Cast Iron Keel

[GordMay]

Originally Posted by blgklr

... A company says to first wash the keel with a 10% phosphoric acid solution and let air dry...

Indeed.

See: Rust converters

[blgklr]

Interesting reading Gord. So much differing information from what are supposed to be reliable sources make it hard to decide on the correct course to take.

[GordMay]

Remove loose rust.
Paint /w Ospho, air dry, then rinse /w water.
Prime, or not.
Then finish paint.
Por15 is a pretty good product, as is Epoxy.

[PAR]

The jury is still out or POR-15 (cyanoacrylate catalyzed polyurethane) as a submersed coating on steel, though other reacted polyurethanes have shown considerable promise (activated reactions).

On the other hand, epoxy has a proven track record (also an activated reaction). As for the above post about coal tar epoxy and the issues you had with it, well any product applied improperly will likely offer less then desirable results. It doesn't mean it's a lousy product, it just means it was applied by amateurs.

All the "rust converter" type products require rust to be present to work effectively. Ask any professional, that's regularly working steel and iron if they want any trace of oxidization on or in their final result and you get a clue about where and how to treat this issue. Ask any auto body professional, if during a restoration they left the rockers/fenders, etc. full of rust and just coated it with plastic goo and hoped for the best under the paint job. Pleeeease, it's doesn't take a rocket scientist to figure out what you have to do with rust.

[David M]

Sorry to say this but forget all those layers of crap and different chemicals. Iron will turn to iron oxide if it is exposed to oxygen, period. Its no more complex than that. I have tried all that stuff and can tell you from experience all it does is somewhat slow down the oxidation.

Also if you have a paint to iron interface, the iron oxide will blister up the paint regardless of whatever fancy coating you put over the iron. Nothing stops the paint blistering regardless of whatever fancy primers were put down over the bare steel.

The best way to prevent oxygen from getting to the iron is to create a tough as nails thick coating such as many layers of an epoxy coating that can resist being hit by something harder than it. As long as the iron is iron oxide free, the epoxy will adhere to it well enough. I have enough steel cable winches and steel hydraulic cylinders on deck to tell you that's how it works.

[blgklr]

I agree 100% with removing all visible rust first, I also agree that a coating that will eliminate O2 by preventing ingress of H2O is the proper solution. A long time ago when some of these products were first coming outI coated a sewage lift pump and motor that came out of a lift station. First I tried the product on a piece of rusty steel and then put the sample in a brine tank. It worked very well. So I'm not against the acid wash as it might eliminate some rust I can't see. Also if the maker of the epoxy says to use a primer before coating metal I would have to go along with that. Thank you all for the input it helps to hear other opinions.

[PAR]

There aren't any "makers" of epoxy as one might expect (all the resins come from just a few common sources), there are just reformulators. There are countless formulations, all suiting a specific set of physical attributes, but a reformulator is little more then an application specific chemist (I've done it). If an epoxy formulator is recommending a primer over the raw metal, after it's cleaned, then they should stick with what they know and avoid metals, because testing proves this to be the wrong way to seal out moisture and moisture vapor.

The three leading marine epoxy formulators all recommend the iron be abated to raw, clean material, then straight, unthickened epoxy applied as soon as it's dry, for best rust prevention. The key is film thickness and a minimum of 10 mils would be my recommendation. More would be wise, but you may want to incorporate reinforcements with the additional film thickness. These reinforcements would improve the physical qualities you might desire, such as abrasion resistance, surface hardness, impact resistance, sand ability (fairing), smoothness, etc.

I'm in contact with the chemists and technicians at West and other manufactures fairly regularly. They are very approachable, happy to help and can quickly resolve any concerns you might have. As a matter of fact give Tom Pawlak a call (I was talking to him two weeks ago) over at West System (the industry leading epoxy formulator) Toll free 866-937-8797 / 989-684-7286 / Fax 989-684-1374. They're good people, they know their stuff, they've done the testing and you'll be happy you called, trust me. Tell Tom I said howdy.

[barnakiel]

Originally Posted by PAR

The three leading marine epoxy formulators all recommend the iron be abated to raw, clean material, then straight, unthickened epoxy applied ... (...) ... The key is film thickness and a minimum of 10 mils would be my recommendation. More would be wise ...

OK. So at one place we hear unthickened epoxy only, at another place we hear 10 mils recommended.

Is it not difficult to achieve more than 10 mils on a vertical surface without thickeners (which at the same time may act as abrasion resistance improvers, rust inhibitor agents, etc) ?

