Aesthetically pleasing walkways and paths enhance virtually any outdoor municipal space. While the paving material you choose will depend on cost, design preference and the effect that is required, there are a few standard best practices that will lead to the best results. Bryan Perrie, MD of The Concrete Institute, provides guidelines on how projects with limited budgets can tackle maintenance-free paving laid with open joints on either a mortar or sand bed.
1. Choose materials for the mortar bed
For the purpose of this article, the options are cement and sand. All cement sold in South Africa must meet the requirements of SANS 50197 for Common cement or SANS 50413 for Masonry cement and the National Regulator for Compulsory Standards (NRCS) requirements as detailed in NRCS VC9085. Bags should be clearly marked with the strength grade, notation indicating composition and a Letter of Authority (LOA) number issued by the NRCS. An LOA is issued for each cement type from each source. Note that masonry cement complying with SANS 50413 is not permitted to be used in concrete.
“A simple way of deciding whether a sand is suitable for mortar is to mix 5 kg of cement with 25 kg of air dry sand and then add enough water to produce a consistency suitable for mortar. If more than 6 litres of water are needed, the sand is unsuitable,” explains Bryan.
Paving units less than 40mm thick should always be laid on a bed of mortar to give a total thickness of not less than 40mm. Thicker units may be laid on a sand bed. The ground below the paving must be firm and stable so that the paving doesn’t settle unevenly with time.
“The ground must also have the same slope as the finished paving. Remove all roots and vegetation from the site, and preferably the topsoil. Then trim the bed to the correct level and slope. Soft areas and areas that have been filled must be well stamped down with, for example, a gumpole. If the fill is very dry, mix in just enough water to dampen it and then compact it. If paving is laid on sand, a kerb should be provided to prevent outward movement,” says Bryan.
2. Follow the correct laying procedures
For mortar projects, mix one-part cement with six parts sand until the colour is uniform and then add water slowly. The mortar must be soft, about the consistency of toothpaste. Alternatively, the in situ soil can be stabilised as follows:
• Loosen the top 50mm of soil and then spread cement at a rate of 1 bag / 8m².
• Mix and add water until the mix has the consistency of a smooth paste.
• Lay small areas of about 1m2 at a time.
• Lay a bed of mortar so that the paving plus mortar will be 40mm or thicker. The mortar layer thickness should not be less than 15mm.
• Place the paving units on the mortar, tap each one down firmly and check that each one is level and at the correct slope.
• The mortar will rise a little into the joint between the units.
For sand projects, spread a layer of loose sand 25mm thick and level it off. Lay the paving units on this and tap each one firmly into place with, for example, a wooden mallet. Check regularly that the paving is at the correct slope and that the units are lined up correctly.
3. Executing correct jointing
For a jointing mortar, mix one-part cement thoroughly with four parts sand, then add water slowly and mix to a soft paste. Completely fill the joints with mortar. If the units are laid on a mortar base, the joints should preferably be filled within about two hours of laying the mortar bedding. This will ensure a good bond between the joint and bedding mortars. Dry sand‐cement mix (1 part cement, 3 parts sand) can be brushed over the paving and lightly watered into place provided that the surfaces of the units are smooth enough to ensure that spillage on the surface can be removed entirely. Use a wet cloth or brush to remove any mortar from the top of the paving while it is still plastic: once it has hardened, it is difficult to remove. Where large areas are paved with mortar‐filled joints, it is advisable to provide contraction joints at intervals of not more than 2 metres. They should be about 10 mm wide, extend right through the paving and be filled with sand.
For sand projects, pour dry sand on the surface of the paving and brush it into the spaces between the units. Then water it lightly to wash the sand well down into the joints. The sand stabilises the paving by limiting the movement of the units.
4. Curing mortar
Cover paving that has been laid with mortar with wet sacking or plastic sheeting for two or three days so that it does not dry too quickly. Premature drying results in the mortar not developing its full strength and the paving may crack.
“It is important to note that the methods of paving for driveways and other areas that will be used by motor vehicles may differ from the methods mentioned. Consult relevant publications before building driveways or other areas which may need to take heavier loads,” concludes Bryan.
For more information, contact The Concrete Institute on Tel: +27 (11) 315 0300 or via www.theconcreteinstitute.org.za.
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