All about timber: classic prep vs glulam prep

Posted Sep 15, 2020, Category: Cabin production

At Eurodita, in our production we use glue laminated timber. We chose this type of material due to its versatility, strength and availability. Compared to other types of timber, glue laminated planks can be made of varied size. This means anything from building a contemporary log cabins for sale, a large, arching dome for an airport or a towering religious structure. Because each plank can be glued together in any size, glulam timber can be used for almost any structure. It’s also true for its strength. The special glue used to bind the timbers together into a singular plank makes them comparable in strength to steel. As for availability, the lamination process can take either full trees or sawn cants, which are unfinished logs, ready to be further processed. This makes the raw materials more readily available and although we use only the highest quality Northern pine, which arrives to us in full logs, glue lamination gives producers more options, even when raw materials are scarce.

There are many clear advantages in choosing the glue lamination for log home manufacture. However, full logs have their own process of drying and usage. In this blog post, we would like to shed some light onto the specific process of drying the logs and compare it with the glue lamination process. You will notice how these two approaches to working with wood differ fundamentally from one another and what it takes to prep full logs vs what it takes to prepare for glue lamination.

Full log prep – classic drying 

There are several ways to dry logs. To highlight the differences in techniques, we will cover 3 different types of drying and using the logs.

Green logs – these are the logs that have not been either air- or kiln-dried. The word “green” here indicates the moisture content and it varies greatly, between 20% and 90%. This variance in the moisture content depending on the tree species, the season in which it was cut or whether sapwood or heartwood is being used. Green logs are cut from the butt forest, then brought to a mill or to a log-house yard, where they have their bark removed. These types of logs are usually used to build a log-house shell (or in handcrafted log houses), or sent through profiling machines and become manufactured logs. After construction, green logs dry over time while in the log building. In about four years, green logs which are part of a completed log house reach an equilibrium with local conditions. This means they also have an equilibrium moisture content, which is between 6% and 12%. It varies between seasons, climate and locations. 

Air-dried logs – these are logs that’ve been let to sit outside in the open air to dry naturally. The timbers sometimes are stacked with spacers between them. This process allows the moisture content of the logs to fall naturally as they dry. Depending on an area’s humidity, it may require as much as one year per 2.5cm of log thickness to dry out. The more arid the location is, the less time it takes. Without proper air circulation, the logs will begin to rot before properly drying. In some locations, the logs must be kept under a roof or cover to reduce the impact of rain and other storms to the drying process. Once the logs have dried, they are profiled for size before shipping. Profiling usually does not take place until just before shipment, to make sure that the logs stay as uniform as possible.

Kiln-dried logs – some mills have a kiln on site have the option to significantly accelerate the drying process. Green logs are placed inside a large oven, where constant heat removes moisture from them. The drawback of this type of drying is that the logs can suffer severe checking and cracking if the heat levels are not monitored properly during the drying process. Using kiln-drying can reduce the process from many months or years to several weeks. At the end of the kiln-drying process, the average moisture content stays at about 18-20%. The usual equilibrium moisture content is at about 6% and 12%, which is less than kiln-dried logs. Because of this, the logs can be expected to shrink and settle over time, but not as extensively as green logs.

Glue lamination process

“Laminated” or “engineered” logs are unlike the previous approaches. full trees or sawn cants are brought to a mill with a dry kiln, the bark is removed and the trees are sawn into boards usually no more than 5cm thick. The dry kiln then does the job and because of their size these boards can be dried without causing severe damage to the wood. Timber assigned for glue lamination must have less than 15% moisture before the lamination process can start. The drying process varies depending on the species of lumber, but can be done in a week or less. Once properly dry, the planks are sent through a surfacer, which perfectly smoothens the face of the lumber. Then it’s time for a machine, which spreads a special glue on the interior boards.

In general, there are two ways to finish the lamination process. First option is the type of glue, which reacts to radio-frequency (RF) energy to cure the glue in minutes. The other option is to use a high-pressure clamp, which keeps the newly assembled timbers under pressure for 24 hours. Once the glue has dried, the result is a “log cant”, which then are run through a profiler, and the end result is a log that is perfectly straight, smooth and uniform.

Final thoughts

Glue lamination process is much more modern and takes much less time. With it, we can calibrate the exact size and profile boards we need, which gives us the flexibility to build bespoke glulam beams houses that our partners require. We are open to talk in depth about our production capabilities with any potential and current partners.