Clear mil thickness?

MikeS

Camaro Nut
Hello group,

I’ve searched the SPI archives and could not find an answer to this question so I’ll ask my first here. Before I do I wanted to say that I have learned so much studying the topics here and it has made my confidence level so high that it felt like I have done BB/CC for years.
Now to the question: For three wet coats of SPI UV Clear (reduced with 4001-1) sprayed out of an Iwata LPH400 with a 1.4/silver cap, fan one turn down from fully open, 3 full turns out on the fluid control and 20 pounds on the gun inlet (trigger pulled) what approximate dry film thickness in mils would you expect? Spraying approximately 5” from the surface the coats went down wet with the last one having produced 2 small runs that were easily removed with a nib file and later with a maple block w/1000 grit paper to feather. I only mention this to give you an idea of my speed. The car surface temperature averaged 68-70 degrees when using an infrared thermometer. I sprayed this last fall in November in a heated garage so I was careful to monitor the surface temps.
I ask this because this is my first time spraying BC/CC (used to do SS) and have wet sanded the clear 4 months later starting with 3M’s Imperial P600 wrapped snug on a 10” 'Preppin Weapon block and the 5.25” 3M black firm block for smaller areas. The shallow orange peel and some dust nibs were removed quickly and I stopped just when the surface had a uniform dullness to it. Then, followed up with dry guide coat and cross hatched directions using 800, 1000, 1500, 2000, 3000 and 5000. The 3000 and 5000 were cushioned backed pads. I started with P600 as a precautionary measure in case there was any urethane wave present and stopped sanding with each grit after all the guide coat was gone. I’ve read in the SPI forum many times how the wave (ripple) became visible only after buffing so I decided to lead off with 600 grit. With a 5000 grit finish the panels’ reflections are very clear and shop light edges straight when looking sideways so I plan on buffing with Meguiars medium cut compound on a foam pad followed up with their swirl remover polish on a foam pad and complete it with carnauba wax.
What keeps tugging at me now is if there is the required minimum 2 mil clear thickness. I don’t want to risk polishing through the clear and hit the base (a solid color being butternut yellow) and cause more work so I’m now second guessing myself and wonder if I should flow coat it, if it is really necessary that is. If I do have to flow coat will using a gray Scotch-Brite pad suffice to prep the surface for two more wet coats of UV clear or gently hit it with P800 wet and a firm sanding pad.
I appreciate your opinions and suggestions.

Thank You,
Mike
 
Three wet coats with that gun, mils would be allover the place but with the couple of runs tell me you sprayed nice and wet, I say don't give it a second thought, I'm thinking (guess) you at 7.5 to 9 mils before sanding.
 
Hi Barry,

Are those numbers you quoted thickness for the clear only or the total bb/cc thickness? My friend is going to loan me his thickness gauge later today. It's the electronic type with a resolution of 0.1 mil. Out of my own curiosity I want to see what my starting point is for reference. I should of thought of that before I began to cut but you know how hindsight goes.

Thank you for the reply!
Mike
 
Mike, it will tell you nothing at this point. My numbers were for clear only, proper way is mil the dried base then subtract from total after clear sets overnight.
 
Hi Barry,

Understood. I'm only doing this to see if I get a much lower reading under your numbers and I do understand yours is a guesstimate. For example, if I get something like 4-5 mils total thickness then I know that area may be too thin and possibly I risk breakthrough. I do have a quarter panel not cut yet so I can compare that to the other quarter that is cut but not buffed just for comparison. Based on what I find will determine if I just scuff with P600 on a block and flow coat it or continue with the buffing stage. I do have a lower front valence that is still in primer and not painted yet so I have something for reference to see roughly what the average epoxy/primer thickness may be at.

Thanks again,
Mike
 
OK...here is what I measured with the paint film thickness meter.
These numbers were based on a 20 point data sample for each painted panel. Of course these are dry film values and not totally accurate unless I had measured the currently painted panels before BC/CC was applied.

* Uncut BC/CC quarter panel: 10 - 12 mils
* Cut (not buffed) BC/CC quarter panel: 7 - 9 mils
* Unpainted front lower valance, cowl cover and upper header panels (primed and ready for base coat): 3 - 4.5 mils. This gives an estimate for a starting base value.
It looks like the BC/CC painting added approximately 7 - 9 mils. If cutting removed approximately 3 mils average and the coats of base color film that was applied are between 1 - 1.5 mils total thereabouts then there is a guesstimate of 3 – 4 mils clear remaining after cut. Your guess of 7.5 - 9 total thickness was pretty darn close, Barry!
So the remaining thickness looks adequate for buffing though on the ‘thin’ side. But my friend looked at the reflections in the 5000 grit areas of the doors flat sections and had seen some small consistent ripples from front to back reflections. I was finally able to see what he was referring to after he pointed it out on a vertical pipe in the reflection and now see the infamous urethane wave though this was more of a faint ripple. He told me it wasn’t bad actually and if I hard block the door a little more with 600 grit and spray 2-3 flow coats, it should eliminate it. Being this is my own car I want it to be the best it can be and am willing to do the flow coats.

Out of curiosity I measured my cars factory paint:
* 1967 Camaro w/metallic Tahoe Turquoise - 3.2 - 3.5 mils. That is an impressive even film for 49 year old paint though on the thin side. Then again in '67 the Camaro was painted by reciprocating spray guns.
* 2014 KIA Forte Koup w/gray metallic: 5.2 - 5.5 mils. Another impressive even paint film though it seems to be 'thin'.
* 2015 Jeep Cherokee w/ solid white: 10-11 mils. The hood and roof were 10 mils and the sides 11 mils.
I was so impressed that I ordered the paint gauge.

Mike
 
Which paint Guage you using? they are really useful when recording all the information I had and lost a magnetic one awhile ago and have been looking to get another one. I would like the one that reads aluminum panels also.
 
The one I used is the Tecpel TG-902. I found it on eBay for $120 and ordered it today.
It comes with a ferrous and non-ferrous calibrating disc. The specs list it can measure aluminum.

Mike [h=5][/h]
 
Mike,
Base depending on color and hiding will normally be 1-2 mil as well as epoxy if used.
If it were mine i would sand slick with 600, 800 your choice and re-clear with 3 or 4 coats, remember the first coats will not count when buffing.
 
Hi Barry,

That's what I am going to do. I started to wet sand the door with P600 and an aluminum block to dull the surface uniformly last night and will work only with that door until I get the flow process worked out and will do the remainder of the car afterwards. I'm not looking for gloss or depth in as much as I am looking for flatness so I don't mind cutting with 800 and working up if that's what it takes so I'll go for 4 coats 30 minutes apart.
I did encounter something though while wet sanding for which I'll start a new thread.

Thank You,
Mike
 
Barry;n81556 said:
Mike,
............. remember the first coats will not count when buffing.

Hi Barry,

Based on your comment above, does that mean if I break through the flow coat layers into the previous clear coat layer then I would see that transition? Sort of like if I were to break through the clear coat and into the base?

Thank You,
Mike
 
Over really cured clear, you might see a ring aroung the breakthrough. Over fresh clear, you might not know. This also depends on which clear was used. Universal bites back into itself pretty well.
 
I had raised this question in a previous post. If you miss the recoat window and have a mechanical bond, there is a good chance you will see the sand thru. If you have a chemical bond within the recoat window, you will not. I have never done it but this is based on what I was told on this forum.
 
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