© 2008 by Raymond Alexander Kukkee
Installing a flagstone patio is an exciting project that can increase the value of your home, create a beautiful spot for leisure or business entertaining, and provide much curb appeal. To install a flagstone patio correctly requires care and detail in excavation and preparation to assure a superior outcome and a beautiful, durable patio.
Supplies and Equipment you will need:
- Wooden pickets or stakes
- Carpenter’s line and line level ( use a laser level or transit level as an alternative)
- Shovel and pick ( a rented Backhoe or tracked Mini-excavator can save you a great deal of work for larger projects, highly recommended for very large projects)
- Gravel (Grade “A”, “B”, or “road base” gravel that will pack firmly. Note that if the incorrect grade of gravel is used, it will not pack and can be problematic.
- Sand Coarse, clean sand is essential because it packs firmly.
- Framing Use treated dimensioned lumber as required, or a manufactured frame as recommended.
- Screed Use two straightedges, (2×4’s , straight steel rod or pipes) for guides, and ‘screed’ or drag the surface of the sand to level. Work the screed (a straight 2×4) back and forth across the support straightedges you have set carefully into the sand.)
Inspect the proposed site and evaluate it for drainage, slope, and location. If drainage is a perpetual problem, consider the installation of a French drain in the process.
If the slope of the lot is more than 1″ in four feet, do consider installing a patio step between two levels for better use of patio furniture, better comfort, and the opportunity for landscaping and design possibilities offered by constructing two levels.
A patio should slope a bit for drainage, but ideally not more than 1/2″ to 1″ every 4′ for optimal general use.
Do obtain building permits if required, and contact utility companies to verify it is safe to dig in your chosen location.
Depth of excavation and the final elevation of the patio will depend upon the thickness of the flagstones chosen. Do make sure you know how thick the stone will be, or select the stone prior to starting the excavation.
Let’s get Started on the Excavation
1. Measure out and install pickets at the corners of the excavation and run a line around the proposed site. If it needs to be changed, now is the time. It’s better to modify your plan before work begins.
2. Using a line level or other system, install level marks on the corner stakes close to ground level if the patio is not to be a raised design. All four corners should be as close to level as possible, but as noted, a slight slope can improve drainage. *Hint: For ease of reference, tack short wooden cross-piece on the stake at 2′ above the proposed finished grade. Use them as “batterboards” to shoot the grade of the final excavation. Measure down from that point or grass carefully and use it for lawn remediation, filling holes, or have it hauled away. How about trading the sod with a neighbor for that extra help you need?
4. Excavate the soil necessary to allow for a minimum of 3″ compacted gravel layer and a 2-3″ bed of coarse bedding sand. Ideally your gravel layer should be 6″ thick when compacted. Do smooth the bottom of the excavation close to level and remove any large stones or tree roots which will cause trouble later.
5. Install the 6″ gravel level and compact it as firmly as possible. Use a mechanically powered vibrating plate packer if possible and water the gravel down for optimum packing. Remember, the better the base layer is compacted, the less likely flagstones will crack or settle later, requiring the annoying and time-consuming repairs requiring removal of the stones, adding sand, and re-setting the stones properly.
6. Install the patio framing if required. Patios with larger stones do not need edging unless desired.
7. Install 2-3″ of coarse sand on top of the gravel in an even layer. Compact or pack the sand layer. Use a mechanical compactor if possible, but if you do not have one, use a 2×4 “Tee” for a tamper, and water the sand down to ensure it packs well. Screed the surface of the sand layer as smoothly and evenly as possible.
8. Begin the installation of the flagstones. Remove or add sand as necessary to ensure the top of the flagstones are even. Make sure none of the flagstones sits unevenly or ‘rocks’ in place. Settle the stones firmly, finish the layout of stones, and fill the cracks and spaces with sand. Wash the sand into the cracks to ensure the cracks are filled completely.
Complete the installation and landscaping as desired, and enjoy the result of your work!
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