Block paving and driveway cleaning and the importance or jointing sand

Following any block paving cleaning or cleaning a driveway great care must be taken to ensure that any joint sand lost in the process of cleaning is replaced. The main strength of block paving lies in the jointing sand between the blocks and the bedding layer and sub base layers the block paving is laid on.

The joints and jointing sand allow the blocks to interlock and bond with each other gripping tightly and spreading any surface load over the entire block paving. This load is then distributed through the bedding layer and the sub base into the ground. Block paving maintains its maximum strength and integrity when all three aspects work together. A failure in any one area can affect the whole paving whilst a failure in the jointing sand can lead to a failure in both the bedding and the base layers.

Using pressure washers when cleaning block paving causes the sand between the blocks to be forced out under the pressure of the water, this lack of sand between the blocks causes a void into which water has access to both the bedding and sub base layers.

Allowing any water access to the base layer when cleaning block paving can cause it to become unstable increasing its inability to withstand any load placed on it. At the surface this allows wheel ruts and depressions to be formed when vehicles and traffic are brought onto the paving. These depressions can cause further problems with water pooling that can occur allowing the base layer to become even more water saturated further compounding the problem. In the most severe of cases the movement can be so much that the blocks themselves break. Any such issue will result in having to relay the bedding and or sub base layer.

Jointing sand can also be flushed away with water introduced from more natural sources and not just when cleaning the driveway or block paving. This can be especially relevant for block paving on a steep slope. Where heavy rain may cause it to be flushed out leaving the paving unprotected. To prevent this and to allow ease of  future cleaning, block paving can be sealed using a clear lacquer that will set hard but retain enough flexibility allowing the blocks to move and settle but to also protect the jointing sand from being removed. Following sealing the sand is in essence glued solidly into the joints with a hard but flexible surface keeping water at bay.

Therefore it is essential that with any cleaning of a block paving surface or driveway the sand is always replaced. All commercial trades should do this without prompting nor with a need to sell it as an extra service following any cleaning or refurbishment work. However resanding can only be carried out when the block paving is sufficiently dry following cleaning. Any moisture will not allow the sand to run smoothly between joints, but merely to clump together and sit on the surface.

It should be accepted that block paving cleaning can use large quantities of water which can take a considerable time to dry especially outside of the summer months. The surface of the blocks may appear dry after cleaning but the joints will take considerably longer to dry especially in shaded areas. Similarly after cleaning it will not be sufficient to use a blower to dry the joints.

If the joints aren’t dry enough after cleaning the jointing sand won’t flow into the entire joint but merely clump at the surface. When the block paving does dry the sand will slump to the bottom leaving a void at the top of the block. At best this will allow weeds and dirt access that will very quickly ensure the paving requires a further clean but at worst it may allow water to destabilise the base layers.

The sand used for filling the joints has a specific function and is purpose made for the job. Referred to as kiln dried sand it can be obtained in 25 Kg bags from any DIY store or builders merchant. As it implies it has been kiln dried to control its moisture content so it best kept in the sealed bag out of the way of possible ingress of water especially if being used in association with the cleaning of any driveway or block paving. Not only is its moisture content controlled but also its grain size for which there is a British Standard all of which ensures that it is easily and readily flows between the joints in the block paving. It is best managed with a clean dry soft broom used to sweep it over the surface of the blocks until the joints are full. Any excess sand not filling the joint should be swept away and  rebagged for further use on the next clean.