The Brew Cabin

I have been asked to comment on problems with a large domestic patio laid in early 2001 in Yorkstone flags.
The owner obtained the flags from Dolmens in West Yorkshire (about 200 sq. m) and asked a contractor to lay them.
Some problems have occurred since which the owner has asked me to look at. Firstly, some of the pointing is breaking up and can be easily rubbed up with the heel of a boot. It looks like a sand grit mix but with a varied and lean cement content. Secondly, some of the slabs are rocking although this is relatively few in relation to the area. After lifting several of the flags, they are very irregular on the underside and have been laid on spot bedding. However, the contractor did lay a 100 thick concrete sub base underneath.
The owner thinks that all the paving needs to be completely relaid due to the spot bedding but as it is on a concrete sub base, I'm not sure if this is overkill, particularly as it's such a large area involved.
Your comments would be very much appreciated. Also, as the joint widths are very irregular and very wide in places, what sort of pointing method is best?

Hi Jeff,

the pointing can be tested in a lab to determine cement content, but, if it's falling apart to the touch, then you don't need a lab to tell you it's crap.

More worrying is the dreaded spot bedding. I've argued with architects, designers, paving manufacturers and even a few site agents about this, but, with almost 50 years experience as a paving company, we never, ever, ever recommend or install using spot bedding. It's a recipe for disaster.

With a concrete sub-base being present, the best option is a 'lift and relay' on a full bed of cement-bound material (10:1 gritsand/cement), but if that isn't feasible, then a wet-grout might resolve the rocking and the pointing issues in one fell swoop.

Joint width should not exceed 20mm as an absolute maximum. 10-15mm is ideal. If folk are paying umpteen quid per square metre for yorkstone paving, then they shouldn't be confronted with 10% naff mortar joints. The joints should be regular and kept to a minimum.

Hi Tony,
Thanks for such a prompt reply!
Are you suggesting that the whole area of paving should be lifted even where it's still firm after two winters or should this be just to those flags that are rocking?

It's up to the client and yourself. I haven't inspected the job, so I can't say, for certain, just what is best, but I'd certainly consider wet-grouting the loose areas to see if that rectifies the situation before considering summat more drastic, such as a lift and relay.