Another paint topic / how to treat rusty steel

[DocSjulle]

Hi.

 

This summer we bought a Dutch steel motorboat, a 40ft Pedro from 1986, because we love to spacious interior and have a dream of going  sailing on the canals in Europe.

 

It is in pretty good condition but needs some updating to the interior and electronics, and at the same time some insulation added.

 

We decided to start with the rear cabin and have removed everything down to the bare hull.

There was a good amount of flaking rust on the sides and some pretty thick scales on the bottom, but I have ultrasound tested it to still have 4mm of steel in the worst parts.

 

So no plates will need replacing, although I might fill the deepest pits with some pad welding.

 

I used a needle scaler and a Tercoo rotating blaster disc to remove all loose rust and paint, and have got at pretty good surface now.

But am still at bit unsure how to proceed to get the best lasting paint job.

 

I have bought some Hempel Hempadur 15570 two part epoxy primer per recommendation from the Pedro factory and a professional marine painter, and that should be possible to apply directly to the prepared steel, but I’m thinking if it might be better to use Owatrol CIP as the first layer, because it is thinner and might penetrate and seal the remaining rust better than the thick epoxy paint.

 

I also got some Brunox Epoxy and am doing a small test in the garage at the moment.

 

From the threads here on the forum I can see a lot of different opinions on rust converters, but I think the temperature is to low at the moment to experiment with that.

 

The sides will be insulated with Armaflex after the painting, so I don’t think there will be problems with rust anytime soon, but the bottom is left only in paint, and although is a dry area, it will still get condensation on it.

 

The small test I have started in the garage with the Owatrol CIP and the Brunox showed that the Owatrol smells a lot like turpentine, and the Brunox is a bit thicker and kind of converts the rust pits to black and encloses it in a sort of epoxy coating.

 

According to Owatrol it should be fine to overcoat the CIP with two part epoxy primer and get a good bond between the two.

 

Here are some pictures of the interior half way through the grinding job.

 

Regards

Kim

[DocSjulle]

Here are some more pictures after finishing the sides one most of the bottom.

 

Everything has been washed down twice with water and soap, and dried of with towels.

 

It is still damp and that it why it looks darker it really is.

 

 

[DocSjulle]

Here a some pictures of the rust found.

[BEngo]

You say above that the steel is still damp.  Unless you can find a damp tolerating  primer, leave it  well alone until the water has warmed up and the steel is no longer damp.  Ideally you want to paint the inside when the boat is on dry land and the weather is warm.  In the meantime I would treat it with Fertan, following the instructions carefully.  That should ensure that the rusting does not restart.  Now is a good time to do any repair welding though!

 

Then when it is warm  you need to choose a paint scheme that is suited to being wet for long periods in order to cope with the condensation.  International used to do Danboline, a specialist bilge paint but if it is still available the colour choice is limited. I expect there are others and any epoxy suited to below water use will be good.

 

N

[David Mack]

1 hour ago, DocSjulle said:

Everything has been washed down twice with water and soap, and dried of with towels.

Soap?  What sort of soap?  I would have thought that might have left a residue which would affect the bond of paint to the steel.

 

[dmr]

I have used Danboline over Owatrol CIP and this has lasted for about 8 years (and still looks mostly ok). I have also used a surface tolerant epoxy primer over steel just a little better derusted than yours. This also has mostly lasted well. The danger with epoxy is that if it does fail it detaches in sheets so can still look ok but can hold water underneath.

I have no experience of epoxy over Owatrol. Trouble is these are all potentially long term things so the only people who can really answer are those who have actually done this 10 years ago, and there are not many of those about.

[DocSjulle]

1 hour ago, BEngo said:

You say above that the steel is still damp.  Unless you can find a damp tolerating  primer, leave it  well alone until the water has warmed up and the steel is no longer damp.  Ideally you want to paint the inside when the boat is on dry land and the weather is warm.  In the meantime I would treat it with Fertan, following the instructions carefully.  That should ensure that the rusting does not restart.  Now is a good time to do any repair welding though!

 

Then when it is warm  you need to choose a paint scheme that is suited to being wet for long periods in order to cope with the condensation.  International used to do Danboline, a specialist bilge paint but if it is still available the colour choice is limited. I expect there are others and any epoxy suited to below water use will be good.

 

N

 

The steel is damp in the pictures because it was just washed with water for the second time.

 

The boat is on land for the winter, and right now we have 5-7 degrees celsius and it dried pretty quickly from the first wash.

 

I also got a dehumidifier I will be running before I start painting, and during some of the curing time.

1 hour ago, David Mack said:

Soap?  What sort of soap?  I would have thought that might have left a residue which would affect the bond of paint to the steel.

 

It was just a little bit of dishwashing soap in the water, and then washed down afterwards with plain water.

 

Everything will be wiped down with acetone before painting.

