Drilling a core in a rubble wall

[Reuben]

Hi, I need to put a couple of vents in a rubble wall to improve sub-floor ventilation. My house is an old cottage with a damp soil subfloor. I have no rising damp, but I want to dry it out to get rid of the damp smell and to prevent any issues with rot - I've just got rid of rotten joist end etc. My plan was to core drill a couple of 125mm holes (separated by about

3 metres), sleeve the holes using underground waste pipe of the right diameter, and chip out enough of the stone on the outside to let me fit airbricks and make it look presentable. My problems are - this is a supporting wall - am I likely to destabilise it by drilling in this way - and, I have never used a core drill before - I'd be grateful for any advice or guidelines. Also grateful for any general advice about this topic.

Thanks,

R.

[Rick Dipper]

Sir

I have rubble walls, which are 600mm thick. Drilling them is a real pain. The rubble is of different hardnesses, some being volcanic round rocks, others being slate. The hard round rocks are almost impossible to drill.

However the problem that you may find, is that once you have the hole, the rubble ablove the hole will fall down and fill the hole in again. Somebody suggested to me that I bang the pipe in right behind the drill, but I have never tried it.

I would not drill a big hole in my walls within 1000mm of the external corners, as the corner stones are at least this long, and apprear to be quite important.

You may also find that if the mortar is poor, the vibrations of the drill with knock the stones out. This happens in some, but not all of my walls.

You may do better to find a big stone, and work directly below it, so the big stone is a sort of lintel to the hole you are drilling. If you have access to both sides then you will find a big stone that goes right through. Im my walls the big stones are neer the bottom. I also have some really huge stones, that you could put a 3 inch pipe throught the middle off and still be a foot from any edge .....

Rick

[Michael Mcneil]

What are you going to use? Presumably a diamond core borer? So all you need to do is introduce the piping from the other side of the wall to the one you are drilling.

What I don't understand is what the cottage wall is sitting on. Usually they had impervious stones laid on rock. The inside was earth with quarry tiles laid straight on them. So what are you drilling into?

Could you not just restore the surrounding of the walls to their former state? There would have been no soil close up to the cottage walls. That was the idea of using the stones from below ground level. They would have put the house high enough for all the rain water etc., to drain away.

[Alan James]

What about periscope ventilators between the joist ends taken through to the outer wall?

I had a similar situation. Got all the "mandatory" stuff done just for the paperwork, pointless DPC etc etc, but the single biggest contribution to reducing moisture levels was to waterproof the soil subfloor. It really does work.

Alan

[Rob Graham]

This had been done to my property (Scottish farm cottage with similar rubble 36" walls) back in the 20's or 30's when the 4 cottages were knocked in to 2. The floors had been dug out to be replaced by properly prepared suspended wooden floors with the type of ventilation the OP mentions. They also lined the walls with lathe and plaster.

I don't know how they did it then, but one thing they did was to allow the nice ventilating underfloor air to ciculate up behind the lathe and plaster. There was therefore only the insulation value of 1" or so of plaster.

One thing to realise about the rubble wall is that it is almost a cavity wall and that moisture doesn't pass through it from the outside.

Rob

[Meoww]

I think I'm with it. You're trying to introduce sub-floor ventilation which is a good idea. I can't see you'll de-stab a house of these dimensions in doing what you're doing. Be very careful though and don't try to drill through the rubble in fill. Soft or hard, it's going to grab hold of your bit and sieze solid. This is when you go round and the drill stays still. Use a drill with a torque check on it!! Best to drill from either side and then try and clear the middle with your hand. (I've done loads of holes through my similarf walls)

If you can get under the floor easily, you'll do as much good by putting a visqueen membrane over the entire floor, tight as you can to the walls. Could be a lot easier...

Cheers

Patrick

[Alan Campbell]

Hi,

I have the same issue - BC want more vents in my 2' thick walls and I am worried about the structural integrity of my home if I add them.

