Once your outdoor landscape design is finished, the next step of the process is to ensure you fully understand the construction basics. There are some so-called professionals who use a one-size-fits-all method to construct exterior rooms; however, it is a flawed construction process. The characteristics of the site and soil can impact what base is necessary to create stability under your walls and patios.
When your landscaping team takes the time to know the soil classification on your property, they will be able to accurately predict a number of factors that can impact your finished patio, including:
- Water holding capacity
- Freeze/thaw expansion
These are factors that will also affect the amount of time necessary to complete the project. If the soil is loose and sandy, it won’t compact properly. If the soil is heavy clay, like our Kansas City soils, it retains moisture and heaves in the winter.
There are three basic particle sizes used when determining your soil type. The testing process uses a sieve analysis gradation ASTM D 422 to determine percentage of the three types of particles in your soil. The three types include coarse-sand; med-silt; and fine-clay. The finer the particle size is, the less suitable it is for the construction of a patio or other structure. Clay is the least desirable type of soil for construction purposes. This means that people with clay soils need extra precautions taken to ensure the longevity of your hardscapes.
Soils that consist of more than 30 percent clay are considered “clay”. The problem with clay soil is that it retains moisture and is slow to drain. This type of soil is also more difficult to compact since it holds moisture and it will contract and expand more during the Mid-West freeze/thaw cycles.
If your design-build landscaping professional understands your soil type, they can create a plan of action that ensures the longevity of your outdoor living area.
The Importance of Compaction
Prior to building anything, it is important for your contractor to compact the soil and base. This process will increase the bearing capacity, help to prevent contraction and swelling, and prevent settlement. Settlement is the top reason so many hardscape features fail.
Most professional landscapers will claim they compact the base prior to laying pavers; however, are they actually testing the compaction? True professionals, will not only compact, but also make sure it is tested to ensure a proper compaction level is achieved.
Helpful Tip: Ask your landscaper if they test the compaction density and what density they compact bases to. If they are unable to answer, or their answer is anything besides that they compact to a minimum of 98 percent standard Proctor Density, then you are likely going to have to pay someone else to fix the project after it settles.
Geotextiles are the synthetic fabrics used for stabilization of hardscape projects. They don’t increase the base’s load bearing capacity, but can preserve the capacity and prevent the smallest particles from settling. They are smart to use in the following situations:
- To provide a barrier between the compacted aggregate and compacted soil so the gravel won’t sink into the soil.
- To provide a barrier between the compacted base and paver bedding sand so no sand settles into the aggregate.
- For concrete bases, geotextiles need to be installed over expansion joints, which is where cracking is most likely to occur.
The base materials used can impact the success of your hardscape project. Common patio bases are:
Ab-3: A mixture of ¾” gravel with jagged edges and small, (as small as dust particle sized), crushed gravel called “fines”. The ideal mixture has 8% fines to lock aggregate in place. Maximum percentage of fines allowed in certified Ab-3 is 12-14%. Use a certified material source to ensure the Ab-3 has not had extra fines added.
This pictures shows what AB-3 looks like after being compacted.
Clean Gravel: Typically a ¾” jagged edge gravel. Allows for free drainage, but allows sand and “fines” to settle. It is suggested that a geotextile be used between gravel and any fine materials. Although clean gravel by itself should never be the sole base for a hardscape project, excessively wet areas can benefit from an extra deep base where clean gravel is installed below Ab-3 for extra drainage.
- (Example, instead of just installing 6” of Ab-3, a contractor could install 6-12” of clean gravel below the Ab-3 as an extra drainage measure. The soil below the gravel and the gravel would still need to meet compaction standards.)
Concrete can also act as a base for pavers if the concrete is free from any cracks or settling. It is suggested to use a concrete base in the following circumstances:
- If adding square footage to an existing concrete patio that will have pavers overlayed. Concrete and aggregate bases expand and contract differently during the freeze/thaw cycle. This can cause pavers to settle differently in each area. A common way to cut corners is to compact an aggregate base next to a concrete slab and then overlay the whole thing with pavers. This can result in the differing in settling and an obvious line where the concrete and aggregate meet. Always meet concrete with concrete and tie them together by drilling re-bar into the existing concrete so they move together.
- Use concrete under pavers where vehicles drive. Many municipalities require concrete under a portion of driveways even if overlaying with pavers. Also, a thicker paver is required where you’ll have traffic.
- For example in Leawood, KS. the following is required
- The 12’ closest to the road called the “apron” can be no wider than 30’ and no narrower than 12’. This is within the city’s Right Of Way (ROW). The concrete must be at least 4” thick if overlaying with pavers, or 6” thick if not. An expansion joint is required at the curb and at the 12’ mark in the concrete. Concrete must be KCMMB (Kansas City Metro Materials Board), approved for ROW.
