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Anyone add hardener to primer?

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I am curious if any do this. I am using a cheap product from Ace hardware  "Ace rust stop primer"... compare to rustoleum.

I am sanding and it is clogging the paper pretty fast. Kind of annoying.

Same time I painted it about 20 hours ago, I may just need to give it a longer drying time. Or it is just cheap primer and always going to clog paper. I dunno.

Also because the body had heavy heavy surface rust, it is not perfectly smooth now .... the top of roof was the worst. Just the top I used a foam roller for a heavy first coat.

Then today I sanded most of it off, while the primer filled the low spots. This also could be why it is clogging the paper ... but is sanding nice.


Todays project is to get it all masked off, hopefully tomorrow or next day,  will spray the cab in primer. I still have holes to weld up, a few dents to fix ... I just have a lot of bare metal that needs to be covered before winter.

I have never heard of anyone mixing hardener into primer. I fully expect spraying 3 coats minimal on primer to bury all the sins, to make it a 20 footer. Will be a lot of sanding. :(

I have a universal hardener I bought from napa for the top color coat. I wonder if it would be any benefit to add to the primer? Or would it cause a problem?

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primer is a substrate that provides protect to the original surface and is to be also able to work to a level and surface for bonding your top coat..therein lies a many problem with the epoxy base as they dry so hard they are not easily worked to allow top coating.  There are a few 2K primers out there but they are readily sandable...are these the primers you are inquiring....otherwise if not 2K I do not recommending adding a catalyst.  Also the better primers are lacquer and most catalyzed paint is enamel based.  

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Yes sir that makes sense, I need to work it. Thank you for advise.

Possibly by tomorrow when has longer to dry, maybe it will not clog the sandpaper so quick. Oil base paints do take time to dry.


Been working on it for 2 years already .... no reason to get in a hurry now  :P

Edited by Los_Control
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now for the next part of your above statement...what paint have you applied as primer that is not sanding well.....I may already know the answer....odds are it is a great unsurpassed product only that you are rushing the chemical process that is the quality of the paint....the new modern primers are expensive and made as such for the in by 8 out by 5 body shops.....you are not in that environment and thus have no need to spend more money for that stuff....

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most oil based product are time involved to cure...though they can easily and rapidly set up for a surface gloss and hardness..they are still raw and 'green' below the surface....you should not rush any oil based primer.....if you need to work immediately after priming , get a lacquer base product.

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Just been too hot to do much work last 6 weeks, then family visiting and of course the motorhome fiasco ... Right now the weather is perfect, the stars are all lined up, I just want to jump all over it. Bring the project to the next level.

I will just slow it down a bit.


Other reason am pushing the roof. I have to start it up and drive it out from under the carport. Then have a plank across the bed to stand on and can easily work on it.

Then drive it back into the carport at night. Getting heavy dew in the mornings, I constantly have to go back over the bare metal to clean the fresh rust. Once the roof is done, the worst part ... I can easily work on everything else without moving it. And it stays dry under the carport. While I am rushing it, I really do not need to, I just want to.

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Oil based primers do take additional time for the solvents to evap out and the fact that you rolled it on means it's a fairly thick application which means even more time.  Give it a couple of days and I think you'll find less clogging of the paper as the primer hardens up. That doesn't mean it's going to sand any easier though,  just less clogging.   Etch primers and epoxy primers both use an activator and are usually followed up with some kind of polyester primer.  

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If you are dry sanding, try wet sanding, and put a little dish washing detergent in the water you dip the paper into.  And don't press hard - let the grit do the work.  I've had success on tractor store enamel with a  light touch and wet sand paper on paint that wasn't hard and would ball up with dry paper.

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Depends on the primer.  We used a two part epoxy primer when I was in the Navy and if you didn't put the hardener in it would never harden, eventually it'd turned into some sort of rubbery goo.


Enamel shouldn't need it, but always follow the manufacturer's instructions, especially on dry times.  I built some roll around storage cabinets for my shop and bought some enamel barn paint, said 8 hours for dry to touch and they were not kidding.  Back in the day places that painted cars with enamel had bake ovens to hasten the cure times. 



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9 hours ago, RNR1957NYer said:

If you are dry sanding, try wet sanding,

Thats a good tip and will remember it, thank you. I think today will be 45 hours dry time and results will be much better.


32 minutes ago, Sniper said:

Enamel shouldn't need it, but always follow the manufacturer's instructions, especially on dry times

Yes sir I agree 100%. It should not need it. That also falls true for enamel paint. Does not "NEED" it, but it does improve it.

@Plymouthy Adams schooled me on the top coat paint several months ago, about proper products to use. And to add hardener even though the directions do not suggest it.

At napa buying the hardener, the kid behind the counter stated, I have used this paint many times, I never added hardener! .... Hrmm, probably not a bad idea though.

I bet today he is adding hardener to it for his own use.


Back when PA was helping me with the color coat, I was planning to not use primer and paint direct to metal like the factory did. And I never asked questions about primer.

Now I realize how crappy my body working skills are, I need primer to assist me :P I need the primer soft and workable, and hardener would ... make it hard.


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4 hours ago, Dave72dt said:

Adding the hardener to those machinery enamels helps reduce color fade.  I've seen bright reds fade to a flat pink color in two years time.

Yes the reds turned pink and the blacks turned gray.

The directions do not say to add hardener, but somewhere along the way people decided it was better to add it..


I trust these peoples opinion because they have actually been there and done that. Even though the directions do not suggest to add the hardener. People just know better and do it anyways.


I guess that is why I asked the question about primer and what others like to do. Read the directions is never a bad idea, but not always a complete idea.

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I just wanted to add. I waited a few days while life got in the way. And tried sanding again and worked perfect. I needed to allow it more cure time then 18 hours.

While in the back of my mind, I was thinking about flash times and windows to apply a second coat etc ... First time paint jobs are fun. :D


You can see in photo what am using the primer for. Filling low spots. I know this photo looks bad ... I accept that. And I am moving forward.

Is rust scale ... just years of rust layers building up on top of solid metal in the West Texas sun. I have tried every way I have to remove it, I can not.

I suspect sandblast is only way, not going to happen any year soon.

The white is acid where the rust has all been treated and ready for paint. It has had ospho on it, it has phosphoric at one time and muriatic first time. Ospho you put on, let it dry and is ready to paint over.


I either move forward and paint it as is, my only goal is to make a daily driver and maybe a 20 footer, that would be fine. Haul lumber materials and groceries. Will never be for sale unless I no longer drive.


I could just park it in the sun and get the patina affect. Or I could just give up and park it out back and forget about it.


I figure 80% of paint will be fine, and the other 20% deal with it as it comes back to bite me.






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