Interlocking Paver Guidelines
Bart Flegg on January 24, 2010, 8:59 pm

Interlock
The theory behind interlock has been around for thousands of years, we just haven’t been building beautiful backyards out of it for that long. Interlock is characterized by stones set on an aggregate (gravel) base and jointed with sand. Let’s examine the interlock system starting with the bottom up

Base
Proper base preparation is one of the most important elements to a high quality long lasting installation. Manufacturers recommend no less than 4” of base material and 1” of bedding sand for low traffic areas.  As the frequency and weight of traffic increase it is recommended to excavate deeper and include more base material. Up to 18” is recommended in commercial applications with slow draining soil.

With a minimum of 4” of base, 1” bedding sand and your common 2.76” tall paver you can calculate the total minimum excavation depth of almost 8”. 

The base when prepared should be level and flat, sloped only for drainage. This is done by a process called screeding. The base material should always be compacted with a large plate tamper.  This is a machine which pounds the ground and makes the base steady and firm.

Watch Out For
Problems with base preparation generally arise in the first two years after a few freeze and thaw cycles. These cycles mentioned are the expanding and contracting of the ground caused by water and moisture. Most notably these problems will manifest themselves as rutting, pooling or ponding of water or settling near the corners and edges.

Generally these problems go unnoticed and discounted as the aging of an installation or a failure of the product itself. In reality a professional installation will last from 10-15 years depending on the climate.

Paver Selection
The selection when choosing paving stones is huge! There are tumbled pavers, weathered pavers, permeable pavers, and even stain resistant pavers. They price anywhere from  $1.70/sqft to $9.00+/sqft.  Merlin Construction highly recommends that you pick up a few catalogs from a local supplier to look through. If you have any questions contact us and we can get a couple catalogs to you as well.

Recently the trend is towards permeable paving systems but they can get expensive, often more expensive than anybody wants to spend on a patio. We can recommend two economical pavers that we often install that look great and function as they are intended.


Unilock Hollandstone
This paver has been around for what seems like forever and will likely never get discontinued. It              is your basic 10mm x 20mm x 6mm paver brick with 4 chamfered edges. Its standard size and simple patterns makes for a fast install.

Unilock Brussels
This paver is extremely popular because of its tumbled look and random pattern possibilities. It has an old world cobblestone feel to it at a price many can afford. Each edge is tumbled to give the paver timeless character. This product also has a wall stone to complement its look.

Sand
At the start of the interlock section I mentioned that the stones were jointed with sand. What I meant is that once the stones are laid on the 1” of sand bedding course on top of your 4” of base and tamped down once more the contractor must sweep sand into the cracks of the patio. Now there are two types of sand.

1.) Normal sand. This sand has a tendency to blow out of cracks or wash away in a heavy rainstorm leaving your interlock unstable.  Normal sand also allows grasses and weeds to grow in between your paving stones.

2.) Polymeric sand. This sand is mixed with a special polymer that gets hard and sets in the same way concrete does. This ensures that the sand remains for years. It remains somewhat flexible but because it is mostly inorganic weeds do not grow in the cracks of your patio.

Clearly the second choice is the more preferable choice.

 

Finishing Interlock
For an experienced landscape contractor building an interlock patio that is flat and well draining should be just another day on the job. The real test comes in the finishing details of the patio. These are some good guidelines.

No gap in the patio should exceed more than ¼”.

Curved borders should consist of bricks tapered on both sides in comparison to using full bricks and wedges.

 Edge restraint is used to ensure that gaps do not appear in the patio.

All polymeric sand should swept from the patio before it is wet down to activate the polymer.

Interlock, Pavers, Paving Guidelines, Contractor Quality Control
......................................................................................................................................

Back In The Office