Some of the exterior wooden panels on my outdoor sauna are letting in water. How best to solve the problem?
Also what is best non flammable sealant for inside of the sauna?
If you’re looking to seal the timber itself, several sealers on the market are designed expressly for this. What you don’t want to do is apply something that will let off fumes each time you heat your sauna.
There is an oil which is used to seal the surface of timber to prevent staining from moisture: https://geni.us/QiS1KMG.
There is also a Finnish product that comes highly recommended, https://tikkurila.com/products/supi-saunasuoja.
You shouldn’t need to seal the outside of the sauna if it’s cedar, but if you are getting leaks through gaps, then you’ll need a silicone sealant that’s mold and mildew resistant. I’ve heard good things about this product: https://geni.us/uEIyeA.
Be aware that it will give off fumes for about a week; however, it should be odorless once completely cured.