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Old 28-12-2020, 10:41   #1
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Hull Stripping & Recoating Advice

I'm fairly new to CF and apologies if this has already been covered. I did search through the forums and couldn't find much on this topic so here goes...

I recently acquired a 36 LOA steel sailboat. The bottom paint was peeling away in many places due to so many layers of different types of antifouling and interleaved coats of primer/sealer. Also a few small spots of rust coming through. So I decided to strip the hull below the waterline as soon as it was hauled for winter (I'm up in frosty Canada).

I considered having the hull sandblasted by a pro but thought to save money by doing it myself. I've made several attempts at getting the layers of paint off. I've tried manual scraping, needle gun, grinder, orbital sander and manual sanding. Grit from 36-80, depending on what's available. Regardless of tool/technique, it is very slow and dusty work, even with vacuum attachments (yes I'm wearing a proper facemask with cartridges, eye protection and am fully clothed - I'd freeze otherwise). A couple days work and I've got about 5 sq ft completed. I estimate the boat to be 330 sq ft under the waterline. That runs to about 60 days of back-breaking work to get it cleaned to bare metal!

So, I'm looking for advice on how to make it go quicker and to achieve a surface quality that is going to ensure a good adhesion to the primer.

I'm considering buying a small used sandblaster i.e 80-100 lb and doing the sandblasting myself. Any advice on this such as what to look for in a (used) sandblaster, types of blast media to use, etc.? Also it is reasonable to think an amateur like myself could do the job well?

Another question is about protecting the hull once this dirty job is done. Advice on pre-primers, primers, and the process of getting the protective layers on, especially in cold weather? I have Ospho to convert any remaining imbedded rust to inert Iron Phosphate, I'm looking at Amercoat Pre-primer 167 and Amercoat 235 or 240 2-part epoxies for the first coats over bare metal but these paints are hard to source for non-commercial use up here in The North. Suggested sources/alternatives?

Thanks for putting up with this long-ish posting and I look forward to the wisdom and experience of the CF community.
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Old 28-12-2020, 10:52   #2
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Re: Hull Stripping & Recoating Advice

I built and use a cabinet sandblaster, and tried to go the same way as you are proposing in a very similar situation with a steel boat. The problem is that to do that job quickly you need a much bigger sandblaster, as in thousands of dollars on the compressor alone. I found that it was much cheaper to have it done by a pro.

Actually, I wish. The "pro" was new to boats and got sand in every imaginable corner of my boat, including sanding a very expensive laminated windshield. Do be careful who you hire - you can do a lot of damage with a sandblaster.
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Old 28-12-2020, 11:00   #3
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Re: Hull Stripping & Recoating Advice

Wow! Two potential traps for you in the same post. Now let's talk about bottom "paint." Every manufacturer has a different set of conditions for application, including such things as the roughness of the metal surface, the viscosity of the gin and tonic you fix afterwards, and the relative humidity at the precise temperature of application. Cut one corner, and it all falls off your boat the next week. That's why so many bottom finishes are labelled "professional" and are hard to get retail. The paint peoplle don't want to hear your tale of woe when it fails.

This is not to say that you cannot do it yourself. It is to say that you'll need to be very careful if you do.

I've been telling you about lessons I learned the hard way, having built a steel boat. Best wishes to you on your project.
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Old 28-12-2020, 11:15   #4
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Re: Hull Stripping & Recoating Advice

The only way to do a good job is sand/grit blasting and very quickly applying the first primer coat. Anything else will not be effective. ( I built a steel boat)
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Old 29-12-2020, 09:41   #5
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Re: Hull Stripping & Recoating Advice

Quote:
Originally Posted by steamgoat View Post
The only way to do a good job is sand/grit blasting and very quickly applying the first primer coat. Anything else will not be effective. ( I built a steel boat)
I very much echo the above quotes. Anything but sandblasting or blasting with something, is a waste of time and money. Grinding polishes the steel to much and is laborious. Use to small a compressor and you cannot maintain the high pressure and volume

required. 110 psi comes to mind but at high flow rates. Also you need the right blasting sand or grit. As far as I am aware you are not allowed to use some kinds in Canada.

