The Lemon Fool

I have a 500mm hole to make in a concrete block wall. Can anyone suggest a good way to do this?

Last time I did something similar (a 400mm hole), I chain drilled using a core drill and finished off with a chisel bit in an SDS drill. It took a long time.

Julian F. G. W.

How thick is the wall?

Is it a square hole?

A petrol disc cutter is the tool you need if the hole is square.

John

Why do you keep making holes in walls?

Dod

It is a round hole.

The first hole was for a fan. This one is for some ducting to vent outside.

I think the wall is about 11 inches including plaster. Thinking about it (based upon a 4" hole I drilled), the blocks are probably hollow. The wall is a bit patchworky (with some brickwork among the blocks) so it could be anything.

Julian F. G. W.

jfgw wrote:It is a round hole.

The first hole was for a fan. This one is for some ducting to vent outside.

I think the wall is about 11 inches including plaster. Thinking about it (based upon a 4" hole I drilled), the blocks are probably hollow. The wall is a bit patchworky (with some brickwork among the blocks) so it could be anything.

Julian F. G. W.

BS EN 771-3 hollow blocks have a standard face size of 440 x 215mm thus your 500 mm hole will be over 2 blocks so chisel out along the pointing and then radius.

I have an SDS drill and hole boring kit that I used for something similar. If you don't want to buy then you can hire something like this....

https://www.hss.com/hire/p/diamond-core-drill-dd150

Other suppliers are available...
Phil

That is a big hole. First thing to do would be to check the position isn't going to cause structural problems. If it's in a structural wall I'd make sure it's not close to another opening or point of bearing of a lintel or steel beam. From other posts you seem to have a good idea on these things but I think a caution is worthwhile in casef anyone else reads this at some stage in the future

If it is safe to make the opening I think the easiest way is to take the plaster bach to the blockwork and see what you are up against. If it is pure blockwork angle grinding a full block out and half of the two blocks above or below as appropriate gets you most of the way there. It creates a lot of dust so the other alternative would be to drill a hole in the wall and then cit the blocks out with a special blade in an alligator saw or similar. It's worth a try although some blockwork saws easier than others. It will still create dust but it's not as fine and easier to tidy up.

If the hole is likely to cause structural problems you might need a structural surveyor to have a look at it.

sg31 wrote:Take the plaster bach to the blockwork and see what you are up against. If it is pure blockwork angle grinding a full block out and half of the two blocks above or below as appropriate gets you most of the way there. It creates a lot of dust so the other alternative would be to drill a hole in the wall and then cit the blocks out with a special blade in an alligator saw or similar

Seconded. Use a big (230mm disk) angle-grinder with a diamond blade - and with great care in case you hit steel: the blade will either go straight through that as well, which might have structural consequences, or kick back, which might have painful consequences.
(I have a big Makita 9000 series grinder that will go straight through just about anything!)

jfgw wrote:I have a 500mm hole to make in a concrete block wall. Can anyone suggest a good way to do this?

Last time I did something similar (a 400mm hole), I chain drilled using a core drill and finished off with a chisel bit in an SDS drill. It took a long time.

West End job?

XFool wrote:

jfgw wrote:I have a 500mm hole to make in a concrete block wall. Can anyone suggest a good way to do this?

Last time I did something similar (a 400mm hole), I chain drilled using a core drill and finished off with a chisel bit in an SDS drill. It took a long time.

West End job?

Something like this?



Scott.

jfgw wrote:I have a 500mm hole to make in a concrete block wall. Can anyone suggest a good way to do this?

Julian F. G. W.

Shaped charge?

bh

The Hatton Garden mob used a mighty Hilti DD350 industrial coring drill that will drill 50cm holes. For extended use you either need good shoulder muscles or a mounting rig

Thank you for your replies.

Removing a block first may work, I'm not sure how the hole will line up with the blocks yet. I don't have an alligator saw but these blades for a reciprocating saw get good reviews, https://www.screwfix.com/p/dewalt-dt242 ... 57mm/2443v although the job might take some time.

I found a Hilti DD350 for hire at £220 for one day. The 500mm core drill would be extra. Unfortunately, there is nothing of significant value the other side of the wall that would justify the cost.

Do B&Q sell shaped charges?


Julian F. G. W.

It might be easier to start with the hole, then build a wall around it

--kiloran

kiloran wrote:It might be easier to start with the hole, then build a wall around it

--kiloran

There is a grain of truth in there. Sometimes it's easier to make a bigger hole by removing blocks and then filling in to the required size by using standard bricks.

Each job is different.

jfgw wrote:
Do B&Q sell shaped charges?

They’re probably cheaper at screwfix...,

But having thought about it, perhaps the t’Thunderbolt and Lightfoot’ method might work too.

Bh