Guide to Jointing Materials for Paving: Types, Best Uses & Common Issues
Jointing, or pointing compounds come in various forms, and it may be fair to say that some will suit the user and purpose of the product better than others, dependent on various factors, including the type or style of finish you are looking for, as well as suitability for use with the paving being pointed.
Traditionally, the primary purpose of pointing was to ‘seal’ the gap between the paving slabs/ bricks/blocks, to prevent weed seeds from colonising the gaps, and to prevent ants from taking up residence under the pavement materials.
Today, the reasons for filling the gaps may be more complex, as some gaps may be left in a permeable condition to allow water to percolate through the joints and also the laying bed and sub-base. Some products lend themselves to being pointed using ‘old-fashioned’ styles of materials, with wider joints, such as reclaimed Yorkstone, whilst others require a closer joint, such as porcelain paving, where close or ‘tight’ joints are preferred by the designer.
Whichever compound you use, it is important to read and follow the instructions provided, paying particular regard to the temperature range and atmospheric requirements of the product, and also the depth of joint to be filled. Some products may stipulate a minimum and maximum depth of the joint as well as the ideal width. Failure to follow these instructions may cause problems with curing and settlement, with ‘slumping’ occurring, with the compound entering any gaps under the paving, thereby leaving a valley in the unfilled joint.
Cleanliness and removal of water laying within the joints may cause problems with curing, and also colour changes in the compound during the drying out process. If too much water remains in the joint, the ratio of compound to mixing water will be diluted and alter the efficacy of the material. Therefore, it is advisable to ensure the bottom of the joint is both clean and dry, perhaps using a leaf blower to assist in the cleaning process.
Sand and Cement
Most natural stone paving projects may be pointed using sand and cement at the ratio of one part Ordinary Portland cement with three or four parts of ‘soft, Builders sand’ (these will vary around the country). This should be installed when the paving is dry, to prevent any staining on the surface of the slabs, semi-dry i.e. mixed to a state that it will stick together when made into a ball, yet crumbly enough to fall part then crushed in your hand. Dress into the joints and press into the gap in a firm manner using a finger trowel or rounded piece of metal to ensure the gap is completely filled. The styles of finish are many and varied, either lightly recessed, or formed into a ‘bird’s beak’, gently rounded or flush/flat. Clean off any excess material with a soft brush.
Ensure the sand is clean, with no micro-lumps of clay or ironstone in the material, as these will cause problems with staining after a while. Whilst mortar plasticers may be used, avoid using washing-up liquid, as this will produce a weak mortar, filled with micro-air bubbles which will become water filled and fail during freeze/thaw temperatures.
Slurry Jointing Compounds
‘Slurry’ compounds are those that are mixed into a custard-like consistency, then spread across the paving to be pointed, having first damped down the slabs to create a wet surface, thereby making a flowable grout, that is pushed into the joints using a squeegee style brush, ensuring each gap is filled with the cementitious material.
Most slurry compound manufacturers recommend a minimum of 28 days from laying to jointing, with a setting time of around 15 minutes at temperatures of 20 degrees. The surface will be ready for cleaning around 30 minutes later, and foot traffic after four hours. All of these timings are approximate, and temperature dependent. Do not use when the temperature is below five degrees or above twenty degrees.
Ensure all ‘ends’ of paving joints are sealed or closed up to prevent the slurry from escaping. All manhole covers, drainage covers, etc are taped up to prevent the slurry from entering any gaps. Similarly, ensure that all brickwork, woodwork etc are covered with boards or sheeting to prevent ‘splash’ marks.
Once cured, the slurry jointing compound will have a compressive strength of almost 50N. They are non-permeable and are mainly used on porcelain paving projects.
Pre-mixed Vacuum-Packed Grouts
A favourite with the DIY market, this is an easy to use product, that can be installed in the rain, as the paving needs to be wet before spreading. It is resin based, and all excess material must be cleaned off once the joints are filled. The compound is air cured, requiring to be pressed into the joints with a finger trowel with a depth of 20-25mm. They are considered to be permeable, and therefore the laying bed should be 1 part Ordinary Portland cement to six parts of sharp sand over a 100mm sub-base of MOT Type 1, making the whole project free-draining. (Any moisture that is allowed to lay within the joint will cause algae to grow, thereby causing unsightly discolouration of the compound.)
(Please note that some natural stone paving products may need to sealed on all sides when using vacuum packed grouts. Please discuss with your supplier.)
Two Part Epoxy Brush-in Grouts
A superior version of the vacuum-packed products, with easier, self-compacting properties, using the same installation methods as above.
Exterior Grade Cementitious Grouts
Ensure dirt and water-free joints, and allowing twenty-one days between laying slabs and pointing, to give time for the laying bed to cure to avoid efflorescence from becoming a problem by migrating through the compound and causing water staining issues within the grout.
Temperatures at the time of use should not exceed twenty degrees to avoid the compound from baking into a heat haze on the surface of the slabs. It is essential to follow the mixing instructions provided by the manufacturer, as these can vary between products, otherwise you may find colour shading issues once the grout dries out. If working in a hard water area, consider using distilled water to avoid this potential staining issue.
The grout is applied as a slurry, with a minimum of two passes to ensure the joints are completely filled, pushing the material into the joints to ensure there are no voids. Once the grout starts to cure – the timing of which is temperature dependent – start to remove the excess grout using a sponge and mechanical washing machine, at 45 degrees across the work. Use minimal water during the cleaning operations, with damp – not wet – sponges.
Epoxy Two-part Grouts
As per cementitious epoxy grouts (above) Two-part grouts may be considered as superior, as they are colour-fast for ten years, with up to 30 different colours. They are fully waterproof and marine rated, with zero efflorescence and are easy to clean, being stain resistant. They may be considered as professional products, following the manufacturers recommendations at all times – especially regarding time scales, as they have a short usability time-frame.
Kiln Dried Sand
Kiln dried sand is a fine, clean and dry aggregate sand for brushing into joints, especially of block paving to help prevent lateral movement, whilst allowing water to drain through the surface. This is usually a dry, lime-free, washed sand, comprising 95% silica.
It is applied between the paving blocks to fill the gaps and provide stability. Most paving blocks will a have a 2-3mm nib on their sides to achieve the requisite gap. Once brushed into the joints, and compacted by a vibrating mechanical plate, kiln-dried sand will secure the blocks, minimising movement and serving as a deterrent against weed growth.
It is best applied when both sand and pavers are dry, but during damper conditions, it may be washed in with a hosepipe, although this process will be more time consuming. If done thoroughly and properly, it can achieve the same results as a dry application, both of which allow the client to use the driveway immediately.
