Due to its sustainability, environmental certification, and cost efficiency, including shortening construction time, reducing static loads and improving overall safety, prefabricated engineered wood is increasingly used in mid-to-high-rise, large and complex buildings around the world.

In keeping with global trends, Australia has also seen an increase in the use of cross-laminated timber (CLT) and glue-laminated timber (glulam) products, which provide many superior options for traditional building materials such as steel and concrete.

Although both CLT and glulam are used in structural timber design, there are differences in materials and properties between the two options. Let's explore it.

Cross-laminated timber (CLT) is a unique engineered wood product that is prefabricated with multiple layers of kiln-dried timber (thin sheets), each layer is glued together at a 90 degree angle on its wide surface. CLT boards are usually composed of three, five, seven or nine layers of wood alternately.

Compared to stacking in one direction, the alternating directions of the layers actually provide higher dimensional stability, ensuring that CLT has a high strength-to-weight ratio, which has advantages in terms of structural, fireproof, thermal and acoustic properties. Like steel, CLT can be designed in different sizes: the plate thickness is usually between 100-300 mm, however, plates up to 500 mm thick can be manufactured. The size of the circuit board ranges from 1.2m to 3m wide and 5m to 19.5m long. Most CLT panels are prefabricated and are easy to transport according to regulations and guidelines.

Glulam (glulam) is made of solid wood of different layers bonded with high-strength glue to form a single structural unit; unlike CLT, these layers are not laid across. Glulam usually has a high member capacity and can be widely used in all types of structures.

In order to create a strong, dimensionally stable building material, glulam is processed and manufactured according to precise specifications. Glulam columns are sold in a variety of standard widths and lengths, and can be customized to meet almost any design requirement. Also similar to steel, the architectural design allows it to "form" without losing structural integrity, making glulam a type of large curved or arched member often used to build arched roofs, domes and even bridges. Material.

Glulam is sturdy and durable, providing higher strength and rigidity than single wood. Steel pins and plates that are bolted together are usually designated for structural timber connections.

The main difference between CLT and glulam:

Layer direction

As mentioned above, the most significant difference is that in cross-laminated wood, the layers are cross-matched at 90 degrees, while glulam is made of different layers and arranged in grain. However, both are engineered wood and manufactured according to design.

So why is this important?

There are some key comparisons and reasons behind these two different products. Since CLT is made of 90-degree alternating layers, it has multi-directional strength, which provides two-way crossing properties similar to concrete slabs, creating primary and secondary directions.

Since glulam is made with all layers in the same direction, it is most commonly used for one-way crossing requirements such as columns, beams, and trusses. Generally, most timber projects use both glulam and CLT, each of which takes advantage of its unique characteristics. Therefore, glulam is commonly used for columns and beams, while CLT is used for structural cores, wall panels and floors.

Wood burns, but before it burns completely, it forms a black outer layer called charcoal. This kind of charcoal first acts as an insulation and can slow down the burning rate, which we call fire resistance. Fire resistance is measured by the elapsed time from the concept of fire to the time when the material cannot work, usually expressed in minutes, such as FRL 30, 45, 60 or 120.

Although charcoal can protect the wood from burning as quickly as possible, as the cross-sectional area decreases, the wood still loses its strength. There must be enough original solid wood behind the carbon layer to support the applied load to reach the designed fire resistance period. In order to prolong the life of wood under fire, each glulam or CLT panel in the building can be treated with intumescent coating, which protects the wood by slowing down the burning speed of wood under fire to a certain time, thereby leaving enough Effective cross section.

Precautions for using and protecting wood

The way to prevent the spread of the flame and the spread of the fire depends on the nature, form and arrangement of the materials involved in the fire and the nature of the fire.

In the combustion test to control the fire characteristics, the qualification between the two stages of fire protection performance can be determined to some extent. The term "flame retardant" or "flame retardant" can be used for treatments that limit the combustion properties.

There are two general methods to reduce the burning properties of wood by using fire protection.

The impregnation treatment applies water-based synthetic compounds to the wood. Many synthetic compounds exhibit flame-retardant properties, but due to cost or other factors, they are rarely considered universally practical.

The treatment of penetration into the wood is usually achieved through vacuum pressure technology. Important considerations include the depth of penetration and the amount of chemicals deposited in the wood.

Another technique to control the burning characteristics of wood is to use an appropriate coating on the surface of the wood. However, all the work is as a thin film coating, which retains the natural beauty of the wood while adding significant fire resistance.

The advantage of these treatments is to reduce the direct flammability of wood and minimize its fuel contribution to the burning fire. If the flame spread rate of the fire spread can be significantly slowed, if the ignition source can be removed or even stopped burning, and if the charcoal enters the wood, the realization of the basic purpose of the intumescent coating can be delayed or controlled.

In continuous and severe fires, no immersion treatment or intumescent coatings can provide fire protection.

The structure that has been built is obviously not suitable for pressure impregnation. In order to get the best results in new buildings, wood should be cut to finished size before treatment, with almost no mechanical interference after treatment.

As with professional materials, although it looks easy to apply, it is important to ensure the correct thickness, adequate coverage, and use the correct product, and a qualified applicator is required.

Aithon product is a water-based swelling agent and is not suitable for external use. If you suffer water damage in an indoor environment, a specific maintenance plan is required.

For more information on using intumescent coatings for wood fire protection, please consult Permax.

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