How To Fix Trellis To Concrete Posts

Installing a Garden Fence

Installing fence posts and panels is a more challenging job than might be imagined so it is important to understand the critical steps in the process and employ a professional if you are not very confident in your ability to do the job properly and have plenty of time to do it.

Once you have chosen your fence panels you need to choose what sort of fence post you will use to mount them to. The main choice is between concrete and timber posts.

Concrete fence posts are probably the most popular choice in the UK and this is probably because of their longevity – they are extremely strong and will never rot or degrade so a well-set concrete post will last for many decades. It is important to consider the size and weight of concrete posts. If you are putting up 6ft high panels then the posts will need to be 8ft long ones and an 8ft lightweight concrete post weighs around 28kg so is challenging to move around and transport. Lightweight concrete posts are lighter versions of conventional concrete posts but they are still heavy.

Most concrete posts have slots down the length of the post for the sides of the panels to slot into. If slotted concrete posts are already set in the ground it is necessary to lift panels the full height of the posts in order to drop them into the slots. The slots are typically 50mm wide which is wide enough to accept most timber fence panels.

There are three types of slotted concrete post:

Intermediate post: these have slots on two opposing sides of the post to accept a panel on each side.
End post: these have just one slotted side for the end of a fence run.
Corner post: these have two slots, at 90-degrees to each other, for use when a fence run turns a 90-degree corner. This is common in back gardens where the fence at the back meets the fence at the side of the garden.

Concrete posts are also available in recessed and morticed versions which are used in conjunction with arris rails and featheredge boards to build up the fence, instead of using ready-made panels.

To maximise the life of a fence run built with concrete posts it is best to also use concrete gravel boards. These are available in 180cm width and 183cm width versions to suit the width of the fence panel they are being used with (see more on panel widths below). There also 183cm wide concrete gravel boards that have 'nibs' on each end that can be removed to reduce the width to 180cm.

Timber Fence Posts are a little less expensive than concrete ones. While they are treated with a preservative to protect them from rotting in the ground they will not last as long as concrete. One benefit of timber posts is that they are nearly half the weight of an equivalent concrete post so they are easier to handle and transport. Some people will also prefer the warmer, more natural look of timber ones which are also available with a smooth planed finish to complement smooth-planed decorative panels.

Slotted timber posts are available so that panels can be simply slotted into the post-recess.

If the timber post is a standard square post then U-brackets will be needed to mount the panels to the posts. The U-brackets screw to the post first, before lowering the panel into them and then securing the panels by screwing through the bracket into the frame of the panel. Four U-brackets should be used for each fence panel with one on each side, approximately 150mm from the top of the panel and one on each side approximately 150mm from the bottom of the panel.

Timber posts with a flat top should be finished with a post cap to ensure water runs off the post and not into its grain.

Setting Fence Posts into the Ground

Setting the posts in the ground is the critical part of a fence run. There is some skill in completing a run of fence posts and panels that is perfectly vertical and straight. If posts are not set solid in the ground then they will move around in the wind and get worse over time. A poorly installed fence run is more likely to be blown over in a storm.

The most common and reliable way of setting a post is to set it in concrete in a hole in the ground. There are a number of readily mixed brands of concrete for fence posts. Read and follow the instructions on the pack. An 8-foot post needs to be set 2-feet deep in the ground.

If using timber posts, dig the hole a little deeper than 2-feet to allow for 1 to 2 inches of gravel at the bottom of the hole which will help with drainage and prevent the bottom of the post from sitting in water. Also, with timber posts, it is a good idea when the concrete is set to form a slight incline around the post so that rain drains away from the post.

Before fixing the first post, set out the desired run of the fence row using a string line and stakes. The first post can then be set in the ground. It is critical that subsequent holes are the correct distance apart. You must account for the exact width of each panel and also how they will be fixed to the posts:

Don't forget that most traditional UK panels are 1828mm / 183cm / 6ft wide. This is a legacy of the imperial measurement system in the UK. These panels typically include Lap Panels, Featheredge and Closeboard panels. Smooth-planed decorative panels are not quite as wide, being 180cm wide, as they originated from continental Europe where the metric system is predominant.
If you are using slotted posts be sure that the distance is measured into the slot recess.
If you are using timber posts and U-brackets to secure the panels then allow an additional 5-6mm between the posts as the back of the brackets will be 2-3mm proud of the post.

Some people will dig a number of holes and set the posts but this method holds the risk of getting the distance between posts wrong. An alternative method is to set the first post and while the concrete is setting, dig the second hole. After 20-30 minutes the concrete on the first post should be strong enough for you to secure the fence panel to the post. Just be careful to support the panel so it is not hanging off the post. With the first panel in place, the second post can be set in concrete, using the panel to ensure that it is in exactly the right place. When using this method of setting the posts, it avoids having to lift the whole panel up to the top of the posts in order to slot it down into the slots of the posts.

A range of metal post fixings are available for mounting posts in the soil, wet concrete or onto timber decking, slabs or set concrete. These metal fixings have a clamp into which the base of the post is clamped up.

The clamps for use in soil have long steel spikes that are driven into the ground using a mallet and driving tool.
The clamps for setting into concrete have a stem to set into the wet concrete.
The clamps for use on decking, slabs or set concrete have a flat plate at the base which is secured to the deck, slabs or concrete using expansion bolts.

With these solutions, no part of the post is below ground so the posts need to be the same length as the panels they are being used with. Before driving metal spikes into the ground it is essential to ensure that there are no underground electric or water services in the area.

For more information, see our handy How to Install a Fence video, our How to Replace a Damaged or Rotten Fence video, our How to Fix a Fence Post into Concrete video and our How to Install a Fence Post into Soil video.