Cutting a new window hole in a 4" thick conrete block wall - tool recommendations?

[trancenotes1776]

Hi again,

I want to cut a hole for a new window in my house. It's got fairly standard cavity walls, built of concrete blocks. Actually the blocks are somewhat n on-standard as they have foam insulation inside them (I mean inside the act ual blocks - not inside the wall's cavity.) The only masonry-cutting tool I own is a 9" angle grinder. This will cut concrete blocks no problem, but o nly to about 3" deep. I suppose could hire a 300mm grinder for about £

28 a day plus the cost of the cutting disk which I'm guessing won't be at a ll cheap.

Rotary grinders in general make an insane amount of dust. Is there any othe r tool that anyone can recommend? (I'm visualising something like a very la rge jig-saw with a diamond blade...)

Thanks for any tips you can offer,

JD

[Dave Plowman (News)]

Mark out, and carefully drill a hole (at right angles to the wall - use a set square etc to check) right through at each corner. Join up the holes inside with a pencil, etc. Cut from both sides with your angle grinder.

[dennis]

Never used one though.

[GB]

Apparently, wet rotary saws make less dust - presumably it ends up as a nasty wet slurry instead. You'd have to hire one, though.

If I had to do it with the tools I have, I'd tape everything up with plastic, then use a 9" angle grinder to make a neat hole on the inside and outside, and then join up those lines with an sds drill and chisel attachment.

[Dave Plowman (News)]

And?

[Huge]

And the answer is ... a chain saw. No, seriously. Fitted with a concrete cutting blade/chain.

[John Rumm]

I have cut right through a solid brick (i.e. 9" double skin - but no cavity) wall with a 9" AG in the past. It can get most of the way through a skin, and then its easy to take the last bit out with a SDS drill.

The only thing that really would fit the bill is either a larger stone saw wit water feed. That cuts down the dust a bit (still very messy and wet as well though), or, go for a wall chaser based on a 9" grinder platform, and only fit one disk to it. Armed with a good cyclone collector you will be able to capture most of the dust.

[Tim Lamb]

In message , Huge writes

Or hire an alligator saw. Still get lots of dust and need two hands. Scaffold tower?

>

[John Rumm]

Last time I did it, I was cutting through a wall from someone's garage into their hall (garage conversion). It started in the garage having completely closed in the space with sheeting etc. Got dressed up in a head to toe bunny suit, respirator, goggles, and ear defenders, and took a 1kW work light with me. I could just about see what I was doing, and I was able to contain most of the dust in the garage, but not quite cutting right through into the hall. Then marking the cut position by drilling through in a few places, before using a wall chaser with collection to cut the remaining half inch from the hall side of things.

Still created a hell of a mess in the garage though.

[Dave Plowman (News)]

No door in the room? The room where you are cutting out the hole for the window is going to need decorating anyway - so a little more dust isn't going to make much difference. I fitted a much larger window to my bathroom using an angle grinder on a 9" brick wall - and the dust wasn't spectacular.

Really? You must be a fast worker. ;-)

[Capitol]

I have, they work quite well on concrete blocks and fairly soft bricks, but struggle on hard stock bricks. Never tried them on engineering bricks.

[GB]

We had a window enlarged when we moved in here - I didn't have the time to DIY it, and frankly I'd have been scared. Out of my league. They did it with a Kango hammer, and managed a very neat result.

[Andrew]

A Petrol 300 mm cutter can be hired by the half day where I live and should have a water sprayer to control the dust. Using one without a dust suppressor in a public area is against H&S rules.

They use a microscope to measure the wear on the diamond blade.

[Brian Gaff]

And then the top of the window hole falls onto your head leaving an interestingly shaped hole and a crack all the way up the wall.

Brian

[nospam]

Yes, I recall my dad doing exactly that about 40 years ago. He took a window out to replace it with patio doors, either forgetting that the window might be structural or assuming that the bricks would support themselves for a while ... there followed a frantic scramble to get an Acro in place!

[Dave Plowman (News)]

I used my trusty DeWalt SDS to first remove the bricks for the Acro then lintel. Once that was in place and the mortar set, cut out the rest with the angle grinder. Wanted a nice neat cut on the external bricks. And it worked very well. First time I'd done this. But did have decent scaffolding since it was first floor.

Angle grinder was a Lidl one with Toolstation diamond blade. Nice soft start - and the two cost less than hiring.

[Dave Plowman (News)]

Ah. My angle grinder cuts through a standard brick. Thought that was why it was the size it is. But even if not, a nice neat edge to the face as deep as it will go followed by splitting should still give a decent job.

[rick]

Use the angle grinder to give you some guide cuts .. and then set to it with bolster & lump hammer.