[DocSjulle]

1 hour ago, dmr said:

I have used Danboline over Owatrol CIP and this has lasted for about 8 years (and still looks mostly ok). I have also used a surface tolerant epoxy primer over steel just a little better derusted than yours. This also has mostly lasted well. The danger with epoxy is that if it does fail it detaches in sheets so can still look ok but can hold water underneath.

I have no experience of epoxy over Owatrol. Trouble is these are all potentially long term things so the only people who can really answer are those who have actually done this 10 years ago, and there are not many of those about.

 

I think that is what I saw when I started removing the interior, big sheets of porous paint/rust that could easily be scraped of the sides.

 

But I don’t think the required thickness was painted originally, as the paint sheets should have been thicker and more dense.

 

You are right about the long term answers are hard to find, but it is promising that your experience with both raw epoxy and Owatrol with Danboline are fairly good.

 

If I have the patience I might wait for my garage test to finish, before I decide what to do.

 

The issue is that the Owatrol CIP needs a minimum of 72 hours drying time before I can put epoxy over it.

[dmr]

Even without any paint rust often forms in sheets and I expect this is what you saw. Paint is not very strong so tends to flake off but epoxy is strong so a whole section can detach as a sheet.

 

Yes, Owatrol CIP does take ages to dry. This really is not a good time of the year to be painting baseplates, even if you use heaters the water will still keep the steel cold. 

[DocSjulle]

1 hour ago, dmr said:

Even without any paint rust often forms in sheets and I expect this is what you saw. Paint is not very strong so tends to flake off but epoxy is strong so a whole section can detach as a sheet.

 

Yes, Owatrol CIP does take ages to dry. This really is not a good time of the year to be painting baseplates, even if you use heaters the water will still keep the steel cold. 

The boat is on land for the winter and if I use a dehumidifier it should be possible to keep to steel dry.

 

I would have liked some warmer weather but as I need to rebuild the complete cabin I have to use all the time I can get.

[dmr]

9 minutes ago, DocSjulle said:

The boat is on land for the winter and if I use a dehumidifier it should be possible to keep to steel dry.

 

I would have liked some warmer weather but as I need to rebuild the complete cabin I have to use all the time I can get.

 

That makes it much easier. I am sure you know there are winter grade epoxies that set in colder weather, but even these can struggle at really low temperatures.

I think if it was me I would spend maybe a bit more time derusting and then go directly to epoxy. Design your fit out so that you can get access to most of the baseplate in future without totally destroying everything that you have done.

[David Mack]

1 hour ago, DocSjulle said:

It was just a little bit of dishwashing soap in the water, and then washed down afterwards with plain water.

Not sure what diswashing soap you have in Denmark, but here in the UK washing up liquid contains silicones, which leave a residue - which makes crockery 'squeaky clean'. Also contains salt, which can encourage rusting.

 

If you want to degrease derusted steel, washing soda would be a better option.

[DocSjulle]

11 minutes ago, dmr said:

 

That makes it much easier. I am sure you know there are winter grade epoxies that set in colder weather, but even these can struggle at really low temperatures.

I think if it was me I would spend maybe a bit more time derusting and then go directly to epoxy. Design your fit out so that you can get access to most of the baseplate in future without totally destroying everything that you have done.

Hmm, it sound like I’m maybe not done grinding rust 🥴

 

The Hempel Hempadur 15570 is suitable down to -10 degrees, it just takes longer to cure.

 

4 minutes ago, David Mack said:

Not sure what diswashing soap you have in Denmark, but here in the UK washing up liquid contains silicones, which leave a residue - which makes crockery 'squeaky clean'. Also contains salt, which can encourage rusting.

 

If you want to degrease derusted steel, washing soda would be a better option.

Thx for the heads up on the soap, I didn’t know that and will have a look at the bottle.

[dmr]

6 minutes ago, DocSjulle said:

Hmm, it sound like I’m maybe not done grinding rust 🥴

 

The Hempel Hempadur 15570 is suitable down to -10 degrees, it just takes longer to cure.

 

Thx for the heads up on the soap, I didn’t know that and will have a look at the bottle.

 

You prep look pretty good to me. There are some lumps in the third photo/second post that might need more grinding or possibly probing with a sharp chisel???

[DocSjulle]

7 minutes ago, dmr said:

 

You prep look pretty good to me. There are some lumps in the third photo/second post that might need more grinding or possibly probing with a sharp chisel???

Yeah I noticed that too in the photos, sometimes it hard to see anything clearly when you have been busting rust for days, with all the safety gear on and all the dust. And after a wash down more areas seem to pop up needing more attention.

 

I actually just got 2 new Tercoo discs as the 2 other are worn out. They are expensive but really worth it for the job they do compared to a knurled wirebrush on the grinder.