I would guess this is exactly why companies like International enrich the epoxy with specific thickeners and re-sell under new names.

???
b.

[PAR]

Unthickened epoxy, applied to a film thickness of 10 mils (three coats under normal temperature ranges). No reinforcements, just activated resin. It's my recommendation of 10 mils, though most formulators suggest 8 - 10. It's wise to have more film thickness, but only to "harden" the coating, which is best done with reinforcements (fabrics, silica, shredded cotton, graphite, aluminum oxide, etc.)

Pre-thickened formulations are sold because they are very high profit items. You pay 10 times the cost of the reinforcement materials, which is just candy to the formulator. If you like, I can formulate for you, a special batch that smells like bacon, so long as you're willing to pay me extra (say 20% more then a regular batch) for the drop or two of fragrance I use per quart.

[barnakiel]

Originally Posted by PAR

Pre-thickened formulations are sold because they are very high profit items. You pay 10 times the cost of the reinforcement materials...

From a German chandlery one kg of West epoxy is 38 versus one liter of Interprotect or VC TAR for 30. Sure 1 kg not = 1 liter. But things adjusted, I still do not see the "10 times" factor. Note that you need many more layers per one layer of the thickened product to build up the thickness. (This also implies more work hours).

So, which particular epoxy vs. re-packed epoxy products do you have in mind when you say we pay 10 times more?

b.

[barnakiel]

Here, I am interested if someone can share a trick for the bottom part of the keel - how to apply the epoxy (and what other materials to use (e.g. glass)) to make sure the epoxy will not crack there when the boat is seated on blocks when in the boatyard.

And how is this issue solved with a lead keel (I think lead is quite soft and might deform still more than steel?).

barnie

[PAR]

Maybe it's a translation thing, but I don't see where there is something to argue over.

If you compare one 10 ounce batch of unthickened 105/206 West System resin/hardener by unit cost, to the say their Six-10 cartridge adhesive (also 10 ounces and the same resin) they use in the neighborhood of 3 ounces of silica and provide a self mixing tip with the cartridge, all for $2+ per ounce of mixed product. If you subtract the resin/hardener amount and assume they charge only the regular retail rate for it (yea, right), the 3 ounces of silica cost $4 per ounce. Now, I don't know about you, but I'm buying silica in bulk at about 43 cents an ounce, which isn't quite 10 times the rate, but close enough to make the point. They charge about twice as much per ounce of resin too, but that's a different issue and includes application specific packaging.

So, which particular epoxy vs. re-packed epoxy products do you have in mind when you say we pay 10 times more

All of them (all major formulators) are charging huge amounts for the addition of filler materials in their standard resin systems, no exceptions.

one kg of West epoxy is 38 versus one liter of Interprotect or VC TAR for 30.

How is it possible you can attempt to compare the price of different formulations from different companies. On the one hand coal tar epoxy isn't even the same product as the typical laminating epoxies used in the marine industry. It's like comparing apples to oranges and second, how is it possible to relate the pricing of these two quite dissimilar products from different manufactures?

how to apply the epoxy (and what other materials to use (e.g. glass)) to make sure the epoxy will not crack there when the boat is seated on blocks when in the boatyard.

The only reason a coating on a iron ballast casting might crack is if there's movement. There's several possible reasons for movement, but the usual reasons are, bubbles in the coating/sheathing, delamination of the sheathing, rusting under the sheathing or physical damage to the casting from impact.

This said, if the coating is applied properly and isn't left unrepaired from breechings when groundings or strikes have occurred, it should remain intact and not crack on the hard.

It's understood that often the bottom of a casting is beat up pretty good before haul out and repair. In these cases, you can only hope your coating/sheathing was thick enough and tough enough for the abuse. In this vain, I'd recommend a heavy silica, cotton fiber mixture on the bottom and wrapped around the ballast edges. This will absorb abuse, improve abrasion resistance and impact damage. Further improvements can be had with a Dynel or better yet a Xynole sheathing, some folks even spring for some Kevlar, but I don't see the cost benefit when it's all said and done for Kevlar.

The trick to not cracking the coating/sheathing when they haul your boat is to be there with some high density foam at haul out time and insert it as blocks or wedges between the ballast casting and the blocking. I have several 1/4" thick rubber mats I use for this very thing and they are placed between what ever blocking the yard uses and my boats.

