The technology behind Unigrit Sanding & Finishing Discs
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  1. #1
    Sr. Global Product & Training Spec Michael Stoops's Avatar
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    The technology behind Unigrit Sanding & Finishing Discs

    Those of you who have started dabbling with wet sanding and damp sanding may have heard terms like "texture leveling" and "texture matching" but aren't quite sure what they mean. You may have heard about certain sanding procedures being less invasive to the paint than aggressive compounding is and wondered "how can that be?".

    Hopefully this article will help clear some of this up and give you a better understanding of the technology involved.

    First off, traditional sand paper is essentially a bonding of abrasive material to a piece of paper. In simplest terms, this is pretty much what's going on, but in practice (at least when talking about Meguiar's Unigrit papers and discs or 3M Trizact papers and discs) it's a bit more high tech than that. For the purposes of this article, we're going to concentrate on grits used for typical defect repair, such as heavy swirls, bird dropping etch marks, etched in water spots, etc when correction is being done via DA sander only. Additionally, these grits are often used to level out the surface following a repaint. We will not be discussing the very aggressive materials used for wet sanding under other circumstances, or sand papers used for hand sanding procedures.

    These grits can be used to either texture level or texture match. So what's the difference?

    Both terms do exactly what their names imply:
    • A texture leveling process will flatten the paint by abrading off the high points of orange peel in order to eliminate texture from the paint. In varying degrees it will either reduce the presence of orange peel or totally eliminate it. But keep in mind that total and complete removal of orange peel means removal of a lot of paint. Texture leveling is usually done with a sanding disc as opposed to a finishing disc - sanding discs have the abrasive media bonded to the base film of the disc while finishing discs carry an integral foam backing between the abrasive media and the backer itself. The more texture is present, the more paint you have to take off. So on factory OEM paint, the smart move is to either go extremely lightly, or don't do it all.
    • A texture matching process will allow you to remove defects such as heavy swirls, scratches, etch marks, etc without flattening out the paint in that area. For spot repair, or even full panel repair, this texture matching is critical. While most people think it would be crazy to sand the paint and not remove the orange peel in the process, think about this: if you are doing a spot repair and you sand an area flat, it will stand out like a sore thumb against the surrounding paint. That's not good.


    Below we see a cross section of what typical orange peel texture would look like:



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    Sanding discs without the foam backer will cut the tops off the orange peel "waves" fairly quickly. The longer you sand, or the more aggressive the grit of the media, the more material you take off and the flatter in appearance the paint becomes. The initial cutting just takes off the tops, or peaks, of the orange peel texture and gives the sort of mottled appearance in the second image below. The dull spots are the peaks that have been sanded, the shinier and darker areas are the low spots, or troughs, of the texture that remain untouched. This is typical of what we expect to see with a 1500 grit sanding disc used on a pneumatic or electric DA buffer/sander.






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    Finishing discs will follow the contours of the orange peel, removing defects without eliminating the orange peel. This allows you to safely remove more severe defects without causing a mismatch in the texture of the paint from the corrected area with that of the rest of the vehicle. The potential downside to this, of course, is that you can't always see just how much material you've taken off since you're sanding both the high spots and low spots at the same time. This yields a uniform greyness as shown in the second image below. We would expect to see this sort of finish with a 1500 grit finishing disc.




    Of course, if you continue to use the 1500 grit sanding disc as described in the first situation above, you'll ultimately achieve this look as well. When texture leveling, that's how you know you've flattened the paint (or are darn close to it) - you've removed enough material that you're now sanding on the low spots. But you've taken off a LOT of paint by that time!!!

    We can take the above, totally flat paint, and refine the sanding marks to such a fine degree that we actually start to see some gloss coming back. By switching to a 3000 grit finishing disc we end up with something like the image below. This highly refined, very predictable and uniform sanding mark is now very easy to buff out.




    The technology that allows this sort of thing to happen is pretty interesting. As previously mentioned, these sanding and finishing discs aren't just tiny rocks glued to some paper. They are highly engineered structures that can independently flex and give, especially in the case of the finishing discs. Let's take a closer look.

    In the image below, the disc on top is a sanding disc and the disc on the bottom is a finishing disc. You can see the foam backing and the cushioning it gives to the finishing disc.



    Seen below is the surface of a 1500 grit sanding disc magnified 300x. You can see that the structure of the abrasive material isn't merely a bunch of small rocks glued to the disc. Far from it, in fact. This is a very uniform abrasive structure that yields a very uniform sanding mark. It's this uniformity and predictability of the sanding scratch that makes it so much easier to buff out, or to refine with further sanding.


    For scale, here is the same sanding disc with the sharp end of a fine sewing needle pressed against it.


