Clear LP over completely cured LP ??

[pescaloco]

Hey guys could use some help

I am making a paint repair to some aluminum windows, the owner will not remove the windows for a complete strip / sandblast / refinish

I work alot more with gelcoat than LP but have transferable skills " I think"

Any way the substarte has an unknow fairing putty , Yellow (stronium) primer and a very nicly sprayed topcoat of LP. Although badly blistered in areas due to failure of the putty/primer

I know whoever did them did them wrong, as the fairing putty is the base material (??) in the mid sections of the frames and other parts have no putty and have the primer directly on the aluminum.

So I and he (the owner) are aware this is strickly for the cosmetic (hopfully) value of removing blistered paint and refinishing untill a proper repair can be made in the future.

So this leads finally to my question, I feel it will be very hard to match the paint and have good blend lines, can I prime and fair the repair areas and then take clear LP mixed with my new top coat to make a semitransparent covering of the old paint system to help blend the repair into old finish.

Since like I said I am no LP expert, don't know if that is doable.

Your help and suggestios would be very much appreciated

What please is LP?

[missinginaction]

I think that he's refering to linear polyurethane paint. Awlgrip, Perfection, etc.

Thanks Mia.

[pescaloco]

Sorry

Polyurethane, Awlgrip

short version, can some tell me if spraying clear over lightly sanded original PU paint system will work to help blend edges in a repair.

Will Awlgrip or Awlcraft adhere to a non primered surface

Thank You

[John Riddle]

When I most recently asked an AwlGrip tech your same question (3 or 4 years ago now), they didn't want me to put topcoat over an unprimed, fully cured topcoat. They said it wouldn't bond in the long term.

The reason I was asking the tech in the first place is that three years earlier, I had clear-coated over what was then a two year old, fully cured and sanded clear coat as part of a repair process. The AwlGrip tech I spoke to at THAT time approved of the method but apparently misunderstood the degree of cure of the existing topcoat. The job looked great with no evidence of an impending problem.

I think it was about three years after making that repair, my customer lightly bumped a dock post or something and the "new" clear "blistered" off the original cured clear surface where the bump occurred. The original clear was fine. It turns out that you could run a thumbnail hard against the topcoat anywhere on the hull and cause that "new" coat to blister.

My solution is a clear 545 primer under the new topcoat. I don't know if that would work in your process.

[gonzo]

Use IMRON from Dupont. You can prime and spray that over any LP.

[GG]

Originally Posted by gonzo

Use IMRON from Dupont. You can prime and spray that over any LP.

I agree and Imron is my paint of choice , scuff , prime , scuff then spray .

[Jimbo1490]

Clears do make blending repairs simple. This is done every day in the automotive re-finish business. Automotive paints are much easier to paint over, though. The polyester urethanes like Awl-Grip are EXTREMELY resistant to chemical attack, which has the effect of making them difficult to get paint to adhere over once fully cured without thoroughly sanding first. The potential adhesion issue is NOT with the new material that is being applied, but with the fully cured Awl-Grip substrate. Just switching to Imron clear (500S)will not address this issue AT ALL. (BTW 500S is ONLY recommended to be used as a LAST COAT over fresh wet Imron; no other use is even recommended!) Scuffing with Crotch Bite pads won't cut it, either; you will have to sand thoroughly. That's the bad news. The good news is that you can (and should) sand with fairly fine paper no coarser than P320 with 400-600 being all good. I'd guide coat the area with flat black lacquer from a spray can, then sand, then wipe down with strong solvent, tack and spray your clear.

Now there are 'conventional' clear adhesion promoters on the market which work by chemically attacking the substrate then bonding a layer of clear acrylic resin, that will work (Like DuPont 222S or Bulldog) in that they WILL get you the adhesion you want with little or no sanding, >>*BUT*<< since you are applying clear instead of some sort of opaque paint, the adhesion promoter will now be exposed to UV light coming through the clear applied over it, something that it was NEVER designed for! It will stick just great right up until the adhesion promoter layer (inevitably) fails from UV degredation, then the clear will fall off. At that point you'd probably blame the clear, too

There is an 'UNconventional' adhesion promoter that might work for you called Prekote. It works in a completely different way than the conventional adhesion promoters, so there is no issue with UV exposure. I'm not sure it will work for this situation, but you could buy a small amount and do an adhesion test before you commit to the whole project. Since your window frames are aluminum, you will want to do some kind of aluminum surface treatment to insure lasting adhesion. Well it just happens that Prekote is primarily used as such a metal surface treatment in place of Alodine (chromic acid conversion) but because of the way it works, it will work on ANY surface, including cured paint and primer past its re-coat window. So even if it turns out that the Prekote won't work to help with your clear coat adhesion issue, it will still be useful to treat the bare aluminum after dressing the corrosion before primer.

