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.

Block Paving and Driveway Cleaning a Basic Introduction

There is currently a wide range of cleaning materials, products and equipment that are suitable for cleaning block paving, paths, patios and driveways. They range from scrapers, brooms, brushes and cleaning agents, to power washers which include those fixed to the end of a hose being water pressure powered to electrical or mechanical petrol or diesel powered pumps. Some with potentially high pressures capable of doing more harm than good when incorrectly used for cleaning on block paving.

There is a multitude of cleaning machines purposely designed and built specifically for the block paving and driveway cleaning market. Gone are the days of hours spent with a lance cleaning a driveway by hand individually jet washing clean each block by block only to finish with a stripy non uniform finish. Now are the times of self propelled rotary cleaners that give a consistent and thorough or deep cleaned finish as it is now called to any paving surface or driveway.

By using this range of equipment most unsightly marks such as mud, dirt, horticultural stains, weeds, moss and slippery algae can be comprehensively removed and any hard surface can be catered for including the cleaning of:

·         Block paving and block paved driveways

·         Patios and paths

·         Slabwork and flagstones

·         Concrete and pattern imprinted concrete

·         Tarmac

·         Stone & brick walls

·         Decking

·         Hard surface sports pitches

A simple cleaning  of any block paving and driveways can always be carried out by giving them a good sweep with a stiff broom to remove any debris, followed by a wash with a proprietary cleaner a hose down after and a quick sanding to replace any lost jointing sand from the cleaning process.

For a more severe clean or for larger areas such as driveway cleaning a power washer can be engaged. A small domestic electric pressure washer connected to a hose can be a useful tool for the removal of weeds and moss that have taken hold in the jointing sand along with cleaning away any dirt and grime.

Prior to any cleaning the area should be swept clear to avoid any surface rubbish becoming a hazard during cleaning. If using a lance it should be kept at a shallow angle to the paving the nozzle of the lance can be adjusted to give the required jet of water sufficient to be effective and the distance it is held from the paving should be enough to clean effectively but without blasting out any jointing sand when cleaning block paving or any pointing when cleaning patios and slab work.

Care should be taken that any dislodged material such as pointing or any surface rubbish does not cause any damage if caught in the spray of the nozzle it can become blasted out in a missile like fashion.

Electric pressure washers now come with small rotary washers as part of the package that can be connected for use thereby reducing the need for the lance on the majority of the job. This will help remove the stripping effect obtained when cleaning a large area with a lance it will also contain a lot of the spray when cleaning block paving but they won’t get into the awkward corners. This is where a lance will have to be used and extreme care must be taken with the force of water when used in such a small environment.

For those large jobs such as driveway cleaning or commercial premises the professional’s choice of cleaning machine will be to use a larger diesel powered pressure washer these can produce extreme pressures of up to 3000 psi or more and can be of greater benefit than an electric powered machine.

However size is not necessarily beneficial more care has to be taken to not blast out jointing material especially when cleaning block paving. For the more powerful machines it could start to affect the sub base material if the force of water is that great that it washes away the jointing sand wand then permeates beneath the blocks in large quantities with potentially dire consequences. Another disadvantage to power washing is that it can damage paving. The pressure should be adjusted to be sufficient to give a good clean. Excess pressure can damage blocks causing them to break up particularly those cheaper blocks on the market. Some natural stone and flag stones can also be damaged by too high a pressure in that they can delaminate where the natural layers of compressed stone come away from each other as water is forced underneath the individual layers when cleaning.

Again with the use of the more powerful machines the jointing material must always be replaced especially for block paving where the sand is integral to the blocks strength as a whole and there is little point in cleaning paving only to allow areas where weeds will manifest themselves thus requiring further cleaning at a later date.

With regards any cleaning preparation as always is the key to a successful job.  The area should be swept first and thought given to the cleaning process. A note should be mentally taken of where any excess water will flow and the sequence of cleaning. All cleaning should be done systematically when cleaning block paving the pattern and landmarks such as building features can used to section off areas for cleaning. Once cleaned the area should  be washed or hosed down any excess water brushed away leaving a clean looking area.

Once block paving or any paving with jointing sand has been cleaned it should look allowed to dry thoroughly before any jointing sand is replaced or pointing undertaken If its slab work.

Pressure washing can not remove all marks or stains chemicals may need to be applied for the removal of oil stain like engine oil or fuel oils. Most pressure washers have the capability to automatically add detergents as they run by connecting the detergent inline to the pressurised water flow. Thus use of such degreasers can be a valuable to cleaning driveways of oil stains. Alternatively a pre-treatment oil displacing agent can be applied prior to cleaning.

Cement, tar and paint will have to be removed by manual methods prior to cleaning with a pressure washer.

Finally cleaning can truly bring back the glory to any paving especially bringing out the colours in natural stone or block paving. But it can only clean what is already there it cant return to new or restore colours that have faded through UV degradation over the years

Once cleaned it may well be worth investing in some form of protection for the paving as well as allowing for something that will offer future ease of cleaning. The remedy would be the provision of a block and paving sealer.