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?