod.