DevPrep 88 alkaline de-greasing before painting

I have read through comments on use of acids like phosphoric on interior rust, and agree that is is best avoided.

I am prepping some dirty oily rusted areas, and considering an alkaline cleaner instead.

I can't get Devprep88 where I am working, so considering making a solution of water based detergent and weak trisodium phosphate. Lots of rinsing after of course.

Any experience with alkaline prep wash?

 

Phosphoric acid is a time tested treatment for steel. It works fine. You can use any strong detergent cleaner for oily areas. Ideally, use a hot water pressure washer with a detergent mixer. It adds the detergent to the water at the suction side. If they are really built up with oil and grease, you can first clean them with kerosene or diesel fuel and a wire brush.

 

Thanks Gonzo. Big controversy on using phosphoric acid on boats. The paint technical support people all told me to never use an acid, especially around pitting, as likely acid will remain there.

I also read that an alkaline environment discourages rust, so my thinking was that an alkaline de-greaser would be good.

Naturally the best is blast to white metal, followed by proper epoxy primer. Many paint companies claim "surface tolerant" primers that can go on over tight rust. The conversion coatings people all say good results over tight rust. Doubtful in my experience.

So the question is, if you just can't blast, what is the second best choice? I plan to de-grease, grind, needle gun and wire wheel, followed next by one of these:

1) Devoe 167 penetrating epoxy primer (very thin)
2) Zinc-rich moisture cure urethane primer
3) Phos acid conversion treatment
4) Traditional epoxy primer
5) POR-15 or similar conversion coating
6) Tannic acid treatment

All seem to have advocates.

After that I plan to build up the coating system with epoxy primers, likely coal tar as it is in the bilge areas.

 

My previous life owning a steel boat we tried almost every combination of otc preps. Sanders, needle guns, acid wash, grinding, converters.... you name it. After about ten years we bought a blast setup and ended up with the bummer conclusion that nothing even came close to long term adhesion. It sucked doing inside tanks, lazarettes and fish holds but the product held up long term.

Began to be a game of masking and air management to blast everything that needed paint. Was a miserable job, but nothing came close to keeping paint on steel.

 

Amen to that. I bought blasting gear too, and even did the inside of a lazerette. It was blast, stop, let the air evacuate then look at work, repeat 100 times.

There is just some cases where even wet blasting is too much, like around bilge frames of fully built sailboat, literally tons of woodwork all around. In this situation we need a second best option.

 

Hi Steelboat, my first text on this forum. I'm following you, as we are totally refitting our BR44 offshore, in Malaysia.
Can I ask what has been your final choice?
Cheers for now

 

Wow. Down to the bare hull. I think Malaysia is a pretty good place to do an interior build- although it's an epic amount of work any place you choose. We have good supply networks, easy customs and beautiful hardwoods at 1/10 the western cost. Paints, tools, materials and millwork is all very cheap.

I have been where you are at, when I built my interior in California. There will be a lot of challenges and days when you want to quit. I recommend going "all in" from the start. A covered work area, big compressor, huge axial fans for cooling, proper workbenches lots of lighting, wet sand blaster, and a comfortable house to recover at night. Keep a high but sustainable pace, make progress goals and take breaks for some fun, it will get done.

Number one unsolicited advice: It does not have to be perfect, it's your standard, nobody else's.

 

Thanks for all your advices and sorry for my late reply.
Just arrived in Langkawi for round 2..
Not yet gone to the boat, tomorrow will be the day if jetlag says ok..
About the standards, at 80% I'm not going to sandblast. It's a very difficult choice for me, but we have to balance a lot of things. And where we are is not allowed and move the boat at this stage it's hard... Tercoo, needle gun, grinder... We need the boat for the next 20 years, it's a compromise..
Anyway I would like to open a tread about our refit asap.
Cheers for now
Giulio

 

It was a cycle of blasting, stopping to let the air clear, checking the progress, and then repeating the process about 100 times.