I've learned the hard way that picking the wrong bit for granite can turn a quick DIY task into a total nightmare in about thirty seconds. If you've ever tried to drill a hole for a new faucet or a soap dispenser through a thick slab of stone, you know exactly what I'm talking about. Granite is incredibly dense, tough, and—let's be honest—completely unforgiving. You can't just grab a standard masonry bit from your toolbox and hope for the best. Well, you could, but you'd likely end up with a ruined bit, a cloud of smoke, and maybe even a cracked countertop.
Choosing a proper bit for granite is less about "making a hole" and more about "grinding through" the material. Since granite is one of the hardest natural stones out there, you need something even harder to get through it. That usually means one thing: diamonds.
Why Diamonds are a Granite's Only Friend
When people talk about a bit for granite, they're almost always talking about diamond-tipped core bits. Here's the thing: you aren't actually "cutting" the stone in the traditional sense. A wood bit has sharp flutes that shave away layers of material. If you tried that on granite, the stone would just laugh at you and dull the edge immediately.
Instead, a diamond bit works like sandpaper on steroids. The tip of the bit is coated in tiny industrial diamond particles that grind the stone into a fine powder. Usually, these bits are hollow—that's why we call them "core bits." They cut a circle around the perimeter and leave a solid "plug" or core in the middle. This is much more efficient than trying to pulverize the entire diameter of the hole.
Vacuum-Brazed vs. Sintered Bits
If you've started shopping, you've probably seen terms like "vacuum-brazed" or "sintered." It sounds like technical jargon, but it actually matters for how long the bit will last.
Vacuum-brazed bits are usually the go-to for most home projects. The diamonds are bonded to the surface of the steel using a specialized process that leaves them very exposed. This makes the bit cut fast and aggressively. The downside? Once that single layer of diamonds wears off, the bit is basically trash.
Sintered bits, on the other hand, have diamonds mixed throughout the metal bond. As the metal wears down, new diamonds are exposed. These are great if you're planning on drilling dozens of holes, but they can be a bit overkill (and pricier) if you just need to install one filtered water tap.
The Big Debate: Wet vs. Dry Drilling
One of the first questions people ask is whether they need to use water. Honestly, if you want your bit for granite to survive more than one hole, always use water.
Heat is the absolute enemy of diamond bits. When that metal spins against stone at high speeds, it generates a massive amount of friction. If it gets too hot, the diamonds can literally "glaze" over or fall off the bit. Water acts as both a coolant and a lubricant. It also keeps the dust down, which is a big deal because granite dust isn't something you want to be breathing in.
If you're working on a finished countertop and don't want to spray water everywhere, you can make a little "dam" using plumber's putty. Just shape it into a ring around where you're drilling and fill it with a little bit of water. It keeps the bit submerged and makes the whole process much cleaner.
Technique is Everything
I've seen people buy the most expensive bit for granite available and still ruin it because they treated it like a regular drill bit. You can't just push down with all your weight.
The trick is to start at an angle. Since these bits don't have a center pilot point (the little pointy bit in the middle), they tend to skate across the polished surface of the granite. If you start flat, the bit will dance around and scratch your beautiful stone.
Instead, hold the drill at about a 45-degree angle to start a small "notch" or groove. Once that groove is deep enough to hold the bit in place, slowly tilt the drill up until it's perfectly vertical. From there, let the diamonds do the work. You only need light to medium pressure. If you're leaning on the drill like you're trying to win a wrestling match, you're going to overheat the bit.
Speed Matters More Than You Think
It's tempting to pull the trigger on your drill all the way and let it rip at max RPM. Don't do that. Most diamond bits actually perform better at lower speeds. If you spin it too fast, you're just creating heat without actually grinding much stone.
Most pros suggest keeping the speed somewhere between 600 and 1,500 RPM, depending on the size of the bit. Smaller bits can handle slightly higher speeds, while those big 1.5-inch bits for faucet holes need to go slower. If you start seeing sparks or smelling something burning, stop immediately. You're going too fast or not using enough water.
Dealing with the "Blowout"
One thing nobody tells you about drilling granite is what happens at the very end. As the bit for granite reaches the bottom of the slab, there's a risk that the last little bit of stone will "blow out" or chip away in a large chunk.
If the underside of the granite is going to be visible (like a bar overhang), this can be a real bummer. The best way to prevent this is to clamp a scrap piece of wood or even another piece of stone tightly against the bottom of the slab. This supports the material as the bit comes through. Alternatively, you can drill about 90% of the way through from the top, then go underneath and finish it off—though lining that up perfectly is a challenge of its own.
Picking the Right Size
Before you click "buy" on that bit, double-check your measurements. Faucet holes are usually 1-3/8 inches, but some high-end fixtures might require something different. Don't guess. Granite isn't like drywall; you can't just "embiggen" the hole easily with a rasp if it's too small.
If you do find yourself needing to slightly enlarge a hole, you can buy a diamond finger bit or a milling bit. These are designed to grind the edges of an existing hole rather than drilling a new one from scratch. They're a lifesaver if your measurements were off by a fraction of an inch.
Making the Bit Last
If you have a lot of holes to drill, you'll notice the bit might start to feel "dull" after a while. This usually happens because the metal bond has melted over the diamonds, or the diamonds have worn down.
A pro tip to "sharpen" or dress a diamond bit is to drill a quick hole into something abrasive, like a cinder block or a piece of scrap sandstone. This wears away the excess metal and exposes fresh diamonds, giving your bit for granite a second life. It's a simple trick, but it can save you thirty bucks on a new bit.
Safety is Non-Negotiable
I know, I know—nobody likes talking about safety gear. But when you're drilling granite, it's actually important. Even if you're using water, tiny shards of stone and diamond can fly up. Wear eye protection. Seriously.
And if you decide to drill dry (which I really don't recommend), you absolutely must wear a high-quality respirator. Granite contains silica, and breathing in fine silica dust is a one-way ticket to some nasty lung issues down the road. Keep it wet, keep it cool, and keep your lungs clean.
The Bottom Line
At the end of the day, getting a clean hole in a slab of stone is incredibly satisfying. It looks professional, and it feels like a major win. Just remember that the bit for granite is a specialty tool. Respect the material, take your time, and don't skimp on the water. If you follow those basic rules, you'll find that granite isn't nearly as scary to work with as it looks.
It really comes down to patience. Let the tool do the work, keep the heat down, and you'll have a perfect, chip-free hole every single time. Happy drilling!