[barnakiel]

Originally Posted by PAR

How is it possible you can attempt to compare the price of different formulations from different companies. On the one hand coal tar epoxy isn't even the same product as the typical laminating epoxies used in the marine industry. It's like comparing apples to oranges and second, how is it possible to relate the pricing of these two quite dissimilar products from different manufactures?

I thought you said they are all the same and they come from but few sources.

Could not find any ready made epoxy primer from West System.

Now, to give you apples and apples, I have looked up at West Marine:

International Epoxy - 50 USD,
International Inerprotect - 47 USD.

Again - where is the "10 times" factor you are talking about? If you talk specific formulations please let me know which ones.

The International VC Tar is not related to coal tar perhaps. They say it is an Epoxy based thing.

I am still digesting what you say about padding. I would think it does not matter whether it is soft or hard but more about how large is the contact area. Maybe (?) it would make sense to make a female form supports in hard wood for the boatyard to place on top of their (always too rough) blocks.

barnie

[brianontheroad]

A product like inter protect is just resin with aluminum oxide (west additive 422)-- not much reason to buy it other than it's pre mixed if you're lazy -- one thing everyone has left out is to wire brush THROUGH the first coat which should be UNTHICKENED epoxy

The unthickened coat is your "primer" to give you a clean surface to bond to so after sand blasting/grinding whatever wipe down with solvent immediatly and coat heavily with epoxy then wire brush through the epoxy to eliminate any flash rust

That's advice as per west systems when I called

[PAR]

Wire brushing is a technique that is also recommended, though if you apply the epoxy right after blasting, it makes little to no difference in film peel strength. I always have to brush it, because I work in a high humidity environment. You can see the iron rust before you eyes in just a few minutes. In the A/C portion of my shop, this wouldn't be necessary, but then again I would do this type of work in there, just from the mess.


Barnie, without a full dissertation of common epoxy formulations, you will be helpless to fully understand the typical combinations of materials, in the usual marine epoxy offerings, from the major formulators. Most folks don't read the material contents labeling, but in this conversation, it would be necessary. It would also be helpful to know why they use the different materials, but it's not essential for this discussion or then to understand these are "modifiers".

Yes, the base resins and hardeners come from the same places. Yes, the formulators add things to the resin and more so the hardener. All formulators do. Everything from reactive dilutes to unreactive modifiers and feature specific particulates, for every imaginable physical attribute is used.Hell, I've seen special formulations with real gold dust flakes added to the resin.


If you can't tell the difference between marine epoxy and epoxy based paint, then I can't help you. A quick tip, look at the solids content on both products. Paint is never 100% solids, but good marine grade epoxy always is. If the epoxy isn't 100% solids (except for epoxy based paint of course) then consider another brand. This is a common issue, the word "epoxy" is now a marketing device, so if any part of the diglylycidol ether of bisphenyl A molecule is used in the formulation of anything, even is in suspension only, it's used as a marketing ploy. This is how you get one part paints that have epoxy in the name. They're not really epoxy, but have epoxy elements in them.


As I said you need to know a wee bit more to understand things better. Coal tar epoxy, is epoxy, in fact the first polyamides developed during WW II. Typical offerings in today's market are 30 to 40% coal tar resins, most solvent free (or at least non-reactive), blended with a non-coal tar epoxy resin. This base mixture is then further modified. Coal tar mixtures are still in wide spread use, especially in difficult environments, such as under ground piping, contaminated environments, high elongation applications, etc. A fairly substantial percentage of garage floor coating where coal tar epoxy bases. From a hull or ballast coating point of view there's a lot to be said about using a coal tar base. And yes, it can be painted over.


In the early 1990's coal tar formulations came under fire from the EPA, and other organizations and since has fallen from favor, though still has a wide market range in industrial applications.

The 10 times factor if of the reinforcements used in both pre-thickened epoxies and primers (paint). Shredded cotton is a common reinforcement used in textured, hard coatings (some paints or as a fillet material in epoxy). Yep, that's right shredded bits of tee shirts. How much do you think a cup full of shredded tee shirts cost? How much do you think you pay for this material, when it's used in epoxy or a paint?

Yes, contact patch is also a key ingredient to blocking a yacht on the hard. Many yards will just sit her down on some chunks of 4" or 6" PT scraps. This patch is too small for a coated casting, though fine for other types of bottoms/keels, etc. I'll never let a yard yank one of my boats without specific instructions on how it'll be blocked. A custom keel trough is a good idea, if a bit cumbersome on larger yachts, though I think I'd still have some rubber between the hardwood trough and the keel.