Jimbo

[GG]

JIMBO1490 ,took my breath away just reading A....l....l.... T....H....A....T....HA HA HA HA

[gonzo]

This is clear over a solid color, since he says there is some kind of primer. That is why I suggested priming and painting with Imron. The clear would be sprayed over the new Imron- fresh as you correctly pointed out.

[Jimbo1490]

Originally Posted by G.G.

JIMBO1490 ,took my breath away just reading A....l....l.... T....H....A....T....HA HA HA HA

Thanks! Your contribution to the thread was most helpful and informative, also

Jimbo

[pescaloco]

Originally Posted by John Riddle

When I most recently asked an AwlGrip tech your same question (3 or 4 years ago now), they didn't want me to put topcoat over an unprimed, fully cured topcoat. They said it wouldn't bond in the long term.

The reason I was asking the tech in the first place is that three years earlier, I had clear-coated over what was then a two year old, fully cured and sanded clear coat as part of a repair process. The AwlGrip tech I spoke to at THAT time approved of the method but apparently misunderstood the degree of cure of the existing topcoat. The job looked great with no evidence of an impending problem.

I think it was about three years after making that repair, my customer lightly bumped a dock post or something and the "new" clear "blistered" off the original cured clear surface where the bump occurred. The original clear was fine. It turns out that you could run a thumbnail hard against the topcoat anywhere on the hull and cause that "new" coat to blister.

My solution is a clear 545 primer under the new topcoat. I don't know if that would work in your process.

John,

Thanks for the insight

I was not aware they had a clear 545, however if we can get a couple years out of this it would be fine. Just trying to restore some cosmetic value, the owner is aware of previous sins in the prep work and will pull the windows for proper repaint

[pescaloco]

Originally Posted by gonzo

Use IMRON from Dupont. You can prime and spray that over any LP.

Gonzo

Thank you for the tip, I assume it has better grab to a cured surface ?

[pescaloco]

Originally Posted by Jimbo1490

Clears do make blending repairs simple. This is done every day in the automotive re-finish business. Automotive paints are much easier to paint over, though. The polyester urethanes like Awl-Grip are EXTREMELY resistant to chemical attack, which has the effect of making them difficult to get paint to adhere over once fully cured without thoroughly sanding first. The potential adhesion issue is NOT with the new material that is being applied, but with the fully cured Awl-Grip substrate. Just switching to Imron clear (500S)will not address this issue AT ALL. (BTW 500S is ONLY recommended to be used as a LAST COAT over fresh wet Imron; no other use is even recommended!) Scuffing with Crotch Bite pads won't cut it, either; you will have to sand thoroughly. That's the bad news. The good news is that you can (and should) sand with fairly fine paper no coarser than P320 with 400-600 being all good. I'd guide coat the area with flat black lacquer from a spray can, then sand, then wipe down with strong solvent, tack and spray your clear.



Now there are 'conventional' clear adhesion promoters on the market which work by chemically attacking the substrate then bonding a layer of clear acrylic resin, that will work (Like DuPont 222S or Bulldog) in that they WILL get you the adhesion you want with little or no sanding, >>*BUT*<< since you are applying clear instead of some sort of opaque paint, the adhesion promoter will now be exposed to UV light coming through the clear applied over it, something that it was NEVER designed for! It will stick just great right up until the adhesion promoter layer (inevitably) fails from UV degredation, then the clear will fall off. At that point you'd probably blame the clear, too

There is an 'UNconventional' adhesion promoter that might work for you called Prekote. It works in a completely different way than the conventional adhesion promoters, so there is no issue with UV exposure. I'm not sure it will work for this situation, but you could buy a small amount and do an adhesion test before you commit to the whole project. Since your window frames are aluminum, you will want to do some kind of aluminum surface treatment to insure lasting adhesion. Well it just happens that Prekote is primarily used as such a metal surface treatment in place of Alodine (chromic acid conversion) but because of the way it works, it will work on ANY surface, including cured paint and primer past its re-coat window. So even if it turns out that the Prekote won't work to help with your clear coat adhesion issue, it will still be useful to treat the bare aluminum after dressing the corrosion before primer.

Jimbo

Thanks Jimbo,

You allways seem to have a welth of good info