Oops..Drilling Asphalt, I Hit a Rock
Installing our BoltHold anchors requires drilling a 1” hole in the asphalt and the layers below it. The depth of the hole is 6” or 12” depending on the length of the anchor.
Usually, once past the asphalt layer, drilling offers low resistance. It takes about the same effort to drill 6” or 12”. However, if you hit a rock, you may find it to be very time consuming to drill a 1” hole through the rock.
We have found that drilling a smaller hole first makes the task go faster. Drill a ⅜” (10mm) hole through the rock to the required depth, then re-drill with ½” and progress to 1”.
We recommend using the small 3/8" drill bit as a pilot hole in all cases. The reason is that asphalt tends to kick the drill before it is truly seated in the hole, because asphalt contains fine gravel and the drill bounces off these.