Sticks & Stones: The Good, The Bad And The Ugly Of Block Walls

Recently my landlord decided to put up a steel carport in which to park a horse trailer. No problem, right? Turns out that the carport is too low for the trailer, so she decided to put it on a short block wall. Again, no problem. Since I was pretty well booked at that time, she hired Joe Blow Handyman to build the two walls and leave the rest for me. On paper -- good idea. In real life -- bad choice! I'll go through the things that, um...bug me on this one.

1) Layout. I had to show him how to get everything square and level. Well, at least everything is within an inch of being square. Level? Way off!

2) Footings. For the footings, he set the rebar (at least he used rebar), then in a great show of laziness he just put the concrete in dry and turned the hose on it. I would bet any amount of money that I could use a hammer and find pockets of dry concrete mix.

3) Block work. In an even bigger show of laziness (and "saving money on mortar"), the guy just set the blocks down, filled the cells with dry cement and again turned the hose on.

4) Anchor bolts. Yeah, you guessed it. He just stuck 'em in wherever he thought it would look right. Nevermind what the steel that needs to be bolted down to it requires.

Now, lucky me. I get to move a few uprights, re-drill all the holes, add steel to pick up the two end anchor bolts then adjust the length of every upright so the top will come out level and not twisted. Just another day, or two, or three...

Enjoy these pictures:

Now I will go over the right way to build a wall. Put down the shovel. First we have a little bit of layout and math to do. Determine where you want the wall and be more exact than "over there", please. Use a few wood stakes, some string and a "string level" (unless you own a transit) to get your forms for the footings straight, level and if applicable, square. It is easiest to set the string 12" above and on the outside edge of your forms, however, remember the footing will be wider than the block and get that string tight! If your string sags, so will your wall!

For a low, non-weight bearing wall, leaving 2" on each side of the block is plenty. For a taller or load-bearing wall, make then 4" or even 6" on each side. So, if 2" on each side, your footing will be 2" + block width + 2". Also, a good rule of thumb is your footing should be as deep as it is wide. Again, be sure your string is level!

If you have a target height that must be met, such as meeting an existing floor, the height of the top of the forms is critical! Blow it here and have fun trying to match the existing floor. If overall height is just higher than the dog jumps, just get it level and straight.

Now get the shovel. Dig a nice, clean ditch and set your forms 12" below the string. Once the forms are in place, recheck everything! Now is the time to find out that you goofed, not after you poured the concrete! Once everything checks out, run two rows of rebar about 2" off the dirt inside your forms. Run vertical pieces every 24" or 48" starting in the center of the first cell. Vertical pieces should "hook" under the horizontal rebar at the bottom.

When pouring the footing, the concrete should be mixed thoroughly and done in one continuous pour when possible. Trowel level with the top of the forms. It's generally a good idea to allow two days for the footing to cure. Next, re-set your string for the first row of block. The string will be exactly 8" above your footing and exactly where you want the outside edge of the block to be. Only one more reminder, get that string tight! The string is only a straight line if it is not sagging!!

Before you start dropping blocks, I'll give you a few tips regarding the mortar:

1) Don't mix more than you can use in a half hour. Anything you're not using is best left sitting in a running mixer. If it sits, it sets.

2) The consistency should be where you can set a block on a 3/4" bed of mortar and tap (not pound) the block down to get it level side to side and front to back, ending up with 3/8" of mortar left under the block.

3) The best way to keep your mortar handy and "fine tune" the consistency is to use a wet 2'x2' piece of 3/4" plywood and keep a water bottle handy. Use your trowel to "fluff up" the mortar and add small amounts of water when needed. Remember, when it sits, it sets!

4) First put down a bed of mortar to set the block in and put mortar on the end of the block that is going against the previous block in that row. Tap the block down so the top outside edge is perfectly in line with (but not quite touching) the string. Check level side to side, front to back. Strike off any excess mud!

Now, check your measurements every 8 or 10 blocks and "finish" the mortar joints so they look nice. Checking measurements is very important on your first row of block. With a wall that is 50' long (37 1/2 blocks) if you were off on your mortar joints by 3/32", that first row will be nearly 3 1/2" too long or too short. Just keep checking and adjust as needed.

A good idea for strength is to use another horizontal length of rebar in the wall. You'll notice that some blocks come with a groove from end to end for this. After the wall is completely built, pour concrete (mixed slightly loose) down all the cells in the blocks until full. Note: Any mounting bolts or straps embedded into the top of the wall should always "hook" under a horizontal run of rebar.

A little bit of closing wisdom -- never arm wrestle a professional block layer. Them boys is strong!

Here's a drawing to illustrate followed by a few pics of a good, well built block wall:

UPDATE 1/12/2010:
The AfterMath

Now that I have all the steel for the carport up let's go over all the extra BS that had to be done due to the sloppiness/laziness of the person that (for lack of a better word) built the two block walls.

Since the carport is located at the side of the garage, it was important (if only visually) to have the two roof lines end up parallel with each other, so even if the garage isn't exactly level the two structures will be in the same horizontal plane. At least to the eye, everything will look correct.

To accomplish this (since the block work has an elevation change of 4 1/2"!?!) I first found the lowest point. That's where the only one of the sixteen poles went full length. The other fifteen poles I had to cut to bring them down to that level. To give you an idea of how nuts this was, see the drawing below that shows how much was cut off of each pole:

We also decided (since Joe Blow Handyman failed to use mortar) to use block and masonry paint to seal up the walls to prevent water from getting between the blocks and freezing. If water between the blocks freezes, it will turn a wall into a stack of loose blocks. Freezing water has been used to split boulders by boring a few holes and filling them with water! If you've never used this type of paint before (like me), that stuff is thick! Thick enough, in fact, to bridge the gaps between the blocks! No worries about runs with that stuff.

Also for a finishing touch, I added some mud at the footing to give it a more finished look.

The moral of this story:

Somebody saved a day by doing sloppy/lazy work, but in doing so cost the owner approximately 3 to 4 days in extra labor and a few hundred $ in extra materials.

Do your math. Do your prep. Don't cut corners. It always costs more when you get sloppy.