Prepping the steel plate without sandblasting

I can't afford sandblasting and it's a difficult thing to arrange in my marine yard in California anyway, so I've managed to grind off the mill scale and prep the external steel plate for painting with abrasive disks and angle grinders. In the last couple of months I feel I've aged ten years! It's like painting with a 20 pound toothbrush.

I've tried everything suggested to me by the usual boatyard pundits (the more expert they purport to be, the useless their suggestions usually are) and everything I can think of, including grinding disk types either solid or pads, treating with acids (yeauch), belt sanders, etc. etc. It seems like I keep having to go back to the bloody solid abrasive grinding disk and my trusty Metabo 4.5" angle grinder, though when I take a lot of painkilling drugs to qualm the arthritis I will use the 7" bugger.

HELP!

Who has done this themselves? I'm suffering the problem of getting through mill scale that seems to be exceptionally hard, and even the local marine hardware stores are amazed I go through abrasive rubber-pad disks in just a couple of square feet...

Here's a picture of what I've managed to do so far (note btw that I have beefed up the struts considerably):
http://api.ning.com/files/kbzCJdfD8...3C2Wx18d7wsaKsxh-uiTWC/PortpropellerApr13.JPG

 

there is a primer that sprays on clear and reacts to the rust and it turns to black paint. It somehow chemically bonds to the rust and turns it into paint. I have used it in automotive applications and it appears to stop rust dead. Than you paint on the color coats over it. I would look into that type of primer, all it requires is to get the loose scale off, the rest can stay.

 

I take it that buying or borrowing your own sandblasting equipment doesn't work?

 

No, the problem is busting through the mill scale. Rust isn't a problem, that's easily taken off, but mill scale on new plate is very hard to take off.

 

Buy a Karcher pressure cleaner and a sand blasting attachment like this:

http://www.pressureparts.com/2637900

 

Ray, I can't imagine tackling that work with arthritis so if you budget is tight, but you can drive, find a used one on Craigslist and sell it when you're finished. Saving yourself aches and pain has value as well you know.

What is the issue with using one in your marine yard? You're not allowed or you'd have to build a temporary enclosure or ?
Also, here in West Los Angeles, on Sawtelle Blvd, I can hire day-laborers who are eager to work. Save your back as well.


A quick search turned up these not far from you:

super cheap used one from SEARS:
http://losangeles.craigslist.org/lgb/tls/3750032846.html

This guy's asking $450 but says to make an offer:
http://losangeles.craigslist.org/wst/tls/3747440837.html

 

It's painstaking work with a grinder, and a few square feet is all I'd care to do by hand. Yes It's very hard and very well attached.

If it's left to weather it comes off much more easily but the secret is to send in off to be sand blasted before hand

One tool might be worth trying is a diamond abrasive cup disk in your angle grinder, they are commonly used for grinding stone and concrete but we use them often on decks to clean nonslip sand paint mixes and surface rust off steel where we cannot sandblast, they are easy to use since the disk is held flat. So they cover a much greater area than the edge of a grinding disk.
They are easy to use in the 5 inch size. I have not tried it on mill scale but I could get someone to try it on Monday.

By the way that P bracket in your picture looks like a very poor design.

 

Interesting, it looks like wet sandblasting can be added to any pressure washer and eliminates the dust issue.

According to wikipedia: "shipbuilders used to leave steel delivered freshly rolled from mills out in the open to allow it to 'weather' till most of the scale fell off due to atmospheric action."

 

The KArcher type sand blasting would be much slower than grinding. These sorts of tools are only good for very small jobs, unfortunately.

 

That's not true. I used it for rust and body coating removal when restoring classic cars. If you come too close or focus on the same spot just a few seconds too long. it quickly eats through the metal.

Just like classical sandblasting you can clean places inaccessible with grinders or brushes. But it is messy, especially when you use the sharp black grit Karcher sells in 25 kg bags.

 

You've hit the 'what do you have more of, time or money?' question.

Sand blast it. Preferably send the plate to professionals and get them to do it. That's what I did for an entire boat supply of plate. I'd do it again in a heartbeat.

I have a sandblast setup and I loathe it intensely, but nowhere near as much as I loathe getting mill scale off with an angle grinder.

PDW

 

I watched someone using one of these setups to try and blast clean a 30 foot steel boat below the waterline. They gave up after an afternoon and using lots of fine expensive grit, they had around 2 square meters well prepared at some high cost in grit and time, it actually failed to take large patches of vinyl coating off at all. But abraded surrounding steel deeply in the areas they kept going over. But it was slow. Maybe it would work better on mill scale.

I'm sure it would abrade rust well. And good for cleaning machinery parts. Have you tried it on large sheets to remove mill scale ?


There is one more solution which is pickling. Phosphoric acid baths are used in some steel industries to remove mill scale. But for a vertical or angled surface you have to get it in gel form sometimes called Naval Jelly.

 

The cup disks would be good if they work, using a grinder with one of these is more like using an orbital sander on steroids. The disk sits flat on the surface and is very safe to use even with one hand. They cover a large area in one pass.

 

> it actually failed to take large patches of vinyl coating off at all

Flexible coatings and sandblasting are a bad mix. I use thin rubber sheets on the areas that I want to *protect* from the sand.

 

Agree. I tried one of those 3M thick abrasive disks on a 5" angle grinder. It did work, was arguably faster than my sandblast setup, but the cost!!!! I think it'd run $80/m2 easily, the rate it wore down. I never tried more than 1.

Those diamond cup wheels may indeed be better in both speed & longevity but - fortunately for me - my interest is now largely academic.

Incidentally if you need some 4mm blasted & primed plate, I have most of a 3000 x 1800 sheet spare. Got 2 3000 x 1800 sheets with the mill scale as well - I was better at nesting than I thought I'd be.

PDW