Clear Coat and Sanding

posted Jun 28, 2013, 7:46 PM by Andrew Stock
Hello Hello!  It's been far too long since my last post... unfortunately work has gotten crazy the last month or two, and it's leaving very little time for hobby fun.  Alas, sometimes you must do what you have to in order to do what you want to... which is modding!  Fortunately, my overbearing work schedule hasn't completely prevented me from making some progress! So much painting to do... it feels like it never ends! 

So, when we last left off, I had put down some matte clear coat on my matte black "inside pieces", and I had a weird issue with white specks being embedded in the surface. After some searching around online, I ultimately concluded that it had everything to do with my cleaning process... which was to follow some very poor advice online and just spray thinner through the gun and call it a day.  Needless to say, that wasn't sufficient... but at that time, I was a spray gun novice, and didn't know any better.  Proper research showed that if you will be setting the gun down for any more than a few hours, it's best to completely tear it down and clean each individual piece with paint thinner, then leave it disassembled to dry. I put this to good practice with my new toy:

It's not an overly expensive setup, but it's better than the old unknown spraygun that my grandfather originally purchased to spray his farm equipment with. 

The spray gun kit came with two such guns... one small HVLP version for doing finishing work and small stuff, and one large HVLP version for doing higher volume stuff. It also came with many "nice to have" items like a cleaning kit, some disposable paint cups, and multiple nozzle sizes from 1.2 up to 1.8. It was a real steal at the local hardware store, too. I researched the gun a bit online first, and it appears to be a very popular one commonly referred to as "the purple gun" which is cheap and medium-low quality by default... but with a bit of customization and TLC ends up being a great gun!

Most of the modifications included replacing the plastic washers (or in many cases, non-existent washers) with some nice new nitrile washers, and replacing a lot of the spray-on thread goop with some nice quality teflon tape. $5 in spare parts with a little labor to turn a chump into a champ? Absolutely! 

The other piece I bought for this outfit was a pressure regulator and air filter / water remover kit... which greatly improves the quality of the job by tightly regulating air flow and removing any contaminants and moisture in the air supply. 

This stuff probably cost me no more than $20 at the local hardware store, too. Well worth it! Anyway, more on this gun later. 

The other issue I was having last post was that I could see some 'patterns' in the shiny black pieces that gave the finish an odd effect... one that certainly wouldn't work out well for the mirror finish I wanted to achieve on my case exterior! I ultimately determined that the issue with these patterns showing up was that I was a bit too stingy on the amount of paint I was using. Everyone says to put only multiple light coats on... but I think perhaps my version of "light" was closer to "transparent".  Anyway, I upped the quantity of paint laid on by slowing down the spray cans as I passed from left to right, and moved the cans in closer to 6-8 inches instead of 8-10 as I was using before. The result was immediately and obviously apparent:

Almost no more lines, and a much healthier "shiny-er" black.  This was just the first pass, and I did two more passes of similar weight switching from up/down to left/right each time. I let that business dry in the paint booth for about 30 minutes before moving on to the next step... clear coat!

Here's the first couple coats of gloss clear drying on the case doors:

Of course, a few specks of dust settled on the surface despite my booth and all the precautions I took... but these easily came off with a wipe of a rag after I let the parts dry for 24 hours, so no big deal. I let the parts dry for about an hour or so in the booth until they were no longer tacky, then lightly took them out and set them on the bench to dry for a day or two. 

My camera skills don't really reveal, but the spray gun so far has done an excellent job of laying down a nice smooth finish. There is orange peel, of course, but I've come to understand that orange peel is just a reality of painting. 

I went on to lay down paint and clear on the remaining pieces, and stood them up around my garage wherever I had room:

Things were going so well... but of course, the very last piece had an issue.  I saw it happen in slow motion... spraying a sweep of clear over the last (and of course, most important/visible) part of the case, a lonely strand of hair floated between the piece and the spray gun, and it was adhered to the surface deep under a layer of clear. I couldn't leave it there, or it would dry between the clear and color coat... giving very little chance of rescuing the finish. I didn't want to have to re-do the whole piece, so I did my best to pull the hair out of the clear... but unfortunately, it messed up the color coat anyway:

It's always the last piece! Oh well, no saving it now. I let the piece dry as is for a day, then set to work sanding it back down to prepare for another few coats of color. 

Of course, I spent the time breaking down and properly cleaning my gun in preparation for another long day to come!

The next day, I sanded the affected area down to flat using some P600 wet sand paper, trying to avoid going all the way back to bare metal, which would require me to start over with the primer coat again. 

I then went on to lay down another triple-set of color coat, followed by a set of clear coat. Fortunately, it completed safely this time without any stray hairs.  In addition to this marred piece, I decided to redo my midplate as it had too much of that white speckled stuff to save. I sanded it back down to bare metal and re-primed it. 

I briefly checked on the other pieces to see how they were drying... partly to remind myself that the extra effort makes it worth it. Drying nicely... 

The following weekend, I decided to work on sanding down the orange peel in preparation for that long sought-after mirror finish. I set up my sanding table and blocks for what I hoped to be a short day:

I started out with some 2000 grit sandpaper, water, and a dab of soap for 15-20 passes lightly... barely any pressure, more letting the block slide than anything:

Only enough to scratch the surface. All the shiny spots are pits that need to be sanded down. And this is only one small piece of the case. I have a looooong day ahead of me.  The sanding with 2000 was taking too long, so I decided to back down to 1500 to get some more cutting action and save myself a few sheets of sandpaper (not to mention some time and a lot of effort). Here we are with 15 minutes of effort or so at 1500:

Some spots are there... but still tons of tiny speckles. After a lot more careful sanding at 1500 to get rid of all the pits, I switched to 2000 and changed directions as well:

Note, I left the orange peel along the edges for now. In this shot, I was just focusing on the center and making sure my process was going to work right.  You can see that the right side that has been done by 2000 grit is starting to get a little shiny, where the left that was done by 1500 only is just hazy. I sanded a bunch more with 2000 grit until I could no longer see the horizontal lines from the 1500, then went to work with a microfiber cloth and some polishing compound meant for cars:

Getting there!  The left is after a hardy polishing, the right is just from the 2000 grit. We're approaching that mirror finish... but this took a LOT of polishing compound and effort. I'm thinking I need some "buffing compound" first that is a higher grit to remove more of the cuts... and once that is done, I follow it up with the polishing compound. I'll see what I can find at the auto shop. 

Needless to say, I have a lot of sanding and polishing to do. Until next time!