There are lots of discussions on this subjects in the archives of this forum. It is also a popular topic on the Grand Banks owners forum.
Bottom line is that a lot of people have done this. I know people who have done this, and there are a number of ways to do it. But it has to be done correctly or it will lead to more problems down the road.
And that is why it's important to get out and talk to people who've done it or had it done successfully to their boats. Because what you'll get on an internet forum like this are a ton of conflicting opinons, some of them valid other's not so much.
It's a big job to do it right, whether you do it or a yard does it. There are people who have replaced teak decks in a short time with a minimum of effort but that's not the best way to do it, although they will tell you that it is.
So best to read everything you can on the subject, talk to shipwrights or yards that have done this, but most of all talk to people, ideally in your area, who have done this job properly.
It's not rocket science to do it, but it does take the right process, the right techniques, the right materials, and the right tools. Or a lot of money to have a pro do it.
Teak decks can also be repaired if the wood itself is still in decent shape. But if the subdeck has rot areas, then there's only one way to fix that properly and that's to get the rotted material out and replace it with new material. You can then cover it back up with teak (applied correctly) or fiberglass (applied correctly).
