Crevice Corrosion Repair Procedure

General boating discussion
ccaywood
Posts: 5
Joined: Wed Sep 02, 2020 10:35 pm
Location: Redmond, WA

Crevice Corrosion Repair Procedure

#1

Post by ccaywood »

Hi,

First off thanks for all the helpful information! I've looked through many posts on corrosion from this site before and after purchasing my boat and learned a lot and certainly appreciate all the effort to help others.

I'm relatively new to boat ownership and purchased a 2016 22' Hewescraft Ocean Pro in July last summer and am slowly trying to fix areas of corrosion. Most of what I see appears to be crevice corrosion with paint bubbles. It's not totally widespread, but there's 8 or 9 areas I've noticed in with paint bubbles indicating crevice corrosion. I'm trying to repair these areas in stages as I get time. At this point I'm working on eliminating the corrosion, then maybe later (months or years from now) look into repainting the spots for aesthetics. As a side note I'll be pulling the plywood flooring up in a month or so to see what kind of surprises are hidden below the foam!
typical looking paint bubbles before any repair
typical looking paint bubbles before any repair
IMG_4939.jpg (49.86 KiB) Viewed 683 times
another example before any repair
another example before any repair
IMG_4935.jpg (45.79 KiB) Viewed 683 times
after starting repair
after starting repair
IMG_4937.jpg (76.91 KiB) Viewed 683 times
Here's my plan for fixing each location, I'm looking for any advice/ feedback/ improvements/ additional steps you can offer. Thanks in advance!

1. Scrape off bubbles.
2. Remove white/ chalky substance down to bare metal. Use either sandpaper or scotch brite pads.
3. Treat area with Aluma Brite Aluminum Cleaner and Brightener (Bosh Chemical). Or if there's any other product recommendations, please advise. Rinse.
4. Replace any screws with passivated stainless steel screws. Passivate with CitriSurf 77 Plus. Coat screws with Tef Gel before installing.
5. At some point later, prep as required and re-paint.
kmorin
Donator 08, 09, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21
Posts: 1582
Joined: Mon Aug 18, 2008 1:37 am
Location: Kenai, Alaska

Re: Crevice Corrosion Repair Procedure

#2

Post by kmorin »

ccaywood,
lots of mid market mfg.s of welded boats still don't think leaving mill scale on their metal boats - then painting- is a key to insuring their boats begin to corrode in a couple years?

Even when the surface prep is done correctly, not shown here, holes are often too small for a paint film to stay as a liner; so.... the paint film has a sharp cut edge where water can get to the boundary between the metal and the coating- starting the local cells you show and lifting the paint.

In all truth, if you can find and install hot dipped galvanized fasteners- there's a WHOLE lot less galvanic potential- even with passivated SS- so hot dipped bolts are great in aluminum. Not very pretty but- much less reactive.

Also and this depends on the location, using a 'nylon' washer under bolt heads and nuts helps to insulate the SS from any contact with the aluminum under bolt heads/nuts etc. This can help make the interface less reactive (along with passivization) and last- over drilling and using a small section of plastic tubing is also a good way to prevent reactions galvanic or crevice. if a kit of this type of fastener is used, and then bedded with some insulating "goop"; Tef-Gel, Teflon pipe paste, or most of the silicon sealers, the site will have a limited supply of water and adjacent surfaces won't be so prone to reaction.

As to Aluma Brite? there are lots of products- the more reactive, aggressive expensive and dangerous they are- the better they seem to work. I have relied on Zep A Lume but have read on some posts that its hard to get in some locations? Depending on your paint repairs, you may want to build a small pot sand blaster to get into place where you can't get power tools' brushes, pads, discs etc? Messy, yes but what some vacuuming up compared to shortening the life of your hull?

Also if the boat isn't being stripped down far- I use a plastic bowl (Tupperware kind) just larger than the size of a sanding or buffing pad to kind of keep the 'throw' of the disc down to a local area. A hole in the bottom of the bowl set around the drive stud before the pad goes on leaves a cheap flexible container on the same plane as the abrasive. Easier to clean-up, there are some commercial products to do this, and I think they have vacuum hose attachments too.... but I try to keep the tool size down so I can get into tight spots, hose is good to have but makes lots of maneuvering kind or hard to do.

