700 mm sandstone wall, how to cut hole

[telnet]

Hi, My sister has a ground floor tenement flat in Glasgow. The outer skin is 700 mm thick sandstone blocks. I want to vent the cooker hood in the new kitchen out through the wall. The spigot is 150 mm round which I will convert to flat channel which will run along the top of the units.

My problem is how to cut the hole. I suppose I could convert the flat channel back to 125 mm round and then go through the wall with a 127 mm core drill. Obviously it would be better to take the rectangular flat channel through the wall. Any suggestions about how to cut a rectangular hole through 700 mm of sandstone would be gratefully accepted.

 

[KenGMac]

telnet,Hi

Bluntly there is no way a rectangular hole could be cut in a Sandstone wall the collateral break out would be huge, imagine you are trying to lever a bit of sandstone out of a hole that small and several hundreds of MM distant, never mind 700.MM away.

Only viable option, unless you are a Stone Mason is using a core drill plus the transition from rectangular to round. I have done this on dozens of jobs for Bathroom, Kitchen, and Gas Flue venting.

Points to consider? the depth of the Lath and Plaster Internally, and the possibility of break out on the external that is if you are too fierce on the last few MM of the core prior to it emerging on the outside this can cause spalling around the core.

Sandstone is highly variable in how it will or will not core, some stones are very hard, others soft and even within the one stone being cored the texture and hardness can and probably will vary not forgetting that some Sandstone does contain embedded iron

Hope this assists?

Ken.

 

[Alastairreid]

I think you will find once you have drilled through the inner and outer skin of block you will hit random rubble infill.

 

[telnet]

Thanks for the replies. I am not actually doing the hole myself. The reason I asked was so that if it was possible to cut the rectangular hole I could have gone into a discussion with my contractor armed with a little knowledge.

Anyway, the contractor took a 127 mm core through the block, which was beautiful solid sandstone. The drama is that instead of sending a pilot through from the inside, he measured up and cut the core in the wrong place!

When I look down the hole I see the corner baton of the internal dry lining running straight down the center line. What a nightmare!

The trouble is that the correct hole will overlap the old hole by about 45%. It would be a little expensive if he was to replace the sandstone block before starting again. What an idiot. It pains me to have to lecture tradesmen on their trade.

 

[ban-all-sheds]

It would be a little expensive if he was to replace the sandstone block before starting again.

Yes, but not for you.

 

[chrisbyrd]

Sorry to hijack this thread, but it's kinda related...

How easy/possible is it to cut a shallow channel in a solid standstone wall? Probably 50mm wide+deep. Do-able?

 

[KenGMac]

chrisbyrd, hi.

Short answer is yes it is possible [and as ever] there is a "but"

Using an angle grinder the type of cut you are seeking is possible [here it comes again] but.

Used inside a grinder can and will cause a lot of dust?
if used outside then that is not a real issue [but]
the dust coming off the grinder can cause a type of discolouration of surrounding Sandstone, that will probably, over time dissipate.

Sandstone is a funny stone, at one time fairly "hard" and on other occasions even on a different part of the same stone the material can be "relatively soft"

If the cut you are contemplating is on a highly visible area of the stone, then attempting to get a nice straight line on the cut can be "problematic"

A method I have seen employed is to mark the line of the cut using a straight edge, once marked a scraping tool can be used to "just" indent the surface of the Sandstone. thereafter using a "Bolster / feather splitter?" the scrape mark can be followed fairly easily in a "controlled manner" to begin to enlarge and deepen the scrape into a small cut.

The use then of a "small" diameter disk will slowly allow the scrape / bolster mark to be "fairly" easily "followed" and a reasonably good line achieved.

Sandstone if poor quality can at times contain "iron inclusions" that will produce very unexpected sparks when using the grinder

Hope this assists?

No doubt other posts will also assist.

Regards.

Ken