This App will calculate the quantity and types of 200 series blocks for concrete core filled, steel reinforced masonry in a standard building.

The different block types allow for concrete core fill to bond beams, lintels above openings and beams under sills.
Show Me Print Block Graph Paper

Drilling Holes Through Concrete Masonry Walls

If you need to drill or cut a hole through a 200 Series concrete filled masonry wall, depending on where the hole needs to go you may have to cut through the entire 190mm of concrete block, through a concrete filled and steel reinforced core, or only through the 2 ~ 45 mm sidewalls of the block into the hollow core (much easier).

To find the empty core centres (the easiest location to cut) do this:
If you can see the block joints, just make sure you position the hole in a hollow core. So from a block end measure Horizontally 100mm or 300mm, and vertically from the horizontal (bed) joints up or down 100 mm to the empty core centre.

If the wall is rendered or sheeted, and you can't see the block joints, from the wall end, measure horizontally to any odd multiple of 100 so: 100, 300, 500, 700, 900 etc. From the bottom of the wall measure up the same odd 100mm measurements to find the centre of the empty cores.

If the wall is not concrete filled, ALL these points are hollow and easy to drill. Normally the wall is concrete filled, as the diagram above shows. Click Grout to see where the concrete and steel goes (preferably not a place to drill)

Usually the top 2 courses of the wall are solid filled (a bond beam from wall top to 400 mm down) All wall ends and corners, each side of all openings, and above all openings are also normally filled. Also vertical cores (top to bottom) at given horizontal centres (maybe 600, 800, 1200 etc) - These you cannot guess easily.

To make sure the position you choose is actually an empty core, drill a very small hole to check - if you go more than about 50 mm without breaking through, you're not in a hollow core.

BE AWARE that any electrical or plumbing work will likely also be placed in these hollow block cores (before the concrete is poured) so once you've drilled through the outer wall of the block and into its hollow core LOOK INSIDE TO CHECK WHAT's THERE. Obviously it's easier to drill into the hollow core from each side of the wall, so you don't need to go into the wall centre.

Also look for electrical, plumbing (or any other) outlets on the inside of the wall first. These will normally be in the centre of a hollow core, and indicate wiring or plumbing running all the way to the top of the wall in that core.

If you have to drill through a solid filled core, try to miss the steel rebar. For vertical bars, avoid the centre of the core (single bar per core). For horizontal steel (bond beams with 2 bars) the steel should be in the upper half of the block.