# galvanized steel primer



## philcav7 (Sep 12, 2013)

i got a request to bid on cleaning up and recoating some existing galvanized structures. I haven't been to the site yet to determine the condition or the scope of the work, but am trying to get some feedback on what dtm has worked well for you in the past. 

Thank in advance for sharing you feedback.


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## MIZZOU (Nov 18, 2012)

Both BM and SW DTM's have worked well for us. We use both with no real preference.


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## Paradigmzz (May 5, 2010)

Wash primer


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## JKingAround (Jun 18, 2012)

Recoating as in there is a coating that already exists on the galvanizing?


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## philcav7 (Sep 12, 2013)

The walk through is tomorrow so I will have a better understanding of the equipment and existing finish. I'm not sure if there is existing paint or not, but there is a bituminous coating that will need to be removed. 


I will get some pics tomorrow if you care to see them.


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## mustangmike3789 (Jun 11, 2011)

philcav7 said:


> The walk through is tomorrow so I will have a better understanding of the equipment and existing finish. I'm not sure if there is existing paint or not, but there is a bituminous coating that will need to be removed.
> 
> 
> I will get some pics tomorrow if you care to see them.


Have fun removing that. I can give a little advice when you find more info as to the scope of work and what type of structures will be coated. Not much too go on right now.


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## philcav7 (Sep 12, 2013)

I did the walk through this morning. Its a secondary tank for a sewage treatment system. It was last painted with a bituminous epoxy back in 1991. As you can see, the galvanized surface is essentially gone and is thoroughly rusted.

The interior walls of the tank are not going to be refinished at this time. They only want the top 16-18" refinished. The upper portion on the interior is heavily rusted, scaled, and beginning to deteriorate.

There are no coatings specified for the job. I would have thought an epoxy would have been spec'd for a tank, but they simply stated "minimum 1 coat of good quality galvanized primer, min 2 coats of good quality DTM paint". 


Any comments are welcomed. Thanks gentleman


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## Toolnut (Nov 23, 2012)

Don't know if applicable for this or not but there is a product called POR (Paint Over Rust) when we were doing hot rods we would use it on car frames and such. Not cheap though. When I was Maintenance Super. we used it on some wrought iron railings that had rust issues. They were pretty ornate and sanding would have been a b$%ch. The finish was great, might be something to look into.


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## MIZZOU (Nov 18, 2012)

Mustang mike can probably give you much better advice with industrial coatings. If it was me and they requested a DTM I would do the following...

CLEAN CLEAN CLEAN that rust. If you don't prep hardcore they may give you a call back in a year or two. I would use an angle grinder with a heavy wire wheel. Then I would use a rust converter, followed by a good rust primer, followed by 2 coats of DTM.


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## Steve Richards (Dec 31, 2010)

philcav7 said:


> Its a secondary tank for a sewage treatment system. It was last painted with a bituminous epoxy back in 1991.
> Any comments are welcomed.


Wear gloves

Some of that brown might not be rust


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## mustangmike3789 (Jun 11, 2011)

philcav7 said:


> i did the walk through this morning. Its a secondary tank for a sewage treatment system. It was last painted with a bituminous epoxy back in 1991. As you can see, the galvanized surface is essentially gone and is thoroughly rusted.
> 
> The interior walls of the tank are not going to be refinished at this time. They only want the top 16-18" refinished. The upper portion on the interior is heavily rusted, scaled, and beginning to deteriorate.
> 
> ...


when you say that the inside will not be painted, i take that only the outside area exposed to the ground and the frames around the cat walk will be painted only.
I would not recommed that you allow any rust or rust convertors be allowed on the surface. Rust convertors can change existing rust into a "paintable" surface but it has not been proven to prevent future rusting. Rust can be loose and it is pourous, which can allow it to hold contaminates that may affect the life of the coating. Complete removal of rust is always the best option.
For your primer, i will talk about sherwin williams products because they are more familiar and more accessible to most people. Zinc clad ii would probably one of the better options but it does require that the surface be prepared by abrassive blasting. Inorganic zinc needs to have a sharp/rough surface profile between 2-3 mils for the best adhesion. This would be difficult to achieve with power tools. Zinc also has a high slip resistance and pencil hardness for those areas around the cat walks that could be damaged by the metal grates.
Another option for primer would be epoxy mastic aluminum ii. This can be applied by brush, roller or sprayer and is easy to work with. Surface prep can be done with hand or power tools.
Before any blasting or hand/power tooling, the surface should be washed and solvent cleaned to remove grease and oils. As you can see in the first picture, upper right corner, the paint is failing at the sharp edges and corners. This is why stripe coating is recommended when painting steel to achieve extra mils for protection in these areas. If you do power tool, it would be a good time to ease those sharp corners to a 1/16"-1/8" radius.
Both of these products can be top coated with the dtm acrylic paint.


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## Jmayspaint (Mar 26, 2013)

Mustangmike, what would you think about Ken Kromik for that application?


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## philcav7 (Sep 12, 2013)

On the top 18" of the inside will be coated. The tank is about 10' deep. 

I have my acct with SW and waiting to hear back from the rep. I also have a call out to a distriibuter that deals with pittsburg and corando to see what they have to offer. 


Thanks again gentlemen.


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## mustangmike3789 (Jun 11, 2011)

jmayspaint said:


> mustangmike, what would you think about ken kromik for that application?


i have never used it so i cant give an opinion. It seems to be the standard shop red shop primer that is simular to the stuff in the rattle cans. I do see steel shipments come into the shop sometimes with it applied as a temporary coat to prevent rusting during shipment but it gets blasted off before any coatings are applied. I always look at the performance characteristics on the data sheets to get an assessment of the paint quality. Adhesion, impact and salt fog resistance is a good starting point. Salt fog is tested by scratching an "x" through the paint down to metal, then tested in a real or simulated salt enviroment for so many hours to see the corrosion rate and resistance.
I think that zinc rich coatings are about as good as it gets behind metallizing (thermal spray)of course.


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## mustangmike3789 (Jun 11, 2011)

mizzou said:


> mustang mike can probably give you much better advice with industrial coatings. If it was me and they requested a dtm i would do the following...
> 
> Clean clean clean that rust. If you don't prep hardcore they may give you a call back in a year or two. I would use an angle grinder with a heavy wire wheel. then i would use a rust converter, followed by a good rust primer, followed by 2 coats of dtm.


im not going to beat up on you here but i can give a little more expaination on why this wouldnt be a good system to practice.
Rust convertors are normaly a blend of tanic acid, phosphoric acid and sometimes citric acid mixed with an acrylic resin. They do convert rust to a "paintable" surface if it is tightly adhered and may stop corrosion for light applications by acting as a barrier coat but they offer very little protection beyond that.
Most paints are named by their generic type resins such as acrylic, alkyd or coal tar. Others are named by the pigments used such as zinc, lead and aluminum.
In the case of rust inhibitor paints like zinc coatings, the metal pigments in the paint need to be in direct contact with the metal surface for them to do their job as an anode. If you have a coat such as an acrylic rust convertor acting as a barrier, the zinc pigment will not be very effective and the hot solvents in zinc paints can eat the underlying acrylic and cause poor adhesion.
Im not saying that rust convertors cant be used or effective in some cases such as light duty applications followed with a good top coat. For long term protection, it is best to completely remove any rust. Even direct to rust paints will recommend that you remove as much rust as possible.


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## Steve Richards (Dec 31, 2010)

mustangmike3789 said:


> For long term protection, it is best to completely remove any rust.


 Even Neil Young knows that (because it never sleeps). Quite profound IMO.


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