View Full Version : Hardner on last coat only

03-21-2007, 08:47 AM
Am ready to prime and paint farm tractor with acrylic enamel. I'm thinking of using hardner in final coat only. Will this bo ok or should I use it in all coats...Thank You...Ben

03-21-2007, 09:12 AM
If you're using hardener in a single stage paint then it should be added to all of the coats. Some base coat/clear coat products the hardener is only added to the clear but for acrylic enamel coatings you'll want hardener in ALL of the paint.

Dennis N. Schmidt
03-21-2007, 03:52 PM
Why would you ever not want hardener in all coats? Spraying AE without hardener is just dumb.

03-21-2007, 06:07 PM
Len thank you for the help. Dennis I didnt know as I'm new to painting, thats why I came here for the info. Now that I know I will be using hardner in all coats...Thank you...Ben

03-21-2007, 06:26 PM
You would either want to use hardener in all coats, or, not use hardener in any coats.

Enamel, if left to dry on it's own, w/out the addition of a hardener, takes a much longer time to reach full cure and hardness, because there is not catalyst added to speed the reaction...you are basically relying on solvent evaporation and that's it (so a longer cure, and a weaker finish).

On the other hand, when you add a hardener, you are introducing something into the mix that will chemically cross-link w/ the resin, accelerate the cure, improve the hardness, and thus improve hold-out, guard against fading, and make for an all around more durable finish.

The question is valid, since there is often more than one way to mix up and spray a batch of enamel...in fact, w/ DuPont's Centari acrylic enamel, there were at one point 4 different ways to mix it up (combining the paint, solvent, and w/ or w/out varying degrees of hardeners/gloss additives, etc.).

Consider it like this...you could spray a can of off the shelf aerosal spray can "enamel"...there is no hardener in that, it basically has the solvents evaporate and that's it...it works, it's just there are ways to make for a more durable finish, and that's to add hardener (plus the fact that an automotive paint technology, in enamel, is a step up from the spray can to start w/).

If you were to add hardener to the final coat, what in fact would happen, is that the hardener accelerates the cure on that final coat, in effect trapping the solvents from the previous coats and preventing them from flashing off (evaporating)...so you'd end up w/ a durable outer layer over a soften "uncured" under layer...and from that, any host of undesirable things could happen. If you sprayed all layers w/out hardener, they'd eventually harden up but it would take much longer and be less durable. The hardener, making the finish "harder" also lets you not only get to the stage of "cutting and buffing" for colorsanding, but also makes that effort hold up better in the long run.

03-22-2007, 09:35 AM

you reminded me with funny story...I hope you could understand it..

anyway... one old fisher man built a wooden fishing boat...18 feet long
and he asked me to apply a fibre glass on his boat... and i were 18 years
old at that time... but...know how to deal with the fibre glass materials

I asked for usd 300.00 but the fisherman got very angry...he said
how dare you ask for this amount you are to young....

the man went to the fibre glass company and bought all the required
material but ... attention he forgot to buy the hardner:confused:

he reached home and applied the fibre glass materials mat 450 and resine
but did not add any hardner to the resin..??...

next day he found that the material is still wet.. and after one week is the
same... he came back to me.. and knoked my home door...
the man.. is really tired and disappointed... i aked him.. what up my dad

he said... the material is still wet... i said maybe the hardner is too old
or you did not add enough hardner.... he answered me...which hardner
you are talking about...they provided me with resin and mat
but they did not gave me the hardner:D

I told him... you were angry when i said usd 300.00... now go and remove
all the material...pay another usd 400.00 and pay me usd 250.00 and will
do it for you...

then he sold the boat.. same day.....

03-23-2007, 02:25 PM
I had a truck about a year ago that I had done the body work on and had someone paint it for me with acrylic enamel. I believe hardner was used, and 3 coats were sprayed. When I sold it about a year later, the paint was still soft underneath when it sat out in the hot sun.

03-23-2007, 06:10 PM
I had a friend have me paint his truck years ago with acrylic enamel with the wet look hardner. We did it at another friends garage who had recently painted his own car with the same materials.

The large plastic cap on those were a measuring cup for the hardner. When I started mixing the second friend who owned the garage was astonished. When the directions said to use a cap full for a quart, I think that was the ratio, he used the very small screw off cap per quart when he painted his car. He was really impressed at how shiny the truck came out. :D