Looking for paint recommendations for ACM / ACP

Looking to see what others have had success with for painting ACM panels. I have access to most quality paint brands and decent facilities (we don't have a spray booth, but have access to one). Looking for advice on a few facets of this:
1) Substrate (brand, factory coating...)
2) Paints used with success for longterm outdoor signage
3) Application method used (airless prayer, auto gun, roll, brush....)
4) Key tools (tip size, pressure, roller covers...)

Thanks in advance for the advice!
 

Jean Shimp

Member
Scuff surface lightly with scotch brite type pad; clean; roll or spray latex acrylic house paint or DTM (direct to metal) paint. Been doing this for over 10 years and it works well.
 

Keep Austin Lit

New Member
Scuff surface lightly with scotch brite type pad; clean; roll or spray latex acrylic house paint or DTM (direct to metal) paint. Been doing this for over 10 years and it works well.

Do either spray latex acrylic house paint, DTM (direct to metal) paint, or auto paint/acrylic poly help make this scratch resistant? I have been in the business close to two years now. The owner would like for me to learn how to paint ACM. I am scuffing entire area with 320 grit. Applying an Rustoleum enamel primer, then top coat with an enamel paint, and applying a clear coat. But, after letting it cure for 48 hrs., I will still able to make light scratches with a fingernail. ANy ideas on how to make it somewhat scratch resistant? Thanks.
 
An update on what I have experimented with so far:

Based on a recommendation I tried some sherwin-williams "extreme bond primer" top coated with their "all surface enamel" in high gloss, I used the latex version but they also have an oil based option of the same paint. I couldn't get an acceptable (to me) finish with any combination of roller or brush and even tried adding floetrol. I ended up buying an airless sprayer (graco truecoat) and that worked very well, smooth finish and pretty decent gloss. The end result was moderately scratch resistant, but I would prefer even better. I am planning to try some SW professional/industrial products in the future to compare, for example they have a "pre-catalized" single component acrylic urethane" I would like to try.
 

signbrad

Member
An update on what I have experimented with so far:

Based on a recommendation I tried some sherwin-williams "extreme bond primer" top coated with their "all surface enamel" in high gloss, I used the latex version but they also have an oil based option of the same paint. I couldn't get an acceptable (to me) finish with any combination of roller or brush and even tried adding floetrol. I ended up buying an airless sprayer (graco truecoat) and that worked very well, smooth finish and pretty decent gloss. The end result was moderately scratch resistant, but I would prefer even better. I am planning to try some SW professional/industrial products in the future to compare, for example they have a "pre-catalized" single component acrylic urethane" I would like to try.

Normally a primer is unnecessary on a pre-painted service if you are using a solvent-based finish.
Thorough sanding is necessary. 360-grit might be a little coarse. Certainly that is the coarsest you would want. I prefer 400-grit on a dual action sander. You can get an electric DA if you don't own a compressor. I also frequently spray-glue a red Scotchbrite pad onto a DA (put a sanding disk on first and glue to that).

Any polyurethane is going to have superior abrasion resistance, as well as superior resistance to moisture penetration. Most polyurethanes and urethanes require a catalyst, and this is what gives them their high durability. They are essentially car paints, and the cross-linking at the molecular level yields a very hard surface. Sherwin-Williams makes a good polyurethane called Polane, sold as a "fleet" paint. Imron is a polyurethane by Dupont with a good reputation. These paints are typically applied with a compressor-driven HVLP spray gun, though an airless could work. They don't brush or roll well. Matthews offers an extensive polyurethane system with tons of tech support and unlimited color matching capabilities. Of course, in most polyurethanes, the catalyst is generally a cyanide compound, so a respirator is essential.
I am not familiar with the "pre-catalyzed" urethane you mentioned.

Brad in Kansas City
 

Notarealsignguy

Active Member
As Brad said a red scotch brite pad is fine and skip the primer. When you hand sand, you usually end up seeing scratches through the paint and a da will help with that. The air dry alkyds, like rust-oleum, take a long time to fully dry and really don't have good gloss retention. IMO the only way to go is with a 2k polyurethane. We use low end polys that are $60 per gallon kit as well as higher end like imron elite. A DTM is pretty dumb to use on a pre-finished panel too, you're painting over a coating, not bare metal.
Another one that can be rolled and tipped to look like it was sprayed is awlgrip. It's real good paint but a little pricey.
 

visual800

Member
prepainted surfaces gets scuffed and then a light 2 part epoxy primer (for nothing more than adhesion of topcoat.) I lay down light coat of BEHR exterior satin latex, let it sit up about 15 minuted and then another coat and then a finish coat. i do not touch it for 3-4 days depending on weather. I use a cheap harbor freight purple gun, it works fine. Sometimes I do roll the latex with foam rollers making sure I backroll in the same direction to prevent roll marks
 
I agree that a 2k poly (acrylic polyurethane for those learning) is by far the best, I personally prefer Mathews, but it is often over complicated and cost prohibitive for some projects. This is especially true for shops that outsource painting. As stated in the original post I wanted to explore "easy entry" methods for painting custom color backer panels and similar that will look good and hold up well.

A quick note on the primer: I agree it's not needed, especially on a factory painted substrate, BUT I was curious so I did a sample test and the results were this: the primed panel and topcoat had almost twice (very subjective) the scratch resistance as the topcoat alone. Both test pieces were prepped with scotchbright. From these results I went ahead and primed before topcoating.

