I would like to know if this deck is screwed into a molded fiberglass deck, or a wooden one: they are very different problems calling for different solutions.
My
teak deck is over
plywood and beams, and I used silicon bronze wood screws when I built her - in 1978. The only shortcoming is that the bronze is soft enough that it is easy to round the internal head (Frearson, or Reed+Prince) when removing them for refastening - so it is very important to remove any glue or debris from the head such that the driver is fully seated. Of course the bronze can develop an oxidized layer if
salt water gets to it, but it doesn't travel (i.e. no visible staining on deck). AFAIK stainless wood screws are not readily available (everyone seems to be using sheet metal screws which are not appropriate for wood). And depriving SS of oxygen (under a bung) while wetting it with
salt water can cause stains - depending on the quality of stainless. Of course using a quality tapered pilot drill with countersink and counterbore is necessary. Refastening with the old screws, and deepening the holes with the same pilot/counterbore, works well.
Putting teak down on a molded fiberglass deck with SS screws is a really bad idea. They leak. A SS screw is the irresistible force to the fiberglass immovable object: something has to give. Typically a SS screw creates pressure as the wider taper is driven into the FG, causing a crushing of the resin. The hole can no longer be sealed with the normal caulking as the loose glass strands prevent penetration. I have helped
repair such holes, and they can be a nightmare to even locate as the
water often gets under the teak elsewhere and then travels to the damage unseen.
Epoxy is probably the only hope for sealing such holes; personally I have drilled a larger, clean hole then filled with caulking and plugged, but I claim no special expertise here. It seems that it is possible to use a pilot that is only slightly smaller than the screw and not always fracture the structure, but in the long run some holes are likely to fail. Driving bronze screws into fiberglass usually deforms the screws, and they can seize in the hole and even break off - not a really good idea. Again, there might be an ideal hole size that only slightly deforms a bronze screw but I wouldn't recommend it. There is a reason that modern boats put teak decks down with
epoxy and a vacuum bag - and no screws at all.
If by chance you have a cored fiberglass deck under the teak then choosing a tapered pilot drill that doesn't allow the screw to pressure the FG but uses the
core for grip should
work. Then a durable solution can be had with screws, assuming the
core is not foam or rotten.
While the screw holes in the fiberglass provide the conduit for
leaks,
leaks often start by
water travelling under the teak to the screws (the
sealant often fails between the teak and FG). If it is just a leaking or missing bung then that is no big deal. But if, as often happens, the water is under the teak already then a proper
repair would include re-laying the planks with
adhesive sealant. At that point removing the teak, filling the holes, then painting the deck is the preferred solution. Or instead of
paint, put down teak (or faux teak) with an
adhesive and no screws.
Greg