How to Core Fill an Existing Block Wall in 7 Steps

Using cinder blocks to build a wall is an economical method for creating a building. By themselves, though, they aren’t the most structurally sound material for construction, and they are unable to resist the flexural stress caused by their own weight or from the gradual ground shift, earthquakes, or storms unless they are reinforced. Core filling an existing block wall is complicated, and building an initially reinforced wall is a better option. If you must core fill an existing cinder block wall, it is possible.

How to Core Fill an Existing Block Wall

Core filling a block wall is hard work and can be messy. If you prefer to attempt this DIY project rather than hire a professional to do it, you will need to get some supplies and closely follow the provided steps for Option One.

Necessary Tools and Supplies

Use a block fill calculator to determine how many bags of 80 lb QUIKRETE Core fill grout or 80 lb QUIKRETE 5000 Concrete Mix you will need for your project.

• Cement drill
• Cement mixer
• #3 Steel Rebar
• 80 lb QUIKRETE Core fill grout or 80 lb QUIKRETE 5000 Concrete Mix
• 5-gallon bucket, mixing tub, or wheelbarrow
• Mixing hoe or shovel
• Cell Funnel
• Trowel
• Safety glasses
• Waterproof gloves
• Garden Hose

Make sure to wear waterproof gloves and eye protection when you’re working with concrete or cement-based products. Depending on whether you intend to do additional concrete jobs, you may want to rent the more expensive and job-specific tools.

1. Drill a Hole Through a Block

Using a cement drill, carefully drill a hole in a block at least four rows up.

2. Install Steel Rebar

Slide a piece of steel rebar through the hole and into the cells for reinforcement.

3. Mix the Concrete or Grout

In the mixing tub, wheelbarrow, or 5-gallon bucket, mix 2 ½ gallons of water with the 80-lb bag of QUIKRETE core fill grout or concrete to the proper consistency. Mix it so that the mortar hangs from the trowel at a 90-angle. This mixture should be enough for 13 blocks.

4. Secure the Cell Funnel

Place the end of the cell funnel within the hole that you drilled. You might want to have a second person help. This way, one can help secure the funnel while the other pours or shovels the concrete or grout into the funnel.

5. Pour the Concrete

Use the trowel to scoop or push the core fill grout or concrete out of the funnel and into the hole you drilled into the block until the cell is full.

6. Smooth the Exterior

Use the trowel to smooth the concrete mix or grout over the hole to make the exterior of the existing block wall appear seamless.

7. Repeat

Move to the block next to the one you drilled the hole into. You will need to repeat the process beginning there. Repeat the process for every vertical row of blocks. Then, repeat the entire process again four rows up.

How Do You Core Fill a Block Wall?

Some experts recommend that rather than core filling an existing wall, it is better to tear it down and start from scratch. Here are the steps for Option Two.

Additional Supplies Needed

In addition to the supplies and tools listed above, you will also require the cinder blocks.

• 8x8x16-inch standard concrete block

Since you are undertaking the construction of a new structure, you should make sure to check your area’s building codes and construction requirements.

• Tear Down the Existing Wall

Use a sledgehammer to knock loose the blocks from the existing wall and responsibly remove and dispose of the broken pieces. Check the website of your local landfill site or consider donating them to a charity. You may be able to salvage some of the blocks for your new wall.

• Use the Original Footings

The cement footings should be a minimum of twice as wide as the concrete blocks you plan to use and deep enough to extend below the frost level. Now is an excellent time to ensure they are up to code.

• Mix the Concrete or Grout

According to the direction, mix the core fill grout or concrete you plan to use.

• Lay the First Four Courses

Use water to dampen the surface of the footing. Lay a row of blocks, using the trowel to spread a one-inch layer of concrete or grout on the bottom of the block and between the block’s ends. Repeat with three more rows or a total of four courses of the block wall, removing excess cement as you go.

• Install Steel Rebar

Drop one rebar rod into every block, leaving one open cell between each.

• Fill Each Cell

Fill each cell with core fill concrete or grout, pulling the rebar into the center of the cell so it won’t be at an angle when the cement has dried.

• Repeat

Once the first course has cured, repeat the process for the remainder of the wall, four rows at a time.

Additional Info

With a project of this size and level of commitment, there are bound to be additional questions.

Why Are Cinder Blocks Used for Constructing Walls?

Concrete blocks are manufactured to be less expensive and more versatile. You can reinforce the block by placing rebar within the cores or cells of the blocks to provide a vertical brace.

Core Fill Grout Vs. Concrete

Grout and concrete are both options for this project. Grout is usually thinner and is often used for filling cracks or gaps. Concrete is thicker and usually less expensive. Both are durable, but grout is more flexible, and concrete is stronger. Which construction material you choose to use is up to you.

Can You Hand-Mix the Concrete?

It takes a bit more work, but you can mix your concrete without a mixer. Place a plastic sheet on a flat surface and measure your materials. Place the dry ingredients on the sheet in a pile and make a crater in the middle. Add the water and begin folding in the dry material with a shovel to mix it thoroughly.

In Conclusion

By filling and reinforcing your concrete block wall, you will provide it with the resistance it needs to stand up to storms and the stress of gravity and time.

It may be a good idea to rent some of the more expensive items like a cement mixer if you don’t think you will be doing concrete work in the future. Or you can use the method of mixing your concrete by hand.

Although this is a little more complex than some of the DIY projects you’ve attempted, it is entirely doable.