    This is the surface of a 1500 grit finishing disc magnified 300x. While quite similar in appearance and structure to the image above (of the same grit, remember), there is something else going on here. As a finishing disc, this will have the foam backer to it, which not only "cushions the blow" but allows for something else to happen.


    That "something else" is this: the structure of the abrasive itself, coupled with the foam backer, actually allows the material to conform to and actually bend around the surface it's applied to. In this case, we can actually press the sharp end of that sewing needle into the surface and get the abrasives to wrap around it.


    When we look at a 3000 grit finishing disc (3000 grit is not available in a sanding disc) we see an even more dramatic example of this abrasive wrapping. The abrasive material here is almost like a series of serrated blocks attached to the disc.


    When we bring the sewing needle into play you can see just how tightly these bricks conform to the shape.


    This video clip, also at 300x magnification, shows the blocks moving and conforming to the tip of the sewing needle. The disc is actually totally dry here, right out of the box in fact.


    With this very fine level of movement provided by the abrasives and the foam it is possible for these blocks to conform to contours as fine as orange peel. This allows you to lightly sand away such things as heavy swirls, fine scratches and other defects while following the texture of the paint rather than leveling it. When used as a stand alone sanding process, 3000 grit DA finishing discs can actually be a less invasive way to remove more severe defects from paint than simply hammering away with a compound and cutting pad on a buffer. The damp sanding process used with these discs introduces no heat to the surface, and it exchanges the randomness of swirls and scratches for a very uniform sanding mark that buffs out with ease. In fact, where it used to be customary to buff out sanding marks with a rotary buffer, a wool pad and a very aggressive compound, we are now seeing more and more people using a DA buffer, microfiber pads and a SMAT abrasive compound such as M105, M101 or M100 to achieve the same result.

    Of course, that doesn't mean you should just start sanding instead of buffing every time you come across some really nasty defects. But with proper techniques, and proper understanding of just what's going on with abrasives like Meguiar's Unigrit and 3M Trizact, it's amazing what can be accomplished with limited risk to the paint.
    Michael Stoops
    Senior Global Product & Training Specialist | Meguiar's Inc.

    Remember, this hobby is supposed to be your therapy, not the reason you need therapy.

  2. #2
    Mr Sparkle davey g-force's Avatar
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    Re: The technology behind Unigrit Sanding & Finishing Discs

    Excellent, informative post Mike, thanks

    I've just learnt something

    So can 3000 grit DA finishing discs be used on a DA such as the G110 v2, or are they for air-powered DA's?
    Quote Originally Posted by Blueline View Post
    I own a silver vehicle and a black vehicle owns me. The black one demands attention, washing, detailing, waxing and an occasional dinner out at a nice restaurant. The silver one demands nothing and it looks just fine. I think the black vehicle is taking advantage of me, and the silver car is more my style. We can go out for a drive without her makeup and she looks fine. If I want to take the black one out, it is three or four hours in the "bathroom" to get ready.

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    Registered Member Selectchoice's Avatar
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    Re: The technology behind Unigrit Sanding & Finishing Discs

    Great post Mike!

    I know this type of post is time consuming to put together, but these make for some of best reading.

    More please?

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    Registered Member Selectchoice's Avatar
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    Re: The technology behind Unigrit Sanding & Finishing Discs

    Quote Originally Posted by davey g-force View Post
    So can 3000 grit DA finishing discs be used on a DA such as the G110 v2, or are they for air-powered DA's?
    They can be used with an electric DA. Use caution with the water though. (You don't want ....... )

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    Re: The technology behind Unigrit Sanding & Finishing Discs

    Great information Mike.

    Whoda thunk that 'sandpaper' can be that technical? Surely no me!

    Bill

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    Sr. Global Product & Training Spec Michael Stoops's Avatar
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    Re: The technology behind Unigrit Sanding & Finishing Discs

    3000 grit finishing discs can indeed be used with an electric DA buffer, but as has been pointed out, water and electricity don't tend to mix very well so caution is critical. Thankfully, when dealing with our Unigrit sanding and finishing discs you use very little water so any risk is greatly reduced. But still......THINK!!! And if you plan on doing any 3000 grit sanding with a DA for removal of heavy swirls, etc then you must use the foam interface pad as well. That's mandatory.
    Michael Stoops
    Senior Global Product & Training Specialist | Meguiar's Inc.

    Remember, this hobby is supposed to be your therapy, not the reason you need therapy.

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    Michael The Guz's Avatar
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    Re: The technology behind Unigrit Sanding & Finishing Discs

    Great article. A couple of my favorite videos are with Jason Rose and Kevin Brown discussing this very topic with Larry from Ammo.

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