The Brew Cabin

I am about to lay a number of Marchalls slate paving flags and a paving circle. Wonder if you could clarify something for me though - I keep seeing conflicting advice as to whether to lay them on sand or on a mortar bed?

if on sand, does the sand need compacting after screeding or is it just a case of screeding then laying? if mortar is the best option, should the bed cover the full size of each flag or a number of blobs?

is it best to use mortar pointing with buttering at the same time as laying or use the dry mortar "brush in" method later? or is jointing sand ok?

thanks in anticipation

(Edited by MikeW at 10:59 am on May 4, 2004)

The choice of bedding depends on the site, the planned use, the type of flags being laid, the weather conditions and lots of other factors. However, for those slate units from Marshalls, I'd actually recommend a full mortar bed.

The main reason for this advice is that the slate flags are scarily thin and need a firm support, but, because of their size, a mortar bed reduces the risk of rocking as they are laid. Also, for DIYers unfamiliar with flag-laying techniques, mortar or cement-bound bedding is more accommodating of minor errors in levels.

So, as mentioned in the previous post about limestone paving, a wettish mortar bed with buttered joints and then dry brush-in would probably be your simplest option. The strength of the bedding mix isn't all that critical. I usually quote a 10:1 mix, but you can 'up' that to 8:1 or even 6:1 if you want. The buttering mortar ought to be 4:1, as should the dry-jointing brush in material.

HTH

Hmmm, this is very similar to my problem...

I've persuaded 'her indoors' that our lovely weed-filled "cottage" garden would be better patio'd, and having toured the builder's merchants have agreed upon the Marshall's Heritage range of flags. Reading the Marshall's literature suggests using a wet-bed of concrete to lay these, however, I'd already digested to best part of the information on your excellent site, and considered either a bed (with 10:1 cement to bind it), or the "semi wet" mix.

Both the dry and semi wet would appear rather easier to work with than a wet mortar bed, so my question is - is it really necessary to use a wet mortar to bed Heritage flags? (prepared area will allow 50-75mm bedding, and covers roughly 20 square metres, intended for light patio use, in a well drained area).

Any advice would be gratefully received

Kind regards

Mike Dodd.

No: a wet mortar isn't essential at all.

Some contractors prefer a wet mix, but I find that a semi-dry is more forgiving, easier to work, and helluva lot less messy.

If you use a wet mix and the bed isn't just right, lifting and adjusting becomes a task and a half because the flags are 'stuck' to the wet mortar, and then your hands are in the damned stuff, and then you've cementy mitt prints all over them, and it's stuck to the bottom of your boots, and it's going off too quick....are you getting the picture?

A semi-dry bed doesn't stick. It doesn't get carried around on your boots and gloves, and it doesn't dry out too quickly. It sets, which is all that's required. This notion that flags have to be 'stuck down' is a nonsense - they just need a firm bed.

Have a go yourself and see what you think, but for my money, and with 30-odd years of flag-laying experience behind me, give me the semi-dry bedding mix any day!