problems polishing granite - Contractor Talk - Professional Construction and Remodeling Forum

bkb0000 · 02-01-2009, 05:08 PM

i've been doing a little granite and marble over the last year- maybe 5 or 6 big jobs requiring some form of polishing, each with dark granites- absolute, quite a bit of pear blue, galaxy, etc. had great results so far. i have an alpha variable speed wet grinder with 2 sets of 2 diamond pads, one about half worn, one brand new and freshly opened up.

decided to give granite slab a try- in my own house first: got a big slab of pre-polished 3cm butterfly blue, cut out the sink, scuffed it a little with this new corner cutter i'm not used to, so i decided to polish it out.

here's what i have now: an 8x2 slab of granite with about 4" of that completely dull and cant get it to polish out. why mott the hoople? never had granite refuse to polish. the butterfly blue is cheaper than most (all) of the granite i've worked with so far, and more porous, but the un-dicked-with section is bright and beautiful shiny.

here's what i've done: cut out sink, roundovered the cutout, polished the roundover, noticed some surface scuffing from my new tool around the sink. started with 400 to rub it out, it rubbed out fine, moved to 800 and the pad stuck to the slab- its a well used pad, still has some tread on it, but it's like it's made of rubber... lots of friction, bogs down my grinder. turn up the speed and water WAY up, move to 1500 which behaves fine, 3000 runs smooth- dry everything off and it's all dull and hazy. i assume my 800 didn't do the job, it looks like it stopped polishing at 800. open up the pad (thinking i might have run it dry at some point), same problem. so i bought a new set of pads, opened them up real good, and try again- same problem.

switch to a fresh chunk of scrap- start with 200, dull it up, work through all the pads, new and old, still cant get it to gloss up. i started to work backward and try some reverse-engineering, and haven't yet gone back behind 3000- i apply 3000 to polished area and it stays perfectly polished, so it snot the 3000. gotta drop back to 1500 and try to polish it out, then 800, etc- is this the correct course of action? and what do i do when i find the pad that's holding me up?

what am i doing wrong?

bkb0000 · 02-01-2009, 08:33 PM

the odd friction of the older 800 grit was cured by opening, BTW. that's not the issue anymore.

Floordude · 02-01-2009, 08:49 PM

Two grits??

Your skipping too many grits to take the scratches out.

bkb0000 · 02-01-2009, 09:06 PM

i didn't skip any- 400, 800, 1500, 3000 on two different sets

wellbuilthome · 04-04-2009, 09:16 AM

I have the same set up , It hard to get the granite perfect after it gets scratched . I try not to run the tool over the edge of the grind . The best thing Ive done is to get the scratch out first, then start polishing lightly use a little presser for a longer time . clean very good between grits. To remove the hayes at the end i have a fine powdered diamond that you use to get the finish shine with the polisher .( It wont be perfect )John

Dan V. · 05-03-2009, 10:52 PM

I've had similar issues when polishing edges on Black Galaxy. You need to drop all the way back to 50 or 100 to get the scratches out. Low RPM (1500 max), plenty of water and don't be afraid to apply some pressure. As you progress through the grits, you need to feather out your working area. Using a wax marker, make concentric circles (or half-circles in your case) around the scratches and as you to move to each higher grit, move out to the next line.

StoneRenew · 05-04-2009, 10:44 AM

Granite polishing is very tough. You say you have polished Black Galaxy? But you can't polish this one?? Doesn't make sense to me. Black Galaxy is probably the toughest granite out there to polish because of the dye's and agers used when its Fabricated. With most dark granites you have to take it up to 8500 grit. It could be that your using the wrong kind of pads. Usually I dont go to resin till about 1000 grit. You also might want to try polishing with Tin Oxide for a final buff. What pads are you using??

StoneRenew · 05-04-2009, 10:45 AM

Quote:

Originally Posted by Floordude

Two grits??

Your skipping too many grits to take the scratches out.

He isnt skipping grits.

So Cal Chando · 07-21-2009, 09:03 PM

go all the way back down to 50 grit take your time make sure its smooth after every grit... use a polishing wheel.. and if that doesnt work u can use like a laquer.. "tiger ager" its used by the shops down here....

Bill_Vincent · 07-25-2009, 10:38 PM

My understanding is it's next to impossible to properly spot polish using a 4" polisher on a flat surface, like on a piece of slab or tile?

GraniteGirl · 08-31-2009, 08:17 PM

Hi Bill!! How are ya?!

Surface polishing is possible - with a lot of practice and the correct tools.

High quality resin pads like ALPHA or comparable brands, along with rigid polishing disks (also ALPHA, although a few others do exist) are vital to the process, along with a high quality buff pad suited to the color (light/dark) of the stone you are polishing.

You will need a variable speed machine and loads and loads of practice and elbow grease.

Suffice to say, not many DIY persons or folks that are not dedicated stone professionals are willing to spend the money or time to learn to do this properly. The initial outlay (cash wise) could end up being $400-$500 depending on the quality of your tools & pads. The rest really takes hours and hours of trial and error to perfect.

Bill_Vincent · 09-03-2009, 08:35 AM

Hey Lady!! Nice to see you found your way over here!!

brzelt · 09-06-2009, 11:23 AM

Is this granite acid sensitive?

From your description, I question whether you have a basalt or a true granite.
Most basalts (cheap chinese dyed 'granites') are almost impossible to polish plus
they are acid sensitive like most marbles.