How to make rectangle hole through stone wall

[joboatbuilder]

Hi everyone. I've read lots of posts about core drilling and stitch drilling, but not entirely sure what to do in this situation:

We are about to replace our ancient kitchen. We need to put ventialtion for the cooker hood extractor through the wall. We have been supplied with a 3m ducting kit, which ends in a rectangular tube to go through the wall. Obviously this is designed for brick walls where you simply take out a brick. If only it was that simple

We have half meter thick stone walls, built late 1800s. Which are random stone, and seem to be rubble filled where I've already put through some 20mm holes for other pipes. (which was NOT fun )
I have also core cut breeze block before, but never stone.
What is the best way to cut the rectangular hole required?!

I am thinking of either drilling 4 pilot holes in the corners as a guide, then using a diamond disc & angle grinder to cut the outer stones out reasonably 'neatly'. Followed by the enenvitable drilling and chiseling to remove the middle 'rubble fill' of the wall.
OR using a core cutter, cut probably three cores through, the square this out with an anle grinder and SDS drill/chisel again...

Both seem quite time consuming (but I don't mind that) and will require making good after. Is there a better method?

Also - once I do have some sort of hole through the wall, is it good enough to simply push the square plastic tube through the wall and then make good around it? Or should I try and mortar the tube in place, or use expanding foam or something else? Is there a danger that any rubble can move over time and crush the plastic?
Most importantly (probably just being paranoid) is there any chance I will weaken the wall?

There is an old wall mounted extractor fan which we will be removing (on the other side of the kitchen so no chance of re using that hole unfortunately) where I can see someone has just smashed through the wall and made good after, so presumably it is possible...!

thanks in advance for any advice!

 

[r896neo]

It would be much easier to buy a new end for your ducting that will run through a normal 4'' Hole cut by a core drill

 

[Chukka63]

vent fascias normally come with an option for rectabgular ducting as well as the obvious round option.or you can buy a rectanglur to round adaptor.

 

[joboatbuilder]

Thanks for the replies guys. so I should look for some round ducting really. Still wondering though, even with a 4" tube going through the wall, do I just push tube through the wall and make good around it? Or do I need to stop the rubble falling down and crushing the tube...?

 

[r896neo]

Just bash a bit of 4inch sewer pipe through and your ducting will fit perfectly through that. Obviously you want a very slight fall towards the outside and make good with mortar or foam or a combination of both.

You can't really mount the screws for a vent cover in foam so mortar is better, or what you can do is do it with foam and once it's cured hack out a bit at each corner and fill with mortar and push your plug into it while still soft

 

[Blagard]

Agreed the round core drill seems the right way to cut the hole, but as it is a rubble filled wall 500mm thick. I would have no idea how much rubble will spill or obstruct the hole after the core drill passes through.

I would suggest asking a reputable diamond drill company if they know how to core it and keep it clear at the same time.

This is really one for some-one who has actual experience of doing it.

Hoping the spill is minimal and obstructions if any easily cleared as you try to get the pipe through! - good luck

 

[Chukka63]

drill the hole,insert the "drain" pipe and nothing more will fall down.put some foam around the pipe and if youre good you can use the foam as an adhesive for the vent grill.

 

[Blagard]

Summing up

Also - once I do have some sort of hole through the wall, is it good enough to simply push the square plastic tube through the wall and then make good around it?

As Chukka63 has said in last his post

Is there a danger that any rubble can move over time and crush the plastic?

Realistically - Not if the Wall is already sound. and your hole has not been left excessively oversize. If you do make the hole too big you will be able to fill if back with mortar rather than injecting foam

Most importantly (probably just being paranoid) is there any chance I will weaken the wall?

Any hole will weaken a wall but in the context of what I think you are worried about, the answer should be not to any degree that would be a problem. If the hole is right next to other holes, or near a lintel or Joist bearing area, now would be a good time to let us know. Ball park, if you are clear by say 300mm all around then fine.