Here's what the surface of the countertop looked like before. Dollops of paint from the painters and generally rough around the edges.
This is the surface after working upwards through 120, 240 and 400 grit discs on the power sander. Much smoother and no more blemishes. The swirls you see are the 'grain' of the concrete, much in the same way wood has grain. It's part of the character of the concrete. You can see how the grain in some places has changed after the powersanding.
Next up, wet sanding of the whole surface by hand, using 800 and 1500 grit tungsten carbide sandpaper. Concrete is itself very abrasive, containing sand and other rough stuff. It really wears thru the paper as you can see in the pic. By the time I finished the wet sanding process, it had been a solid 9 hours of sweat.
Here's how the counter looked like after the whole grinding/polishing process.
Next up, sealing and waterproofing the concrete with acrylic water-based sealant.
Step 1: Saturate the surface with water. I used a sponge for this. Let the water penetrate into the concrete for a few minutes.
Step 2: Wash the surface with 50% sealant solution. Let it soak in for a few minutes
Step 3: Gradually add 100% sealant onto the wet surface until its fully covered with full strength sealant. Let it penetrate for a few minutes. When it's soaked in nicely, wipe up the excess with a damn cloth. Let it cure for 30 mins or so, then repeat a 2nd coat.
Here's what it looks like all done. You can see a slight satin transluscent sheen on the countertop. That's the layer of acrylic that's formed on the surface. It's now waterproof.
And after all that hard work, ladies and gentlemen I present to you, the piece de la resistance...
