Reinforcing an old pontoon deck

I have a boat on the older side, made in '88 with the original floor. Needless to say the old girl is getting a little bendy, a little misshapen, a little warped. Inspecting the underside after a good rain reveals a lot of discoloration in spots, some the size of a basketball. There isn't much life left in this deck. Not much, but still a season or two from what it looks like. The soft spots aren't to the point where someone is going to put their foot through the deck, but they're getting noticeable after a good rain.

Fortunately all of the soft spots are in accessible areas from the underside. It would seem that screwing in a large enough piece from the underside would support the softer spots in the deck until the entire deck was replaced.

My question is: is there a "best" method by which the soft spots could be shored up with some wolmanized/pressure treated stiff 3/4 ply?

Cheers

Note: Replacing the deck this season isn't an option, please don't suggest that. I'm very aware it needs doing

Re: Reinforcing an old pontoon deck

I don't see why you can't take a piece of treated plywood to patch it underneath until you replace the whole thing. As long as you get into good wood for your screws. I would go at-least 6 inches out from the bad spot, it will expand with time so you don't want your screws failing. Some construction adhesive would most likely help too.

Re: Reinforcing an old pontoon deck

Great idea about the construction adhesive.

As far as fasteners go - what type of screws should I be using? Stainless or some kind of high strength decking screw? In theory I'd only have 1-1/4" of material between the new patch and the original deck (wouldn't want the screw tip sticking up through the topside). And that raises another question - screw up from the bottom or down from the top?

Re: Reinforcing an old pontoon deck

No need to go expensive stainless for a relatively short term fix. Stop by any home improvement/hardware store and buy a box of coated decking screws in the length you need. They'll hold up extremely well, even if the temporary fix ended up having to last a few years. After all, they are made for outdoor decks. The only catch is you will be hard pressed to find screws shorter than 1.25". They make them, but they are not as readily available. If that ends up being a problem, try using some thicker support lumber.

Re: Reinforcing an old pontoon deck

Thanks Lurch, any recommendation on screwing bottom-up, or top-down? My initial thought was bottom-up.

I posted the same question on a different site and was told that the newer pressure treated plywood is treated with a process called ACQ, which will corrode aluminum. Any thoughts on that?

Re: Reinforcing an old pontoon deck

Some of the treated plywood (and dimensional lumber) has some kind of copper in the liquid soak. It doesn't react well where it touches aluminum.

There's just no substitute for marine plywood when rebuilding a pontoon boat.

I made the mistake of using heavily painted 3/4" regular CDX plywood on my old pontoon, and it didn't has long.

Re: Reinforcing an old pontoon deck

Its time to replace the deck, patches wont hold, its done, the deck is a good part of the boats structure. The twisting and stress will only make it worse.

Re: Reinforcing an old pontoon deck

I would say you could screw from the bottom up. Just be sure that you are screwing into good wood. If you can't the screw from the top in those locations. When you put the patch on just keep it from touching the aluminum by about a quarter inch. It will not hurt the aluminum unless it is touching it. By glueing it and screwing it it will be a good patch to help hold it together for now. As for the screws just get the coated ones that are made for the new treated. I know a lot of people don't like to patch things, but sometimes you have no choice. As long as you do a good job installing them they will work for a time.

Re: Reinforcing an old pontoon deck

I am with Hawker here, this is not a band aid problem, the deck on a pontoon is a major structural member and if it has deteriorated too where the boat is flexing there really is no quick fix.

I also wonder what other damage you are doing to the boat, it is aluminum and aluminum doesn't like to be bent so you could be trashing your boat, I know that isn't what you want to hear but it is where you are.

Keep going under the boat and inspect the brackets and crossmembers at the bolt point and inspect for damage, once you start seeing that it may be tie shut it down and redeck.

Re: Reinforcing an old pontoon deck

while I know you said replacing it this season isn't an option, not to suggest that.I do agree with the above posts saying it's time now to replace it all. if you know you're going to have to replace it before next season anyway, why not go ahead and do it and have it done. why put it off and risk serious damage that would be a whole lot more expensive to fix? is that an option this season? we'd sure hate to read about you in the paper or online......

Re: Reinforcing an old pontoon deck

While I appreciate the words of caution on potential damage to the aluminum structure of the boat (due to large amounts of flexing, etc) I have to just state that this is not a situation where the deck has turned into a trampoline. There are a few, small soft spots in the deck. Wood that's exposed to water will warp - especially of the course of 20+ years (this is the original deck).

With a few folks throwing red flags about the overall stability of the deck, I called in a few favors and had two guys from local, well-respected marinas stop by and take a look, walk around on it. I even soaked the deck to the point where the soft spots/discoloration was visible from underneath. Both of the guys agree that the deck needs to be replaced, but that a patch to cover the areas in question (two 1'x1' and one about 6"x6" in trafficked areas) should do just fine for a season, if not two. Those guys had the benefit of seeing the deck in person, so I thought I'd add to the thread.

Thanks for the opinions and ideas folks, much appreciated. I'll reply again with an update on how it ended up working out.