Steel Motorsailer Rust....

[ausnp84]

Greetings all,

We've just bought a 40ft steel motorsailer and having spent most of yesterday removing 200-250 gallons from the bilges (she's on the hard), have found quite a bit of surface orange all through the bilges (as you'd expect).

Access is quite good and the epoxy coating seems to be in good condition, but I'd like to take it back to metal and recoat it.

We've just bought a rather handy Dremel tool with grinder attachment which I think would be very useful for the angles and corners, but for the larger flat sections and cross beams, would an angle grinder with a wire brush be more appropriate (larger cross section, more oomph)?

So questions:

- To take the epoxy coating off, angle grind OR can we just use a metal paint scraper?
- Once the epoxy is off, what type of grinder & wire brush should we use to take the surface rust off (there's a LOT of options out there)?
- SAE2.5 / bare shiny metal - does this just mean bare metal? Or is there a certain colour the metal should be when we're done grinding?
- Epoxy.... from bare metal, can someone please explain the process of repainting. Do we need to put on an anti-rust treatment first or from bare metal, just epoxy (Interprotect?) with 5-6 coats, then a good quality bilge paint on top?

We'll be pulling up all the floor panels beforehand and replacing them with much easier access panels - believe it or not, this boat has a full size bath tub also (!) and that will definitely be going as it's a water trap beneath.....

Thanks in advance for the assistance - I'm sure we'll be posting a lot more during the course of this project....

cheers,
nathan

[tommays]

SAE2.5 / bare shiny metal

I will assume which is never good there is finite amount of hull thickness which would mean you really do not want to remove much metal for paint prep

Anything proved to be in good condition may be best left alone

Anything you have to remove by Grinding is going to make a S??T Storm of NOT good for you dust

Chemical Stripper is not much fun but it will remove a lot of paint and get it to the point were it can be wire brushed for prep

Spot sandblasters with vacuum pickup while not cheep will prep it perfect and keep the mess down and remover very little metal

[bljones]

Unless you have at least 50-60 hours during which you really really want to contort yourself into uncomfortable positions whilst breathing through an irritating mask, looking through goggles and sweating through tyvek, I would pass on the angle grinder/ dremel route. Dremel tools are also known as "hobby tools"- your boat is NOT a hobby- it could be a damn career.

Tommays is on the right track when he suggests chemical stripping or media blasting. If you are insistent on getting the entire bilge back to bare metal, these are the only two routes to go, especially with epoxy coatings.

Frankly, i'd rather talk you out of stripping the bilges. If the existing finish is largely in good shape, I'd look at simply roughing up what is already there and applying another coat.

[ausnp84]

Originally Posted by bljones

Unless you have at least 50-60 hours during which you really really want to contort yourself into uncomfortable positions whilst breathing through an irritating mask, looking through goggles and sweating through tyvek, I would pass on the angle grinder/ dremel route. Dremel tools are also known as "hobby tools"- your boat is NOT a hobby- it could be a damn career.

Tommays is on the right track when he suggests chemical stripping or media blasting. If you are insistent on getting the entire bilge back to bare metal, these are the only two routes to go, especially with epoxy coatings.

Frankly, i'd rather talk you out of stripping the bilges. If the existing finish is largely in good shape, I'd look at simply roughing up what is already there and applying another coat.

Points duly noted and trust me, I'm not looking to take on any extra work when it comes to this project so anything that can be left alone, will be.

The concern is that the bilge was holding circa 180 - 250 gallons of water in it for the past year and whilst the epoxy is still present, I noticed once we'd drained the water out, a number of blisters appeared and popping one or two of these produced more liquid. One blister also burst itself and I noted some rust beneath it, hence the thought that perhaps removing the whole lot and starting again might be best. Chemical stripping sounds like it might be the easiest route to follow in order to get right back to basics.

I figured the dremel will make a good tool down the line - once everything is finished and the odd spot of rust comes up that needs a minor grind before repainting can take place.

[TQA]

I lived with a steel boat for 7 years.

You will not achieve a paint finish with good anti rust properties unless you grit blast back to SAE 2.5 AND paint it with zinc rich epoxy primer in low humidity conditions within 1 hour of blasting. In high humidity conditions you can WATCH the rust reappear before you get the primer on. !

So what to do. If your paint film is generally bad and you feel you have to remove the paint then gritblasting is the way to go but you will find it difficult to get a contractor to do this in the USA due to EPA and health considerations. There are places in Venuzuela that will do it though and it is dry there. Varadero Caraibe in Cumana is one.

If you have localised rust with small areas on bare metal grind treat with phosphoric acid then prime with zinc rich epoxy primer and follow up with two three coats of epoxy primer.

But do not expect long lasting results as you will have trapped rust there and the adhesion will not be perfect.

I used Sherwin Williams products and was happy with them.

Try their Fast Clad Zinc HS primer + Recoatable Epoxy Primer

Oh Yeah forget the Dremel. Get yourself a needle gun, a small angle grinder with sanding head and if you have larger areas a 12 inch disc sander.

Steel boats usually die from the inside so you need to pay attention to any areas that may have been hidden from regular maintenance esp inside water tanks that use the hull plating as part of the tank.

However as I am sure you know holes in a steel boat are no big deal. A good fitter welder can replate many square feet per day.

[billyruffn]

I'd second the advice of TQA and add the following -- let it dry out completely, then clean the paint surface as best you can. Break open a few of the blisters and see how far the rust goes beneath the surface. The dremel will be a good tool for this type of investigation but not much help with a really big job.

