SPI Adhesion Promoter after epoxy and blocking

[CJFINAN]

Is there any reason not to use SPI adpro over SPI epoxy primer. I am removing the texture on PP+EPDM bumper trim and have hit some of the plastic texture "Peaks" during blocking exposing parts of the raw plastic. Trim was initially hit with SEM soap and gray scuff pad then 700 W&G remover, followed by SPI adpro and epoxy primer. Surface is probably 70-80% covered in epoxy after blocking and out of epoxy recoat window.

 

[crashtech]

Just spot the adpro in lightly on the bare spots,using a mini gun if possible. Getting it on the epoxy is not ideal, as it actually reduces adhesion slightly in those areas compared to just epoxy-on-epoxy but it will be okay, the alternative, not to use adpro on the bare spots, would be WAY worse.

 

[CJFINAN]

Thanks crash! In hindsight, heavier coats of epoxy would have helped minimize blocking into peaks of texture. Spotting in ad pro may be difficult due to exposed base material being a small percent of overall area.

 

[crashtech]

Also, sometimes it's just best to stop sanding sooner if you can, leaving a bit of unsanded texture in the low spots is not a problem if repriming with epoxy inside the recoat window. While sanding, the primer will start to get a bit transparent right before it breaks through, that's the perfect time to stop on plastic. That way, there will be little in the way of true cut-throughs.

 

[Beobob]

Use an airbrush if the areas are small.

 

[CJFINAN]

Just thinking out loud - What is the stronger bond, PP trim+ Adpro +Epoxy or 7 day old Epoxy on trim with PP spots showing + Adpro + Epoxy? Maybe there is a point where it makes sense to sand epoxy + some texture off and start over if the PP+Adpro+Epoxy is the better bond. Picture of PP+EPDM trim before prep for reference.

 

[crashtech]

You are probably overthinking it a bit for an interior trim part. How about a pic of the part in question? I think you are likely fine to move forward with it without too much worry. Guys get adpro overspray on surrounding finishes every day without issue. It's just not something you are supposed to do intentionally.

 

[CJFINAN]

The parts are exterior bumper impact strips. I'm not too concerned with it, as they are easily removable should any problems show up later, but want to learn best practices for future reference. For now I will just spot in adpro and apply more epoxy. The picture is of one of several similar parts with the issue at hand.

 

[crashtech]

It's hard to tell from the pics, but it's possible you could go either way with the adpro. For future jobs, you might want to consider something with higher build to put over the epoxy the next day when there's that much texture, like a urethane primer. That way when the color changes while sanding to indicate going from urethane to hitting the epoxy, you just finish scuffing up with a red pad and apply more primer with no sand-throughs. Getting rough texture that that all the way out can be tough!