My wife and I are looking to build a short (max height above ground 30" that would be on one side of a patio. All of the patio would be at ground level except one corner where the ground slope down. The retaining wall would be 11ft on one side and 8ft on the other as the ground sloped. We are building this wall ourselves.

My question is this: the brick my wife likes is trapezoidal in shape and we aren't sure if that means we must build a curved wall or if we can use that shape to build a straight wall.

Thanks.

 

You can use it to build a straight wall. You will likely want to backfill behind your retaining wall with some soil, but behind the blocks you should have a generous thickness of gravel for drainage. It's also often good to lay perforated drainage pipe behind the base of the wall like a French drain to ensure that water has an easy way to get out and does not erode your wall. You will likely want to lay cap stones on the very top that will cover the trapezoidal shape of the blocks.

 

Great. Thanks! I will be doing drainage pipes in addition to the gravel.

I had not thought of the cap stones. Thanks for the suggestion.

 

30" is getting high enough that there can be a bit of soil pressure behind the wall. I don't like most retaining blocks sold at home centers especially those that rely on glue to hold the blocks together. I prefer the larger, much heavier (80+ pounds each) commercial style retaining wall blocks. I most often use ones that use fiberglass pins to lock the blocks together as it allows you to build a vertical wall or one with a slight setback/lean. There are also blocks that have a lip formed into them so the block above catches on the one below.

You definetely want to back fill behind the wall with clean gravel/crushed stone. The stone will allow water to easily pass through which relieves pressure on the wall. The stone also acts as a filter holding dirt back so you have cleaner water weeping from the wall which is important next to a patio.

 

I am with Pilot Dane on this.
If I understand your post the wall will be holding up one corner of your patio.
So if it fails in the future you will not only have to fix the wall you will have to rip up and redo part of the patio.
Better to build it extra strong from day one.

 

right. So I have the larger heavier stones. They do have the space in the middle, but I am planning on filling that space with gravel to make them heavier. I will also put the gravel behind (for drainage. And the block have a lip as well. AND I plan on using a little mortar to keep the bricks bricks together.

So in summary, gravel 4" base, flat rocks on gravel, mortar the first row of flat rocks adhering first row of bricks (always check for level front to back and side to side and straight lines). Then second row mortared to first making sure to ... what's it called, when the next layer of brick is on top of the joint between the two bricks below. offset?
End by filling all the gaps with gravel, backfill the space behind with gravel. Capstone on top.

 

No mortar, a retaining wall flexes and mortar is ridged so it will not hold up. If you want some adhesive get the retaining/block adhesive, much better!

 

Do NOT use mortar. Read the instructions for the retaining blocks you are using and I'm sure you will find that they say "do not mortar". Segmented retaining wall blocks are engineered to work dry stacked. This allows the wall to accommodate slight movement without damage and allows for water to drain through the wall.

 

Sorry for going radio silent. Thanks for your input. No mortar. got it. laying first row this weekend.

 

XSleeper - regarding the perforated drainage pipe behind the base of the wall - is that like a 3 or 4" pipe you drill holes in or are there pre-made pipes for this? And they just lay there covered with gravel, right?

 

It's called perforated corregated pipe. Yes, it lays at the bottom of the wall and gets covered in gravel. The gravel provides adequate drainage behind the wall which helps reduce the pressure on the wall from the soil.

 

Thanks for the info on the pipe. So in my case my lowest point where the wall would be is somewhat in the middle of the wall - to either side it slopes up (the wall will be about 24" high). So I guess I cap both ends and at the lowest point I have a T connection with a face grate on the wall. That make sense?

 

I generally build walls independent of the topography. A trench is dug for the length of the wall and the base is installed level. The first row of block set and the drainage pipe behind it. So, no matter how the surface is sloped it doesn't matter to the drainage pipe buried underground. This also allows the pipe to run out the end of the wall without having to bugger around trying to get it out the middle.

 

Ah, I see. That certainly makes it easier! Thanks.