Clearcoat is cracking.....

[Wkillgs]

I coated a cast iron steering steering knuckle with satin clear...It looks like the clear has many spider cracks in it....what is the most likely cause of this? I baked it for about 15 min after flowout at 350 degrees. Then let it cool in oven with heat off. I suspect I either coated too thick, or have an incomplete cure. Whatdoya think?

[Fireblade]

incomplete cure, put it back in the oven and cure again. There are posts on here about this subject, do a search and find some more info.

[Wkillgs]

Got it!.... did a search for 'cracking' and found the advise....undercured. I didn't realize OVERcuring WASN"T a potential problem! I was worried about yellowing. I'll increase my cure times (and temp) for now on. Thanks Again.

Walt

[Fireblade]

Well, there is a limit to cure as well, just as a rule of thumb consider it "twice baked". If it needs to be cured at 380 degrees for 11 mins, than you can really do it for 22 mins if need be. It is just a guide, not set in stone.

[Wkillgs]

I vary my cure time depending on part size....on a large piece like a manifold or bellhousing, I'll start timing the cure once the powder flows out(melts)...

Is powder flow out a reliable indication the part has reached the cure temp? or will flow out occur at a lower temp?

Guess I need to monitor the actual part temperature....and not rely on the old stoves thermostat.

Walt

[Fireblade]

Nope, do it this way. the cure time starts when the part has reached that temperature. It may take 30 mins to reach the temp, depending on the size of the part or density. You should get a IR thermometer and this way you can check the part temperature itself. You may need the part in the oven for 45 mins just to get a cure temp of 380 degrees for 10 mins. Heat up depends alot on the amount of "power" your oven has to emit BTU's into the oven chamber itself. Powder flow out, is kind of a erratic guess, and I would not do it that way.

[PCPuser]

I applied a metallic gold with a clear coat over the gold last night, went to check on it this morning and the clear had cracked...a lot. I did exactly as advised on this thread...placed it back in the oven for the required amount of time after reaching temp. and all cracks are gone, parts look great. Thanks

[itsallgood]

So your saying to use the flow out to determine the length of time, or the actual part temp?
I coated my first batch of powder and was confused on this.
The powder started to flow out way before the part ever reached the specified cure temp.

Specified cure temp 390, started to flow at about 225, where do you start your time at? At what point will clear start to yellow or cloud up?

[Harleydad]

Originally Posted by itsallgood

So your saying to use the flow out to determine the length of time, or the actual part temp?
I coated my first batch of powder and was confused on this.
The powder started to flow out way before the part ever reached the specified cure temp.

Specified cure temp 390, started to flow at about 225, where do you start your time at? At what point will clear start to yellow or cloud up?

Start your your clock when the part reaches cure temp. If you follow the powder manufacturers cure times and temps you should n't have to worry about yellowing, that's from being overcured.

[krisnet55]

Just to clarify...... If my candy coat is cracking due to under cure, do I have to recoat it or can I just put the part back in the oven?

Im so ****ed I did a shift rod in candy gold for a friend of mind and it looked perfect, it almost matched the anodized on his bike, but after a couple of days it started to crack