Left Rear Quarter in Primer!

Well, this part of the work on the left rear quarter panel is kind of anticlimactic………and that is actually a GOOD thing.  Generally speaking, priming a body panel is a relatively straight forward process and the success (or failure) of the primer coat is largely determined by the amount of preparation you put into the panel ahead of time. 

As I have documented over the last several weeks, a lot of time and effort has been put into getting the left rear quarter as straight and clean as possible before shooting the panel in epoxy primer/sealer.  As the day approached to finally get the panel in primer, I was checking and re-checking every detail to do as much as I could to ensure success.  And for the most part, success is what I enjoyed.  However, as I have committed to tell the “whole” story on this blog, I did have one relatively minor “oops” that caught me out that required a little extra effort to fix and a second round of primer/sealer to get everything straightened out.

On the first “cut-in” shoot of all of the edges, wheel and window openings, I queued up my small touch-up 3M PPS cup for the job.  This cup is small and very maneuverable in tight places and allows me to get primer in the detail areas quickly and efficiently.

With the cup full and the HVLP turbine spooled up, I started covering the cut-in areas as quickly as I could to conserve primer and avoid excessive film thickness.  If I had been paying better attention at this point, I would have recognized I was going through the primer too fast to be normal and would have avoided a larger problem later.  But, the signs of trouble were subtle enough and I managed to get the cut-in work complete just as I ran out of primer, so the brief window of enlightenment closed as quickly as it opened.

After letting the cut-in work flash off for about an hour, I switched my gun over to the large 3M PPS cup and started mixing up enough primer to coat the entire quarter with a little bit of material to spare to catch any light spots I may have missed.  With everything checked out, I started spraying from the bottom surfaces up, trying to move quickly enough to avoid applying to much material.  Ya…….that’s how it SHOULD have worked anyway.

After getting the full coat of primer on the panel, I noticed again how much material I seemed to be using and how much more overspray I seemed to have (which is very rare when using a turbine HVLP spray system).  As I started quickly inspecting the freshly coated surface, I began to notice very small sags in the primer at almost every spot where the gun had been triggered or where each pass had overlapped.  What the…..?????!!!!

Then I decided to calm down and give this a “think” for a while and start documenting every tiny detail that may have been out of the ordinary.  After all, the primer was already on the surface and the best thing I could do at this point was let it dry fully before I could do anything remedial.  So, with that, I started my review of every detail.

Pretty soon, I was confident that absolutely everything up to the actual process of spraying the first cut-in coat was as perfect as I could make it.  However, the first subtle hint of an issue manifested itself in a slight “catch” in the trigger pull of the spray gun while adjusting the spray pattern.  While an almost imperceptible difference in the gun, this small detail would ultimately prove to be the single item that caused the domino-effect of the whole issue.

The bottom line is that this “catch” was an indicator that the needle was not seating fully into the spray nozzle as a result of debris and paint residue collecting in an almost hidden area of the trigger assembly that is not mentioned in the gun maintenance and cleaning instructions (and YES, I read them!).  The end result was a small amount of material was flowing through the gun all the time, so even when the gun was not triggered, primer was still flowing ever so slightly, and thereby adding thickness to the base coat and causing several small sags and few runs as well when all things flowed out.

So, after sleeping on this discovery overnight, and given the fact that I wanted to let the primer cure fully before going after the goofed spots with the DA, I set about doing a complete teardown, cleaning, lube and reassembly of my trusty spray gun.  This allowed me to revise my maintenance schedule based on these new discoveries to ensure I never have this problem again.

A few days of cure time on the primer had the scene set to start repairing the problem areas with a combination of shaving and sanding with the DA and a small hand block with 80 grit paper.  The rest of the panel was scuffed with medium Scotch Brite pads and everything was cleaned thoroughly with prep solvent and then tacked off in preparation for round 2 of the priming exercise.

In my usual preparatory fashion, I checked off each “pre-flight” detail as I always do with the extra sensitivity to gun condition firmly implanted into the process.  With all boxes checked and the surface freshly masked, cleaned and tacked, I was ready to give it another go.

This time, the gun performance was stunningly improved and the primer laid down very nicely.  In what seemed like only a few minutes, I had the entire quarter finished and was involved in cleaning up the gun.  At this point I started to question just how long and slow this particular problem had been developing?  Had I been working “around” this issue for months and just not noticed the deterioration in performance?  Who knows?  At the end of the day, the left rear quarter looks great and I am moving operations to the right rear quarter for the same treatment.  Hopefully, without the speckle of drama.

Prep work is complete and the bare metal surfaces are cleaned and ready for masking.

 

The roof was previously primed for protection and this required scuffing with 80-grit paper to prepare it for the primer blending process into the previously primed area.

 

This is a close-up of the bare metal surface I prefer when applying primer.  Most of this surface is created with 80-grit discs on a DA with light pressure.

 

All masked up for the first round of priming.......or so I thought!

 

First step would be priming these "cut-in areas around the window, trunk, door and wheel openings.

 

Shake, shake, shake..........shake your primer!  It really is the only way and this inexpensive pneumatic shaker is ridiculously handy.  Get one!

Objective evaluation of this shot reveals the first hint of trouble:  that surface is far too gloss and "wet" than it should be and is worse in some spots than others.

 

After the first coat was completed, I started noticing more little hints that things were not quite right.  In this shot, the primer has flashed about one hour and it still shows some obviously wet areas that should have started to dull by now.  Uh oh...
 

Out comes my inspection light and my worst fears are confirmed.  Patches of slight to moderate sagging are evident on several areas of the quarter.  *Insert long string of colorful expletives here!*
Careful investigation would reveal a very subtle spray gun fault that was responsible for the entire issue.  Yep......fixed that.

  

Even after a few days of cure time, the panel remains too glossy for a "normal" primer application.  I have my work cut out for me, but a few days of careful shaving and sanding of the problem areas and a complete tune-up of my spray gun and we were ready to give it a proper go.

This image shows a much more agreeable coat of primer.  Not nearly as glossy and heavy looking as on the first round and it's laying very flat and smooth.

 

From another angle, the finish is clearly superior to the first attempt.  Funny how things go when your equipment is up to par!

After the masking was pulled following only a hour of flash time, the surface look great and is noticeably smoother than before.  We got this!