CONSTRUCTION JOINTS

The mortice and tenon joint has been in use for hundreds of years. Since long before any glue was invented. In fact it was designed to hold two pieces of timber together without glue. When glue was introduced it wasn't very good, and didn't last well , so mortice and tenons were still used so that the joint would hold together even after the glue had failed. 

Glues have improved greatly since then, and they do not fail.Modern glues generally have immense strength where there is good contact between the two timber surfaces. However, most glues a much weaker where there is even the slightest gap between the gluing surfaces. Looking closely at mortice joint, the machine used to cut it, by its nature leaves a rough internal surface no matter how sharp it is. That rough surface means that when the joint is glued together, taking a magnified view of what is going on, there is only a small proportion of actual surface to surface contact. In short, the strength is compromised.

In contrast to the mortice joint, we use a double combed joint, which is machined differently and achieves a much smoother gluing surface, which together translates to something like three times the surface area contact compared with a mortice and tenon joint.

Ultimately, the more glue surface contact there is, the stronger the joint is....the longer our windows last.

We have designed our windows following Scandinavian practice which places the gazing rebate and glazing bead internally. There are various important reasons why.

On the continent, and notably among the Scandinavian countries, timber windows have a much stronger track record than in Britain for good performance in wet and harsh climates. For this reason timber is by far the most popular choice of window material.

Put simply, our internal glazing rebate means the exterior weathering face is seamless - No water gets in so our windows last longer

In the past, when the only available glazing was single glass, the accepted method of fixing, was into a rebate on the outside face of the window, which was then filled with linseed oil putty, and 'faced off' to give it a sloped surface. The sloped putty surface meant that rainwater drained off, instead of pooling up. The reason the rebate was positioned on the external face, was that if water found its way into the rebate when the putty eventually cracked, it would not leak to the inside face of the window,

Since the introduction of sealed double glazed units, the accepted method of fixing is by means of a 'glazing bead' pinned to the rebate. This is because linseed putty breaks down the unit edge seal, causing failure.

It is still common practice in this country to have the glazing rebate on the exterior face of the window simply because 'that is the way it always been done'. This means that the glazing bead must also be on the exterior face.

There are inevitably, many joint lines around any glazing bead. When placed externally, these joints are exposed to weather, allowing water into the rebate. Water in the glazing rebate is the most common reason for the failure (misting) of the glazing unit. Once in the rebate, water will remain there, as there is no airflow to evaporate it. In addition, water will penetrate the porous end grain of the bead causing premature failure of the paint finish leading to decay.

The practice of using drained and vented bottom beads was introduced in an attempt to avoid the consequences of water ingress into the glazing rebate on external rebate windows. The assumption is that water will get into the rebate, but will have a channel by which to escape and airflow by which to evaporate. It works to some extent, in preventing the pooling of water in the rebate, so that the glazing unit does not sit in water, but in reality the rebate never really dries out, leading to timber decay.

Benefits of Internal glazing rebate.

• Glazing beads are internal and are not exposed to weather penetration.
• The exterior (weathering) face is one unbroken totally sealed surface.
• It is more secure since intruders cannot remove the glazing bead to gain entry.
• With our internal rebate windows, applied glazing bars are fitted prior to glazing, allowing us to fix them structurally in place, instead of simply sticking them on to the glass as with an external rebate window.

GLAZING BARS

Originating from a time when glass could only be manufactured in small panes, the glazing bar enabled larger areas to be glazed. As manufacturing processes improved, glass panes got bigger, and glazing bars became fewer. Today, whilst the only reason for using glazing bars is for aesthetics, they nevertheless have a huge impact on the appearance of a window. Glazing bar width in traditional windows was commonly 16-20mm, and whilst it may seem insignificant, failure to observe these dimensions can have a detrimental effect on the authentic appearance.

Glazing bars for single glass pose no problems, they are simply manufactured the same way they have been since they were conceived. However, the problem arises with double glazed windows, where the standard approach of taking a glazing rebate from both sides of a solid glazing bar, results in a minimum width of 44mm. A bar this wide can look aesthetically unacceptable in some cases, particularly with multiple pane windows, or in when replicating original details in conservation areas.

The solution is to use ‘applied’ glazing bars, which are two separate timber profiles bonded permanently to both faces of the glass, to mimic the appearance of a single solid bar. This method, often executed poorly, can look very fake . With most other systems where external glazing rebates are used, the external applied bar can only be fitted after glazing, meaning that the only thing supporting it, is the bond on to the glass. In this case it is not uncommon for the bars to fall off after a couple of years of weather.

We have developed our own unique method of constructing applied bars, that is indistinguishable from a solid bar. And by virtue of the fact that we use an Internal rebate as discussed above, this means that we are able to mechanically joint and glue all the external bars as an integral part of the sash, prior to factory finishing.

In short, our windows last longer.