Large gap under concrete gravel board held only by a bolt

12 Nov 2015
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United Kingdom
Fencer in the midst of completing a 6'6" high feather edge fence with concrete post and concrete gravel board.

The fencer is leaving large gaps under the concrete gravel boards. The concrete gravel boards are simple resting on 2 prong galvanized cleats and one bolt attached to concrete post.

Can the concrete post withstand the weight of concrete gravel boards or is this bad practice?
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Its hard to work out from your description what is going on? How is the fence formed? concrete posts with rails bolted to the face of them?

The gravel boards are there to form a solid non rotting base and take up any descrepancy in ground levels. There is no good reason for them to have gaps under them??

As for strength the posts should be plenty strong to hold a gravel board as there is very little force exerted on them?

Discuss this asap with the fencer and get it resolved before more work takes place. The strength is not an issue unless they are very unusally mounted but you dont want large gaps under the fence??
The garden is 200 ft long and slopes gently away from the house. There is one section of the fence is to accomdate the ground level drop. There are numerous mature trees near to the fence which make the ground even more uneven between each concrete post. None of the concrete gravel boards sit on the ground. My concern is the weight of the posts the wooden arris rails and the feather boards will over time sag as the gravel boards are not in contact with the ground. The gaps beneath the ground and the gravel boards vary from 2 inches to 9 inches. The gravel boards are 6 inches deep.

The cleat has two prongs which fit into the posts and a single bolt fixes the boards to the post. The fencer claims the posts can take all the weight and and the concrete gravel boards do not need to rest on the ground.

The fencer claims the gaps are necessary to maintain the overall height total 6 feet 6 inches high.
I think the fencer is obtain the general slope of the land, the gravel boards have to have gaps, and as long as the concrete posts are secure, there's no need to fear that anything will move.
Do post a pic or two so we can see what's what though!
John :)
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The method of instalation sounds fine, you should have no concern about the weights etc. Concrete is rigid and will not sag, the rails carry the potential sagging weight anyway.h

As for the gaps it sounds to me like he couldnt be bothered to dig them in. Normally with gravel boards the high end would be recessed into a shallow trench and then the low end would be resting on the ground. Who wants a fence with 9'' gaps underneath?

The height thing sounds like an excuse to justify the way he has done it. If the exact height needs to be maintained then longer boards should have been used.

It really depends on what was agreed or detailed in the quote.
We measured the gaps again today. The largest gap is 10" and that is large enough for a large dog to squeeze through. How the fencer is going to fill the gaps is beyond me. Take for instance the fence with the 10" gap, if he was going to use two 6" concrete gravel boards to fill the gap there would still remain a smaller gap. Basically he suggested drilling holes into the concrete post to fit the lower (the second) gravel board below the existing gravel board. This still does not solve my issue of not having the concrete boards at least partially resting on the ground.

The next largest gap is 9". We can visually see from concrete posts which are already in the ground that there will further gaps varying from 8" to 10" along the length of the garden. The first 2 fences have a gap between 1 to 2". I cant see a dog squeezing through this small gap. I however worry about the weight of the concrete boards not resting on the soil. Some of the cleats/prongs are not even hammered all the way in.

All the concrete gravel boards had to be cut down to size. I dont really know if this is common practice.

We assumed workman from checkatrader should know what they are doing. There was no detailed paper quote. After the initial meeting, we however communicated with the fencer our requirements via email. We wanted some kind of record kept.

There is only one so called step in the long fence. The 'step' has angled arris rails and he 'angled' the concrete board yesterday which I dont think he should have. He then tried to straighten the concrete gravel board on this one step. He had to remove the cleat/prong and trim the board again. It is still slightly unlevelled and prongs are sticking out. This will means that the feather board will need to be trimmed from the top.

Our garden is somewhat level at the front end and then starts to slop down and then somewhat levels off at the furthest end of the garden. There are several matured trees close to the border line with the neighbours. This has created a couple of bumps and dips along the length of the garden.

Today we have sent the fencer home to come back on monday with a plan to fix the problem. He is asking us what he should do. I dont see why we should be telling a so called professional his job.
Check a trade and similar schemes are not much use in all honesty.

I have said it but will say it again for clarity. There is no issue with gravel board weight/ strength if installed normally. They do not need to rest on the soil for their strength they should just be partially buried or at least in contact with the ground for practical reasons such as animals and aesthetics.

On a sloping site you either step the fence gradually in which case the gravel board should be half buried at one end and level with the ground on the other or you angle the whole lot so gravel boards and top of fence follows the slope or an average of the slope if it varies.

These are the kind of decisions anyone with experience would have ironed out before starting. It sounds like he is reacting to problems rather than working with a plan.
It should be like this, and if the slope is too great then two boards should be used with one mostly buried


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Thank you. If there is no issue of weight/strength, we can live with a 2/3" gap. I cant see a dog being able to crawl under this small gap.

For the rest, it looks like the 'mostly buried boards' needs to be installed first. From the picture, it looks like the fencer will have to remove all the existing boards which he has already installed (the ones with the large/hugh gaps). I cant see how else will he will be able to either partially bury or fix the extra boards without first removing the existing boards/prongs.

Is removing hammered in cleats/prongs in a concrete post a good idea? I am just wondering if they will need to remove the whole post and start again. (n)

As regards the partially buried boards, will the fencer need to drill holes into the concrete post to fix them? Lets say for a 6 or 7" gap, this will not require a deep burial of the additional board however it will still need to be stable enough to not fall over.

For the ones with a 10" gap, even if he partially buries the boards, there will still be gap between the existing board - unless he drills holes to lower the existing board so as to rest on the partially buried board. If lowered then there will be a gap between the feather boards and the top most gravel board.

This may sound like another silly question - is it feasible to drill new holes at the bottom of the concrete post to fix the additional concrete board? Two heavy gravel boards being supported on concrete posts!! :(
Yes normal the buried boards will go in first. he may run into problems trying to retrofit as the concrete holding the post up will get in his way if he tries to dig a trench to sink the board into.

As i said the gravel boards serve no structural purpose and so its mainly about covering the gaps with something rot resistant. It may be possible to hang the lower board off the top one if the cleat arrangement is strong enough.

Ideally you dont want to drill concrete posts if you dont have to.

Regarding the strength you seem worried about, all significant loading on a fence is wind loading laterally, this is why heavy duty posts are well buried in concrete to stop it blowing over. The gravel boards are heavy but all the weight is acting downards and concrete under compression is massively strong, your only possible issue is the holes the cleats are in breaking but i dont know how they are detailed.
A sample of images showing the prong/post/board. Ground here is somewhat level. The board has been cut to fit. These most likely will need replacing. The others which are already in place are somewhat better 'looking'
Gravel boards are intended to stop gravel, earth, plants, animals etc. etc. from moving form one side of the fence to the other while keeping the timber away from damp earth and debris.

Hence they should not have a gap under them.

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