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	Jointing Stone Pavements: Dry Grouting

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Dry Grouting using a cement mortar

Tools: Stiff brush Soft brush Pointing trowel Pointing bar Optional: watering can/hose with fine rose sprinkler

Pointing Tools: Pointing - Brick - Bar - Cleaning brush

Technique: Considered by some to be a suitable alternative to wet grouting, dry brush-in relies on the complete and total absence of water from the mortar mix and pavement surface during the placement phase to allow the water-free, bone-dry sand/cement mix to flow into the empty joints.

The surface of the paving must be completely dry. Any residual dampness will cause the sand/cement mix to "stick" and will probably result in a stain. Consequently, this is a technique that is only really practical during the summer months. A 3:1 ratio of sand and cement are mixed without the addition of ANY water. None. At all. Not a drop. The resulting powder should be of a uniform colour indicating the sand and the cement are thoroughly mixed. It is then scattered onto the surface of the paving and swept into the joints using a soft brush.

Because the dry sand/cement mix is relatively light in weight, it rarely fills the joint properly; instead, it lies in the joint all fluffy and airy and not very convincing as a jointing medium. The better contractors will use a pointing bar or the blade of a trowel to press down the dry mix, compacting it into the joint and then brushing-in additional mix, repeating this sequence until all the joints are properly filled.

An allegedly easier alternative relies on the surface being sprayed with a fine mist or drizzle of clean water once the joints are filled. This has the effect of washing the dry mix into the joint, and simultaneously providing the moisture needed to initiate hydration of the cement content, but, as the surface is then wet, there is no opportunity to 'top up' joints with additional dry mix. On hot summer days, the surface may dry off in a matter of minutes and the whole process can be repeated until all the joints are properly filled, but these conditions exist on very few days over the course of a working year.

Examples
Dry jointing works best with regular joints on smooth flags...	..but joints need to be thoroughly filled
Dry jointing rarely creates a sound joint with riven flags...	..and can cause staining is any moisture is present
Prone to cracking with joint-dependent paving such as these cubes...	...and the joints are easily colonised by weeds

Comments: Left to its own devices, dry brushing-in rarely creates a well-filled, structurally competent joint. The resultant mortar is often a crumbly, friable gap filler that has a very limited lifespan and usually offers an excellent home to all sorts of weeds. This is of little consequence to the less reputable installer, as they will be long gone and the money spent by the time problems start to become apparent.
If the contractor is conscientious and ensures joints are properly packed and filled before spraying with water, a reasonable quality joint is possible, but it is highly unlikely to be as sound as a traditional mortar joint. A better joint is possible if dry brushing-in is combined with freshly-buttered joints when flag laying. The butter mortar (a standard wet mortar) contains sufficient moisture to initiate hydration (hardening) of the dry mix brushed in to top up the joint, and, as long as the dry mix is properly pressed down into the joint and the butter mortar, a reasonable joint can be achieved.
With regard to spraying with water, if care is not exercised the cement-rich brush-in mix may be splashed out of the joints to land on the now-damp pavement surface and result in staining or spotting, the avoidance of which, after all, was the reason for using the dry brush-in technique in the first place.

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