How To Build An Allan Block Retaining Wall

Allan Block retaining walls are a great way to control erosion and add a little color to your landscape, but there’s one problem: they can be hard to build! With the right tools and materials, however, you too can learn how to make an Allan Block wall that you’ll be proud of. By the end of this article, you’ll know how to plan and construct an Allan Block wall from scratch.

Install Base Layer

  • Dig a trench along the top edge of your block wall, using a shovel and pick to remove soil. The trench should be wide enough to accommodate your drainage pipe and gravel pit.
  • Lay down a layer of compactible gravel in the trench, making sure it’s level with the top surface of your block wall. This will provide an even base for installing drainage pipe and for creating an area where excess water can collect during rainstorms, preventing erosion on your property.

Build First Course Of Allan Block

The first course of Allan Block is the most important because it sets the foundation for your retaining wall. Your goal should be to build this first row straight and square, so that all subsequent rows will line up properly. First, take careful measurements to make sure you’re building in a straight line, then use stakes as markers to guide your work.

Once you’ve laid out your first row, begin laying blocks by placing them on top of one another along the back edge with their flat sides facing outwards. Make sure they are level (checked from behind and from above) and then hammer them into place with a mason’s mallet until they are tightly wedged together or braced by smaller stones nearby if needed (to ensure stability). Be sure not to disturb any surrounding soil or plants as this could cause damage over time due to erosion or root displacement.

Build Second Course Of Allan Block

Once you’ve built the first course of Allan Block, it’s time to add a second course.

You’ll need:

  • 2-foot long pieces of 16-inch deep square posts.
  • Wooden blocks that are 5 x 5 x 3 feet long and 1 inch thick.
  • Sand, gravel or dirt (to build up your base).

Build Third Course Of Allan Block

Now that you’ve completed the first two courses, it’s time to build your third course. The key here is to make sure that each block is level and straight.

Do not forget to use a level and straightedge while building this course! It will take some extra time and effort, but if you want your wall to look professional, it’s worth the effort.

Cover Wall With Soil And Stack Blocks

If you are going to use the soil from your site, first use a topsoiler to remove grass and weeds from the area. Then, use a tamping tool to pack the soil into the wall. When packing down dirt, it is important to compact it very well so that water will drain out of it. If there is insufficient compaction, erosion could occur in your retaining wall during heavy rains. Use a vibrating plate compactor for this purpose; these machines vibrate as they are driven over the ground and help break up any large clumps of dirt or stones so that they can be packed more tightly together by hand later on with tools such as tampers (which are basically just long metal rods). Finally, sod strippers are used to remove unwanted vegetation from around your wall before filling them with dirt or other material.

Fill Pit With Gravel And Install Drainage Pipe On Wall

Step 8: Fill Pit With Gravel And Install Drainage Pipe On Wall

  • Lay out the gravel pit area, making sure that it’s level and flat.
  • Begin installing drain pipe with a gravel pit at each corner of your wall, making sure you have one downslope hole for water to exit and one upslope hole for water to enter (see photo). This will allow gravity drainage along the length of your retaining wall, which will help ensure that it stays stable and doesn’t erode away over time due to water damage or erosion caused by rain runoff during storms or heavy winds in certain areas where they may be more susceptible than others because they lack protection from trees or other foliage on top of them like some other parts do too much so when there isn’t enough room left over after getting rid of all those rocks so now there’s less space available then what was originally planned out carefully beforehand before starting any construction project whatsoever!

Better to put a drainage pipe behind the wall and install a gravel pit to collect and move the water, along with an outlet drain.

If you have a wall that’s going to be exposed to heavy rainfall, you may want to consider putting in a drainage pipe behind it and installing a gravel pit so that any water that comes down the wall can collect in this area. You’ll also need to install an outlet drain on top of the ground so that excess water can move away from the wall.

If you’re building your retaining wall on an embankment or hillside, consider using these same methods but with slightly different tools (such as plastic pipes instead of metal ones).


While we’ve attempted to cover a lot of the basics in our “How To Build An Allan Block Retaining Wall” guide, there are some things that simply can’t be covered in written form. That’s why you should visit your local home improvement retailer to get personal assistance from an expert on how to build an Allan block retaining wall. They will have a team of people ready and willing to answer any questions you might have about your project.

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