sub floor ventilation

Can't really advise on the sandstone blocks - our house is double brick on rubble foundations (with a row of bricks beneath the damp course). We created access to the subfloor area by removing the rubble by knocking it out, installed a steel "lintel" then tidied up the opening with a lime putty with fine aggregate added. Had a steel frame and mesh door fabricated and installed into the opening.

You should be able to cut through your sandstone blocks with a diamond saw - see http://www.hoskindiamond.com.au/category91_1.htm. These people should also be able to offer advice. You could hire a saw and provide your own sandstone blade.

Since the hole you require is not large, perhaps it might be possible to remove one block and take it to a stone mason and have him cut a piece out. But this will depend on the size of your blocks.

We also removed bricks at intervals around the house and installed mesh vents to improve cross flow.

Sandstone is a soft stone and easy to cut with any fibre or diamond blade, but be careful with dust as you will create lots of it. I'd probably run a hole through each corner, then use a blade to cut along the straight lines of the hole. If you treat it like a mortise take several cuts if you have to and knock out the waste with a cold chisel. An angle grinder or a saw with suitable blade will work.

Be careful as you get to the back of the whole least you break away a large section form the rear, hopefully you have access from both sides and can work in to the middle from both sides, those initial drilled holes will make a good guide as to where to mark out the lines at the rear of the hole.

An air driven hammer with chisel will also make reasonable work of cleaning out a cut hole, but the strike is too rough for tough stone but will work on most sand stone. It will also be less likely to cause a fracture to the block than an overly energetic belt with a hammer. Your ideal hammer weight would be 2lb to 3lb weight if you go down that path.

You can clean up any dags with an ordinary file or old sharpening stone, this will flatten and chisel marks that are untidy or in the way.


John