Many of us have experienced the problem caused when a heavy gate begins to settle becoming hard to open or close. While there are number of reasons why, most can be remedied at the time of installation by taking a few preventative measures
First, it is important to use an anchor post or pipe large enough to hold the gate. To hang a 14- to 16-foot gate ,use a wood post six to eight inches in diameter, or a six-inch diameter pipe. Steel pipe has the longest life expectancy, but don’t let that deter you if pipe is not readily available or you don’t have the necessary tools to work with pipe.
Pressure-treated 6″x6″ wood timbers, railroad ties, or butt-treated round wood are good alternatives. You can perform all of the necessary steps of installation with hand and battery-operated tools. Because of availability I use a lot of eight-inch diameter butt-treated lodgepole pine, but I have the posts treated above the standard 30″ in order that manure, wet soil and water do not contact the untreated wood above the treat line.
Concrete at the base
One of the main factors in gatepost failure is frost. In moist soil, frost will push the post out of the ground, and as the post rises the weight of the gate begins to pull the post over. To combat this, install a concrete thrust block on the lower 10-12 inches of the post at a minimum depth of 30 inches. To do this, dig the diameter of the hole about 20 to 24 inches for an eight-inch post — approximately three times larger than the diameter of the post.
Before dropping the post into the hole, drive four eight-inch spikes into the post about four inches deep, about six inches from the butt, in opposing directions. If working with pipe, insert and weld short pieces of rebar or steel rod through the lower end of the pipe to achieve the same effect as previously described with wood. This will provide a good anchor in the concrete thrust block.
Set the post in place in the hole and adjust for distance and alignment. Use a level to get the post plumb and temporarily secure it in place. Pour two 80-pound bags of fast-setting concrete into the hole evenly around the post. Gently tamp the dry mix around the post as you go. Pour one gallon of water on top of the mix. It is not necessary to mix fast-setting concrete for posts. Allow 20-30 minutes for the concrete to set up. Finish tamping the native soil material into the hole up to ground level. If the native material is wet or overly sandy, it may be necessary to add dry dirt with better bonding qualities. It is important that the material tamps in tight.
Once the post is securely set you are ready to build it into the rest of the fence complex. Install the top and middle rail/tubing, or a central horizontal brace if you are using wire; then construct a diagonal brace from the top of the gatepost to the ground level of the next post(s) in the series. This is done by looping barbless wire or cable around the top of the gatepost and running it to the bottom of the next post(s) in the series and looping around that post; then running back to the top of the gatepost. Secure the wire or cable to the posts in the appropriate location and twist the wire until you have enough tension to know that the weight of the gate is being shared with the next post(s) in the series. Install the remaining fence materials to complete the fence.
Hanging the gate
Determine how high off of the ground you want the gate to hang and mark the gatepost at the intended locations for the hinges. Drill or cut the top hinge-bolt hole in the center of the gatepost. Use a hand level to insure the hole is cut or drilled level through the post to prevent binding later. Place a hinge bolt through the top hole and hang a plumb bob or tape measure down the post to the level of the bottom hole. Mark the intersection with the mark you made earlier and cut or drill the bottom hinge-bolt hole through the post.
Install the bolt hinges and hang the gate. Place the level in the centre of the gate on a horizontal tube that does not have a crown. Use the nuts on the hinge bolts to adjust the gate to level.
The last step to insure a heavy gate continues to swing for years, involves building a step-block to support the free end of the gate when it is open or closed. You can make the step out of anything that will catch and support the weight of the gate.
When building with wood posts, cut a piece of pressure treated 4″x4″ to the proper height to support the end of the gate. Attach the step to the post so that it bears a small amount of weight. As long as the gate is always placed on the step, in the open or closed position, it will provide you with years of service and never sag.