The Brew Cabin

I just beed a bit of advice on flag laying. I'm doing a job laying 600mm x 600mm flags at the moment - it's a back garden patio area and path. The website seems to advise that either butt jointing and dry sanding (and sand bedding layer) is just as suitable as using a cement/sand mix and mortor jointing. I would prefer to use the standard sharp sand screeding etc. as I would for block paving - is the only advantage of mortor bedding some extra stability?

You can lay B50s on a screeded bed, with either mortar joints or butt-jointed as you see fit.

For non-vehicular areas, butt-jointing is ok because there are no significant loads that could cause adjacent flags to be forced against their neighbours which can cause spalling of the top face.

This type of flag doesn't rely on the jointing for any real strength - it's what we call 'bed dependent', which refers to the fact that the integrity of the laid pavement comes from the bedding rather than relying on firm jointing to hold everything in places, as is the case with, for example, setts.

When flags of this type are laid on individual bedding with buttered and pointed joints, then some of the mortar is forced into the bedding plane, which does add a small degree of 'stability' in helping the flags resist lateral (side-to-side) movement and creep, but for a patio, this isn't a major issue.

Personally, I don't find that a screeded bed works terribly well with this size of flag. Screeding is fine for blocks and small-element paving (450x450 or smaller) but at this size, there's a tendency for the flags to develop a 'rock' over time, as the area of bedding is such that there is more-or-less bound to be a degree of differential settlement within the sand. And as you can't use a vib plate on this size of flag, you have to rely on using a mall to evenly and accurately compact the flag, and its bed, which is easier said than done.

Ok thanks for the advice.
One more thing, what is an acceptable way of retaining the edges of the flags, (if the edges need to be retained that is??)
I know you can partially bed the edge of the flags on wet cement and then haunch up the sides. Is this necessary on flags of this size?
I would assume that haunching cement up the sides of the flags (with the flags bedded only on sand) is not acceptable?

A retaining edge is not essential, but that doesn't mean you can't use on, if the fancy takes you. Have a look at the page dealing with Free Edges for the arguments for and against, along with some examples.

An edge course of block pavers makes a nice, simple, effective retainer edge, or you could use an edging kerb or any of the other edgings illustrated on the site - it's all a matter of personal taste.

If you do want to use a haunching to the flag edge, then follow the example on the Free Edges page metioned above, and lay the outside edge of the flags on a mortar bed that is extended outwards and upwards as a haunch. Slapping a trowelful or two of mortar on top of the sand bedding is just a waste of good mortar!