How to Build a Cinder Block Retaining Wall in a Cold Climate

Excavate into the slope as needed to prepare the wall site, and dig a trench for the wall's foundation. The foundation must extend below the frostline -- the lowest depth at which the soil freezes -- to prevent frost heave. The foundation should have the same thickness as the wall and be twice as wide.

Place concrete forms into the trench. Make sure that the forms are lubricated with a form lubricant or motor oil. Brace the forms securely using scrap wood and place 2-by-4-inch boards cut to fit the form every 3 feet at the top of the inside of the form to maintain the shape of the form once concrete is poured.

Tie steel rod stubs temporarily to the spaced boards at the top of the form extending downward so that the bent end is at a depth where it will be covered by 4 inches of foundation concrete.

Pour concrete into the forms. Smooth off the top of the poured concrete with a wooden board or trowel. Let the concrete cure for at least a week before continuing wall construction.

Do a dry run with the cinder blocks on the mortar-free foundation to plan their locations, determine how many blocks will be needed and make adjustments. Begin with the corner blocks that have a flat side. Use a scrap of 3/8-inch plywood to account for the space that mortar will fill. The steel rods should be in the center of block holes.

Prepare the mortar for the first level. Standard mortar usable for below-grade applications should be suitable for retaining wall construction. If the wall is being built when temperatures are low, consider mixing an accelerator into the mortar mix to force faster curing.

Spread a 1-inch-thick layer of mortar where the blocks will go for the first 3 or 4 feet along the foundation. When working throughout the remainder of the wall, only spread mortar across and work on a few feet at a time.

Place cinder blocks for the first course in the prepared mortar bed. Start at the corner, placing the flat corner block first. Make sure that the corner block is level and aligned correctly. Apply 3/8 inch of mortar to the end of the next block with a trowel, and place the block in position. After every few blocks are laid, use a level or similar straight-edged tool to check alignment and tap blocks into position as needed.

Tie lengths of rebar slightly shorter than the planned wall height to the exposed stubs from the foundation.

Lay the next course of cinder blocks using the same mortaring techniques. Stagger the blocks so that vertical joints do not align, and make sure that each rebar, when standing vertically, is centered in a cinder block hole.

Continue laying courses until the desired dimension is reached.

Fill the spaces within the blocks that contain rebar with grout. Make sure that the rebar is aligned in the center of the hole, and use a wet enough mix to fill the hole in order to limit the possibility of air spaces deeper in the wall.

Place capstones atop the cinder block wall. Capstones are often flat and meant to protect the wall from weathering. Mortar the top of the wall and place capstones so they slightly hang over the face of the wall.

Back-fill behind the wall. Place a perforated drain pipe at the base of the wall and cover it with gravel. The space immediately behind the wall should be filled with coarse gravel to facilitate drainage. Fill in the remainder of the space with soil and vegetate as desired.