WHAT TO EXPECT FROM YOUR GLASS
Although we hope you do not have any issues with your glass we would like to take the opportunity to outline what to expect from your glass and HBD’s criteria for visual defects in glass and their acceptability. The page below will cover the following; double glazed units consisting of toughened, laminate or standard glass. Including any coatings or tints on or within the glass.
Potential Distortions
With all glazing supplied, a certain amount of visual distortion is acceptable in the manufacturing process. There is also an acceptable level of defects that can be evident but occur naturally in this process.
We always class damaged glass as unacceptable, it may be installed temporarily as a necessity to keep your home weather proof. It will always be replaced when new glass has bee ordered and delivered.
Our objective at HBD is to supply and install glass as free as possible of defects caused in manufacture. However you should know what to expect from your glass and accept minor imperfection/manufacturing visual distortions provided they fall within the scope of the following definitions and acceptance criteria.
There will however be distinction between large pane glass units and what would be considered ‘standard size glass’. A large pane glass unit would be any pane over 2.5 sq meters or over. In the vase of large glass the end user/ client must be aware that the defect threshold will increase as the glass area percentage becomes higher.
Condensation
Whether or not a window develops exterior condensation is actually a rather complex issue involving environmental and performance parameters. For example condensation is much less likely to form on a cloudy night. Trees or other obstructions close to windows, bushes under windows and even length, angle and projection of soffits or other overhangs can affect the formation of condensation.
A small change in temperature or humidity
from one room to the next could raise or lower the dew point considerably.
Marks
Roller wave
Roller wave is a common type of visual glass distortion that may be visible in toughened glass. It is caused during the toughening process when heated and slightly molten glass is passed over large rollers while it is cooled. As s result the glass may have a slightly waved finish to the surface.
Stain Patterns
This visual phenomenon can also be known as stain pattern, quench marks, leopard spots or anisotropy is an accepted characteristic of the glass toughening process and is not classes as a glass defect.
Other visual distortions in standard size units
If there are any other visual distortions in glazing they should be inspected to determine what they are and if they are classed as acceptable within the guidelines from GGF.
Upon inspection we will use the guidelines as detailed below whilst looking through the glass in natural light. The glass will be classed ‘acceptable’ if the following are neither obtrusive nor bunched together:
- Bubbles or blisters no longer than 25mm. Small holes partially or wholly enclosed by glass which normally contain air. These may be spherical or non spherical dependent on the mode or formation.
- Fine scratched, no longer than 25mm. A long narrow surface flaw produced by a hard object which produces a perceptible depression.
- Sleek, no longer than 25mm. A fine scratch with no perceptible depression.
- Scare, no longer than 25mm. A scratch which is visibly white.
- Minute particles, no longer than 1mm. Loose manufacturing detritus that may remain within the unit after manufacture.
- Inclusions. Insoluble matter retained within or on the surface of the glass during manufacture.
- Visual effects. Toughened and toughened/ laminated glass as used in HBD installations is a processed glass. It is acceptable that a small amount of distortion may be visible through such glass. Using sealed glass units increases the umber of reflections which may accentuate any visible visual distortion. In addition, metal oxide coatings such as Low-E coatings may produce momentary visual effects in the surface of glass.
Popping noises
In the unlikely event that you experience unusual noises emanating from or near your door, we would like to provide some clarity on why this can occur.
The intermittent popping or cracking noises you may notice are a known and a natural characteristic of large-format glazed systems, rather than a fault with the product itself.
Modern sliding door systems utilise toughened, heat-strengthened, laminated, coated, or composite glass constructions (including systems such as C.U.IN, which incorporate a PVD-treated internal layer) in large panel sizes. Like all materials, glass expands and contracts in response to temperature changes. This is particularly noticeable in installations with significant exposure to sunlight (for example, south- or west-facing elevations), where the glass surface temperature can change rapidly throughout the day. Depending on the glass specification—particularly where coatings or multi-layer constructions are used—thermal absorption and performance characteristics can vary, which can further influence how the glass responds to temperature change.
As the glass expands, very slight movement can occur within the frame or setting blocks, which can occasionally release as a subtle “popping/cracking” sound.
In addition, the surrounding structure plays a critical role. Where doors are installed into rigid openings—such as steel goal post constructions with minimal allowance for movement or compression—there is less capacity for the building fabric to absorb these natural expansions and contractions. Ideally, structural elements such as steel goal posts should be engineered with appropriate consideration for thermal movement and tolerances. Where this is limited, small stresses can build and release audibly, particularly at junctions between materials (glass, aluminium, and steel), each of which expands at different rates.
With large glass panels, there is also a natural acoustic effect to consider. Due to their size and thickness, the panes can resonate at certain frequencies. This means that minor mechanical movements—otherwise imperceptible—can occasionally be amplified, making the sound more noticeable within the room.
It’s important to emphasise that:
- These noises are intermittent and typically occur during periods of temperature change (morning warm-up, evening cool-down, or sudden sunlight exposure).
- They are influenced by the orientation of the property, the structural design around the opening, and the inherent tolerances of high-performance materials.
- They do not indicate a defect in the glass or the sliding door system, nor do they affect performance, safety, or longevity.
In summary, what you are experiencing is a combination of natural thermal movement, structural rigidity around the opening, and the acoustic properties of large-format glazing.
These are all normal characteristics of high-end, large-span glass installations.