I need to drill 2 small holes on the underside of my Silestone countertop to secure a new dishwasher. What kind of drill bit can I use?

AFAIK Silestone is some kind of artificial quartz, but I wonder if it's too hard for normal masonry bit.

  • Out of curiosity, why are there not already dishwasher mounting holes? Is this a new dishwasher where one wasn't installed before? – Mike Powell Dec 13 '10 at 15:04
  • @Mike: it's replacement and does not fit the location of the old mounting holes. – Geoffrey Zheng Dec 13 '10 at 15:56

Silestone is natural quartz aggregate, held together by a polymer binder. I believe it's something like 85% quartz. You'll need a diamond coated bit like this one; it's a tiny hole saw where the rim is covered in diamonds:

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It's a bit tricky to start, you need to hold the drill at a slight angle so that only one side of the circumference is grinding, and then as you start to develop a crescent-shaped groove you gradually move your drill perpendicular and continue with the rest of the hole. If you don't do this the thing will walk all over the place since it has no positive center like a regular hole saw.

For drilling upside down you'll want a spray bottle with water to keep the surface as wet as possible. That Hitachi bit I linked to has a spiral groove going in the opposite direction of a normal drill bit, which serves to draw water into the hole, which will help you when drilling upside down.

Obviously you want to be careful not to drill too far and pop out of the top of your nice counters.

For fastening the dishwasher you'll need a plastic anchor into which to run your screws, and I've found this type works great. In a solid material the plastic will extrude around the screw threads and hold really tightly. They do sell them at my Lowe's but I can't find them on their website. The 3/16" size is probably what you need for your dishwasher, and the diamond bit I linked to above is also 3/16". Good luck!


I had a similar situation and solved it by gluing a strip of wood with the same finish as the cabinets underneath the counter top and securing the dishwasher to it instead. If you have the room underneath your counters for it, this might be something to consider. IIRC, the piece I used was 3/8" high by 1" deep and ran the width of the opening.

If you don't have the room, or just want to screw the dishwasher directly to the counter top, this article on How to Drill Holes in Silestone suggests using a diamond-tipped drill bit and a pool of water for lubrication and cooling. Since you'll be drilling on the underside, the lubrication method they describe won't work; I'd suggest drilling in very short bursts, allowing the area to cool between bursts.

  • Btw if he has little room he can glue a steel stripe instead - it will occupy much less space. – sharptooth Dec 13 '10 at 6:48

With my granite counter top there are steel plates which have been epoxied to the underside of the granite counter. The dishwasher clips then are bolted into these. When my granite counter top was installed the installers left the plates and the epoxy (since the dishwasher was not there yet) but I am sure you can find the same thing at a hardware store.

The other thing to look into is side mounting the dishwasher (I actually have one of the top bolts in use and the other side of my dishwasher is side mounted. This worked the best when I was putting in the dishwasher and allowed me to get it secured with very little movement when it is opened and closed).

Also, just noticed these "Granite Grabbers" on Amazon. I have not used them but they might be worth a try.

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  • 3
    I didn't accept this answer since it's a solution rather than an answer, but it's a much much easier solution, as I'm not handy enough to try the delicate drilling act in the accepted answer. So I bought this piece and it works like a charm! – Geoffrey Zheng Feb 10 '11 at 15:59

If you have trouble getting hold of a diamond tip drill, or simply find that far too expensive, you should be able to use a regular glass drill bit for the job. Two precautions are required:

  1. Don't drill at too high a speed
  2. Keep the it cool

The simplest way to achieve cooling for the bit is to create a circle of putty around he spot to be drilled and fill it with turpentine.

  • I don't believe a glass bit, being hardened steel, is actually hard enough to drill quartz. I think a diamond bit may be the only option and at $14 the one I linked to certainly shouldn't break the bank. – Mike Powell Dec 14 '10 at 1:45
  • @Mike, I can't get hold of a diamond bit for anything less than $50 where I am, so on that score you're lucky. As for the glass drill, I've used them to drill through marble. Just bear the above points in mind. – John Gardeniers Dec 14 '10 at 2:23
  • the OP is in New York, so he should be able to get his hands on one of the $14 versions. Also marble is actually quite soft as minerals go, so I'm not sure that's a great comparison. – Mike Powell Dec 14 '10 at 15:50

I used a bit from Menards store like a Home Depot or Lowes. I cut a 1 3/8 hole in Cambria quartz for a faucet. The Brand was Montana MB-65208 diamond tipped bit. I cut at an angle to start then cut straight through by using the pumping motion, Applying water every few seconds. I did a practice and a real cut no problems. Good Luck all.


Is your dishwasher configured so that you can attach it to the sides of the cabinets instead? This method would only require a normal wood drill bit for a pilot hole. You may want to put some tape or a depth stop collar around the bit so that you don't drill all the way through the cabinet walls though.

An employee at a local kitchen store told me that I should consider using the same clips to side mount the dishwasher to the cabinet using the above method instead of the underside of the counter top. I then looked in the installation manual for my model of dishwasher and sure enough, it's shown right there in black and white.

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