Hi All,
I am polishing the edge of a granite worktop with diamond pads velcroed to a sander. When I get close to the finest pad I can see white dots in the surface which don't seem to polish out. Any idea what I am doing wrong and how to get rid of them?
Many thanks
Lee.
Have you examined them with a hand lens? Are they actual dots or simply pores in the granite that have filled with sanding dust? Most rocks contain small pores if you go fine enough. If that's what they are, then a wash in an ultrasonic bath should shift them. But your worktop is probably too large for that, in which case I'd try a pressure washer with a touch of detergent in the water.
If they're not pores then perhaps they're tiny impurities in the stone. If so, they should sand out but others may appear.
Hi Chris
I think they are probably pores filled with the sanding dust. Will give the pressure washer a try.
Thanks
Lee.
Thanks very much for your reply Chris the pressure washer did the trick. Whilst the freshly polished bit feels at least as smooth as the original bit (might even feel smoother), it is not as shiny as the original one. Will this be remedied by adding granite sealant or do I need to keep polishing it?
The worktop is outside so assume I will need to seal it (any recommendations?)? The newly polished bit is definitely not water proof as it absorbs the water when I clean it and takes a few mins to dry.
Many thanks
Lee.
No idea about using a sealant. You could try a small patch to see if it does what you want.
Normally, when polishing stone, you go finer and finer with the grinding medium, usually ending up with a very fine alumina or even diamond paste, but it's hard work (a bit of a grind, you might say!).
Each polishing stage leaves fine scratches, and the finer the grit, the finer the scratches, until eventually they are finer than the wavelength of visible light and invisible to the knackered eye.
I have only used the diamond disks so far. They go from 50 grit down to 6000 with probably 8 disks between them.
6000 grit is about 2.5 microns. Wavelength of visible light is around 0.5 microns. Grit often used for polishing gemstones is 14,000 (1 micron) although for the best polish 50,000 grit is recommended (getting on for 0.5 microns, i.e. what I was talking about earlier). Only using 6000 grit might explain why you're not getting such a good shine as you would like. 50,000 grit diamond polishing pads are available, as is 50,000 diamond paste for using on a cloth and polishing by hand. Google is your friend, but your bank manager might not agree!
The Internet(tm) says there are granite sealers and waxes.
I'd think that polishing ever-finer will get to "just as shiny", but don't see how it would get the surface waterproof. So skip the tedious part of mirror-polishing, slap a shiny waterproof sealant on it, and done?
Thomas Prufer
Granite is 100% impervious so its likely *adsorbing*, not absorbing. Guess more polishing will reduce surface roughness and fix that
I have never heard of granite needing waterproofing.
My guess is that isn't to seal against water but to sell product and provide a sheen.
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