Is a hardner & primer necessary

[terrysandlin]

I am painting over previous paint on my aluminum boat. Is it necessary to add hardner to the paint (Rust Oleum Paint or Majic Paint from Tractor Supply)? I will be painting over a paint that feels like a 800 grit or finer sandpaper. I am not interested in restoring the boat to its original finish. I am thinking this 14 1/2 ft fishing boat does not need to be sanded for aesthetic purposes. Also, do I need to use a primer over the existing paint?

Thanks for all the help I have been given,

Terry

 

[gm280]

Re: Is a hardner & primer necessary

WOW those are loaded questions for sure. Sanding anything before painting is not solely to get the surface nice and smooth. It also prepares the surface so the new paint will adhere to it. So personally I'd sand it for that reason. Your new paint will only be as good as the old paint was applied. As far as priming, again just me, but primer after sanding makes your top coat easier to apply. There would be no color bleed through with your top coat if you prime. Sometimes you end up using more top color coat when you are trying to high a previous color. So priming can be more cost effective. But they are tons of folks that would just wash the old paint and spray the new paint and have zero issues. I just am not one of them. I like to do a project to last so I don't have to do it again anytime soon... I'm sure others have differing opinions then mine though... :decision:

 

[brnschoneck]

Re: Is a hardner & primer necessary

Yes yes yes u wanna use hadener it will last longer and give u a better shine ...

 

[jbcurt00]

Re: Is a hardner & primer necessary

The hardener will make a tougher finish, have more shine & dry quicker then the same paint applied w/ out it. The hardener REQUIRES a better respirator (someone recently posted that a full face fresh air system is required and full protective gear for the rest of you) to protect you from the isocynates in the hardener.

Primer also acts as an adhesion promoter too. If you're painting an aluminum boat, you'll want to spray a very light coat of Zinc Chromate (ZC) or Self-Etching (SE) primer on any BARE aluminum. Then paint the entire hull w/ primer, this will help prevent the bare aluminum spots from telegraphing thru the top coat & requiring additional top coats.


prep prep prep is key to durability & long term wear of paint, in addition to the look of the finish top coat.

 

[laurentide]

Re: Is a hardner & primer necessary

The hardener will make a tougher finish, have more shine & dry quicker then the same paint applied w/ out it. The hardener REQUIRES a better respirator (someone recently posted that a full face fresh air system is required and full protective gear for the rest of you) to protect you from the isocynates in the hardener.

Primer also acts as an adhesion promoter too. If you're painting an aluminum boat, you'll want to spray a very light coat of Zinc Chromate (ZC) or Self-Etching (SE) primer on any BARE aluminum. Then paint the entire hull w/ primer, this will help prevent the bare aluminum spots from telegraphing thru the top coat & requiring additional top coats.


prep prep prep is key to durability & long term wear of paint, in addition to the look of the finish top coat.

JB, that was me talking about the hardener toxins. It was just a personal choice for me...I'm not saying "don't use it." But I know for a fact that multiple exposures to the isocyanate fumes can essentially make you allergic to those fumes and cause your bronchial airways to constrict.

I'm sure the stuff works great, and I'm even working outside, but I've already done enough damage to my body over the years (I worked in a boat yard as a teenager back when the really nasty bottom paints were still legal, smoked, past tense, for almost 20 years), so I'm just being conservative these days. It probably ain't a big deal.

 

[jbcurt00]

Re: Is a hardner & primer necessary

I knew it was your thread, but it is a big deal. Anyone considering use of the hardener needs to use the correct PPE. It's not the same as using Rusto & an HVLP and wearing a dust mask indoors or out.

Just like grinding fiberglass, you need to protect yourself while working on your project.

 

[laurentide]

Re: Is a hardner & primer necessary

Yep, no argument there ^^^ It's nasty stuff.

...and, while we're on the subject and it's relevant to this particular thread, I'll post the message board thread that got me thinking about pros and cons of the hardener, as well as some pretty awesome low-tech rustoleum brush painting advice. http://www.practicalmachinist.com/vb/antique-machinery-history/repainting-brush-247106/

This was particularly interesting to me:

I was told this technique to paint machinery when you don't have access to spray painting equipment.

What you do is get the machine clean and smooth by any technique you like.

You put the first coat on with a brush being careful to not get any sags or runs, you then wait for the paint to dry enough that when you touch it with you finger you don't get any paint on your fingers but the paint is still wet enough that you will leave fingerprints in the paint. You then put the second coat on again carefully so as not to get any runs or sags then let dry.
The way it was explained to me was the first coat dry's enough to bite to the casting. Then when you put the second coat on the first coat sucks the solvent out of the second coat and it pulls out the brush marks to make a smooth finish that can almost pass for a spray job. I have done this to a couple piece of machinery and was very pleased with the results.

Eh, I don't know. These guys have had good results painting metal this way.