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Every material, whether that's wood, metal, glass or concrete products, will expand and contract excessively during periods of high or low temperature.

But materials can also show signs of movement during relatively small fluctuations in different parts of the same material and may expand and contract or even bend out of shape when exposed to inconsistent sources of heat or cold.

When creating any structure - whether that's an expanse of concrete for functional use or a decorative patio or wall - it is important to consider how a material might react under a curtain set of circumstances.

In landscaping, it's sometimes very difficult to add an expansion joint to an aesthetic work while still masking the artificial and utilitarian nature of what you'd like to achieve but it is really worth considering because if a crack appears in a decorative surface, it is almost impossible to repair after or remove without a major remedial operation.

What is an expansion joint?

An expansion joint is exactly what it says it is.

When a material warms or cools, it literally expands or shrinks - not necessarily by small amounts - and by either accident or by design, an expansion joint will move to absorb or accommodate the movement without damage occurring to the major part of its infrastructure.

In landscaping, materials used for expansion can be wood, rubber, bitumen, plastic, felt, silicone, polymers or even a few millimetres air gap.

In the case of wood, this material by its nature will naturally rot after a period or exposure to water and air and leave a void when it's completely perished. Unsightly weeds will often grow in the deposits that form in the space where the wood once was.

Where would you need an expansion joint?

In large expanses of paving or concrete, vertical walls or where two structures of differing materials meet. The joint will allow movement without causing damage. It's also worth bearing in mind that materials can expand and contract even when they are underground and not exposed directly to heat and cold.

A concrete footing, for example, can react at different speeds than the surrounding soil (heave) so it is important to make sure that it is strengthened and reinforced in the right place. It's a myth that steel bars are only used to stop two plates of concrete moving up or down - concrete, in reaction to the soil movement around it, may also try to pull apart and that's why it is important to use meshed steel that can be retained within concrete and not slide inside.

What if I don't use an expansion joint?

It's not always necessary to use an expansion joint and you might need advice from a structural engineer based on the individual requirements of each project. The more experience you gain, the more instinct will play a part in your decision to use an expansion joint.

If you do not use an expansion joint where one should be used, then the chances are there will me movement at a later date. In the case of concrete, expansion will create movement and stress cracks; fractures may appear at points of least resistance - this may be internal corners or where two separate, but adjoining surfaces were poured over too long a time gap: the lack of chemical fusion will create a weak spot.

If you're pouring a concrete slab for a driveway or pathway, it might not be necessary to use an expanding material but by simply scoring the concrete before it goes hard using a trowel, movement will force tension to move along this line and if the concrete does crack at a later date, it will follow this scored mark and not look unsightly.

Add your own examples, experience and solutions below. Feel free to link to any resource, material or case study you feel is appropriate.

Technical resources:

Concrete Technology - Joints: What Type are Used and Where?

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  • my mums wall at the front of her house 'cracked' (hairline) but very noticable to me ,

    i believe this is the reason ..... No expansion gap / settlement of foundations...

    i saw gaps at a good barn-conversion on a job on a garden wall - done with the above in mind (proper job!)

    its very important , but simple.

     

    Testing

  • PRO
    That's an interesting example Karl. It makes one wonder if the expansion joint wasn't part of the original plan: what's the chances of a crack appearing after the floor had been constructed and the joint inserted afterwards (or would this have been improbably?)



    Karl Harrison said:
    Great post

    Out of interest the most bizarre place I saw an expansion joint was inside the hugh buildings of Smithkline Beecham next to the A4 flyover.

    The polished marble that covered the floor and the £1/2million abyss of lights in the centre of the entrance was abruptly carved across with this seam of stainless with a 50mm rubber joint. I asked the project manager what was this for an he informed me that is was due to expansion across the whole building was so severe this was in place to prevent cracking due to excessive movement.

    The strange thing was that is was at a very peculiar angle compared to the rest of the design.

    In this case the design simply ignored its presence, what a shame as the floor area is at least 2000 sq m.
  • PRO
    I've always planned information articles to be part of LJN Gary but there's not always the time to do as much as I'd like.

    I hope our design and landscape (and architects) can expand on this or any other topic with their own experience and tips.




    Gary @ Acer Paving & Landscaping said:
    Some really good information there Phil.

    Is this to be part of an ongoing series ?

    A few cad drawing details would be good as well - Bet there would be volunteers to supply some !
  • PRO
    I've worked with some talented groundworkers over the years.

    They have a heap of responsibility and I've heard it said that they're as important to the building industry as the sergeant is in the army - as Gary says, often underrated.


    colin said:
    a lot of the problems come down to the lack of knowledge and education.
    it is found with a lot of people that do "groundworks" rather than landscapers. a customer of mine recently had a "groundworks" man do a grage bse i pointed out everything that would be wrong as soon as they were available to be on site and since then when their special order garage has been built they have found out exactly how poorly the concrete has been done. not enough depth, not level, not a square that it was meant to be, the reinforcement was laid on the floor of where the concrete was set not actually within the concrete. etc etc.
  • My house which I built in 1979 has loads of cracks, but it is normal, no point worrying The whole house is floating on the damp proof coarse.
  • a friend of mine ,owns VEXCOLT engineering,and they specialise in these joints,they were in hampshire but now based in exeter
  • I agree with gary from acer, groundworks as a profession is hugley mis understood and not really recoginsed as a proper trade by many ,it covers the majority skill sets needed for a hard landscaper..i come from a groundworks back ground and ive found that its hugely important in any landscaping job i undertake and  sometimes i dont understand the general publics contempt for proper groundwork princaples  in there garden..ie not digging out enough for a footing or a patio base,normally people see it as an unnessercery expense!...intresting post by phil, allways use expansion joints on large concrete pads and bases,retaining walls and large patios.
  • Expansion Joints

    This you tube video is worth a look, got recommended by a friend but I have never used them.
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