How to Build a Walk-through Garden Pergola
Page three: Instructions continued
Page 3 of 4
Step 4: Dig the holes
Mark the centers for the four holes which will be (50mm (2") in from the building line (string line) at the corners.
Take down the string line and dig the four post holes, 350mm (14") square and 600mm (24") deep. They will need to be deeper if in a frost prone area. See notes in page one.
When the holes are dug, replace the string line. (The string outlines the outside faces of the posts.)
Step 5: Mix and pour the concrete
Make a mix of concrete in a wheelbarrow at a ratio of 3 gravel, 2 sand and 1 cement. Add clean water and mix to a uniform consistency until wet enough to fill around the posts, yet stiff enough to hold the posts upright without the need of supports or braces. Of course you will need a wind free day.
Carefully shovel some concrete into the bottom of each hole before placing the posts. (Minimum 75mm (3"))
Step 6: Stand the posts
This step will require two people.
Have one person position a post vertical into one of the holes and next to (but not quite touching) the building lines (string lines) where they meet at the corners.
Check the post is vertical by holding a plumb level against two adjacent sides of the post. The other person can then proceed to shovel concrete around the post to within 50mm (2") from the top of the hole.
Repeat this action until all four posts are concreted in place.
Confirm again that all posts are vertical and leave to set.
A couple of days later
Step7: Trim the tops of the posts
Trim the top off one of the posts 2200mm (88") from the ground. (Remember from the materials list that all posts are slightly over length.)
NOTE: Keeping the top of the pergola as low as possible gives the appearance of a wider opening and less elongated look. However, if you prefer a higher pergola - Then do it.
Measure down from the top of the trimmed post to the building line (string line) and transfer that measurement to the other three posts. This gives a level mark at the top of the posts.
Trim the other three posts.
On the outer side of each post mark a horizontal line 200mm (8") down from the top.
Cut along the mark with a power saw to a depth of 50mm (2") i.e. the thickness of the beam. Do this to all four posts.
Next - Scribe a vertical mark 50mm (2") in from the outer site of each post from the top, down 200mm (8"). Cut down that mark with a sharp handsaw. See fig.2
When using a power saw make sure you have firm footing.
Erect a scaffold if necessary.
Wear safety goggles and earmuffs.