You use Boracol if you have problems with black or green spots which is molds and algae growth on your teak deck.
Before applying Boracol, make sure the teak deck is cleaned properly.
You put Boracol on to the teck deck by brushing. It´s good if it doesn´t rain for the first 5-6 hours after treatment. This makes the Boracol penetrate into the teak. After that rain is just good for the treatment. So a good time to do this treatment with Boracol is in the fall.
After on or two weeks the deck will be clean from black and green spots and will leave the teak in the normal silver grey color.