On Page 1 we discussed some general considerations for building wooden arbors; now it's time for specifics. On the present page we begin with foundations for garden arbors: digging post holes, plumbing the arbor's posts, and pouring the concrete that will hold them in place (but see below).
- Dig 2 holes, spaced as far apart as you want the main posts of your garden arbor to stand (in the project photographed here, the posts stand about 8' apart on center). Make the holes about 1' wide and 3' deep.
- Place about 1/2' of gravel or crushed stone into the holes for drainage.
- Set one 4x4 arbor post in one hole, the other in the other hole.
- Lay a board across the tops of the two arbor posts. Place a carpenter's level on the board. If the board is level, your posts are standing at equal heights -- which is what you want. Otherwise, make the necessary adjustment.
- To ensure that the posts will be plumb (i.e., the vertical equivalent to "level"), nail scrap lumber to each of them to form temporary, stabilizing braces (for a picture of such braces, see photo above). With these braces in place, check for plumbness on all sides with a carpenter's level. If the posts aren't exactly plumb, adjust the positioning of the temporary braces, accordingly.
Garden Arbor Tip:
Be careful, when buying your 4x4 posts, to get the height you'll need. Remember, an 8' post sunk 3' into the ground leaves you with an arbor only 5' tall. If you get a deal that you can't pass up on some 8' 4x4 pressure-treated posts, though, it is possible to compensate for their lack of height. Buy galvanized post anchors for each post. Sink the post anchors into the concrete, instead of the posts themselves. The pressure-treated posts would then be attached to these anchors, meaning all 8' would be above ground. Post anchors, however, can be expensive -- make sure that you're not defeating the purpose of getting the lumber at a cheap price!
Securing the Posts With Concrete
2012 update: Some experts now advise against the concrete footings, warning they hasten the demise of the lumber. They suggest using pea gravel underneath and around the posts. "Soil will seep between the gravel pieces and the sand/clay mixture that invariably comes in the bags of pea gravel," says contributor, Lynn Stevens. She continues, "Well tamped, the combination will be strong but also allow drainage."
If you still wish to pour footings in the traditional fashion, the instructions are as follows:
- Dump a bag of pre-mixed concrete into a wheelbarrow. Add water from a garden hose. Stir the water into the concrete with a shovel, until achieving the right consistency.
- Pour this concrete into one of the holes, around the base of the post. Repeat until hole is filled; and repeat for other hole.
- Allow this concrete to dry, or "cure" for at least one day.
Garden Arbor Tip:
While waiting, lay out the other boards on the ground, make your measurements, and pre-cut and pre-drill as much as possible, to save time.
With the concrete work done, on Page 3 the focus shifts to carpentry. Since these instructions are meant for non-carpenters, the emphasis will be on the easiest way to accomplish each task....