# Forum Home Renovation Structural Renovation  Cutting Bluestone footings

## benb

Hi all, 
New guy here, been reading for a couple of months and picking up lots of handy hints! 
I have a Victorian terrace on bluestone footings, very little sub-floor clearance, and little sub-floor ventilation. (Made worse by the concrete slab poured in the rear half of the house) 
In an effort to improve the situation I am putting in a sub-floor vent fan, and knocking out a few bricks between rooms (below floor level) to increase air flow. In order for these openings to be below joist level, at some points I need to remove some bluestone - about a 1/2 brick size. 
Does anyone have any advice on cutting the bluestone? I was going to try drilling some holes with a hammer drill, then using a chisel or point in the hammer drill. Hoping not to shatter/crack/otherwise disturb the bluestone footing.
Any advice appreciated. 
(Note: I'm not cutting the full depth of the footing, just want to remove a slot about 50mm deep x 100mm wide in a reasonably controlled manner) 
Thanks in advance...

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## Bloss

The masonry drill way would OK, but why run the risk of cracking or damage by trying to create a slot. Just drill holes with a  masonry bit after marking out a suitable pattern - rectangular if you prefer, but could be anything. 
When you really want to preserve the masonry as in this case use a smaller drill to start - say 6-8mm then re-drill to enlarge with the final size - say 10-12mm. You can get long bits that will go through double brick so they should be able  to get through the bluestone. 
You just need to do the maths so that the area opened up for ventilation with the correct number of drill holes is of sufficient size for the airflow you want. 
Of course if you really want a slot you can mark the rectangle drill on the inside of the  lone with a masonry bit and then use a diamond blade to square up the out edge and gently use a small cold chisel to remove the centre piece. 
An alternative would be to use a diamond hole cutting saw which can be bought relatively cheaply or hired. If you got a 50mm one and did two or three holes and Bob's your uncle.

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## PlasterPro

sounds like a bit of work what I would like to know is are you sure that the sub-floor clearance extends right across the room? have you removed floor? when I removed my floor (vic terrace ) I was suprised  :Biggrin:  to find bearers sitting in the soil and in places also the joists,I guess the most clearance was about 100mm from memory down to soil and general (rubbish from build) right up to bottom of floor boards. yes I had terrmite activerty not much live but lots of past.the bearers sitting in soil some where totaly rotted.
apart from that what I found also was the morter is (I believe to be sand and lime) is weak as p!$$ another problem I tried to avoid excess drilling ect where possible. 
I know not all are the same but before I would go putting in fan ect.. I would like to make sure floor boards and sub floor is in good order.anyway good luck with whatever you do and keep it posted here,

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## Bloss

:What he said:   :Arrow Up:  good advice. Worth pulling up a few boards and having a good look around.

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## benb

Thanks for the tips. 
Plasterpro- I currently have the floor pulled up in this room. The sub-floor structure was pretty much all shot, all rotted due to a combination (i believe) of lack of ventilation, DPC failure, and the fact that most of the joist ends butted hard up to the (damp) bluestone and brickwork. 
Rebuild of the sub-floor is in order, so while it's exposed i'm trying to remedy the situation as best as possible. 
Clearance under the joists averages ~ 200mm. A shallow trench has been dug under the existing bearer (yes there's only one!) to give similar clearance. I will do the same under my new bearers. 
This room only has one operable sub-floor vent as a concrete slab has been poured in the rear half of the house, blocking the others. The one vent was at joist level, with a joist pretty much hard up against it. So basically completely ineffective. 
What i'm proposing is;
1. Replacing the DPC by chemical injection method (unfortunately pretty much the whole house needs this- i'd be interested to hear opinions on the DIY option as its an expensive operation to have someone in to do)
2. Install solar powered 'Envirofan' ventilation unit ($430!!), east wall BED 2.
3. Open some pockets into BED 1, below floor level (either side of fireplace) to encourage air drawing right through. Also install extra vents to west exterior wall BED 1. (currently one only) 
Plan attached - any thoughts on ventilation appreciated. Fan supplier recommends another fan blowing air in on the west end... I don't really want to pay for two! Am hoping that the increased openings will suffice. 
Bloss; I like the idea of using a saw to cut holes! Got to be less chance of cracking than the chisel. 
Thank you both. Any more comments / advice most welcome.

