I'm mounting a rafter support for a lean-to at the side of my house (45mm x 120mm wood beam). I know that the bricks are 100mm thick, so I'm wondering what length of expansion plugs (rawl plugs) I can use. I don't want to drill right through the brick obviously but am wondering how far I can go?

  • I am not sure what you mean by lean-to. If the rafters go all the way to the ground, I wouldn't worry too much about it because you're not relying on the fasteners to bear the weight of the ledger or prevent the ledger from pulling away from the wall. If it's a shed roof, it may be necessary to drill all the way through and anchor to the frame of the house for safety. Jan 7, 2019 at 12:52
  • The rafters would go onto another beam held up with fence posts. I digress... I really just want to know how far you can safely drill into a brick without any risk of damaging/cracking the other side as I want to avoid letting water into the insulation cavity of the house. e.g. for 100m thick brick, can you drill 90mm, or 75 etc? Jan 7, 2019 at 13:05
  • 100mm is fairly thick. I don't think you need to go more than 70mm to get the support you need since you'll be putting quite a few in. Since you are drilling you'll probably not crack the brick. Just slow down as you get to the other side. Brick is fairly soft, if not cement brick, and a carbide tipped bit whether hammer or not will go through it. Jan 7, 2019 at 14:19
  • The biggest issue might be the expansion plug cracking the brick -- don't over-tighten. Jan 8, 2019 at 0:49

1 Answer 1


I think 75% of the brick should be fine.. normally there is a "blow out" of the brick within 1cm of reaching the other side... but this is really dependent on the type of brick (cement, clay, etc), moisture contnet, age of brick, diameter of hole and strength of the hammer action of the drill

If it were me, I would drill to about half way, then add some water to the hole and start to reduce my force on the hammer drill in order to slow the drilling speed. -- do not attempt to drill if you have an SDS type drill since the hammer action is not dependent on your applied pressure.

once the plugs are in place, you should have no issue hand tigtening the plug. just dont over-tighten

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