- Hey, YouTube viewers, it's Donnie Smith
and welcome to this video series
that is designed to help you pass the ASE exam.
Now, this video series is specifically
for the paint refinish, and what we're gonna do is
we'll go through the task and give you
the knowledge to pass the test.
What this is not, this is not
really your print test type book.
It's not just test questions.
If you want that, there is a link down in the description.
You can get more information about that.
What this is, this basically goes through
all the tasks that you will need to know to pass the test.
Alright, today we're gonna talk about final sanding,
getting the surface ready for paint,
but before we do, I wanna talk about adhesion.
There's basically two types of adhesion,
and that is there's mechanical adhesion
and there's chemical adhesion.
Now, chemical adhesion may occur, for example,
when you spray some epoxy primer on a surface.
We may have 72 hours to put the next coat on,
and during that 72 hours, for example,
let's say we have some epoxy primer and we're wanting
to put some primer surfacer on top of that,
we have 72 hours to do that without sanding
because during that 72 hours,
it's gonna have that chemical bond.
However, after that 72 hours, you lose the chemical bond
and you're gonna have to provide a mechanical bond,
and that's done by sanding.
Same way with base coat.
A lot of times, you'll put your base coat on
and there's a window you have that you can put
your clear coat on top of that.
The base coats we use is 24 hours.
Now, of course, that's gonna depend
on your technical data sheet and the paints that you use.
Be sure and read those.
During that 24 hours, the clear is gonna bond
to the base coat because of the chemical adhesion.
After that 24 hours, you lose that chemical adhesion
and you're gonna have to sand it,
so chemical adhesion is just where products bond together.
Mechanical adhesion is where you're gonna sand something.
You're gonna rough it up so the paint
can stick to that and doesn't peel off.
Now, I just wanted to touch on the two types of adhesion,
but we're gonna focus on, during this video,
we're gonna be talking about the mechanical adhesion
'cause we're talking about final sanding
and you know, get it rough where the coatings will stick.
So whether you're sanding a paint finish,
let's say a car came in,
just needs to be sanded and painted,
or maybe it's some primer surfacer, it's gonna have
to be final sanded one of two ways, and those two ways
are a dry sand method or a wet sand method.
Now, one of the dry sanding methods is preferred
by most shops, that's by using a DA sander
and an interface pad, because it's much quicker.
It gets the job done much faster,
and the interface pad, it helps go around curves
'cause it's soft and it will follow the curves of the car,
the body lines, and prevent marking, making any marks
that the DA may have made in the paint surface,
so that's gonna be much faster,
and that's why it's preferred by most production shops.
However, you can hand sand with a dry sand method.
They've got a hand pad that you can use, a soft hand pad,
and you can use dry sanding.
Now, it's gonna take longer and more effort to do that
than by doing the DA and interface pad system.
Now, generally, when final sanding,
there's a range of sandpaper from 400 to 600,
and part of that's gonna be preference.
Maybe the shop prefers everything to be done in 600 or 500,
but, you know, that's kind of the range.
Now, waterborne paint, some paint systems are
a little more sensitive, and you know,
they may wanna go up to even 800,
but the way you know for sure is to read
that technical data sheet for the products you're using.
It'll tell you exactly what products
or what grit of sandpaper to use.
Now, keep in mind that we're talking about
getting something right for paint.
We're not really talking about blending
or, you know, just applying clear coat
because if you sand something with 500 grit
and apply clear coat on top of it,
you're probably gonna see the sand scratches,
so when you're applying clear coat, you use finer grits,
but we'll talk about that in a later upcoming video.
Now, before those interface pads was
introduced to the industry, just about everyone
used the wet sanding methods 'cause we didn't have
that dry sanding method, and to do this,
it's gonna use a different type of paper.
It's a sandpaper that won't fall apart when it gets wet.
It's also gonna require some water,
and what I found that works best is a spray bottle,
and as you're sanding, you just spray it.
You can control the amount of water that you put on there,
yet enough to keep your sandpaper clean.
