Wednesday, September 19, 2007

Grinding Concrete countertop

So a year after making the form, and over a month since pouring it, I've started grinding the countertop for the basement bathroom. We're not exposing the aggregate (at least not on purpose), so the first part is all done by hand, starting with a 150 grit grinding pad, then 220, and then 400 grit. There are a few defects in the counter, I'm trying to embrace them, and say they give it character. There's a small upturn at the back of the counter, to meet the backsplash, I routered a piece of melamine to create it, and put packing tape over the rough wood, to give it a smooth surface. Well, you can see where the tape is on the countertop, and there's a few wrinkles from the tape as well. There's a void in the upturn at the corner, not major, will be less noticeable with the grout and tile. There's a fairly major crack at the holes for the faucet as well. It disappeared mostly when I did the slurry (it's kind of like grout). I sanded the slurry coat last night with 400 and 800 grit. It was pitch dark of course, so I was working with the construction light. I thought I'd try the grinding part a little, since things were going so well. I don't have a variable speed grinder, so I was feathering the trigger, and I didn't think it was going too fast. I guess it was, since the hook and loop pad holder blew apart. I tried fixing it to no avail. So I just cleaned up went inside and ordered a new one. 22 bucks for a new one, hope it last longer than the 30 seconds the first one lasted. I may need to rent a variable speed grinder, or just buy a cheap one. They have ones for less than 200, that look not bad. They're not the fancy, Fein ones like Cheng uses, but at least they're variable speed. I noticed on the same site, that the hook and loop pads were only $7. They look identical, they're 4" though, and I need 5. The 4" pads they have are only $12 as well, I paid $40 for mine. Maybe the quality isn't as good, or it's some kind of Cheng mark up. Anyways, it'll be at least a week until I finish grinding the top. It look pretty smooth now, with just the hand sanding, I was just going to sand it and call it a day. I think I'll wait for the new hook and loop pad holder though, it's already been more than a year.

6 comments:

Gary said...

You should have done the grinding one week after pouring. Concrete takes 28 days or so to fully cure and will destroy your pads at this point. The Cheng book indicates to grind after about seven days and polish a few days after grinding to prevent from ruining the diamond pads.

Derek said...

Haven't had a problem sanding it, I know it's fully cured. We're not exposing the aggregate, so what I read in the book says you can wait a little longer. The stones would be harder than the concrete, so you'd think those would wear the pads?

Nick said...

Harbor Freight sells a variable speed polisher (lower speed than an angle grinder) for $30. I bought one of these and it lasted through all 5 of our concrete counters - and we ground enough to expsose the aggregate...

Derek said...

Thanks Nick, I ordered a similar polisher off Amazon, the closest Harbor Freight to us is in Everett. Hopefully it'll make it through all our planned concrete countertop projects.

Mike said...

Hey Nick (or anyone else with advice). I just picked up a 7" variable speed polisher from Harbor Freight. Any advice on what grinding pads to use / where to get them?
I'm assuming I can buy a backing pad smaller than 7" to have more options with pads.
Thanks,
Mike

Phil said...

Hi -

I have just poured my countertops & need some advise on a grinder. Should I just buy the cheap $40 one from harbor freight or a milwakee that costs $120. Both are variable speed and approx the same power.

Thanks in advance.