Block Retaining Walls

I started with a real mess. It's hard to tell from the picture, but the original wall had separated from the house. It was cracked up, and had sagged.

The concrete that ran up to the wall had sunk several times in its history. At some point someone had repoured concrete over the original stuff, in an effort to raise it back up.

The end result was that there was a concrete pad there that was about 8" thick, covering around 24 square feet.

The sidewalk against the house had also sunk down about 4" below where it had began. The sinking was caused by all the water that was flowing into this spot. A large part of that was because there were no rain gutters on the house, and the whole yard sloped toward this point. Bad news!

The gutters I had put on alleviated a large portion of the water that was directed into this location, but I felt like I could do more for it.

Step one was busting out all of the old concrete. This was a real task, since (like I said) it was 8" thick. There was the 2'x6' sidewalk portion, as well as a roughly 4'x4' pad that supported the deck stairs. I used a shovel, a sledgehammer, and a pickax to bust up all the concrete.

I piled up all the concrete that I pulled up, figuring that I could have it taken away when I redid the rest of the sidewalks.

landscaping/100_1805 (used in other blog post showing yard with truck ruts without pool)

Once the concrete was all busted up, I had to take down the old wall. This I busted up with a sledge hammer, then hauled it out as well.

After that, I had to get the deck out of the way so that I could properly dig the trench for the retaining wall. I needed open access to the area behind where the wall would be, in order to properly back fill it.

I used a circular saw, and made a cut all the way across the deck perpendicular to the house.

I then disassembled that whole side of the deck. I tried to not destroy all of the boards. At first I was using a drill to remove the deck screws. That wasn't really easy (or possible) as the deck had been there for many years, and the screw heads had several coats of paint in them. The easiest way to get the deck out of there was to use a hammer and a prybar. I left the main support posts untouched.

Now it was time to start digging the trench for the base of the wall.

I dug a trench that was a few inches longer than was required based on the length of my blocks. The width of the trench was twice that of the blocks. The depth of the trench was such that 1" of block would be buried for every 8" that would be above ground, plus 4". That additional 4" would leave sufficient depth for a proper base of gravel and sand. When digging the trench, I frequently laid a level down into it to ensure that its bottom was mostly level. It didn't try to make it perfect, just reasonably close to level.

In this pic, I have laid out bags of gravel into the trench. This was to ensure that I had sufficient gravel. You'll note that I discovered a live electrical wire here while digging. Turns out this was providing power for one of my sheds which I intend to keep. I saved the wire, and reburied it in the base for the wall.

I put the small gravel (sized 1" or less) into the trench, and ensured that it was consistently 3" deep. I compacted it with a hand compactor from Lowe's, as I couldn't get ahold of a power one. On top of the rocks, I laid 1" of clean sand. The sand is the same sand that I cleaned up after removing the pool in a previous blog post. I also compacted the sand with the hand tamper. When placing the gravel and sand down, I also confirmed that it was close to level across the entire length of the trench.

I purchased the blocks and cap blocks from Menards. They're about 40 lbs each. I went with these because neither of the walls I was building were exceptionally large.

This next step is the absolute most important step in this process. Laying the first row of blocks.

The blocks that I purchased had a lip on the back of them, for overlapping the block below them when stacked. For the base row, I used a hammer and a chisel to bust them off. The pieces that were broken off were set aside to use as part of the backfill.

Each block had to be laid perfectly level both left to right, and front to back. The process is simple: set the block, tap it several times with a big rubber mallet to set it. Then check it for level. The reason the sand was used on top of the gravel is because it is much easier to level blocks in sand than it is in gravel.

The basic techniques are to keep wiggling the block around if it's too high, or lifting it and adding sand under it if it's too low. It is crucial that the block be absolutely level both ways.

Once the base row was in place, the rest was relatively easy. Because the first row was perfectly level, the entire rest of the wall ended up level.

Every other row of blocks required the first block to be cut in half. This I did with a diamond masonry blade on a circular saw. You could also use the much cheaper masonry blades that disintegrate as you use them, if you only needed to cut a few blocks. I really like the diamond blades because you get a cleaner cut, and it's always the same depth. The blades that deteriorate give you consecutively shallower cuts as you use them. Be sure to wear both eye and ear protection when cutting the blocks. Also, it makes a ton of dust, so you may want to wear breathing protection as well.

I laid a piece of landscaping fabric into the bottom of the wall. I made it so that as I built the wall up and back-filled it, the landscaping fabric would rise up with the wall. The goal was to have; from front to back: the wall itself, then 1.5" to 3" aggregate stone, then the layer of landscaping fabric, then the dirt that the wall structure is retaining.

The landscaping fabric helps separate the backfill stone from the dirt behind it, so that dirt doesn't wash through the cracks in the wall during rain.

If you had drainage issues in the part of your yard that the wall was in, you could lay drain tile behind the wall at the base before you start back-filling with stone. You just run it down the length of the wall, and it comes out behind the wall, where the wall ends. This wasn't an option for me because there was no where to direct all the water to except back toward the house, and that's what the whole wall was being built to prevent.

For this wall, as I built it up, I had to do much back-filling behind it. I started by adding the 1.5" to 3" aggregate stone directly behind the wall. I also used the stone to fill the crevices in the back of the wall. The stone back fill was intended to be 6" to 8" deep

Next I would pull up the edge of the landscaping fabric that was behind the stone, and then back fill the rock with dirt. The massive amount of sand that was left over from removing the pool once again came in really handy here.

Every step of the way, whenever I did back fill, I compacted it the same way that I had done for the base. This was to ensure that it doesn't settle significantly later, leaving a low spot or slope toward the wall.

One thing to be careful of when building up your layers is to clean off the previous layer before placing the next one. This ensures that no small pebbles or rocks end up under a block. When that happens, it can throw the next block layer out of level and make your blocks wobble.

Eventually it was time to put the cap blocks on.

You can see that I did a huge amount of back-filling with the remaining pool sand. This worked out really well, as I was able to build everything up high enough to create a proper grade away from the house and the wall.

The last step was adding the caps. With these, you have to build a sort of puzzle that completely covers the top of the wall. They give the wall a really nice finished look.

I cut and dry placed them one at a time. I started by cutting one with a flat edge to go up against the house. Then I started putting them down.

The first few were easy; since there was no curve to the wall, they didn't need to be cut.

Once I got to the curve, I'd place them to determine which angles needed to be cut into them. Frequently, both ends of the block would have to be cut at sharper or shallower angles, depending on which way the stone was facing (they have a long end and a short end). I drew out the angles with a large carpenter's square, and a pencil.

Once the whole wall cap was cut and looked good, it was time to attach it permanently.

I removed the whole cap, being careful to keep the blocks in order. I put the cap blocks upside down, and made sure they were clean. It is sufficient to simply sweep off the dust here. You have to do the same for the top row of wall blocks that they will be attaching to.

I put down quite a bit of Liquid Nails construction adhesive on the top of the top row of wall blocks. I was careful to avoid getting any within 2" of the front edge, since the cap blocks would be set back to match the stagger that the rest of the rows had.

The last step was to replace the cap, starting at the wall.

I would place a block, then wiggle it around a bit to make sure it was stuck good. Once it was in place, it was time to go on to the next; until they were all attached. The construction adhesive allows them to remain slightly movable for half an hour or so, so there was plenty of time to get them all in the proper place.

That was it for the back retaining wall. Here's a picture of how things look today (after new concrete, a new deck, and much of landscaping).

Here's the before and after photos of the retaining wall I built in the front. The step by step process was exactly the same, just on a much smaller scale.