Exploding concrete.

[Colin Stamp]

Hi all,

OK, maybe "exploding" is too strong-a-word for it. "Puffing" might be be more apt, but I needed an attention-grabbing headline. Here's the story.

I was drilling the first of four 6mm holes in the concrete floor of our downstairs toilet this-morning and it all went completely normally until I got to about 10mm deep. Then, all of a sudden, a little jet of dust shot out from around the flutes of the bit and up into my face.

I stopped drilling and checked for water, listened for gas, noted that the lights were still on etc. All seemed normal so I carried on and it happened again - twice before the hole was deep enough. It then happend again at least twice on each of the following three holes.

So, what was going on? I've never seen anything like it, though I haven't drilled all that many holes in concrete floors before. Is it normal?

Cheers,

Colin.

[The Medway Handyman]

Assuming SDS?

Quite normal IME. What I reckon happens is that the bit finds a piece of very hard aggregate in the concrete, hammers it for a short while - and then it disintegrates.

I've had the same experience many times.

[Donwill]

I've always put it down to the flutes of the drill blocking until sufficient pressure built up, hence the puff when the flutes unblock themselves. It happens particularly when drilling downwards when the flutes have to clear the debris against gravity. Don

[TheOldFellow]

Yes, flints in the aggregate do this especially, IME.

R.

[Dave Liquorice]

I get it when drilling the fairly homogeneous sandstone or limestone here. A SDS can drill very quickly but the flutes aren't rotating particulary fast, the volume occupied by the spoil is going to be higher than the substrate it came from and the body of the drill is also in the hole. I reckon it's simply down to the drill not clearing the spoil fast enough. It builds up to a point then just "explodes" out when the blockage fails.

[John Rumm]

Might even be an element of converting moisture in a damp material into steam from all the heat...

[Colin Stamp]

Thanks all for the replies. It's good to know it's not just me.

It wasn't an SDS, by the way, just a cordless drill with hammer on. The floor might well be a bit damp since it's the main toilet used by a pair of small boys ;o)

Cheers,

Colin.

[Mike P the 1st]

On Mon, 08 Mar 2010 20:44:50 +0000, Colin Stamp gently dipped his quill in the best Quink that money could buy:

Oh ... gross ...... train them to sit down ... the boys in our family were :-)

Mike P the 1st