Ospho

Bob S

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Sep 27, 2007
1,771
Beneteau 393 New Bedford, MA
I hired an outfit to sand blast my cast iron keel and apply an epoxy barrier coat. They use Sea Hawk Tuff Stuff and claims he's never had issues. I bought a gallon of Ospho and was going to apply it shortly after blasting and have him come back to paint 24 hours later. He won't be able to come back closer to 48 hours. Reading the Ospho directions it says "Test trial samples before using epoxy or other paint systems." Now I'm concerned yet many have sworn by this product. Any advise would be appreciated!
 

Bob S

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Sep 27, 2007
1,771
Beneteau 393 New Bedford, MA
As far as Sea Hawk products? I was more worried about using the Ospho. From internet searches I have not found any complaints about the product. I'm more concerned about the process. I will check it out though, thanks.
 
Apr 8, 2010
1,942
Ericson Yachts Olson 34 28400 Portland OR
After some more research you might find that the product 'best use' instructions do not predict a "yes or no" scenario, but rather a scale of time where the results are less and less predictable. Chemicals are often that way. The vendor should have more complete information.
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
Could wrapping the keel in plastic after you apply it slow down the process? Is that practical?
 

Bob S

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Sep 27, 2007
1,771
Beneteau 393 New Bedford, MA
There have been many sailors here that have Ospho treated their keels before barrier coating. I would think if they had issues they would have said so. Problem is I research too much and have seen people that have had issues with every product. It's all in the process. I guess what caught my eye was the directions specifically say to do a test specimen when applying and epoxy based product which barrier coats are. I'm not worried about the time it sits as directions say a minimum of 24 hours before painting.
 
Sep 14, 2014
1,251
Catalina 22 Pensacola, Florida
You need to apply barrier or paint right after ospho as it will quickly get rust specks after you rinse off the soluble iron phosphate you created to get the clean metal.
 

capta

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Jun 4, 2009
4,766
Pearson 530 Admiralty Bay, Bequia SVG
I would suggest you down load a product data sheet for ospho and the paint you are planning to use.
I've only used ospho with enamel paints without a primer between the two part and the oshpho.
You biggest problem is going to be getting the sand blasting dust out of the pores of the steel and getting something on there which seals the metal from rusting, a process that begins in hours on the microscopic level,
 
Feb 8, 2014
1,300
Columbia 36 Muskegon
We use Ospho a lot on the commercial boats ( all steel construction) but we always paint the next day. Not sure what happens if you delay. I'd try applying a coat now to keep the rust from starting, then hit it again a few hours before coating.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Do not know Ospho, nor have I used the Sea Hawk products.

What I do know its when over coating, especially with epoxy products, the time between coats is to optimize the ability of the over coat to chemically and physically bond with the under coat. With paints if you wait too long you must rough up the "primer" coat to provide a surface for the New coat to attach. If a second or third coat is desired, some products are chemically ready to accept another coat. If you wait too long the product is no longer chemically ready and the ability to apply an over coat is compromised.

Your best bet is to contact the manufacturers and have them tell you the time window. Then you have the best guidance.
 
Jan 7, 2014
395
Beneteau 45F5 51551 Port Jefferson
I don't know about Seahawk, but I also used ospho on my iron keel this season. Everything I read said cover the bare metal immediately after sandblasting or you run the risk of rust from the moisture in the air. I didn't like the fact that the ospho could not be topcoated or epoxied until 24 hours. So, I applied the ospho, waited 24 hours then sandblasted. I figured any rust missed by the sandblasting was converted by the ospho. We'll see. I did apply west systems epoxy and interlux 2000E over the ospho treated metal.
 
May 4, 2005
4,062
Macgregor 26d Ft Lauderdale, Fl
I have used Ospho, on autos. Its Alright but it needs a top coat to protect it.

Now I use POR-15. its got a thicker, and better bond IMO. its more epoxy like, where Ospho was acid.
 

dLj

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Mar 23, 2017
3,373
Belliure 41 Sailing back to the Chesapeake
Ospho essentially turns iron oxide into iron phosphate. Iron phosphate is a hard, non-porous oxide-like coating. That's why you have to cover it with a barrier coat of some sort (your epoxy or whatever paint system). You want the 24 hours for the reaction to be complete is my understanding. I wouldn't think the 48 hours would be a problem, but as others have said, always best to ask the manufacturer.

It's also my understanding that the testing is more of a CYA than anything else as the manufacturer can not test every combination of coating systems, it's just not feasible. Certainly ask both product manufacturers if they have knowledge of the combination of the two systems you are using - they may or may not have knowledge directly, but may have "close enough" data... If they can't tell you directly, then glean as much as you can and then make a more educated guess. Testing is the best method, but you do need to have the set-up to do it... That's not a small ask... One of the reasons professionals are often a good option... LOL

dj
 
Oct 24, 2010
2,405
Hunter 30 Everett, WA
It's great stuff. Chemically it causes the oxidation to become a barrier to further oxidation. After 6 years our cast iron keel shows no sign of rust through.

Our keel was pretty bad when we bought the boat. Sanded some. Applied OSPHO, 3 coats of barrier coat, then bottom paint.

I don't think 48 hours will be a problem. Also this stuff goes a long way. Our keel took about 4 ounces and I even painted it on a particularly rusty jackstand. Out in the weather that jackstand still looks okay without painting 6 years later.

Ken
Ken
 
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