How to Build a Concrete Block Foundation
It’s time for another Pro-Follow update as we follow along with contractor Steve Wartman and his crew. If you remember, Steve brought in Victor and his team from Luciano Cristofaro Contractors to build the foundation, and today’s article shares how they built the block wall foundation. If you missed it, read up on how Victor’s team dug the footers, laid rebar and poured the footers at those links.
Here’s how everything looked after the concrete cured and a little bit of rain.
Step 1: Mix Mortar
The guys used a gas-powered mixer to mix sand, water and type-S masonry cement. Then they would shovel the cement in to large tubs for the block layers.
Pro-Tip: Wet the tubs before adding the mortar to help prevent it from drying out.
Step 2: Measure Length
From the blueprints, Victor and his crew determined the location of the foundation walls. Next, they would mark out each section and calculate the number of blocks per section.
Pro-Tip: Concrete blocks measure 8″ x 16″ including the joint.
Step 3: Clean Footer & Strike a Line
After the guys cleaned the footer with a foxtail brush, they would strike a chalk line.
Step 4: Set Corners
For each section, Victor’s crew would start at the corners and work their way into the middle. For that reason it was really important that the corners be perfect because they act as a reference for the rest of that section of wall.
If you look closely, you’ll notice the corner blocks are slightly different with a finished outside corner.
Often, the guys would run a long metal beam with a level on top (not pictured) to check that the corners were in line with each other.
Step 5: Run String Guide
Once the corners were in place, Victor’s crew would run a string along the top corner of the block and use that as a guide for the rest of that section.
Pro-Talk: The bracket for securing a string is called a dogbone or line-stretcher.
At times they also used a wooden corner block.
Step 6: Lay First Course
Using the chalk line as a reference, the guys laid a bed of mortar and began laying block.
Each block was checked for level and that it followed the string.
Pro-Tip: Joints should measure 1/2″ and the width of a finger is a good approximation.
After each section, excess mortar and broken pieces of block were used to fill the corners for additional reinforcement.
Here’s a look at how the concrete footer steps down and the guys laid the block.
Step 7: Turn the Corner
Keeping the corners square is very important, and the guys employed a little trigonometry (3-4-5 Pythagorean triple) to double-check their measurements.
Step 8: Wall Ties
Every 2-3 courses, the guys used wall ties and nails to anchor the block wall to the existing foundation.
They would bend a wall tie in place, nail it to the foundation and embed the rest of the tie in the joint between blocks.
Step 9: Cutting Block
It was often necessary to cut the last block of a section or in order to stagger the joints on the next course of block, and they used two different methods. The first method was to use a brick hammer along the cut line, and after a few well-place whacks it would break.
When precision was necessary, the guys used a concrete saw to cut the block.
Step 10: Site Guides
After the first course of block was laid, Victor’s crew used a transit to site a level line at all the corners. To do this, they first setup the transit in view of all the corners.
Next, the guys hammered stakes at all the corners.
Setting the laser detector onto the stake allowed the guys to mark a consistent, level line. Measuring off that line enabled them to make sure each course of the foundation was level with the rest.
Step 11: Lay Additional Courses
After the first course was completed, Victor’s team was able to work much faster. They continued laying block in a similar fashion, starting at the corners and working inward.
Here’s a picture of one of the guys checking the height to make sure it was in line with the rest of the foundation.
Most of the foundation consisted of two courses of 8″ block and two courses of 4″ block. The only exception was were the footer stepped down, and this area required an additional course of 8″ block.
When the guys pour the concrete floor, the concrete will actually conceal all the 8″ block and sit on the lip between the 8″ and 4″ block. That way, if the ground shifts or settles, the concrete floor will still be supported.
Pro-Tip: The final height of the foundation should be at least 4″ above grade.
At one point, the guys were about 1/2″ too high even if they “cheated” a little with thinner joints. To correct the height, they needed to trim about 15 blocks to the right height.
That brought them back level with the rest of the foundation.
Step 12: Fill Block
Victor’s crew filled the top two courses with mortar to reinforce them.
Step 13: Insert J-Bolts
At the same time, they placed J-bolts approximately every 4′ for anchoring the sill plate.
Step 14: Tool Joints
It’s important to tool over all the joints with a striking tool to press mortar into the joint, and it makes the joints look nicer too.
Step 15: Brush Clean
After the joints had set for while, they guys brushed the block clean. They only did this for the inside of the top two courses because that’s all that will be visible, and the outside will be parged.
Pro-Talk: Parging is a technique used to finish the surface of a masonry wall with a thin layer of mortar.
If you’re looking closely, you’ll notice that not all the blocks are filled at this point. The guys use left over mortar to eliminate waste, and even though I’m calling this finished, they still have some filling left to do.
The next step is to call in an inspection before backfilling around the foundation and let the plumbers complete their rough-in.
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