I’ve built a few of these, but used a different mix this time and a pretty complex form so I’m going to be doing much more grinding and finishing than I’ve ever needed to do… anyone had to do grinding of a countertop before (client wants exposed aggregate, and going to have to clean up radiused edges).
I’d rather not buy some expensive tools for what’s likely to be one use. Anything that will work well on a RO sander or angle grinder?
Thanks…
PaulB
A pro painter evaluates a variety of drywall sanders and dust collection systems for quality of finish, user fatigue, and more.
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Replies
How about a diamond faced peel-n-stick sanding paper? or a concrete surface softner that has a 30 minute open time so you could sand using regular grit paper?
Seriously though, your probably doomed. I saw my blue stone sub using a killer carborimdum cone shaped disc on hos dedicated drill motor.
Good luck.
This might be messy and I've never done exposed aggregate concrete, but couldn't you use a hose and spray off the cement surface while it's still wet to expose the aggregate rather than grinding after it's cured? I soppose the customer wants it smooth and spraying it off would leave it rough. What about renting a terrazzo grinder?
There are a lot of both silicon carbide and diamond abrasives that will do the job for you. The cheapest abrasive for small projects is 7" silicon carbide sandpaper. I use it with a porter cable fiberglass backer as it keeps it nice and flat. I would guess some 60, 120 and 220 grit would take care of most of the EDGE work (I am not sure how effective sandpaper would be on grinding a TOP down to exposed aggregate). I run the paper on a makita 9218sb (4000 rpm pistol grip with a 5/8" threaded spindle) This is in almost every stone countertop fabricators toolbox.
You could try 5" silicon carbide grindstones (on the same makita 9218) but until you get the feel for doing it, balancing a new wheel with a wheel dressing tool is challenging. A new stone will chatter and vibrate to the point that it does more damage than good. Balancing these stones is a skill well worth developing as they are cheap and very effective.
Get a 24, 36, 60 and 80 grit if you go this route. The higher grits don't work well for me (stones clog up, chatter, and end up doing damage)
You could go to a granite fabricators supply house and get some diamond impregnated resin discs and velcro backers. Run these on the makita as well but keep wetting them as you go. Keep a bucket of water and a grout sponge handy for this.
Get the 5" diamond pads, buy cheap as concrete is so abrasive it will wear out the bonding matrix (resin) before it wears the diamonds. I would recommend the hard plastic resin ones (very inflexible) in 30 grit, 50 grit, 120 grit, 220 grit and 500 grit. Also get a 4" diamond turbo cup wheel to take down really big irregularities before starting the resin pads. I always buy a velcro adapter for each diamond pad and just spin it on the grinder rather than using the velcro. They will get out of balance if you try to swap pads on just one velcro backer. Especially on the 30 and50 grit pads.
I wouldn't pay much more than 10 dollars a piece for these low end diamond pads but I haven't bought for a while, Prices seem to be dropping on diamond abrasives.
Braxton Bragg is very helpful and has a comprehensive inventory. Granite city tool seems ok, lower prices, sometimes out of stock but ok if you are trying to keep costs down.
Get the best dust mask you can afford. I use a 3m silicone rubber mask with replaceable filters. Paper masks are no substitute. Silica dust is very bad for your lungs. I use as many wet processes as possible to avoid dust.
Had to level some bad stair treads poured in a Nursing home fire stair well..we used diamomd cup stones..I think
http://www.mscdirect.com can hook ya up, if not, http://www.mcmaster-carr.com has em. Ezy and wet it down first..CUP is operative here..not a disc.
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Fu-Tung Cheng (the concrete countertop guy) has an online store for supplies. Try this link:
http://www.concreteexchange.com
look under the finishing links, they have diamond pads that will work on a 5" grinder
Thanks guys...some great tips as well as a "duh"...I don't know why I didn't check Buddy Rhodes (I used his mix) or Cheng first. Must be overtired.
Just as a footnote... wound up using 60 grit on a ROS to level it all out. Worked quite well (although went through quiteeeee a bit ;) )
I think you meant quiiiiiiiiiiiiiiiite a bit!!
What's up with the threads you post lately? Seems by the time you get responses, you have a solution.
Must be Prospero................yourcontractor@aol.com
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Hey Paul,
How about some pics of this concrete counter top?
I'm sure I'm not alone when I say I'd love to see it!
Ericyourcontractor@aol.com
It's Never Too Late To Become What You Might Have Been
Funny you ask Eric... I was thinking about photographing the whole process since questions about it seem to come up quite a bit here. Believe it or not, I gave away every single camera I owned (sour grapes?) but I'm doing another one* and I've been thinking I oughta bite the bullet and buy a high end digital (yeah, I feel like a traitor) so maybe I'll be able to oblige.
(*P.S...when the client says "oh by the way...can we move the sink knock out a few inches this way... don't forget to move the faucet knock outs as well... want a concrete countertop?)
Paul"The Distracted"B
Try http://www.counter-weight.com they have a tools list, a how to video and a lightweight concrete mix for countertops that works great, you can grind it the day after the pour.
I've ground concrete using a diamond pad setup. Never tried regular sandpaper. How long had you let the concrete cure? What kind of paper....al-oxide??? Did you do this wet or dry?Thanks, I'm always looking for another way.
It was still pretty green (24 hrs). I used dry 60 grit on a ROS to flatten some trowel marks and ease the edges. Used 150 for a finer finish but went through bazillions of them. If the client wanted a really polished surface I'm sure sanding wouldn't be the way to go but in this case it was a cheap, quick solution that worked quite well.