The Brew Cabin

My rear drive has been laid for about a month now,
but there is a sandy coloured water mark all over my blocks (Driveline 50 - and its been there since laid), that dosn't disappear.
It almost looks like cats paws, as if cats trod in sandy dust and walked all over them.

My guess is that as the contractor didn't use a rubber cover on the vibrator it has gound up the sand, could this be.

The contractor is returning on Monday, and talks about 'acid'.

Have you come across this sort of problem?

Are you sure it's not efflorescence?

Acid washing only works on cement stains, such a sthose cuased by spilt mortar or concrete. It won't work on efflorescence and it won't work on crushed sand. Also, you need to be very careful with acid washing as it can alter the colouring of the paving.

The use of a rubber mat on the plate of a vibrating plate compactor is not essential and many contractors prefer not to use one for residential driveway/patio work with concrete pavers. The are a good ide with clay pavers, or with concrete pavers that have no spacer lugs, but, for the vast majority of British and Irish concrete paving blkocks, they are a waste of time and money.

Very OT, but can I have a pint of what your drinking please Tony.....<G>

MikeT.

That was before I'd had a drink, Mike! I was rushing to get the message posted before I had to go out. I had Mrs Taz haranguing me on one side and the youngest daughter on t'other - you're lucky it's as comprehensible as it is! ;)

I'm not really sure what efflorescence is on block paving. I'd guess that it is the same as the white stuff (saltpeter?) that comes through on new brick work.

What I can say is
1. It is more obvious on the sloped area
2. It is the same colour as builder's soft sand
I expect I can find this out elsewhere on the site, but are there sands that you are and are not supposed to use to fill the gaps?

Yep, effloresence is the 'salt' that weeps out from high quality concrete products - it's nowt to worry about and it diappears after a summer of British rain. :)

These marks could be crushed sand, but, if they are,, they should be able to be shifted by rubbing with a wire brush. I'd try that before resorting to an acid wash.

And finally, yes: the jointing sand is a specially selected sand of specific grain sizes. The full grading envelope is given on the Pointing and Jointing page. Your contractor should be using sand that comes in bags marked as "Jointing Sand" or "Kiln Dried sand for block paving" and not just using any old sand that's lying around.