Georgian bar fixing on Timber and PVC windows – Guaranteed
When PVC windows first appeared they were admired not just for their low cost, but for the low maintenance required, and the clean lines and improved light provided. After a while, however, it was realized that large sheets of plain glass did not suit many buildings, particularly older buildings, and manufacturers set about mimicking the more ornate styles of traditional windows. This included the inclusion of Georgian Bar effects. The first attempts, using a visible spacer bar inside the double-glazed unit, were a poor compromise. So The external Georgian bar (or cottage bar) appeared, either mechanically fixed or stuck to the glass. And Technibond as the recognized leaders in foam tapes were at the forefront of these self-adhesive bars.
Timber windows by contrast were traditionally made with smaller panes of glass, as large sheets of quality glass only became available with the float glass method commercialized in the late 1950’s. Timber windows always had rather small panes of glass separated by narrow timber glazing bars, hence the “traditional” look of these windows. Float glass, of course, made large timber windows possible, and the adoption of double-glazing pushed timber windows in this direction. Numerous small double glazed panels in a window are very expensive. Not only that, the glazing bars have to become quite wide to accommodate the increased depth of the double-glazed unit, so they hardly look “traditional” and significantly cut down on light transmission. Self-adhesive bars solves this problem and again, Technibond were at the forefront.
Adhesive fixing of timber and PVC glazing bars not only overcomes this width problem, it makes the windows far more economical, and has has many other advantages. No additional tooling is required, any pattern of bars can be applied, and by sealing the gap behind the bar, ingress of dirt and insects is prevented. The bars can also be fitted (and replaced) on site. But there are potential problems and there have been many failures in the field. Here are our hints for trouble-free Georgian bars:
Download our Georgian bar application report
Use the right tape…
Experience has shown that the successful bonding of decorative window glazing bars requires a tape with significantly greater performance than the security glazing tapes used to fix the double glazed unit in place. This is due to unavoidable natural movement of the bars:
- uPVC bars undergo significant thermal expansion and contraction on a day to day basis at a rate that is very different from the glass it is bonded to. A 1 metre bar can easily move by 1 to 2mm relative to the glass
- Wooden bars can show signs of twisting and warping as the moisture content of the wood varies through the seasons.
These movements may visually appear small, but actually exert significant shear and peel forces on the adhesive bond, requiring a high performance adhesive. Technibond HSA offers an automotive grade pure acrylic adhesive that is designed to withstand very high shear forces and temperature variations. HSA is ideal for factory fitted bars and offers the highest level of performance.
For bars that are bonded on-site Technibond recommend HPA, a product with a greater degree of the tack than the HSA product. That can be applied at lower temperatures, but still with a cohesive strength significantly greater than competitive glazing tapes.
Choose the correct tape thickness…
Many uPVC bars have a flange or a recess at the back. We suggest you measure any recess and add 1mm to achieve the correct tape thickness. This allows sufficient depth of foam to achieve the necessary compression to form the bond.
For timber bars we recommend a 2mm thick tape. In our experience thinner tapes often do not bond fully which will cause problems. Water will penetrate behind the bar and loosen the adhesive; it will carry dirt that can be visible and unsightly, and in time the bar may fail causing expensive re-work.
Picture of poorly bonded wooden glazing bar with water penetration after only a few weeks
Cut the glazing bars slightly short
Because cosmetic considerations encourage a tight fit, bars are often cut too long. In extreme cases the bar will ride up the frame profile and the adhesive will not make contact with the glass at all. In other cases the frame profile will prevent compression of the tape during application, and only weak contact will be made. And in all cases a tight fitting bar has no room for the expansion that will take place, caused by temperature or moisture changes.
As a good technical / cosmetic compromise, we recommend that the bar is cut 1mm shorter than the aperture.
Cut the bars to the correct profile
Related to the above, it is important that the glazing bars are cut to a profile matching the frame profile. Hand cut bars are often cut at the wrong angle. Factory cut bars with a complex profile need to be cut taking account of the tape thickness. Failure here will either result in poor cosmetics, or will result in poor adhesive contact with the glass.
Clean the glass – with the right cleaner
Glazing bars stuck to dirty windows will stick to the dirt, not the glass. Of course, the glass is rarely “dirty” – but it is rarely spotlessly clean either!
A real problem is glass cleaned with some proprietary glass cleaners. These can leave the glass looking sparklingly clean, but with an invisible residue that badly affects the bond strength. To combat this we now supply our own cleaner, which will not leave any residue.
Finally…..
We have recently found that some modern paints are becoming extremely difficult to bond to. Paint manufacturers continually develop their paints for finish, colour, weathering, chip resistance, economy…..not for their receptiveness to adhesives. And paints do change. We can test this for you.
For the best advice send us your profile and we will test any paint, measure any recess and recommend a tape, width and thickness.
We also design and supply tape applicators to quickly and accurately apply our tapes to your profile. This ensures accuracy and performance, avoids stretching the tape, and saves you time. Our applicators can even be built into your production line.
In any doubt?
Technibond offer a 10 year guarantee on the performance of our tapes when used on a profile that has successfully passed the accelerated weather testing in our dedicated applications laboratory.
Call us for details of our free testing service on 01628 642800.
