Depending on the geographical location, fence
height, and fencing materials used, post hole size may vary. In general for residential
chain link fences, dig holes 6" in diameter by 30" deep (or below frost line in
your area). Another rule of thumb is to dig the holes three times the diameter of the
post, i.e. a 2" diameter post would require a 6" diameter hole, and put one
third of the height of fence that's above ground - in the ground. Typically gate
post holes are dug larger in diameter and deeper to withstand the additional stress of a
moving gate. The guide string may be removed temporarily prior to excavating to prevent
cutting it. Be sure to replace it as it was originally stretched.
Restretch guide string and check holes for
accuracy visually and/or by placing a post in the hole and plumbing in all directions.
If the hole needs 'shaved' or moved, do it now. If holes are shallow because
you hit an object you can't remove, 'bell' the hole at the bottom. To 'bell' a
hole, use a post
hole digger and/ or spud bar to make the bottom of the hole larger than the top. This
further anchors the concrete footer which will support your fence. 'Belling' will
compensate for holes as shallow as 18" deep. If necessary, move the hole
slightly to miss any obstructions. This will change your post spacing. However,
there is no harm in the case of line posts. If you must move it more than a couple
of feet, consider installing an extra post midway in the enlarged space. Other ways of
dealing with obstructions include bending posts below ground and welding plates on to
posts to secure to large rocks.
Mix concrete with water using pre-mixed bag.
Go easy on the water. Mix should look like thick gray mud, not like Mom's
watered-down chili. If it doesn't pile up on the shovel, it's too thin; add more mix
to dry it up. If you are mixing from scratch using aggregate like gravel, limestone
or sea shells, concrete sand and Portland cement, mix 3 to 4 parts (shovels) of aggregate
to 2 parts sand and 1 part cement.
Mark post grade mark. End, corner and
gate posts should be marked at the height of the fence plus 1 inch; 49" for a
4' fence, 61" for a 5' fence, etc. Mark intermediate or line posts at height of
the fence minus 3 inches; 45" for 4' fence, 57" for 5' fence, etc. When
you add your line post cap and top rail, the height will be accurate. Grade marks
represent the bottom of the fence and are essential in setting posts to the correct depth.
If you bury the post hiding the grade mark by 1", you will need to trench to bury the
fence here. If your grade mark is above ground by 3", your fence will be off the
ground by three inches and you better plan to cut it off later or fill under the fence if
a tight fit is necessary.
Fill holes with wet cement. Do not fill too
many and risk having the concrete cure before you can 'stick' your posts. Do not fill
holes to the the top with concrete, leave the concrete down 3-4". Filling the hole
completely with cement is a common mistake. If this is done, water will collect under this
'lip' of concrete. When it freezes, the ground will literally squeeze the concrete footer
and 'heave' the post up, much like squeezing a tube of toothpaste.
Stick Posts. Most chain link posts can be
installed by actually pouring the cement in the hole first and then 'sticking' the post in
the wet cement. Simply push the post into the cement mix in the center of the hole. Set
terminal posts as tight to the string as possible without touching the string. Set line
posts approx. 1/8"-1/4" off string. This will account for the differences in
fence post diameters. Another way of setting posts is for one person to hold the post
plumb to the string line while another shovels concrete mix around the post. The first
method explained is actually easier, a more efficient way of setting fence posts, and
assures there is concrete around the post, under it, as well as in it.
After setting each post to grade, backfill
with dirt and step on the backfill to hold the post to height. Repeat for all posts in
this length of fence.
Sight posts. To 'sight' in posts, stand at end
of length of fence and look across the tops of the posts. Adjust heights of posts as
necessary to account for gradual slopes and changes in grade. The goal is to have smooth
transitions between posts and to avoid sharp changes. This is easiest for two people to
accomplish: one persons sights posts while the other adjusts and checks for post plumb. Be
sure to check plumb on each post after adjusting and watch the grade mark as noted above.
Install gate posts with the exact opening size
as recommended by gate supplier or manufacturer. The opening size is the distance between
the two gate posts, inside to inside. If possible make the tops of gate posts level to
each other by placing a post across the tops of the posts and checking with a level.
If the ground slopes off sharply under the gate, set the gate posts to grade.
It won't look proper to make them level.
Let concrete cure for at least 24 hours prior
to continuing work.
Related Images: (Click to Enlarge)
Set posts to the depth of the grade mark
first. Be sure to set fence posts tight to any buildings if animal containment is
After 'sticking' post in hole with concrete mix, backfill with loose dirt.
Plumb post while stepping on dirt around post. This will help hold the post plumb in the
After setting posts to grade marks, adjust height slightly to account for
Holes next to buildings often must be dug by hand. Take caution as drain
pipes and other utilities can be located near foundations.
Some obstructions such as the one above can be difficult to deal with. A
post may be bent in this case to miss the pipe. Measure the depth of the bend first.
Notice how the post remains tight to the house, yet is still dug to depth
with a sufficient concrete footer.