- For example in Leawood, KS. the following is required
- If concrete already exists in the exact shape you’d like to install pavers/stone in. Two things to keep in mind:
- Existing concrete must be low enough to allow for 1” of sand and the depth of the paver/stone. If concrete is poured at close to the height of thresholds or sill-plates, there will not be room for pavers and another option will have to be considered.
- Existing concrete must be free from settling and cracks. No installer can guarantee the durability of something they didn’t build. This means that typically a warranty is voided on this type of project.
Aggregate/Dry Concrete Hybrid Base
In extremely poor soils, professionals can use a hybrid method where they compact Ab-3 and sprinkle a layer of dry concrete for extra re-enforcement. This both allows for flexibility and adds extra strength. These bases are very durable. High Prairie Landscape Group prefers this base method because Kansas City soils tend to have a high clay content and this allows for extra protection against frost heaving.
CONTRACTOR HINT: Ask your contractor if they get their base materials from a certified quarry. Quarries certified by a city, state, or highway organization are required to meet quality standards for use as a base. “Cheaper” suppliers can add extra “fine” particles to their mixes to cut on price. This sacrifices quality because too many “fines” decreases base strength, increases frost heaving, and drainage decreases.
There are specific, accepted standards regarding the base depth for various hardscape projects. These include:
- Paths, patios, sidewalks: 4” after compaction in well-drained soil. For Kansas City home’s a 6” base is a better option due to the slow draining nature of the soil present.
- Drives and other areas with vehicular traffic: 8 to 10” of compacted aggregate with a 4” pad of KMMB concrete. (KMMB concrete is a high-grade, durable concrete mixture approved by the Kansas City Metro Materials Board.)
Improper edge re-enforcements are the second leading cause of patio failure. This is because weak edges can allow the pavers to separate or settle. A compacted base needs to be extended, at the very least, 6” outside of the paver area to install the edge restraints on a solid, secure base. Restraints should never be placed on the sand.
The edge restraints can be made from a number of different materials. In order of durability, there is plastic, aluminum, steel, stone and poured-in-place concrete. Some companies use a combination edge restraint with a plastic or aluminum restraint and a concrete curb. These edges are the surest way to prevent separation.
Here is an example of the base and re-bar re-enforcement installed prior to concrete being poured. High Prairie Landscape Group installed the pavers on a concrete base on this project in Leawood because we were installing a heating system below the pavers:
Understanding Sand and Sealers
There are different types of sand required to complete your patio project, which include:
- Bedding Sand: 1” layer of sand installed above the base and below the pavers to set the pavers on. Bedding sand is a coarse sand that allows for drainage. Using fine sands such as mason’s sand slows the drainage and can cause a ripple effect in your patio over time.
- Joint Sand: A finer sand compacted into the joints in pavers. Mason’s sand can be used for this. The finer sand sweeps more easily into the joints and compacts uniformly. If using joint sand, a joint stabilizing sealer is suggested to keep sand from washing.
- Quality control check: The Putty Knife Test- To check that the joints are completely full after compacting, try to insert a putty knife into the joint. If the joints are full, the knife will barely move into the joint even with intense pressure.
- Polymeric Sand: An alternative to joint sand with joint stabilizing sealer is to use a polymer enhanced sand that hardens when water is applied. The polymers in the sand form a solid base with the sand and prevent the sand from washing.
Sealers are often used as an upgrade that is only necessary when regular joint sand is used during the construction process. Some of the reasons to use sealers include:
- Joint stabilization
- Moss and weed control in the joints
- Color enhancement
- Protection from stains for porous materials
In some cases, sealers are treated as a separate step because they are only able to be applied in certain temperatures. This means that your contractor may complete the patio and then apply the sealer upgrade when the temperature is right. If a sealer is used, it will need to be reapplied every one to three years.
This picture shows the pavers prior to sand being installed.
A second reason for waiting to seal pavers is that concrete pavers sometimes have a whitish haze appear a few weeks or months after installation. This whitish haze is a natural occurrence called efflorescence and there’s nothing that can be done to prevent it. It is a chemical reaction that happens as the calcium hydroxide in the concrete meets moisture at the surface of the paver. The good news is that there are cleaners available to remove the haze if it appears.
Ideally, your contractor would either use a sealer that allows the efflorescence to escape, or they’d do a follow up service visit a few months after construction to clean and seal as a separate phase.
As you can see, to properly construct a patio, quite a bit of thought, planning and testing must be done. If your landscaper does not take the proper steps, there is a good chance you’ll have to repair their work. When trying to understand competing proposals, it is important that you understand what their construction methods will be. Extra investment in proper construction methods and high-grade materials will save you thousands of dollars in the long run. Nothing is more expensive than hiring an amateur – so be sure to hire one of the best Kansas City patio contractors for your patio project.
Questions on your Kansas City area patio construction process? Contact High Prairie Landscape Group today.