Superspan mechanical joints from Tremco illbruck

Tremco illbruck specification manager Simon Foy on how mechanical joints can be simpler, cheaper and more elegant.

Tremco illbruck specification manager Simon Foy on how mechanical joints can be simpler, cheaper and more elegant.

Waterproof joints are predominantly used in car parks and podiums.

Podiums include areas above basements, a common form of construction in London and other cities.

Car decks are generally constructed using a combination of either concrete coated with a coloured resin, which gives highly coloured bays, or concrete with an asphalt top coat that makes it look like a roadway.

There are two approaches to using Superspan, a mechanical joint.

The asphalt type has a long side sealing sheet designed to stick to the concrete deck.

This prevents any water from leaking out of the asphalt deck.

The non-asphalt type usually has a rebate in the concrete deck and the joint sits in it and is sealed on the short side.

So each scenario has its own joint version.

Shopping centres also tend to get redeveloped and when that happens the car park is often revamped.

That may well involve new joints.

The key issues when designing one of these car parks or podiums, so far as the movement joint is concerned, is the location and the drainage.

There is a tendency to install the linear slotted drainage beside the movement joint.

In an ideal world the movement joint would be at the highest point, far away from the drainage.

This minimises the risk of failure in the joint or the drainage.

Concrete has been used since Roman times but it is surprisingly subject to expansion all the same.

I've seen a gap in the top of a wide car deck shrink as much as 30 mm on a very hot day! Today's concrete slab can be a huge structure and expansion of less than a millimetre per cubic metre, can add up to a hefty total.

One problem that occurs every now and then is that engineers design the building and movement joint in a way that makes it easy to build.

Unfortunately they then seem to come back to the design to consider waterproofing and at that stage things can become complex.

The path of a joint can get moved higgledy piggledy and this obviously adds to the cost.

The best idea is usually to keep it simple.

This often means creating a straight line joint at the highest point and thinking about waterproofing right at the start.

If only it was always like that.

I've even seen movement joints running through the middle of an individual stall in a toilet block.

In fact I've only ever once seen an architect start a design from the movement joints and work out, but perhaps that's how it should always be done.

Sometimes the building seems almost to have been built before they started to think about the movement joints.

With a little thought considerable difficulties can be overcome.

Lots of elements can be combined to produce just the right joint.

For example our Superspan is really a bespoke system so we make each product in the factory to suit the individual needs of each building site.

It is not just a question of making the standard components fit somehow.

Each site is surveyed to discover exactly what is required.

That means examining all the likely cause of movement, the traffic will have to carry, the floor make up and waterproofing.

Sophisticated movement joint manufacturers like Tremco can even make new types of joint for one off conditions.

For example sometimes we are able to cope with angles that are not quite 90deg.

That means a tailor made joint and seal.

Movement joints may need to be decorative as well as functional.

If you have a high rise tower, movement joints will be needed underneath because that building is going to settle.

Joints like that are almost invariably made to look like they fit in comfortably with the environment.

Perhaps these days you'd think every design should be wrapped up by a computer but in reality when it comes to components as individual and specialised as movement joints, the human interface often plays a vital role in the project.

Designing a building is more than its look, the impact on the environment, functionality, light and shade.

The building process itself, the materials used and the way they are put together, is a vital and sometimes neglected aspect of the process.

A design and build package may start out as little more than a shell.

That's when we find ourselves having to help the contractor shoehorn a movement joint into a building that isn't really prepared for it.

The joint has to work with a variety of materials and different situations.

This can mean it is tough to make the system work.

Drawing a line on a computer may not be enough.

Some architects, particularly experienced ones, have got the message.

Clearly this is something people tend to learn on the hoof rather than at design school.

Things are improving but I still get to see movement joints that run north-south and a drainage system that runs east-west.

Clearly that won't work because the water pipes are not going to accommodate flexing at the point where they cross the joint! Any gasket seal on the butt joint of a unit trough is going to break thanks to the cyclic movement, and drip through.

Let's hope if that happens it won't be the movement joint that gets the blame!.

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