Adding a block retaining wall to your property does not have to be difficult or confusing. It does, however, require careful attention to detail. One of the most important issues concerning retaining walls is the foundation. Experts agree that the key to successful retaining wall construction is a level foundation course of block.
Here are some tips to help you get started with a block retaining wall:
When you are planning a block retaining wall remember that the foundation course of block must be below ground level. This is done so that the soil will remain firmly in place. If the soil moves, the wall may fail.
Once you know where the wall is going to be located, measure out and mark the key points of the wall. You can use string or garden hoses for this. Try to lay out the wall as close as possible to what you want in the end.
Begin at the lowest point and shovel out the dirt, making a trench for the foundation. As you do this, keep in mind that the trench needs to be about 4" deep. This will vary, however, depending on the type of block you are using. For general purpose block, 4" is appropriate. Once the trench is dug out, tamp it down firmly.
Once the soil is tamped down, add between 1" - 2" of sand. Tamp this down firmly as well. Make sure that you spend enough time tamping. This is an important part of the job. Back breaking perhaps, but important.
If the line of the retaining wall is on sloping ground, you may need to dig your trench in steps. You would do this by digging a series of steps, each equal to the height of the blocks that you are using. As you move along, you want to build up the lower sections with block until the stepped areas are large enough to take additional blocks. This needs to be done carefully in order to get a level result.
It is critical that you check the level of the foundation course before you start the second course. If you find areas that are not level, add or remove soil to make it level. Masons of all ages will tell you that the first course is the most important. If this one is off, everything else you do will be off.
Now that you have a level trench you can begin to lay the next course. Check for level as you build each course.
To build a course, you set the first block in place and check it for level. If it is off, tap it gently with the butt end of a hammer to adjust it.
If you are building on level ground, continue placing the rest of the foundation course. Once the entire foundation course is in place, you want to set one block in place at each end of the foundation course. Make sure that the lip of each block fits right against the back of the foundation course block.
You can use a line level to ensure that the first and last blocks are level with one another. If they are off, make sure you adjust them now.
At this point you need to cut one block in half for the start of the second course. Doing this will allow the first and second courses to be staggered rather than sitting straight atop each other.
You can now continue placing blocks along the second course, making sure all is level as you go. You also want to make sure that the trench stays filled with soil.