P80 sandpaper?! Holy crap!
It's like rubbing it with a brick! If I were to do something like that, I wouldn't use anything less than 220 or 240 (most probably, even 320)...
BTW, there are some problems with the matte finish done by sanding (i.e. scratching)... First, it looks uneven, no matter how good you are at doing it. May look great from afar, but up close it's not that impressive, and literally screams
Another problem is that wet and especially oily fingers will leave spots on the surface, when those micro-scratches are filling with liquid (water is not a big problem, but oily residue can leave quite long lasting spots). Blech... Ugly.
There is another method for getting rid of a glossy finish on plastic cases, which gives more uniform look and feel, and more consistent results (after certain practice). It doesn't truly make a "matte" finish, but leaves a nice textured surface -- definitely better than a high gloss. My buddies and I used this method a lot (and I mean a LOT) back in our university years (late '80s) to finish ABS plastic casings for various DIY electronis which we were selling. So, for those of you with an itch to experiment, here is what you need:
1. A chemical called dichloroethane
). It's an industrial solvent, with a nasty smell kinda similar to chloroform, but stronger. It's very aggressive to plastics like ABS, celluloid and acrylic (plexiglas). I am not sure how easy it is to find nowadays, though (back in the old years in Russia it was not a problem
)... As a replacement, you can use acetone
(widely available in hardware stores, it works, but not as good, and requires more practice), or toluene
(I never tried it myself, but it should work). Basically, you need an aggressive solvent that instantly dissolves an ABS plastic that the casing is made of.
2. A foam sponge. You might need to change it in the process, as it deteriorates quckly when soaked in solvent, and may ruin your work.
Before you begin, make sure to clean your surface from oil, dirt and other crap (alcohol wipes work great). Needless to say, you need to either disassemble your phone, or somehow protect areas that you do not want to touch -- I'll leave it up to you to think of the best way to do that.
OK, it's showtime now.
Soak a foam in a solvent, making sure it's quite wet, but not dripping. Then start touching the surface in a very quick vertical motion (like tap-tap-tap), but do NOT drag the sponge across the surface
-- just tap and lift immediately, tap and lift, tap and lift. Keep doing that, slowly going across all the surface you need to finish. This "buffing" will dissolve the surface layer of the plastic, and leave a uniform bumpy texture. Don't overdo it!
Like I said, you may need to change your sponge as it starts falling apart from a solvent, so have extra pieces ready. Luckily, the phone casing is very small, so you can finish it quickly, with less chance of a screw-up. Once done, let the case sit for several hours (or better yet, overnight), so the surface nardens.
The solvent evaporates very quickly, but it actually penetrates the plastic, which remains soft for quite some time. It you touch it before it hardens, especially with a hard object, you'll ruin it.
Before doing this on your phone, practice on some scrap glossy plastic
-- you can probably find plenty of old electronics or toys with suitable cases to be your guinea pigs.
At first, you may screw it up, but you'll get a hang of it very quickly -- just need to try it. The more you soak your sponge, the smoother your surface will be. Use less solvent, and you'll get more pronounced texture. But if your sponge is too dry, you will just end up with ugly blemishes. Just experiment and find out what works best for you -- it's much easier to do than to describe, trust me.
We were able to finish fairly large cases like this (surfaces approx. 20x20 cm or even more) with very good results -- the final look was very nice and professional. This is not just a theory -- it's a tried and true method! Just practice first, and you won't be disappointed.