Yes, you technically can use sandblasted teak outdoor furniture without treating it, but it comes with significant considerations. Sandblasted teak has a distinctive, textured grey finish achieved by removing the soft grain, leaving the hard grain exposed. This process does not strip away teak's natural oils and rubber entirely, which are its primary defenses against rot, insects, and weather.
Untreated sandblasted teak will weather naturally. It will turn from its initial light grey to a uniform silvery-grey patina over time. This patina is stable and is considered desirable by many for its natural, weathered look. The wood's core durability remains largely intact.
However, leaving it untreated has downsides. The surface will become more porous and may accumulate dirt more easily. It can also develop slight surface checks or cracks as it adjusts to moisture changes. While structurally sound, untreated teak may have a slightly rougher feel.
For long-term preservation of a specific color and to minimize surface weathering effects, applying a teak sealer or oil is recommended. This requires annual maintenance. Choosing to leave it untreated is a valid, low-maintenance option, accepting the elegant silver-grey patina as the natural destiny of this durable hardwood.