We are in Guatemala where most anything goes. They use river sand here! They do a lot of wet blasting with river sand on fibreglass boats to remove antifouling. Works a treat. Doing so on a steel boat, outside only, might be an option followed by sweep blasting to remove freshly formed rust. (My idea, i have not heard it done, others might disagree. Would allow easier painting as final sweep blasting to the proper profile and standard would be fast.)

One boat out here, maybe 44 ft and deep draft, was quoted 2000 Yankee dollars for inside and another 2k outside. Suspect higher in Canada.

Re painting; when we did so in Canada we stopped every two hours to paint. And we only blasted and painted on cool dry days. Keep in mind you also have to complete the epoxy paint system when the epoxy is still green for each coat.

Also it cannot be stressed enough that the inside is far more important than the outside. Do nod skimp on prep and paint work there if you want it, the boat, to last.

We used zn rich epoxy on the topsides and deck and it has lasted for many man years. We also made everything inside easily removable so we can check and maintain.

Jim sv Gaia
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Old 29-12-2020, 10:50   #6
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Re: Hull Stripping & Recoating Advice

Search around for SODA blasting
Softer, works well
Less environmental damage
Bag the boat, blast, takes about a day... day and a half
clean ready for whatever coating immediately



Quote:
Originally Posted by Gaia View Post
I very much echo the above quotes. Anything but sandblasting or blasting with something, is a waste of time and money. Grinding polishes the steel to much and is laborious. Use to small a compressor and you cannot maintain the high pressure and volume

required. 110 psi comes to mind but at high flow rates. Also you need the right blasting sand or grit. As far as I am aware you are not allowed to use some kinds in Canada.

We are in Guatemala where most anything goes. They use river sand here! They do a lot of wet blasting with river sand on fibreglass boats to remove antifouling. Works a treat. Doing so on a steel boat, outside only, might be an option followed by sweep blasting to remove freshly formed rust. (My idea, i have not heard it done, others might disagree. Would allow easier painting as final sweep blasting to the proper profile and standard would be fast.)

One boat out here, maybe 44 ft and deep draft, was quoted 2000 Yankee dollars for inside and another 2k outside. Suspect higher in Canada.

Re painting; when we did so in Canada we stopped every two hours to paint. And we only blasted and painted on cool dry days. Keep in mind you also have to complete the epoxy paint system when the epoxy is still green for each coat.

Also it cannot be stressed enough that the inside is far more important than the outside. Do nod skimp on prep and paint work there if you want it, the boat, to last.

We used zn rich epoxy on the topsides and deck and it has lasted for many man years. We also made everything inside easily removable so we can check and maintain.

Jim sv Gaia
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Old 29-12-2020, 14:59   #7
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Re: Hull Stripping & Recoating Advice

What do the local commercial fishermen use? Most trawlers and work boats such as harbour tugs are steel. They will have worked out how to manage local circumstances and should provide you with a system that works plus they may give you some advice about just what to avoid.
They may even suggest that you have your boat done when one or more of theirs are being done. Potential savings all round (blasting, sharing bulk paint purchases etc.). Steel is a great material but needs to be treated with considerable respect when painting. Seek professional advice. It matters. Do it properly. Do it once.

if you go to a paint company, they may tell you what conditions you will need for the steel prep. and their paint application but they obviously can't assist you with how the locals manage the prep.
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Old 29-12-2020, 18:05   #8
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The work work you describe really requires professional equipment I have spent weeks at a time needling gunning rust out of steel barges.Duck tape the handle down put in your ear buds under the ear muffs then push for how ever long you can stand it.once you get most of the paint and rust off then sand blast to white metal.Its best to be ready to patch and paint as soon as you can.The sand blaster I used was a monster powered by a 1200cfpm screw compressor shooting coal slag abrasive..Any thing less explains the hodge podge paint matrix that has built up over the years.It aint rocket science
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Old 29-12-2020, 23:55   #9
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Re: Hull Stripping & Recoating Advice

