It sounds hollow!

[Rolyan]

The flags are laid, the pointing is nearly done, and everything seems perfect......

Then I notice that a couple of the flags sound a bit hollow, caused no doubt by a lack of bedding material fully supporting them. They are the ones laid on the thicker mix (approximately 75mm thick) of 6 parts 10mm gravel to 3 parts grit sand to 1 part cement (I think we did a bit more gravel than this...it was a bit gravelly!). Not only that (and now I'm starting to panic) but at first I noticed the hollow sound on one flag, then another, now I think there are three. By the way, there is no rocking that I can feel, or any movement, the three flags just sound a bit hollow in places.

So, before I give up DIY for good (every job I do goes to pot), I need some help. I know the best idea is to lift and redo, but if I don't do this, what is the next best option, and am I heading for calamity.

1) Is the thicker mix starting to collapse (perhaps because the mix was wrong). It goes up to an edge, to form a step, which I've faced off with cut stone. It's mortared on the top of the cut piece, so 90% of the flag is on the mix, and 10% is mortared onto the step.

2) If I accept the hollow sounds, will the flags stay put, or will they collapse over a few months or years.

3) If I did a very wet 3:1 mix with plasticiser, could I pour this into the gaps (these are not pointed yet), then point up as normal when dry. Would it seep into the gaps, and help support the flags. Would this help, or is it a total waste of time.

4) If I do number 3 above, do I buy the plasticiser, or is a squirt of washing up liquid to a full bucket a good idea. I once tried to do this before, and the mix sank to the bottom of the watering can, even though I mixed it really well. I ended up pouring dirty water out, and the mix was in the bottom.

Many thanks for your help on this, 'cos I'm a bit worried.

[Tony McC]

I think you're worrying unnecessarily. Quite often, even the slightest 'gap' in the bedding can cause some types of flags to sound hollow. If you're confident you used a more-or-less full bed when the flags were laid, then then flags will be adequately supported.

Pouring in a slurry can often sort out minor problems such as this, but, as you've already got them pointed, I think you can forget all about it for now!

[Rolyan]

Thanks Tony. I think I was worrying unecessarily as you say. Now they are pointed they don't sound as bad anyway, so many thanks for the comments, which put my mind at ease.