You don’t have to get the slab dimensions perfect, but the closer they come to it, the easier things will be later. If you hate doing concrete work, skip this section, photocopy it and give it to your concrete mason. A crew can do the work for about $1,200 while you’re out shopping for lumber or cutting parts (but you can cut the cost to a couple of hundred if you do it!). There’s also an article in our May ’00 issue on pouring concrete that’ll fill in a lot of gaps in this subject area. Follow Fig. B closely if you decide to do it yourself.
To build your own gazebo, begin by driving a 2-ft. piece of rigid electrical conduit at the intended center of the gazebo. Drive it in 18 in. Remove the sod with a rented sod cutter. You’ll need to excavate a 9-in. deep area radiating out about 78 in. from the conduit. After that you’ll set forms and put in a layer of 1/4-in. gravel to the dimensions shown in Fig. B. The idea is to have the outside foot or more of the slab thicker to support the weight of the structure.
Build your forms after carefully examining Fig. B. Set your circular saw at 22-1/2 degrees and cut eight 2×8 exterior forms with the short side measuring 57-1/2 in. Screw the forms together with 3-in. deck screws. Have a friend help you align the forms so the eight corners of the forms are all the same distance from the conduit center. If these measurements are all equal, your slab will be a perfect octagon- get it as close as you can. Drive 3/4 in. x 2-1/2 in. stakes along the outside of the forms at each intersection, level the forms and screw the forms to the stakes.
Now build a square inner form for the patio inlay, 72-1/2 in. on each side. Center it as shown and drive in the stakes on the inside of the forms and screw them together.
The slab will require about 1-1/2 yds. of concrete and four 10-ft. pieces of No. 4 rebar. Have plenty of help (at least three strong backs and two heavy-duty wheelbarrows). Wheelbarrow the concrete and dump it into the forms, lay rebar 4 in. in along the perimeter, screed the concrete with a straight 2×4, then run the hand float over it. Set your anchors in at the locations shown in Fig. B. Wait till the concrete is firm (you should have to push hard to leave a thumbprint). Smooth it with a steel trowel, cover it with 4-mil clear plastic and let it set for two days. Keep kids and pets away.