The paver patio featured in “Paving Partners,” (HANDY, May/June 2008, p. 26) was an ambitious project. Besides creating a great space for walking, dining, lounging and overall recreating, the homeowners hardscaped around a large tree and enhanced the new area with lighting (photos 1 and 2). Here, we will describe the steps to building these elements — whether you make them as part of a patio project or as stand-alone features. Both structures were constructed of retaining wall blocks to complement the pavers used in the patio.
IMPORTANT: Be sure to call 811 to have underground utilities marked before your dig.
Tree Ring
In addition to being an attractive design element, a border encircling a tree is practical in many ways. It protects the tree trunk from contact with lawn mowers, and it corrals mulch from spreading to the lawn. Depending on the height of the border and the material used, a tree ring can provide a pleasant seating area, as well. In general, a tree ring is an all-around good idea — AS LONG AS it’s installed with the tree’s health in mind.
As shown in Illustration 1, a tree’s roots extend far beyond the drip line and much of the root system is near the surface of the soil. So, be sure to cut the trench for the base layer of blocks as shallow and as far away from the tree as possible (4 to 6 in. deep).
To allow air to circulate to the tree’s skin (bark), it’s important to protect the base of the trunk from a buildup of soil or mulch. Also, it’s good to preserve the established soil depth that covers the tree’s root system. With these cautions in mind, here are the basic steps to take:
o To avoid having to cut blocks, set a circle around the tree before you mark the diameter of the ring, adjusting to a size that uses full-size units. If the tree is young, be sure to make the ring large enough to plan for growth. Remember that the farther out you go from the trunk, the easier it will be to trench. Mark an outline of the ring’s diameter.
o Dig a trench about 6-in. deep and a few inches wider than the base course of block. Compact the soil with a tamper.
o Add gravel in 2-in. layers, tamping after each addition.
o Lay the base course of block (using a cold chisel to remove the lip, so the block lays flat) (photo 3). The bottom inch or two of the block should be below the finished grade to prevent shifting.
o Backfill and front-fill the trench with gravel and tamp to compress the gravel.
o For subsequent courses of block, use blocks that are faced on the front and back (also called free-standing block) so it’s attractive from the inside, as well. Apply a bead of construction adhesive between the layers (photo 4).
o To fit the cap pieces on top, you may need to cut new angles so the sides butt tightly. Again, use adhesive to secure them to the previous layer.
o You can add a thin layer of black dirt for planting flowers inside the ring, but no more than a top dressing — so the tree’s roots can breathe. Keep in mind that additional vegetation will compete with the tree for moisture and nutrients, so feed and water accordingly. Mulch is best; a 2- to 3-in. layer helps to retain moisture and block weed growth. Remember to not cover the base of the trunk.
o The addition of a paver patio or walkway along the outside of the ring will hold the bottom course of blocks in place. If the tree is independent of a patio surface, a thin top dressing of soil and grass around the outside perimeter of the tree ring will help to secure the blocks, as well.
Pillars and Light Posts
The pillars shown in “Paving Partners” were designed as light posts, but you can use these same techniques to build posts as decorative structures on either side of an entry or between fence sections or even as stand-alone features in a garden. Because of the height and weight of these pillars, the foundation must be well constructed (photo 5).
o First, dig a square hole that is about 6 to 10 in. larger that the finished dimensions of the pillar. Try to not disturb the soil below the hole’s depth of about 15 in.
o Pack the dirt at the base with a power compactor, such as the Jumping Jack (available at rental centers). The hole’s depth allows for 6 in. of gravel plus 1-1/2 courses of block to be below grade — as added insurance that the stacked blocks will remain straight and solid.
o If your pillar is intended to become a light post, this is the time to plumb in conduit for the electrical wiring. See Illustration 2 as a guide. Be sure that the vertical section of conduit is on center with the post.
o Add compactable gravel in 2-in. layers, packing after each addition until you have 6 in. of gravel and a smooth, level surface.
o Lay a base course of blocks for the pillars. This layer does not need to be decorative (faced) material, but it does need to be perfectly level.
o Lay the second and third courses of block, staggering the joints with each layer and applying exterior-rated construction adhesive between each layer. Backfill around the base with gravel, tamping each layer.
o Add the remaining courses of block to reach the desired height (ideally no more than 36 in.), checking for plumb as you go. Apply adhesive between courses.
o To build a cap that has finished outside edges, cut eight wedge-shape cap pieces. This leaves an opening in the center for the conduit to extend through. Place and glue the pieces on top of the post.
o A second cap piece covers the center opening. To recreate the natural-looking rough surface on the four outside edges, use a snapper to cut a square smaller than the post base, but larger than the base of the light fixture.
o Bore a hole in the center, using a hammer drill and masonry bit. Mark and bore holes as needed for the light fixtures fasteners (photo 6).
o Secure the finish cap to the post cap with adhesive, making sure it is square with the previous layer.
o Attach the fixture to the cap with concrete anchors and bolts and complete the wiring installation (photo 7).
TIP: Be sure to choose a light fixture that suits the style of your house (matching other exterior fixtures, if possible). Equally important, be sure the fixture is to scale with the pillar and doesn’t appear to be wimpy or overwhelming in comparison to its perch.
Related Projects
Paving Partners
Light Up Your Yard: Installing Light Posts
New Trends in Outdoor Lighting