Pitting/corrosion on jon boat bottom

[Douglasdzaster]

Hello everyone. I have a 1983 Monark 16/52. There’s some pitting in the cross members under the floor and other discoloration in spots on the bottom. I don’t know if it’s ever been in saltwater. I’m keeping it in freshwater only.
Im about the remove the floor again this week and want to treat/clean up the bottom.
Do I use vinegar and water and scrub it down? Once it is clean can I coat it with self etching primer or do I need to do more? When I’m finished I’ll put the floor back in and I’m putting a new cover on the boat finally.

 

[Grub54891]

Pictures please. Depends on how deep the pitting is.

 

[robert graham]

I use bleach and a scrub brush on the bottom of my 40 year old aluminum canoe….cleans and removes everything real well…rinse with fresh water….I’ve never painted or coated any parts of the hull but I guess a coating of some kind wouldn’t hurt…seen folks use pick-up truck bed liner…

 

[Douglasdzaster]

Pictures please. Depends on how deep the pitting is.

Here’s pictures of the bottom at the stern. Which is what a lot of it looks like under the floor.I haven’t removed the floor yet. The pitting on the cross members is anywhere from shallow to small holes. No pitting on the actual bottom. Just this discoloration that looks like corrosion to me. I had the floor out a month ago to clean it when I saw all of this. There where leaves and dirt blocking the channels so water had been standing in spots under the floor. I want to fix all and keep it covered from now on. If you need more pictures I can probably pull the floor Monday and post. For all I know the boat may have been green at one point and this is paint. Lol
Thanks for replying it’s appreciated.

 

[Grub54891]

Makes we wonder if a battery leaked and got down there. Scrub it with baking soda just to make sure its neutralized.

 

[Douglasdzaster]

Makes we wonder if a battery leaked and got down there. Scrub it with baking soda just to make sure its neutralized.

Thanks I didn’t think of that. Motor is a pull start. But they had lights on the boat. Thanks that’ll be part of the cleaning when I remove the floor. I’d like to paint it. My neighbor used self etching primer on his and didn’t paint over it. Is the self etching necessary?

 

[Grub54891]

I think I would use the primer; it will help the paint stick better. besides, the primer helps you see where the repairs are needed better.
I always prime/ sand and repair defects while I'm there, after repairs I prime again.

 

[Jim Hawkins]

The floor your talking about removing, what is it made of?

 

[Douglasdzaster]

The floor your talking about removing, what is it made of?

There’s one sheet of plywood that starts at the seats in the stern. It’s coated with what looks like a thick clear resin. Doesn’t look treated other than that. Then where the plywood stops there’s a couple of old metal signs. Then there’s painted sheet metal on top of all that with a nice none slip material on top. I had no idea it was put together that way on the bottom until I took it apart the first time. I thought I had a great floor. Only had the boat for a year. And had to bring it back to life. Now I found this and working on the trailer. The areas I noticed the most problems is where levees and dirt had gathered under the floor causing it to hold water in areas. I don’t know what metal the signs are made of but they have no corrosion. They could be causing the aluminum to react as far as I know. Before I put the floor back in I got some weather striping thats used between camper shells and pickup beds. Covered the cross members to make a barrier until I could get back to it. I’ll have to remove it and it’s adhesive as well. I want to prime and paint everything once I get it prepped.
I will post pics on Monday when I remove the floor.

 

[Grub54891]

When replacing the floor, do not use treated plywood. It does corrode the aluminum.

 

[Douglasdzaster]

When replacing the floor, do not use treated plywood. It does corrode the aluminum.

The one piece it has doesn’t look treated but it is incased in a thick coat of either fiberglass resin or epoxy. Still in good shape and sup heavy to handle because of the coating. If it is treated would the coating be a barrier? The bottom doesn’t look as bad under the plywood either. It’s wear they payed those metal signs towards the front to fill in under the floor top. The signs have no corrosion but the boat does under them. Why they didn’t use all plywood I don’t know?
when I get the floor out tomorrow I’ll post pictures.

 

[Grub54891]

Encasing treated wood don't work to well as it makes the epoxy hard to stick/stay on there. it's wet from the treating chemicals.

 

[Douglasdzaster]

Encasing treated wood don't work to well as it makes the epoxy hard to stick/stay on there. it's wet from the treating chemicals.

It’s probably not treated then because this stuff is on there good. I have some untreated to replace the signs with and thinking about putting several coats of urethane. The plywood will be under the metal sheet covered with a non slip material. I’m not sure what the material is called but it’s holding up well and is attached to the metal with adhesive.

 

[Bob Sander]

Here’s pictures of the bottom at the stern.

That looks like pressure treated wood was used in there at some point. I would give that a light sand blast to clean it up and I'm not sure I would do anything more to it other than fine sand and a polish. There is always standing water at the stern, and if it's fresh water then it isn't really an issue for aluminum.

I do see what looks like a bit of calking there, which is a bit worrisome. Check out why its there before you do any kind of finishing. A bit of mig welding always lasts a heck of a lot longer than calking.

 

[Douglasdzaster]

That looks like pressure treated wood was used in there at some point. I would give that a light sand blast to clean it up and I'm not sure I would do anything more to it other than fine sand and a polish. There is always standing water at the stern, and if it's fresh water then it isn't really an issue for aluminum.

