Retaining wall blocks are really heavy. You don’t want to lift them twice. Learn how to build a rock solid retaining wall right the first time.
Build a Long-Lasting Retaining Wall in Raleigh
Anyone with a strong back can stack up a bunch of blocks and build a pretty stone retaining wall. But it takes skill and planning to construct an attractive wall that can also handle immense pressure, shrug off the forces of gravity, stand for decades and laugh in the face of Mother Nature.
That’s the kind of retaining wall you want to build here in Raleigh, so here is a brief overview. We also shared a few handy tips they’ve picked up over the years.
Make the trench wide, deep and level for the Retaining Wall
Size the trench so there’s enough room for the block and at least 8-in. of space behind it. Excavate deep enough to completely bury at least one full course, including space for 6 to 8-in. of base material. Establish a level trench to ensure an even layer of base material. That will help prevent the wall from tipping after freeze/thaw cycles. Our experts use a laser level and a story pole to determine the depth of the trench.
Compact the trench for the Retaining Wall
Compact the soil for the retaining wall in the trench bottom with a hand tamper or vibrating plate compactor. This step is often neglected. The excavator, and even hand shovels, can disturb and loosen the top inch or two of soil, and that’s enough to make your wall settle—settling is bad! Raleigh area soils are clay and do move over time. This is a key step!
Lay a crushed stone base for the Retaining Wall
Our experts prefer crushed stone for the base rather than naturally occurring gravel dug from a pit. Crushed stone is a little more expensive. However, it provides better drainage, and because of the sharper angles on the stone, it requires less compacting, and once it’s compacted, it stays that way.
Joe and Jake have found that crushed stone sized between 1/2 in. and 3/4 in. is best suited to handle the heaving forces created by the harsh freeze/thaw cycles here in Minnesota. Avoid rounded stones like pea gravel or river rock; they don’t form strong interlocking bonds like angular stone.
Leave the stone no more than 1/2 in. higher than you want the final height to be, and then make a couple passes with a hand tamper or plate compactor. You’ll notice the stone is almost 100 percent compacted as soon as it’s laid in the trench. The same type of stone will be used for backfilling, which also eliminates the need for hauling in multiple materials.
Get the first course right
Use a torpedo level to level each block front to back and a 4- or 6-ft. level to keep each course level and even. Set the blocks with a heavy rubber or plastic mallet. Getting the first course flat and level is extremely important, so take your time. Try to lay the course as close to the center of the trench as possible.
Sweep before stacking
Even a small pebble on the surface of a block will throw the one above it out of alignment. And that crooked block will affect the one above it, and so on. That little stone could eventually create an unattractive hump in the top course.
Step up after two full courses are below grade
If the wall runs up a hill, continue each base course into the hill until the top of the second course is level with the grade, and then start your second base course at that point. If you have the option, it can be easier to excavate and lay the lowest course before excavating the trench for the next step, especially if you have to step up several times. Save yourself some money and install the cheapest style/color that matches the wall style (usually the gray ones) on the bottom course since it won’t be seen.
Retaining Wall Draining
Retaining wall drainage is an incredibly important part of building a stone wall. Once a few rows have been stacked, backfill the wall with rock so it matches the grade height in front of the wall, and then lay down perforated drain tile on top of the rock. Install drain tee fittings and a drain grate every 25 ft. to 50 ft., depending on how much rainwater is expected to run down to the wall. Cut one block down to accommodate the drain grate. Screw the drain tile parts together so they won’t come apart when they get covered with more rock. Also, drain the tile to daylight at the ends of the walls whenever possible.
Split blocks for a rough finish
If the end of a block will be visible, and you’d like it to match the other rough surfaces, use a block splitter. You can rent a splitter like this for about $85 per day.
Make smooth cuts with a saw
Use a gas-powered cutoff saw like this one for a smooth cut. This saw can cut with or without water. Water eliminates the dust but creates a messy slurry that can permanently stain surfaces like driveways and sidewalks. You can rent a saw like this for about $80 per day. If you don’t use water, make sure the dust doesn’t blow into the house or on a neighbor’s house.
Mark cuts with a soapstone pencil
These pros who build retaining walls like soapstone because the lines created by grease pencils and markers can stay visible for a long time, whereas soapstone washes off in the rain. The downside is that soapstone doesn’t work as well on wet blocks.
Stagger joints and keep them tight
Stagger the overlaps (at least 4 in. for this Fayblock product) and try to keep the butt joint between the blocks as tight as possible when building a retaining wall. Large gaps can create a pathway for water and sediment. Whichever type of block you use, make sure you follow the manufacturer’s instructions.
Backfill with stone
Versa-Lok recommends compacting the angular stone as you backfill, but check the installation instructions for the type of block you’re using. Backfill about 8 to 10 in. below the top of the capstones of your retaining wall. This will allow enough room for the topsoil and turf.
Align the capstones
Secure the capstones with a specialty landscape block adhesive, which stays flexible over time in the construction of your retaining wall. Make sure the blocks are dry before applying the adhesive. Overhang the capstones about 1 to 1-1/2 in. Joe and Jake use a scrap 2×4 as a guide.
Tall walls need engineering
Walls more than 4 ft. tall will likely require a building permit and a plan made by a licensed engineer. The engineer will specify the base’s width and depth, how far down the base course should be buried, and whether or not a geogrid (soil reinforcement system) should be used.