damp patches on newly laid slabs - spot bedding?

Hi, It looks as though your landscaper has done a very neat job indeed. The trouble with these kind of slabs is that they are very porous. The dob and dab method is just fine as I lay slabs in this manor too as most of us would. It may be down to a high salt content within the cement and it is coming through, because these are not natural stone and pre-cast from cement it looks as though they have reacted. Sealing will not help it will just seal in the stain, do not scrub or apply detergent as this may remove the dye or colour from the slabs. It's a shame as the cost of these per sqm you could have used natural sandstone and this would not have happened. Its not a fault of the tradesman just perhaps the quality of the paving as I have seen this happen from time to time. One client I had this happen to did take it further with the manufacturer and was partially refunded but it was a battle. Its just an unfortunate situation as the cement can react with pre-cast slabs. I hope it fades for you which is still possible, but if you do take it further and get a result do go for natural stone, you can bleach, scrub and clean it with no harm. Try infinitepaving.com they are my main supplier of natural stone and fantastic prices.. Ok so he has used hardcore and compacted it, thats fine anything from crushed brick or concrete can be used. It should 4:1 ratio of sharp sand and cement, spot bedding is fine as long as you damp the underneath of the slab first and use plenty of mix to then tamper the slabs down into the mix with a rubber mallet, I have laid many patios this way and they have always been good and solid with no movement I only ever use sandstone so have never seen this damp stain come through on them. If the slabs are set tight and firm why does he need to re-lay them? Are they rocking about then!! As for pointing its a 3:1 ratio, but to be honest the best mortar is Easy joint sold in tubs for about £25 2 tubs would do about 20sqm, this stuff you just mix with water and brush in, comes in Grey, mushroom (beige) better than cement pointing as it does not crack in the weather or in the cold, we are all using it now to point and saves hours. Marshalls also do a weather point 365 check it out very good product. If he is re-laying the slabs he could lay a plastic membrane down first then bed onto this, this may stop the damp coming through, if its bedded on to a mix couple inches thick then this should not happen anyway. His method of laying the slabs is just fine, it could just be the minerals in the sand and cement reacting, his work does look very neat, but the choice of slabs are very porous ones and only made from cast cement themselves... One point on the pointing remember the colour can change due to weather conditions, if its very warm and sunny the pointing can dry too quick and cause issues like cracking, for a colour match he would need to mix a batch enough to do the whole area in one hit, sometimes the second batch is not always the same shade. seriously consider the the pointing compound I suggested its awesome stuff. Paul

He has spot bedded them if you can see it through the paving. You cant see anything if they have been laid properly on a full bed of mortar. He may referring to a concrete slab as a base for the paving and not the mortar. They should be laid on a full bed though so it needs sorting!!

regarding the drainage, the dot system he`s used is best as the water will have somewhere to go ie through the slabs and soak away into the hardcore, if used with the easyjoint which is a lot more porous then cement the water would very quickly soak away