I do see what looks like a bit of calking there, which is a bit worrisome. Check out why its there before you do any kind of finishing. A bit of mig welding always lasts a heck of a lot longer than calking.

Previous owner may have had wood in there at one time. I was thinking a battery. I got the boat cheap and went to work on it a year ago. Finally got the motor running and now I’m working on this. It was neglected maintenance wise and there’s no telling what’s been patched and with what. I use it quite a bit now and no leaks. At least not yet. After this I’m redoing the way the trailer is set up. It’s a pain getting it off and on the trailer.

 

[Bob Sander]

I was thinking a battery.

Could be. Typically though, it's only one side of the boat affected if it's a battery acid issue (the immediate vicinity of the battery)

 

[Douglasdzaster]

Could be. Typically though, it's only one side of the boat affected if it's a battery acid issue (the immediate vicinity of the battery)

Let me ask you something please.
The front of the boat has some old metal signs ( don’t know if they are tin or aluminum) that are supporting that part of the floor. The signs have no corrosion at all but the boat has corrosion that looks similar to this and pitting on the cross members. When I first removed the floor about a month ago it was real damp and I could tell water had been standing there. Debris had the channels blocked going under the cross members and the boat wasn’t draining after a rain. I’m replacing the signs with untreated plywood which I’m coating with spar urethane. I have been reading a lot online trying to find out how to treat and neutralize the corrosion. What one site says another says never do. I have myself so confused I’ve put off going to get any type of brush or steal wool etc. I was going to wash the boat first with purple power vehicle and boat soap (they say it’s good for removing wax and prep things you want to redcoat, does ph matter on aluminum?), mix vinegar with distilled water next but now I’m not sure about that. Then sand it and cover the bottom with self etching primer then paint. Can you tell me if I’m on the right track? I’m so afraid now I’m going to do something that does more harm than good. I’m not a chemist. I stopped looking at websites and getting more confused. Sorry I haven’t removed the floor as planned today and have pictures yet. I had other things come up. But tomorrow for sure. If not this evening. Once it’s finished I have a new cover for it to keep out debris and water. Oh one spot in the pics I did post looks like the previous owner used 5200 to patch it. I can’t get it welded at this time. Is any of the stuff I’m using going to mess that up? It’s not leaking now.
See how confused I am. Lol

 

[Jim Hawkins]

See how confused I am. Lol

Get everything out of the boat that could cause corrosion from acid or dissimilar metals.

Give the boat a good wash with water and dish soap. Lightly brush if you want but don't worry about getting the corrosion off as it can actually make a protective barrier against further corrosion.

Once the boat is clean and dry if you need a floor then put in something plastic or aluminum that can be lifted out for regular cleaning.

Keep your boat clean and dry between uses and enjoy.

 

[dingbat]

Signs would not be tin. Tin is a very soft material.

Aluminum is stable with a ph between 6.4 and 8.5

To “clean” need a product outside these limits.

Take what you read on the internet about aluminum cleaning with a grain of salt.

Don’t tell them producers (mills) acid clean using sulphuric (H2SO4) or phosphoric (H3PO4) acid solutions and surfactants.

Alkaline cleaning processes are based on sodium hydroxide (NaOH) solutions.

In your case, sounds like your “corrosion” issue is caused by standing water. Wire brush to remove any loose material and call it good. Just need to keep the are free of standing water

 

[Bob Sander]

Let me ask you something please.
The front of the boat has some old metal signs ( don’t know if they are tin or aluminum) that are supporting that part of the floor. The signs have no corrosion at all but the boat has corrosion that looks similar to this and pitting on the cross members. When I first removed the floor about a month ago it was real damp and I could tell water had been standing there. Debris had the channels blocked going under the cross members and the boat wasn’t draining after a rain. I’m replacing the signs with untreated plywood which I’m coating with spar urethane. I have been reading a lot online trying to find out how to treat and neutralize the corrosion. What one site says another says never do. I have myself so confused I’ve put off going to get any type of brush or steal wool etc. I was going to wash the boat first with purple power vehicle and boat soap (they say it’s good for removing wax and prep things you want to redcoat, does ph matter on aluminum?), mix vinegar with distilled water next but now I’m not sure about that. Then sand it and cover the bottom with self etching primer then paint. Can you tell me if I’m on the right track? I’m so afraid now I’m going to do something that does more harm than good. I’m not a chemist. I stopped looking at websites and getting more confused. Sorry I haven’t removed the floor as planned today and have pictures yet. I had other things come up. But tomorrow for sure. If not this evening. Once it’s finished I have a new cover for it to keep out debris and water. Oh one spot in the pics I did post looks like the previous owner used 5200 to patch it. I can’t get it welded at this time. Is any of the stuff I’m using going to mess that up? It’s not leaking now.
See how confused I am. Lol

Agree with others. As far as I know, if you get rid of what ever acid or chemical is or was causing the corrosion (sand blast or soda wash... etc) then that's as far as you need to go. People of course paint their aluminum boats to beautify, but I haven't heard of people treating aluminum to protect from (fresh) water unless it's going to be used with some corrosive chemical.

Untreated aluminum will last DECADES in fresh water without anything on it. Heck, we just sold a 40 year old 14 foot aluminum boat with the (raw) aluminum in pristine condition. Of course we redid the transom wood and seats over again probably about 1/2 a dozen times over its life.... just used regular 3/4 ply.... nothing special.