Primer Sanding: Perfection Required?

[Ziggler]

Topside painting at the primer sanding stage. Using Pettit 6149 EZ Primer before last step of Pettit Poly EZ Poxy".

Question: How perfect, how baby-butt smooth does the sanding of the last coat of primer need to be? If I sand with 150 paper as suggested by Pettit specs I invariably tiny sand paper lines on the surface. Do I need to worry about that or will it the final coat "fill" these tiny 150 grit lines? I've seen recommendations for 220 at this step, but never by the manufacturers of the paints.

I've done such meticulous prepping to get to this point and refuse to mess it up now! Thanks for any help.

P.S. If interested, this is a Paceship 23, 1979, named "Zeitgeist".

 

[BioAndy]

Ziggler,
I've done a fair amount of painting over the years with good results. I would stick with Pettit's reccomendation on sanding grit for the Pettit 6149 EZ Primer before topcoating. It's probably the optimum grit for proper adhesion for the topcoat. Their technical bulliten does specify finer grits for sanding between topcoat finishes. http://www.pettitpaint.com/fileshare/product_pds/Apply-Topside-Finishes.pdf
Sould be a rewarding project. Post some photos when you're done.
Andy

 

[Ziggler]

Ziggler,
I've done a fair amount of painting over the years with good results. I would stick with Pettit's reccomendation on sanding grit for the Pettit 6149 EZ Primer before topcoating. It's probably the optimum grit for proper adhesion for the topcoat. Their technical bulliten does specify finer grits for sanding between topcoat finishes. http://www.pettitpaint.com/fileshare/product_pds/Apply-Topside-Finishes.pdf
Sould be a rewarding project. Post some photos when you're done.
Andy

Andy:

Thank you for the affirmation that I should adhere to the recommended sanding grit. I'll have to trust that the lines I'm seeing will dissipate under the next 2 coats of 2-Part paint. Here's a little "before"-type picture. She's going to gleam in a few more weeks!

 

[Ralph Johnstone]

If I sand with 150 paper as suggested by Pettit specs I invariably tiny sand paper lines on the surface. Do I need to worry about that or will it the final coat "fill" these tiny 150 grit lines?

Try, if possible, to sand more in a light circular fashion rather that parallel strokes to avoid the parallel grit lines. This criss-cross action reduces the depth of the lines. Although the final coat(s) should fill the lines, like me, you probably don't want to take the chance after all the prep work.

 

[Ziggler]

Ralph: Eureka! That makes sense. While I was experimenting with different strokes the back and forth (parallel) action was easiest. But certainly circular has the best chance of erasing the faint gouge lines I was seeing. Thank you!

 

[Ted]

Primer Sanding

Ziggler: How are you handling the fine cracks in the gel coat? Are you going to open them up, fill and fair them before priming? Just wondering if they would begin to open up again after the job was completed. +1 for the comments made by BioAndy.

 

[Daydreamer]

Anything you can see in the primer you will see in the topcoat paint.
Spending a little extra time on this step pays off.

Stripped the old paint with 100.
Faired gouges and sanded with 150
Three coats of primer sanded 220 in between. ( the second coat ran )
Sanded 320 in between two topcoats, and I can still find lines if I look close.

I used a single part primer and topcoat and sprayed with HVLP gun.
I'm happy with the results.

I hope you will be with yours too

 

[Joe]

I got a more consistent result using 180 grit on a VS orbital on low speed for the primer coats... 320 or 400 by hand on the topcoats.. final coat... nothing... just let it dry to that beautiful gloss hard shell.

 

[Ziggler]

Daydreamer & Joe:

I appreciate the "anything you see in the primer coat, you see in the final" reminder. I find myself feeling more and more like the horse getting close to the barn - I want to hurry up and get there after 8 months of work on this project, but patience will pay off.

Joe, I tried a power sander and soon found it wore past the primer coat back to fiberglass. No doubt it was mostly operator error, but int he nooks and crannies of the topside it seems its 90% hand sanding.

Lastly, I am going to use just one coat of primer. I was out there for 4 hours yesterday and think 1 coat on 80% of the boat is acceptable. There is that last 20% which needs a second coat (e.g. where speaker holes were glassed over, etc.)

BUT, please yell at me if I'm talking crazy when I say "1 coat of primer"

 

[Ziggler]

Re: Primer Sanding

Ted:

About the gelcoat cracks... I sanded the whole topside and was able to sand out some of the problems like that. Happily, my boat didn't have widespread "crazing" (which I think is widespread pattern of gelcoat cracking). There were some mild cracks and I am breaking a rule or two, I'm sure, by simply having sanded them down a bit and relying on primer to cover.

Oh, and I did use a Pettit fairing compound to fill gouges, etc. just before the primer coat. That stuff was essential for the many nicks and gaps. And, going even further back in this eternal project I did fiberglassing work to cover up many bigger holes (e.g. removal of obsolete hardware (out of use autohelm, speaker holes, lazarette latches, etc.)

I'm aiming for "really really good" but my wife has convinced me that "perfect" will drive me mad (and likely her along with me).