The goal: to install a somewhat flimsy prefabricated wood arbor into the ground to ensure stability. The arbor's four posts do not provide extra space to sink posts deeply into the ground with concrete. You'll need to dig holes about a foot deep, mix concrete in a wheel barrow, and pour it into the holes. While this tutorial is for a prefabricated arbor, you can use it for digging holes and installing posts for decks, fences, gazebos, and other outdoor structures.
Measure Center Lines
Start off the project by measuring center lines of each post to determine where to dig holes for a total of four measurements for four holes. Each hole should be approximately 1 foot in diameter and 1 foot deep.
Embed Metal Post Anchors
Embed the anchors into the concrete, eliminating the need to sink the posts in the concrete. We purchased fairly shallow anchors because the arbor will only support the weight of vines. If this was for a fence or deck, you'd want deeper holes for longer, stronger post anchors.
Saddle the Posts
Saddle the posts into the anchors. You want to have an air space between the bottom of the post and the saddle so that it doesn’t retain moisture and has a way to dry. To do this use scraps of floor tiles approximately 1/4-inch thick. You can also use 1/4-inch or 3/8-inch plywood scrap.
Drill corresponding holes. Some anchors have holes that allow them to be nailed into the posts, but for extra reinforcement, drill the holes and bolt them in.
After drilling holes in posts, attach the anchors securely with purchased fasteners. Place a flat washer on each side of the hole and a lock washer on the end where you install the nut. The lock washer will ensure that the nut won’t back out.
At this point, the anchor is tightly bolted into the post.
Measure the Distance
Since this particular arbor is somewhat flimsy, you will need to determine the top width of the arbor to clamp the bottom posts at the same distance so that the arbor is squared up. Measure the top of arbor from the center line of each post.
Clamp for Solidity
Mark the center lines on the 2x4s and clamp each post to that center line mark with a C-clamp. This way we now have a solid, squared structure that can be positioned over the holes to prepare to pour the concrete.
Suspend arbor over holes by placing bricks, 2x4s or, in this case, pieces of broken cement and 2x4s. The goal is to use the support materials to space the arbor in increments until it's level and square to the ground. Use the clamped 2x4s from Step 7 as a basis for leveling horizontally and the posts themselves to level vertically. Add or remove spacers until you achieve proper alignment.
Mix and Pour Concrete
After double-checking your measurements and levels, add water to concrete mix per directions on the bag. Use a large bucket or wheelbarrow to mix the concrete. When the concrete reaches the desired consistency, which should be like an extra-thick milkshake, pour it into the holes. Wait approximately 24 hours or whatever the concrete mix instructions recommend.
The Finished Project: A Safe and Sturdy Arbor
Remove spacers, unclamp 2x4s last used in Step 8, and clear away loose concrete. Fill holes with dirt and proceed to put in ground cover, pavers, plants, or whatever else you have in mind. Enjoy your arbor, knowing the posts have been imbedded securely into the ground. Congratulations: you did it!