Sandblasting - or?

Hi all, yes I know this has been brought up before, but..

I am this season coming to the end of the steel-works on my hull (http://www.justmueller.com/boats/) and plan painting before next winter.

Now, I have built several hulls before, and we always sandblasted ourselves with rented equipment and then painted with zinc-epoxy. These are not very pleasant memories, but over more than 20 years, these boats were literally maintenance free, and I still belive this to a near perfect solution.

On the other hand, getting old and lazy and afraid of my neighbours, I still try to look at alternatives even if they are less than perfect.

The hull was built from black steel and is by now unevenly rusted. Even after a Winter in rain and snow, some places still have the millscale on.

So here are in loose order a number of questions that I really would appreciate your input on:

- Does anybody have personal experience with alternative methods on black steel?

- Is there a chemical way to REMOVE (not convert) rust from steel leaving a clean surface? ... same question for millscale, and same question again for rests of welding shlag in corners...

- Is there a way to ACCELERATE rust?? I tried sprinkling water, leaving outside and so on, but I have still find a fast way to get an even rust-cover without any rests of millscale.

- Rust converters - any experience? What happens to areas that are not evenly rusted and still covered with millscale?

- Millscale - what would happen to millscale if it was painted over so it could not rust?

- Zinc flame spraying: what surface preparation is required? what about millscale and rust in that case? What about the heat?

- Liquid Zink applications a la ZINGA (http://www.zinga-uk.com/zinga_main.html) - does anbody have any eperience with that?

- If sandblasted (and I am afraid it will come to that), what are your experiences with different paint options, both for the first coat (Zinga, epoxy...) as well as for following coats


All ideas very much appreciated, even if I think I already know the bitter end...

Gerd

 

www.metalboatsociety.com - quite a few threads there.

 

Yago,

There is not a way to avoid sandblasting, I think. But after sandblasting, then it is advantageous to wash the boat with Chlor-rid. This solution will remove the salts from the metal, after sandblasting, so that it won't rust again. You can learn more about Chlor-rid at:

http://www.chlor-rid.com/

Eric

 

Hi Gerd,

Rather sand/shotblast the hull and paint with Epoxy paint system.

When I used to built boats, I once tried rust removers and converters. Were not impressed at all and this is to invite disaster.
The converter however, was the better call as it converts rust to fosfate and stays (according to manufactures) active under the paint. But this I doubt very much and your problem is that there are still mill scale present.

BTW, the surface after blasting (velcro like) give excellent purchase for the paint to grip.

 

Thanks for the answers ;-)
Yes, I know sandblasting and epoxy, have done it several times with excellent results and this is what I would recommend to everybody at all times. But I also know it's a royal pain, its very expensive and it does not improve neighberhood relationship ;-) It also requires a lot of timing, good weather, everything ready, never weld after it, and so on which creates a lot of stress.

My question is: what is second best??! What are the alterantives?

I have also done some research in other areas, not necessarily boatbuilding. In particular in restoring of vintage cars etc, there is one product that comes up all the time, that's POR 15, www.por-15.com, seems to be extremely tough, and comes with prior rust-neutralizer/etcher preparation as well as follow up topcoats, it's not just a rustconverter. I hear only the best about that stuff, tough, hard, bonds to metal, very difficult to grind off, flexible enough to work on springs etc without flaking, can be applied in humid conditions and so on... The underbody of a car lives, both mechanically and chemically in a far more agressive environment than for example the inside of a hull, no? I guess I will order some to run tests.
Gerd

 

I don't have experience with black steel, but I do with rust!!

Rust can be chemically removed using a Sodium Hydroxide solution. This is really brutal stuff though, it is usually found as a hot-dip for cleaning car parts. It doesn't eat mill scale to my knowlege.

mild acid wash will accelerate rust like crazy!!

I hate rust converters, I haven't found one that worked well for me. The labels on some of them suggest coating entire areas regardless of rust or not.

Mill Scale will promote rust even if you bury it.

 

If you want any life expectancy then you should shot blast. Any other treatment will only lead to high ongoing maintenance, paint disbondment and blistering. Mill scale will give you an active galvanic cell if any moisture gets in there.

If you cannot shot blast then you need to mechanically clean with abrasive disks and rotary wire brushes but inside access is poor in and around the framing for this method (at this point you realise that you should have bought pre-blasted pre-primed material) !

Prime the insides the topsides the deck and superstructure with a zinc rich primer. as immediately as possible to the freshly cleaned metal.

We have found that on the decks and superstructure and inside a vessel that that a zinc rich clorinated rubber base primer followed by a modern acrylic steel roof paint to be very effective cheap and easy to re-coat. In fact we now specify this scheme for steel work boats ( decks included) and despite the rough treatment it works as well if not better than other coatings. In the past we always specified epoxy zinc primer and epoxy topcoat but modern coatings are improving continually.

The clorinated rubber bases have the advantage of drying almost instantly and can be used to good advantage to follow along behind the shot blaster.

A steel boat should have an easily re-patched paint system to that end I would avoid at all cost the Polyurethane paints.

Bootline and below the waterline must be straight epoxy, no metalic undercoats. I have found vinyl or chlorinated rubber based paints a poor option below the WL.
Followed of course by antifouling.

The brands available in Australia will vary, but feel free to contact me if you want more information.

 

Thanks for the hints, Mike, but apart from the fact that pre-primed was not available here it's exactly the inside corners and welds that make that I would not have choosen pre-primed anyway. Most of the boats I have seen that were built outside from pre-primed were in such a poor state at the end of the steelworks, that to get a good result you would have been better off sandblasting all of it. It's not the open flat surfaces that are a problem, these could easily be done with a brush, it's the edges and corners and the welds where the preprimed is destroyed from cutting/burning/welding and inaccessible. I am not a strong believer in the virtues of pre-primed for outdoor amateur construction.

No need to convince me for blasting, been there, got the t-shirt (several, actually) and know it's the best .... what I am after now is the second best solution and an idea how much "second" that would be

Brands in Australia may vary, unfortunately over here in Hungary they do not

 

Yago
Ideally you do both , the material is de-scaled and primed at the steel manufacturer but the primer is not what we want for marine use anyway so it is just a anti-oxidisation coating for the duration of construction you then blast afterwards to remove the primer and clean up the weld zones prior to undercoat. The 2nd blasting is a less expensive and faster operation.
It all depends on your pre-primed raw steel price from the yard.

 

Sandblasting Alternative

There is an alternative to sandblasting and the product is currently being applied over rust on the largest casino boat (without berths) in the world in Michigan City, Indiana. Call me at 843-813-6402 and I will be glad to send pictures as well as literature on this patented product.

John Grey

 

My question is: what is second best??! What are the alterantives?


Teach a kid a trade and have the kid sand blast to WATER WHITE , the only way to a 20 year coating.

Then teach him to spray Epoxy!

Its only an extra a bit of currency ,

FAST FRED

 

thanks Fred, but you miss the point : this is the fifth steel boat I build, the other four were sandblasted and epoxied a quarter of a century ago and they were still as new last time I heard about them. So, no need to convince me
the question is: If it turns out that I can't sandblast, for different reasons, what is second best??

 

If you want to do the same good work as in the past years. None.

 

If it turns out that I can't sandblast, for different reasons, what is second best??


The Military used a "needle gun" which looks like an electric drill but the working end is an inch in diameter and contains dozens of needles that pound away at smaller areas.

IF you can limit your repairs to a modest area there not bad , as the residue is minor and can be vacumed up.

Hard on an entire interior tho,

FAST FRED

 

It's called a de-scaler and is commonly used by welders to clean slag off arc welding runs...