Sandblasting - or?

[gonzo]

A de-scaler or needle-gun will dent the plating on a boat. They are OK on a ship's plating or heavy machinery.

[alaskatrawler]

The best way in my view is to sandblast to white metal (dry). However a few of the large ship yards around my area (seattle) are water blasting, in other words using blast media mixed with high pressure water. I have been told this method works well. I have not witnessed it but it may be worth checking out further especially if dust from dry blasting is a concern. I questioned this method with our local Ameron Rep and he stated that the modern coatings they carry can be applied over wet blasted steel even if it has turned orange. Anyway may be worth checking out.

[cyclops]

I would go for the wet blasting if the residue left on the steel was going to improve the paint bond. Otherwise, forget it. Why go backwards?

[FAST FRED]

"Why go backwards?"

The goodfolks that daily repaint supertankers and other ships think water blasting is a huge step foward.
No tons and tons of "toxic waste" medium to dispose of and the entire process is quite automated.

The inside of a cruising boat probably will not be fun with water at 40,000PSI being blasted about.

FAST FRED

[yago]

[quote=FAST FRED
No tons and tons of "toxic waste" medium to dispose of ...[/QUOTE]

wet blasting also needs medium, or do they use just water?

I have seen normal (but strong & good quality) home pressure washers being mentioned somewhere, maybe for car repairs, can't find the reference, with add on tubing and nozzel to add media - anybody has any info or experience on that?

[alaskatrawler]

I wrote in an earlier post about the possibility of wet blasting. I feel it is probably the way sandblasting will be done in the future because of the enviromental concerns of dry blasting.
One thing I forgot to mention is you can buy for a conventional blaster what is called a water ring or WIN Nozzle. This device mixes water at the rate of 2 to 6 garts per minute to a conventional blast stream. It removes about 90% of the dust associated with dry blasting. If I were to use this method I would dry blast the interior of the vessel and use the wet nozzel on the exterior.
I do know a boat builder who used a 4000 psi pressure washer with a sand mixing nozzle,. The abrasive he used was fine silica. The pressure was enough to rmove the mill scale but was very slow. This may be because of the media he was using. I hope this info helps.

[yago]

Originally Posted by alaskatrawler

I do know a boat builder who used a 4000 psi pressure washer with a sand mixing nozzle

Yes, that sound interesting, if it is efficient enough. do you still have contact with that builder?
Also, like that you could do it bit by bit, over time, and speed would not be an issue, neither the weather. One problem with sandblasting is that you really need a lucky stretch of fair weather for the time you rent the equipment, and every interruption costs lots of money.

[FAST FRED]

40,000PSI is NOT avilable from the usual pressure washers. The commercial units have 200 to 400hp engines.

If a hand held unit could be worked inside the Rustibus system might work.

www.rustibus.com

FAST FRED

[alaskatrawler]

I still know the builder he is a friend of mine. However I would seriosly look at the water ring or WIn Nozzle either of these would be much better than using a pressure washer with sand injection.
The water ring and/or Win nozzle cost about 45 to 200.00 US dollars. For more information on these nozzles go to www.marcousa.com.
I assume you already have the dry blasting equipment so this would be a minor cost to pay for removal of 90% of the dust. After all that is the biggest concern about dry blasting. The pressure washer uses twice as much water and would be very slow. I guess if you were removing paint it would be faster but any tight millscale would be much slower. If time is no issue I am sure the pressure washer would do the job. A 3ft X 3ft area took about 45 minutes to remove the millscale. Another issue is the feeding of the media... the pressure washer has to suck up the sand out of a tub which also contibutes to erratic feed etc. Let me know if you need more info.

[D'ARTOIS]

Just as everybody else had said: there is no real substitute for shot-blasting.
It is as simple as that.

We have the strongest environmental laws in the world here in Tulipstan and I they trap you shorblasting w/o proper measurements, you may find yourself in goal.

If you have a boat build out of black steel - even with mill scale on - then you should blast and blast - there is no other option.

If you go for a next boat, use steel that is preprimered.

In that case you can use substitute methods.

[cyclops]

Curious. Would the flailing balls type of paint chippers used to remove all the dried paint on paint spray booth floors also work? No air or water problems.

[yago]

Originally Posted by alaskatrawler

I still know the builder he is a friend of mine.

Yes, if you could create a contact, I would appreciate, thanks.

[quote=alaskatrawler]I assume you already have the dry blasting equipment so this would be a minor cost to pay for removal of 90% of the dust. [quote]
Well, no, I do not have that.So it's really all open.

There are 4 main reasons against blasting:
Noise - my neighbours are already not very happy about the grinding and the rustpile in the garden. That would go also against needle treatment it seams
Dust - could dbe diminished with a water ring
Cost
Timing - if I have to rent the material, timing and planning becomes difficult, and I have such a busy day-job that I would find it near impossible to get a clean, sunny, free week, plus prolongations it the weather turns bad, the sand runs out, the compressor breaks down etc. I have had all of that before, and am not getting any younger either, so the only alternative would be to hire somebody else to do it, which again increases cost and at the same time will maybe not give me the perfect result I would get if I did it myself.

When I was doing my last boats 25 years ago in france, there were people that would, over the weekends, sand your hull for less than it would cost you to hire the material, but here in Hungary I have not yet managed to find anbody. I have heard first prices of about 15 to 20 euro / square meter, plus sand, plus paint and they still want me to transport the hull to their place and back, so cost is a very real issue.

All of the above, combined, make me think I might have to look for a solution where I would get a reasonably good long term result inside, and where I get a couple of outside years that would give me the time to find a place later where I can get a proper blasting and eopxy job done for the outsides on a key or riverbank somewhere else.

[alaskatrawler]

Hello Gerd

I have been in a similar situation as far as weather was concerned. I built a Roberts kit hull a while ago. Built the hull in a tent outside. When I got the steel it was pre-primed but it did not take long for the hold over primer to start rusting. It took me about a year to get it ready to concentrate on getting paint on the exterior. I accomplished this by renting a 600 lb blast pot , a 375 cfm air compressor. I blasted on decent days only enough area that I could get a coat of epoxy primer on the same day. This strategy worked quite well. I did not have the neighbor problems you write about so I was lucky there. I don't know what yopur budget is for the project you are involved in, so what worked for me may not be workable with you. If you care to discuss the issue further my direct e-mail is alaskatrawler@comcast.net. I will be glad to help anyway I can.

Dan

[FAST FRED]

Sherwin Williams and other Industrial paint mfg have sites where paint for bridges , tanks and oil rigs is sold.

If you cruise the site you will find the surface preperation required varies . Perhaps you can find a paint system (even if it needs to be imported) that will work on steel in salt water with only surface grinding , or brushing with a power brush cup in a grinder.

Many of their No skis paints work great on decks .

Good hunting,

FAST FRED

[FAST FRED]

You may also wish to look at www.aurand.net .

They offer hand held units that might meet surface preperation specifications, for close enough to sandblasting.

FAST FRED