You may find it interesting (and a very effective way to kill a bunch of spare time) checking out the Dangar Marine channel. He took an old steel boat and brought it back from the brink. He also was faced with the the issue of stripping the hull and you might find his choices and observations useful.


https://www.youtube.com/user/DangarMarine


Good luck
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Old 30-12-2020, 08:46   #10
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Re: Hull Stripping & Recoating Advice

Hi OP,

Good coating maintenance starts with proper surface preparation, usually with sand blasting to the hull. You can usually rent that equipment, but on a lower budget pressure washing and sanding by hand could also work (although it would be time consuming). You might be better off hiring a sand blasting pro...as the coating won't adhere properly if you haven't prepped the hull, and your coating system could fail after you apply it.

Once you've prepped the surface, you'll need to consider the right coating for you boat. The article I linked suggests an antifouling coating to handle the microorganisms that attach to your hull and eat away at it. Looks like Sherwin Williams and PPG have coatings that might do the trick.
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Old 30-12-2020, 09:06   #11
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Re: Hull Stripping & Recoating Advice

I didn't see this specifically mentioned in the replies, so will write it now: BEWARE silica sand and believe the warnings about potential for getting silicosis from blasting with sand.
Most tool rental companies of any size will provide large air compressors and grit blasting gear, usually requiring the renter to buy wear parts like the ceramic nozzles that fit in the gun, as well as extra charges for the respirator hood. They can supply suitable grit, such as "black beauty" which is often touted as safer than silica, but has toxic products since it is boiler slag.
Red garnet is better, but more costly.
Another concern is the breathing air you will need in the respirator hood.
It is possible to use air from the compressor with a few caveats.
Since oil burned by hot parts in the compressor may form hazardous oxides, including Carbon Monoxide, which can build up in your blood over time.
So, if they have a filter with a CO detector, add that to your rental bill.
Canada has an excellent workplace Health and Safety Executive that will have more information on this subject. In the US, we are to use Grade D breathing air or better.
Also, the dust on your clothes and in work area will expose you to respirable particles and increases the risk, so avoid dry blow off of dust.
Too bad your weather there will likely be freezing much of the winter, and not conducive to wet slurry blasting, which removes some of the concerns in the above.
A soda blasting contractor will make quick work of the job, and you'll have time and energy left to devote to doing a bang-up job on priming and painting. I've stripped with abrasives and with chemicals, and for that size job would definitely hire a soda blaster, if the service is available in your area.
One other thing to comment is how to treat the steel after blasting.
A quick way to protect the steel both in clean and areas with remaining small minor pitted rust, is to use a phosphoric acid wash like OSPHO, to treat the fresh steel and convert the minor pits.
Check with people who have experience using P-O-R coatings, as well.
You will find that the OSPHO pretreatment will help prevent flash rust in between the stripping activities, and the P-O-R or other coating system you choose. I don't know if you have access to Sherwin Williams Industrial/Marine coatings in your area (their motto is "cover the Earth", lol), but SW Industrial has helped me with coating systems for refinishing steel, and they have marine market penetration in mega-yachts and large ocean going ships.
Save your knees, back, elbows, shoulders and lungs for the days you will enjoy your pride and joy out there on the water.
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Old 30-12-2020, 13:05   #12
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Re: Hull Stripping & Recoating Advice

Sorry for this tardy reply. I was under the boat trying out some new techniques.


