Patio

[domblack]

I have just has a patio put in, with dark sandstone slabs.

The firm who laid it were supposed to point it up properly with wet mortar, but instead they decided to brush dry mortar into the gaps and let it go off over the next few days. The company supplying the stone psecifically advise against this because of staining.

My concern is that this left a fine dusting of dry cement over tha slabs. It then rained a bit, enough to wet the cement but not enough to wash it off. I thought about hosing it down, but that would probably have washed the mortar out of the joints.

The slabs now seem dulled, probably they have a very fine cement coating. Will this weather away over the next few weeks or is there a serious problem?

[The Medway Handyman]

I'd always dry point to avoid staining. Wet mortar is much more likely to stain the slabs. Standard proceedure is to brush in dry mix, run a pointing tool over the joins, brush of the excess.

They should have swept/brushed most of it away, but some residue is bound to remain.

I don't think it's a serious problem. Any coating that fine won't survive long.

[Weatherlawyer]

With some floors it is necessary to seal the tiles properly and that means a wet mix. What you then do is cover a section of the still wet floor with straw or saw dust and get on your hands and knees and polish it off.

If you strew it all over the floor, the danger is that the grout will dry out before you can get to it, to polish it.

It is a quick enough job once you get into it. But a drudge if you over reach yourself.

In the case of the OP I'd check my contract and if they broke it, stop the cheque and wait for the boss to send someone out to inspect it. Of course this IS a diy group -so if I was the OP I'd have more sense than to post to a group of people who are likely to tell you that it serves you bloody well right.

Serve him bloody well right.

[Hzatph]

The traditional solution to this is brick acid but I would not try it on natural stone because it can cause severe staining by attacking the iron in the stone. You could try pressure washing and the sooner the better, taking care not to go into the pointing.

Have you tried

- they have an excellent forum too

[The Natural Philosopher]

I had precisely this problem when I tried the dry brushed method - I simply tossed a few pints of brick acid all over and scrubbed away with a stiff broom.

Yes, it does attack the joints as well, but they are a lot thicker. If you are really picky use a nail brush, rubber gloves and do it bit by bit on your knees.

[The Natural Philosopher]

Its fine on sandstone. You may get some leaching of manganese - I have a puddle of red manganese salts - but these wash away in time.

Its a disaster on limestone of course..and concrete flags...but its OK on slate also.

Not good if the cement has dried. Brick acid first, THEN pressure wash.