pontoons turn blackish with rainbow color Fresh water only

[harley707]

Just polished pontoons to a mirror finish they were beutiful been out about 8 times a few over nighters. Pontoons again are turning blackish with a rainbow hue to them. I know I can sealthem with sharkhide etc. but I don't mind polishing as its not that hard to maintain them,
My concern is why are the tunes turning blackish and rainbow colors ?
Almost seems like I am getting a chemical reaction. I see other toons and the toons are aluminum color and they seem to yellow some but mine are blackish? That was the reason i decided to polish the to begin with. Boat is a 2004 Sun Cruiser by Lowe 60 hp Mercury EFI 4 stroke.
Thanks for any help Brian

 

[MH Hawker]

Re: pontoons turn blackish with rainbow color Fresh water only

I had hoped some one who knew the answer would come along. As a pure guess its some sort of after effect of the polishing compounds you used.

 

[OK Toon]

Re: pontoons turn blackish with rainbow color Fresh water only

Brian - I've got a 2003 Suncruiser and my toons had that same blackish and some rainbow colors. I used that Napa Aluminum Brightner for the first time this year. It did a great job of getting the toons back to a nice dull aluminum. I haven't had it on the water yet this year to see how quickly it will start turning back to blackish. If it does, I'll clean it again next year and then do the Sharkhyde treatment. I'm not interested in mirror-shine. I just don't like the nasty blackish stains -- just makes the toons look old.

Here's a "before" and "after" of my toons after cleaning.

 

[Uncle Dave]

Re: pontoons turn blackish with rainbow color Fresh water only

Nice photos OK, but the dog doesnt seem to impressed with it all :>)

 

[harley707]

Re: pontoons turn blackish with rainbow color Fresh water only

Hello and Thanks for the input. The toons were blackish to begin with hence the reason I polished them.
OK TOON has the 2003 model mine is 2004 Mine look just like OK TOONS.
If I didn't know better I would think it was in a fire as the discolering looks like it has got real hot.
As far as chemmical reaction That was my thought wondering if it was possible some one had used screws that were not stainless or aluminum and I am getting a reaction from the two metals ???

 

[harley707]

Re: pontoons turn blackish with rainbow color Fresh water only

Thanks >>>> OK TOONYea the before pics look similar to mine. Like I say had mine to a mirror finish now they are getting blackish again. They are still very smooth just lost that high lustre They had geuse i just need to get the bufffer back out. Thanks all Brian

 

[WaterDR]

Re: pontoons turn blackish with rainbow color Fresh water only

Guys, alumunum corrodes to aluminum oxide. Thats what it does. The color is dark. Once the alum-oxide forms, this acts as a protective layer to the aluminum and corrosion stops. It is essentially a protective layer for aluminum.

When you remove it with acid and then polish, you are essentially removing the protective layer and the corrosion will start once again. You are basically making the metal thiner over time. Is it enough to make a difference or cause problems? I am not sure, but I have the tools and access to a lab to actually measure the effects on a pontoon. I have a very strong industrial water treatment background and some background in metalurgy. 25 years.

 

[5150abf]

Re: pontoons turn blackish with rainbow color Fresh water only

Correct, polished is not a natural state for aluminum, same as copper, they corrode to form a protective barrier.

The only way to stop them from turning to is to protect them from oxygen with Shark hide or a similar product.

 

[WaterDR]

Re: pontoons turn blackish with rainbow color Fresh water only

Just remember, Sharkhide won't do jack, if the toon is stored in the water.