Rust bleeding through primer?

[drsportster]

You must mechanically remove all underlying rust first then prime {which holds moisture ]

 

[showcrop]

You must mechanically remove all underlying rust first then prime {which holds moisture ]

Are you meaning that primer holds moisture under it on the metal?

 

[drsportster]

More like it absorbs moisture

 

[Stephen Newell]

Primer is very porous. In very humid weather water can go right through the primer and start the metal from rusting. This is what sets epoxy primer apart, it won't allow water through.

 

[da.bees]

Epoxies work very well if one is up to the task of doing it properly. I'm old and usually not up to the task on large projects which require hours non-stop work or lots of solvent and cleanup when done over a period of time like after work.
My mo is sand,scrap,wash small section as needed then wipe with rust converter and apply aluminum paint to protect until I can get back to it. After a month when everything is in aluminum and ready for paint I apply primer/sealer on entire project. If there's sheet metal I want looking good, I apply sanding primer followed by guide coat. From there I spot spackle,spot prime and sand until ready for topcoat.

If you think that's hillbilly,you sure won't like this. When I have occasion to use rust converter I might walk around with converter and brush hitting spots on various things then follow with aluminum paint. On a nice day I will go back with matching paint,washing brush between color changes. The idea behind dabbing different colors on a sigle day apposed to doing each color on different days is to save cleaning solvent. When granny hand washed clothes she had a b & c rinse tubs. When a becomes loaded with soap it's used to wash next batch, b moves to a, c moves to b and c gets clean tub of water. In many cases a is actually gasoline for brush washing.

Now that you think I'm a slob, I have brushes older than some of you guys but those have never been washed in gasoline. Although not as old as some my brushes, my HVLP is 35 years old and still works great. It's hard to spend what good brushes cost until you've had one in your hand and seen the difference it makes. I'll always remember the day I was converted. We hired a painter through the local union to come out and amongst other things, paint a sign on side of building. I noticed him using 3 and 4 inch brushes cutting in without any tape. Following a sip from his Wild Turkey and 15 minutes instructions I was hooked and bought nice brushes shortly after. I've since worked around painters that drank enough in a day to float a jon boat but they never fail to meticulously clean their machines and tools before quitting for the day.

 

[showcrop]

Epoxies work very well if one is up to the task of doing it properly. I'm old and usually not up to the task on large projects which require hours non-stop work or lots of solvent and cleanup when done over a period of time like after work.
My mo is sand,scrap,wash small section as needed then wipe with rust converter and apply aluminum paint to protect until I can get back to it. After a month when everything is in aluminum and ready for paint I apply primer/sealer on entire project. If there's sheet metal I want looking good, I apply sanding primer followed by guide coat. From there I spot spackle,spot prime and sand until ready for topcoat.

If you think that's hillbilly,you sure won't like this. When I have occasion to use rust converter I might walk around with converter and brush hitting spots on various things then follow with aluminum paint. On a nice day I will go back with matching paint,washing brush between color changes. The idea behind dabbing different colors on a sigle day apposed to doing each color on different days is to save cleaning solvent. When granny hand washed clothes she had a b & c rinse tubs. When a becomes loaded with soap it's used to wash next batch, b moves to a, c moves to b and c gets clean tub of water. In many cases a is actually gasoline for brush washing.

Now that you think I'm a slob, I have brushes older than some of you guys but those have never been washed in gasoline. Although not as old as some my brushes, my HVLP is 35 years old and still works great. It's hard to spend what good brushes cost until you've had one in your hand and seen the difference it makes. I'll always remember the day I was converted. We hired a painter through the local union to come out and amongst other things, paint a sign on side of building. I noticed him using 3 and 4 inch brushes cutting in without any tape. Following a sip from his Wild Turkey and 15 minutes instructions I was hooked and bought nice brushes shortly after. I've since worked around painters that drank enough in a day to float a jon boat but they never fail to meticulously clean their machines and tools before quitting for the day.

I am 76 years old and for the most part see where you are coming from in your statements. I have to question however about the aluminum paint. I can't see how something that rubs off so easily under your finger can provide an adhesion base for the primer or sealer ot top coat over it. Your grandmother's washing procedure is actually the same concept as how water flow works in the largest industrial laundry washing machines. They are called tunnel machines. Fabrics are moved slowly upgrade by an auger through a thirty-sixty foot long tube, while fresh water is introduced at the rinse end, and slowly flows downgrade to the entrance end. Chemicals and steam are added as needed along the way.