Good luck with your clean up and repairs,

Cheers,
Kevin Morin
Kenai, AK
kmorin
ccaywood
Posts: 5
Joined: Wed Sep 02, 2020 10:35 pm
Location: Redmond, WA

Re: Crevice Corrosion Repair Procedure

#3

Post by ccaywood »

Kevin,

Thanks for the reply. Yeah, price point was certainly a factor in choosing a boat. With some work hopefully I can fix some of the issues. I have a feeling it might be some trial and error on my part to figure out what works best for removing the paint and corrosion. I might try the sand blasting technique. There's some cheap sand blasters our there- do you see any concerns with purchasing a new one vs. building one?

Some of the fasteners are SS tapped into the aluminum plate with difficult access to the back side so I'll have to think about what I can do using hot dip galvanized fasteners. Not sure I can find the same thread pattern with the hot dip galvanized but I'll see what I can find.

Yeah, a search online I can't find Zep-a-Lume but i'll see if I can find an aggresive cleaner.

Thanks, Cory
kmorin
Donator 08, 09, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21
Posts: 1582
Joined: Mon Aug 18, 2008 1:37 am
Location: Kenai, Alaska

Re: Crevice Corrosion Repair Procedure

#4

Post by kmorin »

Cory,

here's some info about Zep http://images.zep.com/zepcorporate/tds/psr_1063.pdf its used by tank truck cleaners to get aluminum cleaned- not shined! So that is a place where the product might be available in your area?

As to SS fasteners tapped- especially self tapped screws- that is almost assured to be a galvanic site. Even w Tef-Gel, one side of the threads' surface is metal to metal in order for the screw fastener to hold or pull on the aluminum- so there's going to be a galvanic component to those sites and passivation is about the best you'll end up doing. When fasteners have the their threads rolled or cut-in SS anyway- the stress on the surface layer does release more free iron from the surrounding molecular alloy structure. But sealing the heads along with passivating the bodies will help reduce galvanic cell formation.

I understand that hot dipped bolts is limited to a bolt/nut combo and won't be available in a self-tapping or threaded bolt size so not an option. And if access to the 'back side' of a fastener isn't possible due to design, then threads are the go-to fastener anchor.

www.longlok.com/site/pdf/selfseal.pdf this link is to a thread fastener product line that has a built in O-ring machined into the underside of the head so that it forms a heat and expansion independent seal with the surface. Not inexpensive but... a way to improve the head's seal to the paint or aluminum surfaces. They are worth your consideration as potential to eliminate water penetration into the metal to metal thread joints in tapped areas of your repairs.

I usually build old fire extinguisher bodies into blasters- that way i can get a low cost quick opening top on a very small 3-4" dia X 10-20" long 'pot' and just tap or weld aluminum fittings on the side and bottom. I'm sure any small commercial blaster would work? Just hadn't seen one small enough to do the work I was picturing of a 4" -6" circle of lifted paint? Media can be lots of different materials as long as its not 'garnet sand' (!) for steel at 150 psi! just thinking of getting a white metal level clean surface that will 'dig out' the corrosion pockets better than sanding or even wire wheel and was compact enough to get into under sole areas or bilges.

Also in cleaning up corroded or lifted paint in small areas- there are paint removers that do great preliminary work. http://www.jasco-help.com/product/premi ... xy-remover this stuff has the dreaded methyl chloride and is noxious but... will lift almost any paint. There is a misconception that working this requires dilution water and that is not the absolute last word.

By dabbing it on like peanut butter, and letting it stand you can confine the very thick liquid to your primary area of work. Then instead of rinsing it off with water that runs every where- sprinkle a heavy coating of dry sawdust on the paint stripper. mix with a brush and the wood fibers will largely (98%) soak up the spent stripped and if you put a Scotch Brite (tm) pad on a DRILL motor with a 3" - 4" hook and loop pad while the two are mixing you will additionally scour the metal clean of paint. The saw dust acts as a very nice powdered abrasive, on the face of the abrasive pad, that lifts the partly dissolved paint film but does nothing but shin the underlying metal. That process will allow you to vacuum up the saw dust - even if its damp- and then use a damp sponge to clean any residue before using further tools to clean down into the aluminum.

This works very well to confine the patch cleaning to a well defined area on whatever surface of the boat you're working- without quite the level of mess usually associated with paint stripper. Once the metal is cleaned of paint, the work on the metal surface usually results in a dust that can be pulled out of the work area by a shop vac nozzle close by the work area? Just notes in case your work plan leaves as much of the boat serviceable as possible during the spot repairs?