 

My plan is also to sand the sides with an orbital sander with a vacuum attached, to get some of the surface rust away just before painting, and then use the wirebrush for the last prep.

 

The rust was much worse in the starboard aft of the cabin, so I hope the rest of the boat will be easier the deal with.

At least the front cabin sides are still in a gray paint color (the parts I can under the bed).

[dmr]

5 minutes ago, DocSjulle said:

Yeah I noticed that too in the photos, sometimes it hard to see anything clearly when you have been busting rust for days, with all the safety gear on and all the dust. And after a wash down more areas seem to pop up needing more attention.

 

I actually just got 2 new Tercoo discs as the 2 other are worn out. They are expensive but really worth it for the job they do compared to a knurled wirebrush on the grinder.

 

My plan is also to sand the sides with an orbital sander with a vacuum attached, to get some of the surface rust away just before painting, and then use the wirebrush for the last prep.

 

The rust was much worse in the starboard aft of the cabin, so I hope the rest of the boat will be easier the deal with.

At least the front cabin sides are still in a gray paint color (the parts I can under the bed).

 

But remember that a smooth surface is bad and a rough surface is good to get best adhesion of the epoxy.

[Mike55]

I've previously used Vactan followed by Bonda primer and finished off with Danboline for a bow locker that does get water ingress through the scuppers. It's remained rust free for about 4 years now and still looks fine even though it has things like an anchor frequently stored in it. To my surprise the Danboline has been very resistant to the inevitable knocks. I used Vactan rather than Fertan because (I believe) Fertan requires washing with water after application which then requires to be dried. Vactan can go straight to the next coat once dry the following day.

[blackrose]

I wouldn't use owatrol under your epoxy. Seems like a bad idea to me unless that's what's recommend in the technical data sheet for the paint? I'm not familiar with your particular epoxy but have a look at the TDS. If you want to reduce the viscosity of the mixed paint you should be able to thin it with up to 10% thinners specified in the TDS (not any old thinners!). Only add thinners after parts A & B have been thoroughly mixed.

[blackrose]

11 hours ago, DocSjulle said:

 

Here are some pictures of the interior half way through the grinding job.

 

Regards

Kim

 

If that's halfway through your prep fair enough. You do need to get rid of all contaminants and the majority of corrosion in the pits. Even surface tolerant epoxies require clean substrates.

 

 

[Higgs]

If it hasn't already been said; clean small areas and treat. Cleaned metal begins to oxidise immediately. Get some paint on, then move on. In the water, this time of the year, that could be a tall ask. 

 

 

Edited December 16, 2021 by Higgs

[blackrose]

7 minutes ago, Higgs said:

If it hasn't already been said; clean small areas and treat. Cleaned metal begins to oxidise immediately. Get some paint on, then move on. In the water, this time of the year, that could be a tall ask. 

 

 

 

Yes, you should certainly do that rather than prepping the entire hull interior. Alternatively, prep the entire area but go over smaller areas just prior to painting them. 

 

By the way, you mentioned grinding earlier. I hope you're not using abrasive wheels that remove good steel? 

[Higgs]

11 minutes ago, blackrose said:

By the way, you mentioned grinding earlier. I hope you're not using abrasive wheels that remove good steel? 

 

Must be the OP you refer to. But I personally wouldn't go heavy with the grinding wheels. And don't mention needle guns. Used one for fifteen minutes, and knew I wanted my hearing more. 

 

Heavy pitting on horizontal surfaces is always likely to trap water in the future, I would be inclined to use an epoxy filler. 

 

 

 

Edited December 16, 2021 by Higgs

[blackrose]

1 hour ago, Higgs said:

 

Must be the OP you refer to. But I personally wouldn't go heavy with the grinding wheels. And don't mention needle guns. Used one for fifteen minutes, and knew I wanted my hearing more. 

 

Heavy pitting on horizontal surfaces is always likely to trap water in the future, I would be inclined to use an epoxy filler. 

 

 

 

 

Yes sorry, quoted you but I was referring to what the OP had said earlier about grinding.

[DocSjulle]

I mostly used Tercoo rotating blaster discs for the electric drill, as that removes paint and rust pretty easy while not polishing the surface or removing base material, and leaving sort of a hammered finish.

Then the needle gun (wearing earplugs under the hearing protection) for the heavy scaling on the bottom, and a chisel between the hull and stingers.

 

My plan right now is to go over the sides again in smaller sections, and wiping with acetone and painting as I go.

Edited December 16, 2021 by DocSjulle

[Mike Adams]

Looking at your boat I would guess that most of the water has come in via the rudder stock. Make sure you have no wear in the bearing and the seal is good otherwise as soon as you load the rudder  with the engine running water will seep up the shaft and into the bilge. I have coated the bilges in the past with some sort of wax/oil grease made in Holland. I forget the name now but it's what they use in dutch barges.