The end goal of this is to find something easy to get (walk in and get a custom color same day), easy to spray/brush/roll and cleanup, and that has a good look and durability. Thanks guys for your feedback and input!

Products I have on my list to research and try:
1. https://www.sherwin-williams.com/pa...o-industrial-precatalyzed-waterbased-urethane
Water based single component acrylic poly, very intriguing, longish cure time due to the lack of catalyst.

2.https://www.concopaints.com/product...ength_maintenance/industrial_strength_enamels
8000 Acrylic high gloss

Anything else I should look into?
 

Notarealsignguy

Active Member
I don't like acrylic or synthetic (alkyd) enamels. No fan of waterborne or DTMs either. Our goto paint is BLP Mobile in polyprothane for basic white/black/gray and mothane for the colors that the sun tears up like reds and yellows. You can't beat the quality for the price. For a step up we use nason 2k urethane and every now and then Imron if we get asked for it. Ppg has omni which is equal to nason 2k and they also have AUE-300 which costs less and sprays nice. SW industrial has high solids polyurethane which is not crazy expensive but I never liked it. My vote is for mothane if you can find it. We spray about 30 gals a week of that and polyprothane but use nason reducer in it as it seems to give better results than their mothane branded reducer
 

signbrad

Member
I did a sample test and the results were this: the primed panel and topcoat had almost twice (very subjective) the scratch resistance as the topcoat alone. Both test pieces were prepped with scotchbright. From these results I went ahead and primed before topcoating.

Film thickness
Consider the possibility that you got twice the scratch resistance because you had twice the film thickness.
Achieving a minimum dry film thickness is essential for optimum durability and hardness. With Matthews, for example, a single heavy pass is not enough. You need two wet coats with a flash in between to get the recommended dry film thickness.

When I paint factory coated aluminum with Matthews I don't count the factory coat as the "first pass." I still use the double wet coat method, essentially two coats, to achieve film thickness. However, I skip the Matthews primer.
I first discovered how film thickness affected hardness many years ago when sign shops in my area used Kem Lustral Gloss White as the finish coat of choice. Kem Lustral was a slow-drying "long oil" that had a high gloss and excellent hiding power. The standard operating procedure was to roller coat MDO board with a coat of blocking out white, which dried quickly, then finish coat with Kem Lustral. All my coating out was outside in my yard at that time, so if a panel got messed up by some dust or bugs, I sanded and applied a second finish coat. I was always amazed at how much harder the surface seemed after the additional topcoat, not to mention the increased gloss.

Comparing a primer plus a single topcoat versus a single topcoat by itself may not be a true 'apples to apples' comparison. Especially if all coats are relatively fresh and soft. The topcoat by itself may have seemed inferior because it was just too thin. Also, the hardness of some of the factory finishes can be a factor and may explain the better performance of a high bond primer applied between the factory coat and the topcoat. Of course, both of these things, the added film thickness and the hardness of the factory finish, are arguments for a high bond primer.

PVDF factory coatings
I believe that scuffing with a Scotchbrite is not always adequate prepping for coil-coated aluminum. Years ago it was common for a factory finish to be a cheaper polyester paint. You could wipe it down with lacquer thinner as a prep, which made it sticky to the touch, and a topcoat seemed to bond like crazy. More and more, though, the paint used on factory painted aluminum is Polyvinylidene Fluoride (PVDF). These coatings are extremely hard and require a thorough sanding for a top coat to achieve a good bond. The paint is so hard that metal painted with PVDF can be formed by machinery after painting without damage to the paint film. It's the coating of choice for the metal roof industry. That's why my prep method of choice is 400-grit on a DA sander, so as to thoroughly and evenly cut the gloss. I sand till it's dead flat.

Brad in Kansas City
 

signbrad

Member
. A DTM is pretty dumb to use on a pre-finished panel too, you're painting over a coating, not bare metal

It's possible that the DTM series is just a marketing ploy for a self-priming paint. Self-priming paints have actually been around for a long time. Even so, I would not use DTM on raw aluminum without an etching primer first. What DTM is good for, in my opinion, is painting sign poles, where long life and perfect finish is not required. In the field, it eliminates two trips (one for spot priming).
 

visual800

Member
Products I have on my list to research and try: 1. [URL said:
https://www.sherwin-williams.com/pa...o-industrial-precatalyzed-waterbased-urethane[/URL]
Water based single component acrylic poly, very intriguing, longish cure time due to the lack of catalyst.

2.https://www.concopaints.com/product...ength_maintenance/industrial_strength_enamels
8000 Acrylic high gloss

Anything else I should look into?


if you want try new stuff I think thats cool but do keep in mind high gloss on signage is really distracting
 
Thanks for the info Brad! I enjoy learning from others experience when they are willing to share. I do not have a film gauge yet but plan to get one as I continue experimenting. I forgot to mention that the topcoat for my test was done as two passes per the PDS recommendation (assuming I estimated the thickness correctly).
 

Jean Shimp

Member
We get yearly visits from the local fire marshal. They are very strict about what kind of paints you can spray if you do not have a spray booth that complies with the fire code requirements. For a small company like ours, this type of booth is cost prohibitive. We have experimented with different types of water based paints. (BTW, DTM paint is not restricted to painting bare metal, so it is NOT a dumb idea to use it on different surfaces). Keep in mind that latex paints can take up to 30 days to cure. Also, not all ACM's have the same type of finish. Some are baked enamel, some are polyester. As I mentioned before, we have been using water based paints for 20+ years with excellent results. They are much healthier to use too.
 
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