Laying Patio Paving
Posted Monday, September 21st, 2009
After several years, concrete slab pavings on domestic patios often need to be taken up and re-laid because of settlement. It's almost imposssible to lay paving slabs so they will never settle and become uneven - the only way to prevent settlement would be to lay them on a reinforced concrete base. But they can at least be laid to last a couple of decades or more before the job needs doing again.
When the slabs are old, they become saturated with dampness in the autumn and seem to stay that way until the warmth of the following spring, giving the patio a drabness that lasts the whole winter. If they are butt-jointed with no mortar, or even jointed with mortar, water finds its way underneath and expands in freezing weather, causing the slabs to lift up slightly. Mortar jointing only delays this process until it is itself damaged by frost.
A number of winters later the integrity of the original job, no matter how well done, is destroyed by the continual action of the weather and other forces of nature like weeds and the simple fact that the ground we live on never remains completely static and inert. Raking out and re-pointing mortar joints every few years does help, but the time comes when a concrete slabbed patio needs to be re-laid from scratch. This is what we did in the month of September.
Marshalls Perfecta concrete paving slabs
We replaced the original plain 'dimpled' 2ft x 2ft x 2in slabs with Marshalls Perfecta 595 x 595 x 50mm metric pavings, which meant that the joints would be slightly wider as we kept the same chequerboard layout as before. And instead of pointing the joints with sand and cement mortar we used GeoFix jointing compound, a ready-for-use sand mixture with Polybutadiene bonding agent that is simply brushed in and lightly compacted with a pointing tool or rubber-gloved finger.
When applying GeoFix it's hard to believe it will really harden into a strong joint. It has such a light sandy texture even after compaction but after a few hours of exposure to the atmosphere it's rock solid. This is presumably why it's so expensive at around £30 for a 20-litre tub. We used six tubs for 160 paving slabs, even after the joints were pre-filled with sand and cement mortar up to one inch below the finished level.
Before laying the new pavings, the already hard and gritty base was pummelled with a sledge hammer to make it completely firm, then each slab was rubber-hammered down on four dabs of strong sand and cement mortar (like the original job 24 years earlier) taking care to achieve a very precise alignment, level, and fall. The same mortar mix was then worked hard into the joints with sticks, forcing it underneath the edges of the paving slabs for extra support and water resistance. Completion of the joints with GeoFix jointing compound was done only when everything was completely set and dry, and when no rain was forecast for at least 24 hours.
Laying large paving slabs (flags, as we call them in the North West) is quite a physical task. They're heavy and you're leaning over a lot. To move them about we used a Faithfull heavy duty sack truck, worth its weight in gold.
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