Tremco illbruck on why silicone may not be enough

Tremco illbruck business development manager Steve Wild goes beyond u values and WER's to look at a more innovative approach to window installation specification.

When it comes to the sealing of facades, the traditional method is to use silicone, but there are more sophisticated ways of doing the job, as many people in the aluminium window and curtain walling industry are aware.

Whilst silicone has many appropriate and effective applications, it is by no means the only solution.

Beware the one trick pony, the supplier who offers only silicone and nothing else.

The sensible answer is to be able to offer more sophisticated solutions with products to suit each individual location and any problems which arise.

There are now methods of providing an internal airtight and external weather tight seal with special membranes, by applying around the frame, either before fitting the window or afterwards.

These illbruck Duo membranes can also be used on curtain walling.

Additionally, impregnated foam tapes offer proven performance over many years and can accommodate varying joint sizes.

Compriband 600 is an open cell impregnated foam tape, impregnated with resin and compressed on a roll to about 20% of its original thickness which enables a minimum of 600 Pascals weather performance, but with the capability of over 1,000 Pascals depending on circumstances.

There is no need to cover the tape with a wet sealant since it can withstand the weather on its own.

One leading composite timber/aluminium window company, for example, specifies Compriband on nearly all of its installations, sealing between the timber part of the frame and the structure.

Whilst It would be perfectly possible to alternatively silicone seal the exterior, The applicator would have to position the cartridge nozzle into the gap around the aluminium frame to bead in the silicone and that would not be easy.

It would take skill and care since the gap could be at least 15 mm wide.

That's too wide for silicone alone so a backer rod would be needed to ensure correct joint geometry.

Backer rods are basically circular polyethylene foam and are applied oversize: if the joint is 8 mm, a 12 mm diameter backer rod could be used, followed by the sealant.

The silicone would then need to be tooled off to a good finish.

All in all, it is a demanding task for any but the most skilful operative.

With impregnated foam tape, all that's required is to simply insert it into the gap and once it's there nothing else is needed to finish the job.

Almost anyone can do it.

It can work equally well with wider gaps and even variably sized gaps, since it follows any contours, offering up to 10 - 12 mm of tolerance.

That takes away the skill factor required in applying a variable sized silicone bead.

Since upmarket windows like composites, are taking a bigger share of the market these days, it is to be expected that installers will be looking for more sophisticated ways to weather seal.

To meet Building Regulations, most windows have a u value of between 1 and 2 but even a high spec window's performance can be compromised if it isn't properly air tight.

Energy conservation is about much more than just picking a window with a good u value, a fact recognised to a certain extent in Window Energy Rating.

But WER clearly does not go far enough since it doesn't take into account sealing the gap around the perimeter.

i3 is a new concept, which looks at intelligent weather sealing, airtightness and thermal insulation together.

One new i3 generation product is Compriband Trio, another impregnated foam tape, which achieves all three functions in one product.

The benefits of i3 can equally be achieved by using Compriband on the outside, PU foam injected into the gap and an airtight membrane such as illbruck Duo on the inside.

One guiding principal is that the inside should be tighter than the outside.

The external seal should be weather-tight but it makes sense if it is also breathable.

This is because there may be some moisture left over from installation or a subsequent breakdown in the exterior envelope and it's a good idea to let it escape.

But on the inside, the aim is to make the perimeter seal air tight.

At the moment the air-leakage pass figure is not particularly tight.

It's a fairly relaxed standard which is relatively easily achieved so long as there are no significant holes in the structure.

Word on the grapevine, however, suggests that the current pass figure of 10 m3/m2/hr is possibly going to be halved in 2010.

That will make it a lot harder to achieve and inevitably require a more robust approach.

Responsible and forward thinking developers are already designing to meet air leakage figures between 1 and 3.

The incorporation of such products as discussed above provides an easily achievable and durable solution.

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