CONSTRUCTION AND ASSEMBLY INFORMATION
Assembly and construction techniques can vary with your own specific applications and experiences. Please see our slideshow for details and further guidance.
The mold should be cleaned and lubricated before and after each use. Silicone spray, WD40 and common cooking spray work well as lubricants. After use, clean with soap and water. Store on a flat surface when not in use.
A precast concrete anchor should be attached to the bench molds in each of the pre-drilled holes (14 per bench) prior to pouring the concrete. The anchor should be 3/8-16, 1 3/8”. Any bolt 3/8-16 can be used to temporarily attach the anchors to the molds during the pouring process. We have had success with Nova Precast Anchor Inserts.
Screws to assemble the benches should be 3/8-16, 2 ¼” assuming 2 X 4 slats are chosen. Any generic screw meeting that criteria will do. For a more finished look, we have had success using Socket Flat Head Screws or Socket Button Head Screws that are available in Zinc Plated or more economical Alloy Steel with Black Oxide Finish. Again, you will need 14 per bench.
No special concrete mix is needed. Any concrete mix available at your local hardware store with 3/8 inch aggregate is sufficient. Other mixes can be used. Approximately 120lb of dry mix is needed for each side. (3 x 80lb bags per bench.) Mixing concrete at home is easy. For tips, please click on this article or watch this video.
Lay the mold on a level surface to ensure the concrete spreads evenly. Begin to fill with concrete. Add rebar when mold is half full (see below). At various intervals of pouring the concrete, stop and gently tap around the circumference of the mold with a rubber mallet (or a hammer and wooden block). This will help the concrete set evenly and release air bubbles. Do not over-tap as this will change the uniform consistency of the concrete mix. Fill the molds just below the brim. Once full, sparingly repeat the tapping process to remove additional air bubbles. Lightly trowel the open end to gain a smoother surface.
Reinforcing rods may be placed in the poured concrete in critical areas, such as the bench back and support area. ½ inch rebar works well.
Concrete can be removed from the mold after 36-48 hours, depending on local drying conditions. The concrete will reach ¾ of its maximum strength in 7-10 days and maximum strength in 28 days. It is recommended that you allow maximum drying time prior to assembling and using the benches. Otherwise crumbling and cracking may occur.
You can perfect the surface of the dried concrete using an ordinary masonry brick. You can achieve a smoother appearance by using the brick to gently rub the surface and round off the inside edges. If you don't have a brick, you can purchase a rub brick from your local hardware store. This should only be attempted after at least 3 days of drying time.
It is recommended that 7 ft 2x4 inch boards be used for strength and durability. The boards should be pre-drilled with 1/2 inch holes and fastened so that the outside edge of each concrete support is 12 inches from the end of the finished bench. Do not forget to install the bottom stabilizer board. Bench material and dimensions can be adjusted for your particular needs and tastes. Your local lumber supplier can advise on suitable types of wood for your climate.