Question Painting Aluminum Sign Blanks with Matthews

[armandolo]

Hi everyone,

Im trying to Paint Aluminum Sign Blanks with Matthews. I dont know if priming is necessary or not. I cant find the infor on Matthews website or by calling them. They have a great material prep guide but it does not cover aluminum sign blanks which are painted. It only covers raw aluminum

Im wondering if anyone painted this stuff before and what is the outcome or even if it will fail long term without a primer.

 

[signbrad]

armandolo,

If the blanks are new you should not need to prime them, although Matthews recommends doing so. I just sand and wipe with a tack cloth. I use 360 or 400 grit paper on a DA sander. You can also stick a red Scotchbrite pad on a DA, but I prefer the more aggressive use of sandpaper.
Of course, there is always a chance that a prepainted blank will have a finish that will not accept Matthews paint, but I have never seen this happen.

If the paint is old and badly oxidized or scratched or chipped, you will need to sand as much of the old off as is practical. You will probably end up with a multi-colored-looking surface, including sand-throughs to the bare aluminum. Matthews recommends priming this with their Epoxy Primer. There should be a listing for prepping prepainted surfaces in your substrate prep guide.
Here's the guide online. Page 16 has pre-painted surfaces.
Matthews Paint Substrate Preparation Guide

The epoxy comes in black and white, which I like to mix to make a gray. The gray seems to cover well (the white does not always). And then any top color should cover the gray well. I usually wait an hour or longer before top coating the epoxy, but if you wait longer than 24 hours you will need to sand it. It just gets too hard when it fully cures.

Under no circumstances should you use Matthews' acid wash primers (PT Filler and HBPT) on prepainted metal. It will not adhere. These primers are for raw aluminum and steel only.

Here is a link to the epoxy primers:
Black & White Epoxy Primers 274 808SP / 274 908SP

Brad in Kansas City

 

[armandolo]

Thank You Brad. Yes I'll be using new Aluminum sheets (pre painted 080 kind). They are for monuments and I don't want the paint to fail say in couple of years. We will sand it with 400 grit but Sounds like priming also may be a good idea.

i also thought Mathews also has a gray primer?

 

[signbrad]

Matthews has a Polyester Primer/Surfacer that is gray. It was developed for use on HDU foam primarily and that is the only thing I use it for. It smells exactly like Bondo autobody filler.

 

[spectrum maine]

12

 

[spectrum maine]

raw aluminum should be sanded & a matthews acid etch product like hb-ef. keep surface from drying 100% between coats. the acid etches the surface & works better if wetness is maintained between coats of primer. pre finished aluminum just scotchbrite & paint, no primer.

 

[signbrad]

the acid etches the surface & works better if wetness is maintained between coats of primer

This is a good point. Once the acid etch primers are dry they are no longer etching. So put the second coat before the first coat has dried. This extends the etching action.

Also, DO NOT force-dry the acid etch primers. They are engineered to stay wet long enough to get a good etch. If you force-dry them they don't stay wet long enough.
In fact, I turn the paint booth exhaust fan off while these primers are drying to give them their best chance at bonding.

One other point. Once you have activated these primers by adding the acid, they have a shortened shelf life. For example, PT Filler is only good for a week after activating. After that it won't etch properly.