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## Compleat Amateu

Just a few points to consider, may or may not be relevant: 
1. Can you add/replace existing vents with new ones?  Aleta vents (wire mesh and 2-3 x the size, therefore 20 x the ventilation) are the ducks guts.  They also come in varying sizes, so even just replacing a terracotta vent (if that's what you have) with an Aleta vent same size is a big improvement; 
2. I had some 150mm holes to cut in double solid brickwork, so may not be quite comparable - and a big friendly guy with a commercial hole saw took about 6 minutes and $75 cash .... the alternative for me would have been days!  I wonder if where you live there are guys who have done this before, must be .... 
3. As an additional step, I have laid heavy plastic over the subfloor to stop rising moisture.  I gather it worked, tho no hard evidence on this one, I sold the house. 
Good luck!

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## Bloss

Paying someone can often be the cheapest and best option as compleat says. And the point about vents is well made - older vents and especially the terracotta ones often had less than 25% gap vs solid - the newer ones even pressed metal are better than 50% - wire ones over 85%.

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## PlasterPro

<TABLE class=tborder style="BORDER-TOP-WIDTH: 0px" cellSpacing=1 cellPadding=6 width="100%" align=center border=0><TBODY><TR title="Post 753901" vAlign=top><TD class=alt2 align=middle width=125>quote: 
Compleat Amateu
</TD><TD class=alt1> 
3. As an additional step, I have laid heavy plastic over the subfloor to stop rising moisture. I gather it worked
</TD></TR></TBODY></TABLE>
 anyone got any thoughts on this idea?

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## Bloss

> <TABLE class=tborder style="BORDER-TOP-WIDTH: 0px" cellSpacing=1 cellPadding=6 width="100%" align=center border=0><TBODY><TR title="Post 753901" vAlign=top><TD class=alt2 align=middle width=125>quote: 
> Compleat Amateu
> </TD><TD class=alt1> 
> 3. As an additional step, I have laid heavy plastic over the subfloor to stop rising moisture. I gather it worked
> </TD></TR></TBODY></TABLE>
>  anyone got any thoughts on this idea?

  Waste of time . . . a solution from a misunderstanding of the problems of damp & moisture in sub-floor areas IMO.

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## seriph1

I reckon holesawing/core drilling for ventilation is the way to go for minimal impact on the foundations provided the mortar can handle the lateral pressure ... believe it or not, it is possible to dislodge a chunk of rock with a house on top of it. 
I believe that without cross ventilation, a single fan is a waste of time, simply creating a slight positive pressure in the subfloor area without enabling effective air movement throughout the space  -  hence the vent questions, I guess.  :Biggrin:  :Biggrin:  Personally, I think $430 is a bunch of money for a fan, so I am obviously missing something about this fan unit. 
BTW what suburb are you in Ben? I would love to see the project before the work is completed ... period architecture fanatic here  :Smilie:   
regarding the DIY solution for rising damp, I believe it is a straightforward process to achieve good results  -  the only thing I would consider is that there is no warranty when you do a job like that yourself.... mind you, while the pro's would know more about it than you as a first-timer, the products will be the same and whoever supplies you with that is likely to be able to provide you with oodles of good information to support what theyre selling! 
Finally  .... best of luck with the project. I for one, look forward to seeing how it all goes for you and will be happy to offer any help or share ideas along the way.

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## benb

Thank you all for your input and advice. 
I ended up drilling pilot holes and carefully breaking away the bluestone. I now have 2 decent size openings below joist level between the bedrooms, one on either side of the fireplace. And increased the vent size to the rear (east) of the house. When I pull up the floor in the front bedroom i'll be able to get 3 or 4 vents to the exterior (west) there. 
Re: subfloor fan. I've decided to go with an Aleta vent and keep an eye on it for the time being. $430 was a lot to spend on a fan when i didn't feel confident of the results. I'm planning on making a manhole into the subfloor when i lay the boards in a couple of weeks. 
Next step: Damp proofing. Still tossing up between Tech-Dry DIY (yet to cost out) and professional installation (about $5000 for whole house. eep!) 
Thanks again, all advice appreciated.

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## Compleat Amateu

Nahh, Bloss, not a misunderstanding about rising damp, but a view that subfloor damp could well be a combination of things, including (but not limited to):
1. Shot DPCs, esp in older houses, esp esp inner city terraces
2. Poor ventilation/ no crossflow, esp inner city terraces as above
3. Moist subfloor caused moisture flow under there
4. Other factors I haven't thought of 
I reckon if one had the time to sit there and view changing dampness over time, one could probably form a more precise theory in each case, but .... 
My theory is you get one shot at this, esp as one can't easily crawl under afterwards.  So more different solutions are good.  Rather nuke the problem once than pull it all out again.  I HATE rework! 
Compleat

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## ekiec

Have you thought about using a product called Solarventi. It directs warm dry air into the source of the problem (whatever the cause) and eliminates the damp over time, in time your floor and structure dries out, preventing future damage and keeping termites at bay.  www.solarventi.com.au

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