SPS Contributor Robert Wadley built a cinderblock ledge at his local skatepark. It is 23-inches tall, 2-feet wide and 112-inches long reinforced with an 8x8-inch grid of 3/8-inch rebar. For the grinding edge he used 6x6-inch square tubing with 3/8-inch walls. Type N mortar (mortar mix) was used on the blocks and Type S mortar (mason mix) was used under the tube steel to secure it. No welding was required.
The beast ledge uses inexpensive
materials and requires very little
building experience.
Disclaimer: This step-by-step describes how this ledge was built. You may find better ways to do it. If you do, please share your method with us and we'll make it available to others.
Materials:
Cinder Blocks (approx. 30-35)
Type N Mortar (Mortar Mix)
Type S Mortar (Mason Mix)
6x6-inch Square Steel Tubing (Coping)
3/8-inch rebar
Rebar tie-wire
2 18” L Bolts (Coping anchors)
Straight 2x4s or 2x6s (Form)
Concrete Mix
Hammer/nails or Driver/screws (for wood guides and forms)
Water
Sheet plastic (Visqueen); duct tape
Tools:
Wheelbarrow
Level
Mortar Trowel(s)
Hardwood float(s)
Magnesium (mag) float(s)
Tape Measure
Drill (roto-hammer)
Extension cord(s)
Broom
Hose(s) or water containers
Gloves & eye protection
Boombox, AC/DC
Camera
Step by Step:
Arrange the bricks how the ledge will be built as the
last step before you commit.
1. Dry-lay the cinder blocks to confirm placement, size, and fit. Be sure to take your "before" picture now.
1. Dry-lay the cinder blocks to confirm placement, size, and fit.
You'll need rebar anchors into the slab to prevent
the whole ledge from sliding.
2. With the hammer drill, drill 3/8-inch holes into the ground under the four corner blocks and pound the rebar into the asphalt. The rebar should stick up higher than the height of the cinderblock by a few inches. If the rebar doesn't fit snugly into the hole, you may use an epoxy to secure it.
A taut string will help you keep your blocks lined
up nicely.
3. Align the first layer of cinderblocks using a taut string as a guide to keep the blocks straight. Mix up a batch of the mortar mix (Type N) once you’re absolutely sure that everything looks right. Put a layer of mortar mix on the ground about an inch deep and place your cinderblock firmly into it, then mortar the side that will be against the next block. Continue to mortar underneath and between each cinderblock with enough mortar mix that it squishes out the sides. Clean the sides with a trowel.
Don't fill up the cinder blocks with mortar. You only
need mortar where the blocks touch each other.
4. The second course can be laid in the same fashion. Add plenty of mortar mix to the tops and sides of the blocks. Again, use a string to help align the cinderblocks perfectly. Clean the sides with a trowel.
The ledge should be solid. Pack it with stuff.
5. Let the mortar mix set up for an hour. Then fill the inside of the ledge with dirt, bricks, rocks, old wheels and bearing, or anything else you can find.
Once your rebar pins are in the back-row cinder block
holes, fill those holes with Type N mortar. The pins
should stick out about 18 inches.
6. Cut enough rebar for every hole in the ledge. (The ledge pictured has 32 holes.) Each piece of rebar along the back (non-grinding) side of the ledge should be long enough to stick up out of the hole by 18-inches. The front side of the ledge can be flush with the top of the cinderblocks (about 17 inches long). With a fresh batch of mortar mix (Type N again), pack the mix into each hole around the rebar.
The coping should have two bolts in its underside that
sink into the mortar. The rebar should be bent over so
that it's well below the top of the coping.
7. Drill two holes into the steel tube coping. Insert the two long bolts into the holes then set it into the wet mortar, bolts down into the mortar, to help anchor the tube. (We felt this method was easier than welding pins to the coping.)
You'll be removing the coping in a later step and resetting it with a different type of mortar. Make sure the holes in the coping are larger than the anchor bolts so the coping is easy to slip onto the anchors again.
With long pieces of rebar you'll make a cage that will
strengthen the top of the ledge.
8. Wire two long lengths of rebar to the shorter, bent-over lengths. to create a grid of approximately 8-inch squares.
Under the coping you can see the thick layer of
Type S mortar. (Note: This photo was taken after the
next step. Nevermind the 2x4.)
9. Slip the rail up off the long bolts and mix a batch of mason mix (Type S). Trowel a layer of mason mix an inch thick or so and place the rail back onto the bolts firmly so that the mix squeezes slightly out of the sides. Use a level and a mallet to make the coping level. Scrape off the excess mix from the sides.
You might want to consider higher grade 2x4s for your
top form. Low grade beams can be warped or have a
rough texture.
10. Build a form using straight 2x4s or 2x6s for the top pad. The form should be flush with the top of the coping. Make sure all the sides are level and that the inside edge of the form is against the outside of the blocks.
Check your form when you're done to make sure everything is level and fits well.
Shovel the wet concrete into the form with special
care that it gets into all of the nooks and crannies.
11. Fill the form with cement-rich concrete. (The amount of concrete you need is dependent on the size of your ledge. The concrete bag should indicate how much concrete it will produce.) Pack the concrete into the form as tightly as you can with a shovel and pop the sides of the form with a hammer lightly to knock out any bubbles. Scree off the excess concrete from above the form using a spare 2x4 by gently sliding it along the top of the form. Scree the ledge from one end to the other. This will push any excess concrete higher than the top of the form off the end.
Use floats to push the aggregate down into the mixture a bit and give the top a nice, smooth finish. (Don't overdo it or the surface can become brittle.)
12. Use a hardwood float to smooth the surface of the concrete. After the concrete has firmed up a bit, finish it with a magnesium float until it’s glossy. Don’t float the concrete too much or you will push the aggregate too deeply and it will tend to chip or spall. You can use an edger to give the sides and back a nice round trim if you want.
Wrapping up the ledge so it can cure slowly is an important part of the process.
13. Cover the whole structure tightly with plastic or a tarp and let cure for a full week. The moisture must evaporate slowly from the concrete or it will become very weak and crack. (Fix any holes in the plastic you see.)
Congratulations! You've got a new ledge!
14. In a week you can unveil your masterpiece and do some product testing!
If you had any questions about this project or would like to share your DIY projects, please visit the DIY forum .
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