I assume the fenders flares are currently bare plastic ..or are they primed? Do you know if they're ABS?

Adhesion promoter is simply a very aggressive solvent, more aggressive than, say, lacquer thinner, which 'softens' the surface of the plastic a few minutes after it has been applied. Then, what one would do is follow up within a short period of time with a primer (or sealer) while it's still 'softened'. The advantage of using adhesion promotor vs just sanding the flares is you get a chemical adhesion (much better) vs. a mechanical adhesion ...with just sanding. Then one would follow up with the paint process

That said, I've done it both ways on automotive bumpers (sanding vs promoter). I haven't had many bumpers delaminate with just sanding, but there's no question, adhesion promoter will give a better, more secure bond. But that assumes the person did a comprehensive job sanding the plastic, (didn't miss any areas -- which often occurs), and sanding takes a while. Quite a while. Therefore, it's faster and less likely to have non-prepped areas using the promoter.

I'm convinced adhesion promotor is the same basic solvent as PVC cleaner (solvent) for 10x more money. I've used it before for spot and small repairs on plastic bumpers. Works great at much lower cost. If I were doing fender flares I'd be half tempted to get a $3 can of PVC cleaner (solvent) and spray it as the adhesion promotor out of a touch-up gun. Double-check beforehand that it will 'softened' the very 'top' layer of the plastic. Let the solvent flash off, prior to priming or sealing. Use a primer if you plan to sand out any blemishes, or a polyurethane 2-part sealer if you plan to just paint as-is. You use the sealer b/c the sealer (once it become hand-slick) essentially forms a barrier and projects the paint's solvents outward giving you a higher DOI (Distinctiveness of Image -- better shine), and to hide fine sand scratches (if there are any) ..and other minor imperfections. Sorry if you knew that, I put it down for the benefit of other who might read this. BTW, if you weren't aware, PPG adhesive promotor has a purple tint too (like PVC solvent), so the tint shouldn't be a factor. Or you can just go and buy a small container of Adhesion Promoter too.

Bear in mind, adhesion promoter (and all solvents) need to be sprayed in a VERY WELL ventilated area using the correct and appropriate PPE. I hope it helps.

Good luck!!

 

 

Sorry, I misunderstood your intentions. I thought you were installing new flares and/or bumper ends.

If yours are still painted, you could go either way. If painted, I would just sand and repaint, personally. If there's no paint left, mostly just bare plastic, then you could also go either way. I myself generally only tend to use adhesion promoter on new (bare) plastic and bumper covers. If you sand them you need to do a thorough job so there are sufficient scratches for the new primer/sealer to adhere to ..obviously. But I've seen guys scuff plastic lightly and say, "Good enough" and light scuffing is not good enough.

Are they going to be body color or black?

 

 

If you do a good job sanding them, that's what I would do. 3m makes really good scuff pads (sanding sponge) and if you do a very good job, you will be fine. Just be thorough and don't leave even an 1/8" unsanded or scuffed. My flares need re-painting too ...hopefully next summer, and I'm just going to wet-sand and/or scuff them. Wetsand with soapy water in a bucket does two important things: carries the dust away and de-greases at the same time. It is acceptable paint and autobody practice. Only lazy shops would adhesion promote them. ( ...I bet I get some blow-back on THIS one ). I used to work at a paint and body shop for many years when I was going to college.... We did things both ways depending on the situation. I personally almost never use adhesion promoter on paint. Just not necessary. High production shops value time over cost so they tend to use it more.

Adhesion promoter isn't a panacea either. Sometimes it 'lifts' under edges of exposed paint and primer areas ...which you would need to fix prior to painting (if it occurred) ...or may telegraph through the final paint surface.

 

 

No problem. It was a very good question. There is a time and place for it. Someone may chime in that they use it all the time. There are multiple schooIs of thought. Its a good product to be aware of ...and when the time arises, you'll know to use it. It's also pretty expensive...

 

What was stated is about it! only thing I would add is if you sand down to bare plastic then use it. becomes more of an issue on like bumper covers and such that will see flexing and such and without the adhesion promoter the paint will peel when flexed also have a flex agent you can use but another ball game. we need not get into!