Wow! Thanks for all the advice. Let me synthesize what I'm thinking at this point:
  1. Probably best to wait until warmer weather i.e. March and hire a company to sodablast the hull to white metal, then get the chosen protective coats on ASAP before flash rust occurs. BTW I'm getting quotes around $CAD4000 so it's not a cheap option.
  2. Use the time in between to research and purchase the best coatings I can find/afford, so that there are no delays once the hull is prepped.
  3. Also use my time till March working on interior surfaces. In fact I'd already started this and have found a few very small spots - under the removeable lead ballast and around a couple thru-hulls. Therefore I'm removing all ballast and thu-hulls, grind away, repair and recoat. I'm also replacing most of the bronze or welded pipe thru-hulls with composite wide-base seacocks like the ones from Marelon or Tru-Design.
  4. My sailboat is a swing keel design with the keel recessing up into a keel box that is only 5" wide by 36" high and nearly 7 feet long. I doubt any sandblaster will be able to get a big nozzle properly into such a small space so I'm thinking to manually sand that all down over the next couple weeks to bare steel and prep for painting. I can easily isolate this small volume and heat it up to a suitable temperature/humidity for priming.
  5. I've already got the keel off and am sanding that down manually as well. I'll also use that and other associated cover/access plates etc, to test and refine my prepping & painting process. I might even do some destructive testing of a fully primed/cured part to see how it adheres.
  6. On these manually stripped keel and keel box surfaces I've found the following technique works well:
    1. 7" disc variable speed sander with 36 grit paper on very low speed (300-400 RPM I'm estimating) removes the layers with good penetration control, quickly, with little heat build-up and with very little airborne dust.
    2. Follow up with 5" orbital; sander using 40 grit paper, connected to a vacuum cleaner gives a rough but even finish, also with little dust creation.
    3. Knotted wire wheel on a grinder in rusted/pitted areas removes most embedded rust.
    4. OSPHO applied to all exposed metal does a great job of converting any remaining embedded rust to Iron Phosphate. Brush away the remaining white film with wire weld cleaning brush.
Ninedotsix, thanks for the Silica warnings. I've been reading up on that. There are good alternatives to sand, like Ebony Grit which has very low silica content. My main concerns now are to avoid being poisoned by the dust created by removal of antifouling. I'll also check out Sherwin Williams marine options.



Yes, we do have companies that do sodablasting up in my neck of the woods and I've contacted a few of them.

Calaban Alleria, I've been watching Dangar Marine over last several weeks. Whoa! My boat isn't nearly in that kind of state, thankfully. He's a brave guy and I've learned a few things from him. Mostly, "DON'T PANIC!" The most useful aspect of his videos is that I show them to my wife, so that when she then sees OUR boat's blemishes, she doesn't sweat them as much.

Bilgewater: Nice suggestion but not really practical for me to double up on some other boat work. I'm on the hard already in the middle of a yacht club. No commercial boats to be seen. Also, here in the Great Lakes, other than the Lakers, most commercial boats are plastic or aluminum, from what I can see.

I have one other question: As I'm sanding away, I find that the original (white coloured) barrier coat on the bare steel is in excellent shape and comes away very reluctantly. Would you recommend removing this anyway? I'm thinking that by keeping the primer layer wherever it is solidly intact and not showing any rust coming through, I have a "free" barrier coat that will supplement whatever I'm going to add. I also have less exposed steel to worry about flash rusting.

Thanks and looking forward to your further insights and suggestions.
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Old 31-12-2020, 03:00   #13
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Re: Hull Stripping & Recoating Advice

(Quote)
I have one other question: As I'm sanding away, I find that the original (white coloured) barrier coat on the bare steel is in excellent shape and comes away very reluctantly. Would you recommend removing this anyway? I'm thinking that by keeping the primer layer wherever it is solidly intact and not showing any rust coming through, I have a "free" barrier coat that will supplement whatever I'm going to add. I also have less exposed steel to worry about flash rusting.

Thanks and looking forward to your further insights and suggestions.[/QUOTE]

A very important point, to save effort and resources.
Maybe can you can identify the coating system, so you can use compatible system to the old edge, and for over coating.

It will help if you can get a qualified coatings expert to look at the substrate coating and help determine its makeup. Or, you may have available knowledge from the former owner as to what coating system was used.

It is probably epoxy of some sort.
Maybe a regular recreational marine barrier coat, such as Pettit Protect, or Interlux Interprotect.

Wondering if it resists solvents?

Cheers
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Old 31-12-2020, 09:03   #14
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Re: Hull Stripping & Recoating Advice

Hi Ninedotsix,


I will contact the PO. He is still in contact with original owner so perhaps I'll be lucky. Thanks for the advice!
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Old 31-12-2020, 12:00   #15
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Hull Stripping & Recoating Advice

Donít forget about bagging the boat or others may not like have blast material on their boat and you have to remove the blast material and paint off the ground
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