FAQ for Contractors
- Off the record, just using a ballpark, what is the going rate per square foot for installing pavers in my area?
- I recently removed old pavement, and there is already stone underneath. If properly compacted, can I lay pavers over it?
- Can geotextile be used in lieu of base?
- In order to prevent scuffing, is it necessary to protect the surface of concrete pavers from a plate compactor?
- What are the differences between American and Canadian standards for pavers?
- Don't concrete pavers cost more than ready mix concrete or asphalt?
- Can bedding sand be used for joint sand?
- Why are screening and stone dust not recommended for the bedding layer?
- How do you go about laying paver next to a new foundation? Do you need a special fill? Do you need to wait a certain period?
- How can I minimize sand washing out of the joints and also minimize weed growth?
While tempting, bidding projects by the square foot (sometimes even before seeing the project!) is a recipe for disaster for contractors. Every job is different, and so is every contractor. A successful contractor bids their company's price for a specific job, using labor hours for each job function and their own markups for overhead and profit. They do not quote square foot pricing simply based on competitive rates.
"The Complete Business Manual for Concrete Paver Contractors" by Charles Vander Kooi is an excellent resource for profitable bidding systems, and is available by accessing the ICPI Publications Catalog on this website.
This is not usually recommended. If the existing pavement is rutted, deformed, uneven or severely damaged, the base or sub-grade underneath the original installation is likely inadequate. Remember that the subgrade and base are the most important part of an interlocking concrete pavement. ICP's are flexible pavements, and as such, rely on load distribution in the base and adequate support from the soil subgrade. Sometimes the stresses on the pavement are from below, especially in freeze thaw areas of the country, so even residential patios and sidewalks need to have a proper base.
ICPI recommends a minimum base thickness of 4 inches (100 mm) for residential patios and walkways and 6 inches (150 mm) for driveways in non freeze thaw areas. In colder climates these base thicknesses are increased and most contractors will use 6 and 10 inches (150 mm and 250 mm) respectively. Gradation is another factor. The ICPI only recommends the use of base material meeting gradation requirements of ASTM-D2940 with 6 to 12% passing the no. 200 (80 micron) sieve.
No. Geotextiles are designed to retain the intended load bearing capacity of a pavement and should not be used to decrease the thickness of the base. As a separation fabric, geotextiles prevent contamination of the base from the subgrade and are especially helpful over silt or clay soils.
Depending on the type of paver used, some contractors use sand or geotextile as a protective layer between the plate and the surface of the pavers. Protective mats for plate compactors are also available. There is no specific guideline from the ICPI for this, please contact the paver manufacturer for specific recommendations for their product.
There are two sets of standards commonly used for pavers manufactured in North America: in the United States, it's referred to as ASTM-936, and the Canadian version is listed as CSA-A231.2. While all the differences are too numerous to list here, there are two very important ones worth noting.
First is freeze-thaw durability testing. ASTM-936 requires that units shall have no breakage or more than 1% dry mass loss after 50 freeze-thaw cycles in water as tested per ASTM C-67. With some exceptions the Canadian test is similar but with one important addition: the pavers are freeze-thawed in 3% saline solution to resemble the deterioration caused by de-icing salts.
A second difference is ASTM-936 requires that the compressive test strength of the test specimens to be at least 8000 psi and that no sample test under 7200 psi. The Canadian standard allows for the average compressive strength psi of the samples to be 50 Mpa (7250 psi), with no unit below 45 Mpa (6525 psi). The difference is that the Canadians test using a 1:1:1 dimensioned cube that saw cut out of the paver itself; while the ASTM standard allows for full or one-half units to be tested (minor variations are made for non-rectangular/square pavers). Many of the remaining differences involve the number of samples used, the frequency of the tests, and other details in the execution of both tests.
To learn more about both ASTM-936 and CSA-A231.2-95, please contact the ICPI.
The initial costs of segmental pavements over concrete or asphalt may be more, but it has been shown that the life cycle cost of an interlocking concrete pavement system over a 40 year period is actually less. This is because pavers make up a maintenance free pavement.
Because of the system of sand filled joints, unlike concrete or asphalt pavements, an interlocking concrete pavement will not crack. If there is maintenance that needs to be performed underneath the pavement, pavers can be easily unzipped then reinstated when the work is done- as opposed to noisy and messy demolition, disposal and replacement of concrete or asphalt. Stains are easily treated as most pavers can either be cleaned with special cleaners or easily replaced.
Even in the short run, there are many advantages to using concrete pavers. Unlike asphalt or concrete, which need time to dry or cure once laid, pavers can be enjoyed as soon as they are installed. Finally, adding in the benefits of many more color and design choices available, it is easy to see why pavers offer the best value.
Yes, however a contractor needs to remember that washed concrete sand meeting the gradation requirements of ASTM C33 and CSA A23.1 is the only material the ICPI recommends for the setting bed. This being the case, some of the largest particles in the sand may be more difficult to sweep and compact into the joints. Still, some contractors prefer to use the bedding sand material for their jointing material since it means having one less material to control on a job site and they also feel that they achieve better interlock between the pavers.
There are some alternatives to consider. ASTM C-144 and CSA 179 graded mason's sand contains more fine particles and tend to fill the joints faster, making final compaction less time consuming. Both materials are approved alternatives by ICPI. Using mason's sand makes sense if the time saved sweeping and compacting the sand into the joints outweighs the costs and inconvenience of having two kinds of sand at the jobsite. If not, then consider using bedding sand. Some contractors feel that finer sands create tighter, less permeable joints.
A third alternative is prepackaged polymeric sand. When activated with water according to manufacturers instructions, this sand will harden, inhibiting weed growth, insect infestation, and sand run off from the joints. Generally, polymeric joint sands tend to cost more than C-33 washed concrete sand and masons sand, and require extra steps and time, so this should also be estimated into the project costs accordingly.
Whatever the final decision may be, the ICPI does NOT recommend using stone dust, limestone screenings or other materials that do not conform to either C-33 or C-144 gradation specifications.
For more information on joint sands, refer to ICPI Tech Spec # 2, Construction of Interlocking Concrete Pavements.
Screenings have excessive amounts of fines (passing the No. 200 screen), which compromises the ability to bear and distribute loads. These small particles hold excessive amounts of water, causing the bedding layer to become saturated. This liquefied layer then becomes unstable and can even pump out of the joints. Properly graded course multi grained sands conforming to ASTM C33 and CSA A23.1 will perform better over time. This type of sand is readily available from your local supplier. Most suppliers may refer to this product as washed concrete sand. Ask your supplier for confirmation from the quarry that this material complies with the ASTM or CSA, specification especially regarding the amount passing the number 200 sieve. It is recommended that the maximum amount passing this sieve is 1%.
Installing any new pavement next to a new foundation can always be tricky. Typically, new foundations are not backfilled in layers and rarely compacted throughout. As a result, these areas are prone to settlement. A paver contractor needs to evaluate every situation on a case by case scenario. To encourage settlement of the soil before construction, some contractors will attach a pipe with a high pressure nozzle to the end of a hose and stick it in the ground at regular intervals around the foundation. This is then followed by compaction with a vibratory plate compactor. Never start laying pavers until the sub grade and base are compacted to ICPI standards.
There are several types of joint sand stabilizers available on the market today. Some are dry additives that are bagged and pre-blended with sand and some come in different size buckets that you can mix on site with your own sand. There are also liquid sealers that also act as joint sand stabilizers that can be applied directly over a typical joint sand application. The best alternative should be determined by the contractor, considering application method, experience, manufacturer's recommendations, job conditions and budget.