Corrosion on floor

[MIQ]

Hello all,

Looking for some help with the floor on my boat that is starting to corrode. Typically the manufacturer that made my boat used the vinyl over plywood floors in their boats. But Mine came optioned with a aluminum diamond plate floor instead.
The deck is not self bailing, and the Sheet Aluminum is screwed down to marine grade plywood. Per the manufacturer the Diamond Plate is 5052 aluminum.

From day 1 on parts of the floor there has been a small gap between the sheets of Alloy, and salt water is definately able to find its way inside these cracks. That said, after each use in the salt the boat gets a thorough cleaning with fresh water, soapy water and sometimes it gets a good soaking with saltaway.

Even with my best efforts the floor is corroding at the seams between the sheets of flooring. Recently the boat has sat in a garage for a period of time and im seeing some "ooze" forming at the sight of the corrosion. I havnt seen this before now, but it does seem to be related to the corrosion. I probably had been washing it away during normal use, and wasnt noticing it. The aluminum feels gritty at the site of corrosion and in the one bad spot the alloy seems to have been eaten away and become chalky. So far the issue is just on the seams, and it hasnt seemed to progress more than 1/8 oof an inch from the edge of the sheet



My question is, what do you think is the cause of this corrosion? Salt getting trapped under the floor? Corrosion affect from the SS Screws that are used to hold the floor down? Possible reaction with the Marine Plywood/glue?

Any suggestions on how to minimize this from happening again if i get a new floor?

Im in the process of working with the manufacturer to address the problem, and have the floor fixed. But im interested in seeing what some opinions are to the cause, so that I can minimize the chance of having the same thing happen again. Im looking at 2 options. Replacing the floor again with the diamond plate or just having it replaced with the standard vinyl over plywood. My preferance is to go Metal again, as the floor has much more traction and resistance to wear, cuts, gouges and staining... But If the trade off is corrosion, Im not sure I want to repeat this every 3-4 years.

[welder]

Some problems are...
1) Some soap is actually corrosive to all alloys.
2) With the Plywood under the Alloy it WILL keep moisture between the two and not have a chance to dry out.
3) With the wood/Allot staying wet for long periods of time then you throw thw SS screws in the mix guess what? We have a battery .
4) By replacing with the same you WILL have the same problem again and soon.
5) Can you use some thicker Diamond plate and loose the wood?
6) Use plenty of of anything that prevents corrosion between dissimilar metals.

I"m sure more will be along soon to help out here.

[JETTYWOLF]

Aluminum screwed down to plywood?????

What the heck...If the boats worth it, I'd have all that changed out and get rid of every stick of wood!


Ditto what Welder said.

K Morin may have a few building comments to add, as I'd like to read them.

[John@Ironwood]

Hey MIQ

My quick thoughts.

If you where able to lift the sheet up even 1" and take some pictures that would be great.

1.) The sheet may not be 5052.
2.) Is the console/deck in any way used as part of the boat electrical system. Disconnect the negative off the battery. With the 12volt power run a test meter between the negative terminal and the deck checking for power.

The soap is not really soap...but a gel that is made when alum. corrodes. I'f I spent more time in chemistry class rather than haunting boat yards I'd be able to give you the scientific name of the gel.


If the wood is pressure treated that isn't helping

Replacing the wood or replacing the alum with galss or vinyl deck is ideal.

Barring tthat the alum needs to be isolate from the wood. This can be done by coating the wood with glass/epoxy or by fastening some kind of plastic (Polythene, Starboard, Seaboard, UHMW) to the wood and then screwing alum deck into the plasctic. The plastic has to sit 1/8" higher than the wood

A 1/8" x 2" covering strip can be used to over the corrosion if you don't like seeing it.

Connect each of the deck plates together and then connect them to the boats grounding strap or zinc

The screws should be put in with Tef Gel or isolation washers.

Putting some vents in the hull to dry the wood or leaving hatches open is good.

Take Care
John