Another method that I've seen and used is with a water hose.
You barely turn it on, the faucet on,
and let the water trinkle out.
That's gonna produce more water and make a bigger mess,
but it is something that you can use.
But one thing I do wanna mention,
if you're using a hose, you need to cut the end off
'cause those metal ends, they can rub up
against the paint surface and scratch it,
so make sure that you're either using an adapter
that you can screw on there with the end cut off
or just cut the end off the water hose.
Now, it's not gonna be good for putting
a sprinkler on after that, but you know,
it's better than scratching your paint surface.
And the other method that I've used is
to fill a bucket up with water and get a sponge
and you dip your sponge in the water
and you hold it over where you're sanding
and that water will trinkle out
and keep your sandpaper clean,
so that's just some different methods
for wet sanding that I've seen.
Any of 'em will work.
In my opinion, I think the spray bottle's
gonna produce the best results.
Now, wet sanding follows the same grits,
anywhere from four to 600.
That's what you use for final sanding,
but again, with your specific paint that you're using,
there's a bunch of different paints out there,
so read your technical data sheet
so you know for sure what they recommend.
Now, regardless of what method we're using,
wet, dry, it's all the same goal.
What we're trying to do is we're trying to provide
that mechanical adhesion where the paint,
whenever it is applied, it's gonna stick.
It's gonna have something to grab to and not peel off.
Now, whenever you're sanding glossy paint,
you know, like a car came in, you're gonna sand it,
you wanna sand it until everything's dull
'cause when you sand something, it gets dull,
and you won't be able to see the gloss,
but that's a good indication 'cause if you sand something
and you look at it and you see some glossy spots,
well, that's an indication that you missed that spot.
Need to go re-sand that, so make sure
any glossy spots are removed by final sanding.
And one common place that I see a lot of glossy spots,
and you know, it's easy to do
'cause they're hard areas to get is your edges.
Make sure your edges are sanded good.
If they're glossy, come back and hit 'em again
and make sure they are sanded properly,
because if paint's gonna peel, you know,
it's a lot easier for it to start from the edge
than in the middle of a panel, so it's very important
to make sure those edges are sanded well.
Now, some areas are just gonna be hard to get,
you know, if you're DA sanding or even hand sanding.
Some of 'em, you'll have to get by hand,
some of the hard to get areas, but even then,
sometimes, the sandpaper don't get in there well,
so one thing you can do to make sure
all hard to get areas are sanded good is
to use a Scotch-Brite, a scuff pad,
and that kinda gets in there and forms to those edges
or areas a lot better than sandpaper does,
so I always, after I've done final sanding,
all the sanding's done, I'll come back with a scuff pad
and for whenever painting something, just the red scuff pad,
3M's red scuff pad, and I will scuff everything.
I'll give it one last scuff,
but I really pay attention to the edges.
Make sure those are good, and all the hard to get areas.
I make sure those are sanded well.
Now, they make some other colored scuff pads,
and for example, if you're just blending
or just clear coating, you may just wanna use the gray
'cause it's a finer grit, but like I said,
we'll talk more about that in a later video.
And there's also other products out there
that can be used, like a paste.
There's some final scuff paste that you can get
and it goes on the surface and it has some grit in it,
and that helps sand the areas, and I think this is
really used a lot for blend panels and things like that,
but you know, it's something out there
that you may need to be aware of.
So final sanding is basically the process
of providing mechanical adhesion
so that the paint adheres properly and will not peel.
It is my goal to keep these videos short,
so that's all we're gonna cover in this video.
Just give you little chunks at a time.
Lets you absorb that, and then you can watch the next video.
Down below is a link to the test prep books that I have,
but also there's a link that'll take you
to all these videos if you're wanting to go through
more than one video at a time,
and take you through the entire playlist,
so be sure and check that out to go through
the ones that I've already uploaded,
and as they become available,
they'll also be put on this site as well.
Thanks for watching this video.
I hope this helps, and good luck with your ASE exam.