The first reason that concrete pavers – and any paver that interlocks – has to do with the material that they are constructed from. Concrete pavers are rated multiple times stronger than poured concrete. This is due in part to the way the pavers are formed, but it’s also due to the ‘interlocking nature’ of the material.
The Secret: The Interlocking Action
Interlocking pavers remain durable and new looking even after years of abuse and weather precisely due to the ‘interlocking action’ of the paving stones. Interlocking concrete pavers are designed specifically to leave gaps in between each brick – in other words, they do not sit exactly flush to each other. It is this space, paradoxically, that gives the entire structure its strength as soon as these joints are filled with an appopriate joint material, such as sand. The pavers are laid in a particular pattern (the pattern really is just how the joints are arranged), leaving a bit of space in between each and every paver. Mortar is not used to bind these joints together, as this would destroy the benefits of the sand-interlocked paver.
Though sand is the most popular material used for the joints, it is not the only one – special joint material is put out by the concrete paver companies for this purpose, but it’s generally quite expensive. Bluestone screenings are another popular material, though there may be problems with this material when the surface is compacted, as the small stones may scratch the surface of the brick. Thus, sand remains the most popular joint material for most projects and contractors.
How the Interlocking Works
When the sand fills the joints, it helps hold the pavers together in two ways. First, the small pits and holes in the stone interlock pavers through friction. The small gaps ‘join together’ and help the paving stones cohere. The sand also fills these holes, increasing the friction between the pavers even more. Second, the sand itself, when compacted, gets very tight. Thus, not only does the sand help the pavers stick together, it actually helps all the sand stick together as well, as the closely packed grains of sand cannot move without great force (this movement is resisted by friction). When the entire structure is surrounded with edging and compacted, it holds together as a whole even though the paving stones are not directly touching each other across their entire faces.
The material doesn’t matter here, either. Interlocking brick pavers or natural stone work the same way as their concrete brethren. It all has to do with the roughness of the bricks, the joints, and the sand that fills the gaps between them.
It is this strength and toughness that makes paving stones such a great option for homeowners. For instance, interlocking patio pavers withstand the constant pitter-patter of feet and the damaging effects of weather due to this cohesion. They are so strong that they will withstand the actions of vehicles – parking, sitting, accelerating, and so on. The surface is also quite flat, so it’s easy to plow or shovel snow off of it as needed.
Best of all, these types of installations are strong yet flexible. As water drains through the patio, for example, it collects in the base underneath. If it is cold out, the water will freeze. In other applications, such as concrete or asphalt, this freezing would expand the base, putting extreme pressure on the structure above and perhaps causing cracks or fissures. However, paving stone applications bend and flex with this freezing due to the flexibility of the joints and the sand. There is no “solid” structure above, but one that shifts and changes with the elements. Thus, the concrete paver project resists damage as the ice thaws, returning the structure to its original position, freezes again, thaws again, and so on.
The only disadvantages to this system lie in the fact that there is sand in between the pavers, and sometimes this sand escapes. Whether it’s due to the action of water or wind, or the action of ants building anthills, or your own power washing of the surface, sand levels will lower with time. This can weaken and even damage the structure. Luckily it’s quite easy to put sand back into the joints to replace the lost material. In addition, one of the benefits of sealing pavers lies in the fact that the sealant can help keep the sand where it belongs.