There are many reasons why a tree trunk should be weatherproofed: The first is simply that wood exposed to constant moisture rots very quickly - and the construction project is therefore doomed from the start, more or less quickly depending on the type of wood.
Outdoor tree trunks should be protected from moisture
Impregnating tree trunks without chemicals
If the tree trunk is to be used indoors or on a covered (and thus protected from rain) terrace, you can impregnate it with natural agents such as oil or wax. If you are using plain beeswax, warm it up slightly before brushing. It's easier to spread that way. The downside, however, is that waxed surfaces tend to soften or melt a bit in warm weather, so this method is not necessarily appropriate for seating and/or very sunny, warm locations. Alternatively, treatment with wood oil is possible. The advantage of both agents is their non-toxicity, which is particularly important indoors - after all, you don't necessarily want to inhale toxic gases from the wood preservative glaze.
Impregnation with varnish, glaze or tar
However, logs placed outdoors are constantly exposed to moisture and therefore need more permanent protection. Treat this wood with a suitable varnish, a glaze or wood protection paint or even tar. You can achieve a particularly high level of protection in this way: soak the log in a liquid wood preservative for a few days. Use a thin glaze for this, as this penetrates deep into the wood. If "bathing" the trunk is not possible, simply paint over it several times at intervals of several days. Don't forget to treat the floor as well! The aim is for the wood to soak up the glaze. Then seal the trunk with wood protection varnish or tar.
tips
Furthermore, you should preferably use hard wood such as oak or beech for outdoor projects, even if they are significantly more expensive such as spruce & Co. However, they are significantly more resistant to moisture and last much longer.