My current vents have been put in the walls below the windows where the walls are thinner and don't have a cavity filled with rubble. I've been thinking about increasing the size of these vents so that the size is up to regulation. The regs say this -

"Permanent ventilation of the underfloor space direct to the outside air by ventilators in 2 external walls on opposite sides of the building to provide an open area in each wall of either

1500mm2 for at least every metre run of the wall, or 500mm2 for at least every square metre of floor area, this open area also being provided in internal sleeper walls or similar obstructions to maintain the underfloor ventilation; the ventilated space to be 75mm in height from the site covering to the underside of any wall-plates and 150mm to the underside of the floor joists."

So, in theory, my plan will work. I still need to see my architect to see what he says as if he signs it off, BC will be happy.

Perhaps this plan will work for you too?.

Alan.

[Reuben]

Thanks to everyone who has commented on this so far - seems like the consensus is that this should be OK, but that I may have problems with drilling through rubble, and that I need a drill which will run slowly with a clutch of some description. I found Rick's comments about using a larger stone as a "lintel" particularly helpful. I plan to have a go this weekend, weather permitting so we'll see how it goes. A few comments in response to yours: Michael - the construction of my house is nothing like you describe, and this will be most likely due to regional differences. What you describe sounds sensible and well designed - that's not the way my house has been built. I think mine is a typical farm labourers cottage for my area (Fife in Scotland) built as cheaply as possible with local materials - whin, sandstone, lime mortar. The soil subfloor (solum) is level with or lower than ground level outside, so it is alway damp unless it is actively dried. Like many houses of this kind, the joists were actually resting in the soil when I moved in - I've rectified that now, and replaced rotten parts. I reckon if I get this cracked, I can finally put the boards down the way I want them and forget about the subfloor pretty much forever. Rob - your house sounds exactly like mine. As I understand it, there is meant to be ventilation between the lathe and plaster and the stone. What I plan to do is reline the walls with a thin high performance insulation material e.g. Airtec, and plasterboard over that. This should give me far better insulation than I had, as well as vapour barrier and will still allow that air I'm trying to introduce to whistle up the back into the eaves. I'm thinking about putting something similar under my floorboards also. Mind you, I also need to vent fresh air into the room for my fireplace. Alan - I think I know what you mean by periscope vents, but I still need to get through the wall for fresh air. I've also been through the loop of using professional dampproofers, which was a complete waste of money. Anyone could do what they did, and they did it very badly and took far too long. I'm not talking abut a cowboy firm here, but a very large company. Once you get to grips with it the issues are very simple and the risks of damp are overplayed.

Thanks,

Reuben.

[Dave Liquorice]

What's Airtec? Have a similar problem with rubble walls and interior lining. 2" of celotex + gaps + plaster board is rather a lot of room to loose...

I've googled but the site that looks promising has stupid flash only access.

[Michael Mcneil]

It sounds like someone put the joists in without any previous experience some time ago. He should have used a laywer of viquene instead under a slab of concrete.

Put a cpouple of inches of polystyrene on the ground and then the sheet then the slab. When the slab is just dry enough to resist pressure get a board to stand on and start working the surfave to a smooth even finish with a steel trowel.

If you need to keep the same level dig out some of the soil. The slab should be 4 inches thick.

In the centuries that it has stood the garden was lovingly tended and the soil built up around your house I am almost certain. That and a few inches of settlement has put the inside and outside levels at variance. That is possibly why the joists were laid.

[Jerry Built]

Is there any ventilation at all? As stated by someone, putting down a DPM will help a lot.

You may have problems with the wall knocking holes in it. You are also unlikely to be able to safely use a core drill in a non-coherent medium. Pressure grouting might be the answer, but may pose other issues.

J.B.

[G&M]

It's an aluminium foil/plastic sandwich. Not as good as 2" of Celotex but if you're short on space it sort of works. Screwfix sell it.

[Dave Liquorice]

Ah, glorified bubble wrap... Starting with a bare wall I think celotex/kingspan WHY would be easier to fit.

[G&M]

Yep. You're supposed to ensure the bubble stuff doesn't touch either surface as well. Easier said than done.

[Jerry Built]

Is there any ventilation at all? As stated by someone, putting down a DPM will help a lot.

You may have problems with the wall knocking holes in it. You are also unlikely to be able to safely use a core drill in a non-coherent medium. Pressure grouting might be the answer, but may pose other issues.

J.B.