Cheers,
Kevin Morin
Kenai, AK
kmorin
ccaywood
Posts: 5
Joined: Wed Sep 02, 2020 10:35 pm
Location: Redmond, WA

Re: Crevice Corrosion Repair Procedure

#5

Post by ccaywood »

Thanks again! I'll make note of all this for when I get further into the repairs.

I'll continue searching for Zep-A-Lume. There's one place online I found but shipping was over $100 for a gallon, perhaps due to the toxicity. Anybody aware of places in the Seattle area that sell it? If not I'll start calling around.

Yes, that was my thought as well on the SS screws- the Tef-Gel may help but still can't prevent the contact between SS and aluminum.
kmorin
Donator 08, 09, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21
Posts: 1582
Joined: Mon Aug 18, 2008 1:37 am
Location: Kenai, Alaska

Re: Crevice Corrosion Repair Procedure

#6

Post by kmorin »

Cory, PM AAB.com Forum coating expert (member name) Chaps... he's bound to know what, where, how much and if anything is available in the Puget Sound basin? Chaps is THE go-to expert (here) for all things to do with working on welded aluminum hull coatings.

Cheers,
Kevin Morin
kmorin
Chaps
Donator '09
Posts: 2184
Joined: Sun Jan 13, 2008 12:19 am
Location: Seattle, WA

Re: Crevice Corrosion Repair Procedure

#7

Post by Chaps »

Hey Cory, Ben's Cleaner Sales in Seattle will have aluminum cleaning, brightening products. Looks to me like you would do better with sandblasting though. You can pick up small, inexpensive blasters at harbor freight stores but blasting requires quite a bit of compressed air so you'll need a decent compressor but those can be rented for a day. Crushed glass blasting media (not glass beads) will strip those areas and leave the aluminum bright white and abraded, ready for an anti-corrosion primer and your choice of topcoat.
1987 24' LaConner pilothouse workboat, 225 Suzuki
Image
please view and like: https://www.facebook.com/bottompainting/
ccaywood
Posts: 5
Joined: Wed Sep 02, 2020 10:35 pm
Location: Redmond, WA

Re: Crevice Corrosion Repair Procedure

#8

Post by ccaywood »

Chaps- Thanks for the suggestions- those sound good. Yeah I've just got a small pancake compressor so may need to rent one for sandblasting. I'm thinking in while I'll take the plunge and investigate how the foam and aluminum look under the plywood. If there's additional corrosion down there, it makes sense to take all the foam out and repair it all at once with a sandblaster. The joys of owning a mid-market boat!

Thanks, Cory
Chaps
Donator '09
Posts: 2184
Joined: Sun Jan 13, 2008 12:19 am
Location: Seattle, WA

Re: Crevice Corrosion Repair Procedure

#9

Post by Chaps »

Definitely take the opportunity to remove foam and find all the issues. If it gets to be a bigger prep & paint job than you feel like dealing with yourself we could likely help you out. I've got a big sandblast system and shoot lots of alloy boats (mainly bottoms). Look up Agate Pass Marine, primarily on facebook but I have a small website too.
1987 24' LaConner pilothouse workboat, 225 Suzuki
Image
please view and like: https://www.facebook.com/bottompainting/
Tfitz
Donator '16
Posts: 341
Joined: Mon Jun 23, 2014 10:08 pm

Re: Crevice Corrosion Repair Procedure

#10

Post by Tfitz »

I found Zep-a-lume at a Kenworth Trucking supply store in Fairbanks. They use it to clean aluminum flatbed trailers
ccaywood
Posts: 5
Joined: Wed Sep 02, 2020 10:35 pm
Location: Redmond, WA

Re: Crevice Corrosion Repair Procedure

#11

Post by ccaywood »

Chaps- thanks, I'm hoping to find the motivation/ time to start tackling the foam soon- may reach out to you depending on how things look. It is bugging me a bit not knowing how it looks under there.
User avatar
gandrfab
Posts: 533
Joined: Fri Mar 28, 2008 12:33 pm
Location: Edgewater Fl

Re: Crevice Corrosion Repair Procedure

#12

Post by gandrfab »

Foam removal tool tip I have used with some success. Chuck the long end of a 1/4" Allen key in a hand drill. Plunge the spinning short end into the foam. Proceed with caution.
Post Reply Previous topicNext topic