With the dremel grind the edges of a blister until you get bright metal and with a clean edge of paint adhearing to the metal -- no black or brown lines between shiny metal and paint. A blister 1/2 " in diameter might require grinding a 1" or a 3" diameter around the original blister. If you've got relatively few blisters and they don't require a lot of grinding to get to clean metal and good paint edges, then you might be able to "spot" treat the areas. If you have lots of blisters, sluffing rust flakes and find you need to grind big areas around the blisters, then it's a different story.

Bringing the spot repairs back is time consuming because the paint schedule will require: Ospho (or other rust converter), then an etching primer, then several coats of epoxy primers or bilge paint.

If you have a big job to do, and have the time, consider taking the boat somewhere with inexpensive labor rates. I'm not sure I'd go to Venezeula these days, but this type of work can be done very expertly in Trinidad. There may be other places in Central America, I don't know. Look for places where commercial fishing fleets lay up their boats for repair. They will have the sandblasting and metal painting expertise you need.

Good luck. Steel boats are a labor of love. And, trust me, you don't want to hit a rock in anything else.

[ausnp84]

Many thanks for the advice guys, it's exactly what we were after.

We're actually in sunny old England (not likely!) which makes the drying out quite difficult with winter on the way, but we have a dehumidifier working overtime at the moment and worst come to worst, we have plenty of other jobs that can be done before attacking the bilges next summer.

The other question I had is regading the cross beam supporting structure in the bilge. These are elevated and haven't been sitting in water, yet some of the paint is flaking away and there's a brown tinge beneath (nothing serious, just a bit of surface rust). I was thinking about attacking a few of these with the dremel this weekend just to see how deep any rust is - would I be correct this is the correct process?

- Grind back to bare metal
- Ospho / rust converter
- etching primer
- bilge paint

Between the first two points, do I also need to hit the bare metal with a wire brush in order to give it a better surface for the paint to stick to?

Many thanks again...

cheers,
nathan

[billyruffn]

You might want to hit everything with some acid first --- get something with phosphoric acid in it.

The “brown tinge” you refer to might be just surface staining. If it’s just on the surface and the paint beneath it is intact there’s not need to remove the paint. If the paint is flaking, it might have to be removed and treated as you described in your post.

Try cleaning the paint with a detergent and then with an acid bath. The acid will remove the rust stain from the paint surface. Then leave it alone for a while and see if the rust comes back.

Another rust removal tool that’s helpful in many situations is a metal hammer with a pointed spike on one side and a chisel like blade on the other. This tool is great for busting up flaking rust. If you hit rust with the pointy end, it will generally come loose. Paint that’s well adhered to the underlying metal usually is uneffected by the “tap, tap, tap” of this tool. (A needle gun does the same thing, but with less effort on your part).

The general rule in rust repairs is you use anything and everything at your disposal to get rid of as much of the rust as you can. The rust is ferrous oxide. What you want to do is get rid of the oxygen. Knocking off old rust gets rid of some of it, but unless you use a grit blaster you’ll never get it all. Rust converting chemicals (in the US the best know brand is probably Ospho) containing phosphoric acid will react with the FeO and strip off the oxygen molecule, replacing the O with a phosphate. I believe ferrous phosphate is essentially inert. You can coat it with paint and the paint stays put. If you don’t get rid of the oxygen the rusting process will continue. So, you grind off as much FeO as you can and then chemically remove what you can’t grind/sand off. Then coat everything with new paint -- to keep the oxygen in the air away from the metal.

Thus ends the chem lesson. Chip on, brave mariner!

PS. If you’re going to grind rust off make sure you’ve got a good shop vacuum and keep the inlet hose an inch or so from the grinder. If you let the grinding dust contaminate the surrounding area, you’ll soon have lots of rust stains on what is basically sound paint. Sweeping it up after you’re finished grinding doesn’t work very well. Strong suction is the way to go. Yes, rust sucks! But nothing beats steel when the water gets thin and the bottom’s hard.

[tdw]

Originally Posted by ausnp84

Many thanks for the advice guys, it's exactly what we were after.

We're actually in sunny old England (not likely!) which makes the drying out quite difficult with winter on the way, but we have a dehumidifier working overtime at the moment and worst come to worst, we have plenty of other jobs that can be done before attacking the bilges next summer.

The other question I had is regading the cross beam supporting structure in the bilge. These are elevated and haven't been sitting in water, yet some of the paint is flaking away and there's a brown tinge beneath (nothing serious, just a bit of surface rust). I was thinking about attacking a few of these with the dremel this weekend just to see how deep any rust is - would I be correct this is the correct process?

- Grind back to bare metal
- Ospho / rust converter
- etching primer
- bilge paint

Between the first two points, do I also need to hit the bare metal with a wire brush in order to give it a better surface for the paint to stick to?

Many thanks again...

cheers,
nathan

What BillyRuffin said.

You are heading into overkill territory. Cleaning up the 'brown stained' areas with acid ..we use a timber restorer/cleaner that has acid in it...will show the true story and I reckon you'll find most of it is as BR says...staining.

Exposing bare steel is the last thing you want to do as TomMays alludes to. We've found that liberal quantities of POR15 does work remarkably well.

POR15, Inc. - Stop Rust Permanently - Repair Gas & Fuel Tanks

though my yard manager reckons any old red primer works just as well.

[ausnp84]

And this is why I come here for information - many thanks guys. We have another weekend coming up in which to dry out the bilge, then begin throwing out a lot of the old interior (bathtub, mattress, cushions, stove), before taking down all the measurements for the wall panels that will be replaced. I'm thinking we'll let the dry bilge sit for a few weeks (with the dehumidifier running) to ensure everything is as dry as possible, then begin with the cleaning and rust removal. There are a couple of small holes that will also need welding up next summer so I don't want to do much repainting around those areas now (only for the welding to destroy the coating later) - more to follow!

cheers,
nathan