Thread: Enamel paint curing

Hi,
I'm painting my south bend 13 with an alkyd enamel paint. I read online that if you lay the paint on too thick that it wont ever dry beneath the surface. I've also read that enamels can take years to completely cure. If that's true if you put down multiple layers of paint how do the bottom layers ever completely cure?

Did you prime it first? Did you wipe off the old paint with lacquer thinner before you painted ? I suspect there was a chemical reaction in the old paint and new. You should always prime when your not using the same type of paint.

Time and temperature affect it. Re-coating is OK but you have to wait a day or so for the first coat to set up. if its colder or wetter, the paint dries slower. If you do a second coat before the first is decently cured, the thinner in the top coat can actually loosen the under coat and the paint will slump.

I should have clarified on my first post. There isn't any problems with my paint. I was just curious how covered paint layers continue to cure once they're recoated or if they don't. So say if I painted one layer of paint, waited the 16 hours until recoat, and layed another layer down. Will the first layer stop curing once I recoat it? I got to wondering about this because I'm planning on laying bondo down after priming the whole pedestal, and I read online that paint if layed to thick wont ever dry because oxygen wont get past the dryed layer. It doesn't make any sense to me. The primer I'm using seems kinda soft after the 16 hours it calls for before recoat. So If I lay bondo on top will it remain soft and lift off in the future? Or is there something about how this paint cures that I don't understand?

The first layer will cure slower, but it won't stop curing. Curing requires oxygen, and the paint is permeable to oxygen.

Originally Posted by Dog250

I should have clarified on my first post. There isn't any problems with my paint. I was just curious how covered paint layers continue to cure once they're recoated or if they don't. So say if I painted one layer of paint, waited the 16 hours until recoat, and layed another layer down. Will the first layer stop curing once I recoat it? I got to wondering about this because I'm planning on laying bondo down after priming the whole pedestal, and I read online that paint if layed to thick wont ever dry because oxygen wont get past the dryed layer. It doesn't make any sense to me. The primer I'm using seems kinda soft after the 16 hours it calls for before recoat. So If I lay bondo on top will it remain soft and lift off in the future? Or is there something about how this paint cures that I don't understand?

No.

A can of paint left open long enough will cure to the bottom through four inches of paint. The top paint layer is not impermeable. Diffusion will continue through ten layers of paint. Most items have successfully been painted with multi layers for hundreds of years.

Denis

(I do hope this question is on the level)

There is also the fact that you don't actually want the layer underneath to be absolutely completely cured fefore the next coat goes on. If it is, you've only got mechanical grip holding the new paint to the old. If the paint's not completely cured, then you get some interaction between they layers that ends up making it more like a single solid coat.

Follow the directions on the can for when to recoat. Most give a time in hours. If you try to put another coat on too early, it will likely pull the undercoat. I have brush painted several machines with alkyd enamel and had excellent results. Trick is don't over work it. Slap it on nice and thick and leave it alone. The brush marks will flow out if you don't keep going over it. Worst thing to do is go back and try to fix something an hour or two later. It has achieved the consistency of bubble gum at that point and will grab the brush. It'll pull wrinkles and tears in the skin, then you are hosed.

Alkyd enamels cure, just like epoxies. They don't actually dry, but crosslink to form a hard resin. That's how it hardens under the top layer. In fact, enamels never stop hardening. That's why they eventually crack and chip over many decades. They get so hard and brittle that they can't expand and contract with the material they are painted on.

Do NOT apply bondo to anything but bare metal as it simply will not stick very well.

There are fillers that look like tooth paste for filling on top of paint.

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I did some research recently and found that baking paint does not make it harder it just cures it faster. The final product is no harder then air dried after several days or weeks. Same thing for adding the hardener. Of course two part catalyst paint does not harden without the catalyst.
Bill D.

Originally Posted by Dog250

................. and I read online that paint if layed to thick wont ever dry because oxygen wont get past the dryed layer. It doesn't make any sense to me. ..................

Which is why you go by the information on the side of the can and ignore conflicting advice that you got on some internet forum.

Steve

On oil based enamels you can add Japan drier.

Thanks for the replies, this makes much more sense now. I've got one last question. Is is better to have a thick layer of primer and a thin layer of paint, or a thin layer of primer and thick paint? Thanks!

If you are using one-part paint then it will never cure and harden like real two-part paint.

My paint can instructions have recoat window times and cure times. For example, at this time of year some of my paint cure times can take up to 2 weeks. A heated space helps the cure time decrease.

We used rust Oleum from lowes for ours.

Both hd and lowes sell what looks the same but one thins with acetone.

It sprays on better and you can mix it a little thick.

We used the hf detail gun and applied many coats to the SB 14.5 and it filled in the ugly cast spots well but it does take time to cure but it has a good surface when done.

But it takes a good long time to get hard when applied thick.

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Originally Posted by Tony Quiring

We used rust Oleum from lowes for ours.


But it takes a good long time to get hard when applied thick.

For the hardware I painted red, that would fit in a toaster oven, I cured my rust oleum paint at 175F and it got really hard in the first 24 hours. as opposed to the lathe bed and other hardware which i spray painted grey, it did not get as hard, But i also primed and painted it at 50F perhaps its the same hardness now, a year later, but i have no real way to prove it.

I just add this enamel hardener and the paint feels dry and not gummy that day.

Buy online top recommended Valspar (4625-6PK) Enamel Hardener - 8 oz., (Pack of 6) on carkart.com

Do NOT apply bondo to anything but bare metal as it simply will not stick very well

My experience is that applying it over 2 part epoxy primer works fine. One approach I've used when I absolutely cannot avoid painting something is to sandblast it, spray a quick saturation coat of epoxy primer, and then apply auto-body filler with less pressure from condensation or other rust. After sanding the filler I'll spot prime bare metal patches and occasionally add another all over coat for contrast/background when i think the filling process is about done. Then shoot tractor enamel on top of that.

smt

what exactly do you guys call enamel paint? does "enamel" have any meaning at all?

Heat heat!! Can you put a heat lamp on it??