Confused on grit choices for bc/cc

T

Tuna55

Promoted Users
Hello!

Most of my truck is now in Motobase basecoat. I plan to do light wet sanding at 1500 grit per the SPI perfect paint job before clear.

That's when the instructions seem to get strange.

I need 4-5 coats of universal clear. When do I wet-sand the clear? With what grit?The perfect paint job makes reference to 800 grit between clear coats, but that seems coarse, then no sanding on the final coat, just buffing? When do you start buffing?

Thanks
 
There is a sticky that will answer most of your questions.

The "Jim C. cutting and buffing method" summarized

Many people are interested in using the @Jim C method for cutting and buffing. Jim has been very gracious and helpful to all of us who ask for his advice. The "Jim C. method" is mentioned in several threads. And, he has updated it over time. It is hard to find a simple, current summary of...
www.spiuserforum.com

Don
 
dhutton01 said:
Never sand basecoat without respraying more base. I am pretty sure the perfect paint job does not say to sand base before clear.

Don
Click to expand...
Oh gosh I guess I misread this:

If your basecoat is not perfect:

After two coats of base the vehicle should sit overnight, and then do any minor wet sanding with 1500 grit sandpaper to remove any orange peel or trash. Apply the next two coats with 45 minutes of flash time in between coats. Some colors will require additional coats. If this is the case always wait 45 minutes between coats.

Let the basecoat sit overnight.

A word of caution: There are 2-4 basecoats types that cannot be sanded, or you will lose adhesion so avoid those basecoats. Check with your basecoat manufacturer.

Clear Option 1: Applying the clear in a single day

The following day tack off the vehicle, then apply a wet coat of SPI Universal Clear and let the first coat of clear sit 30 minutes.

Spray the second wet coat of clear and let it sit 30 minutes. Let the clear sit for 30 minutes before applying each additional coat as well.

DO NOT BAKE! The booth heat can be set at 80°-90° if you wish.

Normally 4-5 coats of clear are applied during this process.

Then proceed with normal wet sanding and buffing when you are ready.

So I only wet sand the basecoat that isn't "perfect", and then proceed directly to clear after sitting overnight? What is the last basecoat has orange peel or any texture at all as it does? Why is that last coat of color not to be sanded?

Yes, that link helped a great deal with understanding how to sand the clear, but I always thought it was to be done wet. Thanks for that.
 
Don’t sand your basecoat. Spray however many coats you need to get coverage.

The next day spray 4 coats of clear. Don’t sand in between them.

Once the clear is cured enough, you will start sanding (cutting) and then buffing.

You’ll probably need to start with 1000 grit, then 1200, 1500, 2000, 2500, 3000 trizact, then buff.

I’m not a fan of the dry disks but I’ve only tried those on single stage and not UV clear.
 
The only time to sand base is if you have a run or trash. Gently sand it out and spray fresh base over the sanded area. I use 800 grit sanding sponges and give the nibs a quick swipe.

If you don’t spray more base on the sanded areas you will see it when cleared. Dont ask me how I know…. :)
 
dhutton01 said:
There is a sticky that will answer most of your questions.

The "Jim C. cutting and buffing method" summarized

Many people are interested in using the @Jim C method for cutting and buffing. Jim has been very gracious and helpful to all of us who ask for his advice. The "Jim C. method" is mentioned in several threads. And, he has updated it over time. It is hard to find a simple, current summary of...
www.spiuserforum.com

Don
Click to expand...
Goodness you only ever touch the clear with a DA? Neat.

SPI support shared this video, which more or less meshes with what this link shows.

 
Tuna55 said:
Goodness you only ever touch the clear with a DA? Neat.

SPI support shared this video, which more or less meshes with what this link shows.

Click to expand...
Steer clear of the 3M compounds. They are full of fillers and will die back. There are much better products..

There are much better discs than 1500 Trizact too… :)

Don
 
dhutton01 said:
Steer clear of the 3M compounds. They are full of fillers and will die back. There are much better products..

There are much better discs than 1500 Trizact too… :)

Don
Click to expand...
I have some meguir stuff left over from the quickie single stage I used a few years back. What do you recommend? The "Jim C" method has sone brands there, are those useful recommendations?
 
An adjacent question since the weather this weekend is iffy, is there a humidity level which is too high to safely spray? I won't be in the rain, and it won't be raining outside, but it will be maybe between rainstorms.
 
Tuna55 said:
An adjacent question since the weather this weekend is iffy, is there a humidity level which is too high to safely spray? I won't be in the rain, and it won't be raining outside, but it will be maybe between rainstorms.
Click to expand...

Speaking for myself, I won't spray anything above 65% humidity.
 
Relative Humidity is a misleading measurement. Dew point is the real measurement of moisture in the air.
It can be pouring rain with a relatively low Dew Point.
I'm in the Pacific Northwest. If I couldn't paint when it's raining outside, I would be very limited.
Always important to have proper filtering and drying equipment in the air system.
And don't wet the dang floor!

 
Dean Jenkins said:
Relative Humidity is a misleading measurement. Dew point is the real measurement of moisture in the air.
It can be pouring rain with a relatively low Dew Point.
I'm in the Pacific Northwest. If I couldn't paint when it's raining outside, I would be very limited.
Always important to have proper filtering and drying equipment in the air system.
And don't wet the dang floor!

Click to expand...
Being he is in South Carolina, and it's mid May you can bet the dewpoint is going to be high along with the RH.
Just to be the contrarian, I'm in Southern VA about an hour and a half north of Durham NC. We have many days with a very high dewpoint in the summer as would Tuna in SC. I've never noticed a big difference on those days when spraying but when it's raining there is a definite difference. Being I'm not doing production I won't spray in the rain now. Clear won't lay out as well and it cures harder when it is raining at least here in the South.
Tuna if you can wait for a dry sunny day then do so. If you have to spray in the rain, use quality slow or very slow reducer (SPI), slow or very slow activator and 1-2 ounces of urethane retarder per 32 ounces RTS clear. That will help offset the humidity effects on urethane clear.
 
Thanks everyone!

I was able to handle it well enough on high humidity days, now I'm trying to handle an issue of patching a thin spot on the base coat which didn't blend well under the clear. I created a separate thread when I should have just put it here to keep the same interested helpful people around.
 
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