This comes from an earlier discussion. Teak Decks are one of those items where opinions vary widely and a case can be made either way. In their favor, teak decks provide good traction and a beautiful appearance. Nothing speaks of old world charm like a well-maintained teak deck.
The negatives are also very real. However you cut it, sooner or later, a teak deck is high maintenance. There are a lot of theories about how to maintain. On one hand there are the more traditional methods using teak oils, sealers, and mild abrasives in block form to minimize eating out the softer wood. At the other end of the maintenance scale are those who simply believe in washing down periodically, eschewing detergents or scrubbing in any form. In between are believers in washing and scrubbing like any other deck material. This last approach typically results in the shortage lifespan.
The scrubbing process eats out the grain and erodes the depth of the wood comparatively rapidly. In the sun, UV degradation accelerates the oxidation of the surface of the teak. Left to its own devices teak has a wonderful defense against surface deterioration. Teak (like many species of wood) turns gray as its surface oxidizes. That grayed surface acts as a kind of insulator retarding oxidation and sunburning of the teak below. The oxidized layer on teak is particularly efficient at protecting the heart of the teak as compared to other wood species.
Simply washing the decks leaves this barrier largely intact and so the teak lasts a lot longer than if it is scrubbed where the weathered wood surface is easily eroded away by scrubbing and detergents, exposing new wood to deterioration. But simply hosing off the decks allows dirt and mold to form making for a deck that is grimy and not especially appealing.
Although surface oxidation causes surface deterioration to take place at a retarded rate, the sub-surface does still continue to deteriorate. The oxidized teak holds moisture and in freeze thaw circumstances that trapped moisture can accelerate checking and surface deterioration. The pourous nature of the surface also draws essential oils out of the teak below the surface accelerating checking and rot deeper in the wood and lossening the plugs over fastenings.
Oiling and sealing teak prevents the formation of the protective oxidation layer. In echange it renews the oils in the teak, and in the best cases the oils contain UV screens. But the oils can build up and become stick over time, and can become darkened as dirt, and pollution bind to the oils. This means that the deck oils need to be stripped and the decks need to be sanded from to time.
Over time, no matter which method of maintenance is used the decks erode and become thinner. On a 1939 Stadel cutter that I owned with my Dad and restored in the 1970’s, the erosion exceeded well over a 1/4" with 3/8” erosion occurring in many places over the 33 years life of the boat. This meant that fastenings were proud of the surface and water was seeping into the framing below and the deck planks were too thin to hold caulking and keep water out.
It is not all that unusual to find 10 to 20 year old teak-decked boats with serious deck problems. There is no one single answer to your question because the methods of building teak over glass decks vary widely and the extent of the problems will vary with construction type, climate and maintenance that the individual boat has received.
For example, the under layers vary from heavily glassed foam coring, to heavily glassed marine plywood, to lightly glassed non-marine plywood. Fastening varies from planks epoxied in places without fastenings left in place, to bronze wood screws, to stainless steel pan head screws, to steel (galvanized or not). Bedding varies from epoxy, to 3M 5200, to none.
And when the seems in the deck begin to leak there is damage to the under layer. It is my (albeit pessimistic) belief that with any screw fastened teak deck you can expect to find pretty large areas of rotted coring at some point in the life of the boat.
Having owned and repaired boats with teak decks I personally view them as a deal breaker. I see them as a high maintenance deck that in most cases is inherently unreliable since it is nearly impossible to assess the condition of the core below a teak deck. I also have a real problem with the weight that teak decks add to a boat esoecially located as high as it is above the vertical center of buoyancy, which reduces carry capacity, stability, motion comfort, and performance. But that is just my opinion. I know that there are completely opposite opinions of teak decks out there and believe that for those who love teak decks an equally good case can for having them.