Sir. According to article https://www.mataverdedecking.com/blog/can-you-prevent-checks-and-cracks-in-large-timbers, i made some preparations of my long timber elements on the building external construction. It's work. The structure of the elements is less cracking then others not prepared elements.

Hello Yue Kong,

Cracking, warping and other defects are serious problem in wood. this is largely due to moisture imbalance and hygroscopic nature of wood. while some controlled or scheduled drying have some effect in reducing these defects, there is still a lot to be done. One way is applying hydrophobic layer coatings on wood either with some transparent silicon coatings or constructing hierarchical layers on wood surface after scheduled drying. But the major drawback may be the size of the wood. However, sawn wood for large constructions can be treated as well. Some laboratory experiments have proven to successfully coat wood with transparent and hydrophobic coatings.

you can check these article and may be able to adopt the methodologies for large wood surface

Article Fabrication of transparent and durable superhydrophobic poly...

Article Environment-Friendly and Two-Component Method for Fabricatio...

Cracking in large-scale wood element is induced by the moisture variation in the wood material. Timber in construction must be dried enough, free from moisture at the early age of construction. There are some chemical coating products use to protect timber against moisture. Also, Various physical and chemical sterilization methods are used for killing of pests in biologically damaged wood, including heating, freezing and exposure to ultrasound.