If you are thinking of building a fence in the UAE, it may look simple enough to dig some holes in the sand and go. Sandy desert, hot climate, and tough local regulations – setting up a fence is far from simple. Precast concrete foundation blocks offer a fast, cheap and secure solution – when done correctly.
Here’s an overview of how to install it properly so your fence doesn’t fall on your foot.
What Are Precast Concrete Foundation Blocks?
Precast concrete blocks are factory-made pre-mix concrete blocks. These blocks are delivered to the site cured or “set up”, unlike the concrete foundation poured on site.
They are used to support fence posts. The blocks may have a hole or groove in the top to hold the fence post.
Concrete blocks in the UAE will usually be in accordance to the standard BS 8500 (the British Standard for concrete specification) or follow local Dubai regulations from either the Dubai Municipality, the Department of Urban Planning and Municipalities (DoUPM) Abu Dhabi, or local emirate authorities.
Concrete Blocks Foundation are Ideal in UAE
In foundation work in the UAE two challenges are faced in particular: soft and sandy soil types and heat.
Batched concrete cannot withstand the expansion and contraction of the hot weather, which can get as high as 45°C in summer. Precast blocks are made under optimum humidity and temperature conditions and are hence stronger and denser.
Concrete can also break down rapidly as a result of being exposed to sandy soil and especially sabkha soil (the salt-laden coastal area). A high-quality precast blocks are made with sulfur resistant cement, which is required by BS EN 206 in aggressive environments.
Precast also saves time. You don’t have to wait for concrete to set on-site. You set up the block, line up the pole and off you go. In the UAE construction industry, with ever-shrinking schedules, that’s a good thing.
Materials and Tools Needed
Gather your materials: There’s nothing like three trips back to the hardware store.
You will need:
- Concrete footings (same diameter as the post)
- Tape and paint or coloured stakes
- A post hole digger or auger
- A spirit level
- A rubber mallet
- Bed of coarse sand or gravel
- Bolts or struts to hold posts in place
- Safety gloves and googles
- A line to string the fence
If your fencing is within your property lines or meets a public road, check with your municipality. In Dubai, you may require a No Objection Certificate (NOC) from Dubai Municipality to build a boundary wall.
Step 1: Decide and Check on a Fence Line
Set out a line of stakes and string. Decide on how far apart you will place your posts. In the UAE, a general rule of thumb is to have fence posts for conventional fence lines to be set out at 2 to 3 metres apart (depending on type of fence panel and wind load).
Check wind load factors. Shamal winds (north westerly winds, prevalent in summer) have a high wind load in the UAE. Posts and block sizes will have to take this into account. If you are building a wall, be sure to check with the UAE Fire and Life Safety Code and local building regulations.
Finally, check with local government to find out how high your buffer fence will need to be. Residential wall boundaries in Dubai should not exceed 2 metres in height without permission of local authorities, according to the Dubai Building Code.
Step 2 – Mark & Dig Post Holes
Once the line is finalised, determine where to place the posts. You can use a post-hole digger, or a gas-powered auger (for hire in UAE).
The size of your post holes will depend on two factors: soil and posthole depth. In UAE, when the ground is sandy, we want our post foundation block to be buried deep enough to have at least one-third of the post length below the ground surface.
The standard excavation size for fabricated block is from 400mm to 600mm, but will vary with different block manufacturers, so check on their specification sheet.
Remove any loose dirt from the bottom of the hole. You need a solid compacted foundation.
Step 3 – Set the Base
Lay 50–75mm of compacted coarse sand or fine gravel at the bottom of the holes. This would act as a drainage element and allow water to drain out of any area and can be a concern particularly if dealing with Abu Dhabi coastal sabkha areas, Sharjah development and Dubai waterfront projects.
Thoroughly compact it with the back of a tamper or the sole of a post. Don’t neglect this. This is the reason why a good fence is crooked at the end of the first season of rainfall.
Double check and level the layer where you are placing your foundation block using a small spirit level. This will save time in the future rectifying will be time well spent.
Step 4 – Insert Precast Concrete Foundation Blocks
Place the precast foundation block into the hole. Ensure it is sitting on your post line.
Level the block in two directions, across and along runs (front-back, and side-side). The bubble on the block is now checked with a spirit level on top of the block. Tip it around until it’s level and adjust the amount of sand.
This is the crucial step. It will also introduce that error into your post, and into your panels. Check it twice.
Step 5 – Place and Level the Post
Your fence post should fit snugly into the “socket” in the precast block. All precast blocks used in the UAE have sockets moulded to receive steel 50mm x 50mm square posts or 75mm round posts (posts vary in size).
You will need to check pivoting post is plumb (upright) in two directions using a spirit level. If level, place the post in temporarily using a wedging piece of timber to hold post on position or wedge into place with sand or non shrink grout (depending on block design).
To permanently bed the post in place, fill in the socket with a non-shrink cementitious grout (available in UAE from Sika, Fosroc, etc). This will prevent movement of the block and any water leaks.
Step 6 – Re-fill and Compact the Hole
The post is now in place and the socket is filled, so fill the hole with the block. Try to use soil removed from the hole but, if it’s too soft or contains large rocks, use sand.
You should lift backfill in layers (200mm) and then tamp them into the hole. This procedure will prevent voids occurring around the block over time (hence how posts start to move some months after being installed).
Leave the top 100mm of what will be the final ground level alone, and try and get the top to slope away from the block.
Step 7 – Wait, Check
Allow your post socket grout to cure. Most non-shrinking grouts gain “working strength” in 24–48 hours in the UAE climate but continue to cure.
When the posts are cured, make sure the level is correct with a string line. Make sure the posts are plumb and in line. It’s easier to install higher or lower or in a different position before hanging the panel.
Mistakes to Avoid
Eternal sin no. 1 is the foundation. These are the issue that affects all concrete blocks foundations in the Dubai sandy beaches (Dubailand City) in the United Arab Emirates (UAE).
The second mistake is using non sulfate-resistant precast concrete blocks in coastal regions and sabkhas (salt marshes) where concrete blocks are located. Salt attack is very severe and a “slow death”.
Not getting municipality permission is an error that can result in jail and charges to be demolished. Always check that you have a NOC/permission for work.
Final Thoughts
Laying the foundations for fencing in UAE from precast concrete blocks is straightforward but it does take into consideration the local market, building regulations and climatic extremes.
With this mindset, your fence will sail through the shamals, the summer heat and even the HOA’s musings.
Take the steps in order, use quality materials to the UAE and British Standards, and check with the municipality before beginning your project. It’s that form of planning and adherence that will get you a fence to be proud, rather than one to regret.