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  1. #1
    Senior Chief Petty Officer greg82255's Avatar
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    Default 2 Part vs. 1 Part Polyurethane Paint?

    Hello,

    I am planning on painting my boat in a few weeks, and I am looking around for different types of paint. I am looking at the interlux paints and I see 2 different types: 2-part polyurethane for $50/quart, and 1 part polyurethane for $25/quart. Here are links to the two types:

    http://www.********************/pc/IL...ane+Paint.html

    http://www.********************/pc/IL...nt-+Quart.html

    I am wondering if the 2 part paint is really worth the extra $25/quart, or if the Interlux Brightside 1 part paint will be good enough.

  2. #2
    Commander redfury's Avatar
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    Default Re: 2 Part vs. 1 Part Polyurethane Paint?

    $50/gallon is relatively cheap for paint considering the cost of some of the alternatives out there.

    Two part epoxy paint is going to be far superior in durability to 1 part paint.

    I use polyurethanes for hardwood flooring. The most expensive stuff I use is $125/gal. It is a water based polyurethane that uses a chemical catalyst. The less expensive stuff catalyzes with exposure to oxygen. The two part stuff is far superior and easier to work with in this case.

  3. #3
    Senior Chief Petty Officer
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    Default Re: 2 Part vs. 1 Part Polyurethane Paint?

    We painted our boat with 2 part on the hull and 1 part on the top. The bottom paint seems like its tough as hell. The top paint just seems softer. You can see pics on our thread in my sig.

  4. #4
    Seaman
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    Default Re: 2 Part vs. 1 Part Polyurethane Paint?

    For the most part any paint that incorporates a hardener is going to be more durable. I would never use a paint without hardener where looks and longevity are important.
    Chris
    1989 Baretta Success 185

  5. #5
    Petty Officer 2nd Class fauxmeister's Avatar
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    Default Re: 2 Part vs. 1 Part Polyurethane Paint?

    Sorry to break in but once the 2 parts are mixed what is your working time and can any leftovers be stored afterwards?
    Fauxmeister
    85 Rinker 15' Open-bow 115hp Chrysler Charger
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  6. #6
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    Default Re: 2 Part vs. 1 Part Polyurethane Paint?

    Quote Originally Posted by fauxmeister View Post
    Sorry to break in but once the 2 parts are mixed what is your working time and can any leftovers be stored afterwards?
    Maybe my comments will both re-enforce what's already been said and help to answer your questions.
    Polyurethane paint comes in 1 part and 2 part varieties.

    Both cure (not dry) like epoxy (epoxy is a cousin in the same plastic family). The curing process is by catalytic reaction between two chemicals. One part paints have the A & B chemicals mixed, but the part B, is deactivated by a third chemical that needs to dry away by exposure to air. Once released, the "part B" chemical does its curing reaction with the "part A".

    With two part paint you mix the A & B parts when you are ready to begin painting.

    You get 2 hours working time - ( for Inerlux Perfection @ 72 degrees F - other brands may vary ) The instructions are on the can and at the paint company's web site.

    Once the reaction has been triggered by mixing, all the mixed paint should be used. If only part of the paint is mixed, but leftover mixed paint is returned to a can of unmixed paint, it will still trigger a reaction that will slowly, but un-stoppably cure (harden) the whole can - even if the can is sealed closed.

    Since the 2 part paints mix more consistantly they generally produce a better finish.

    An error in judgement many 1 part users make is to re-coat before the first coat completely cures - which can take days in cool and/or humid working environments. The second coat prevents the first from ever curing completely so the entire job is perceived to be soft or forms wrinkles.
    .

  7. #7
    Petty Officer 2nd Class fauxmeister's Avatar
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    Default Re: 2 Part vs. 1 Part Polyurethane Paint?

    thanks...that helps.
    Fauxmeister
    85 Rinker 15' Open-bow 115hp Chrysler Charger
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  8. #8
    Lieutenant Commander NSBCraig's Avatar
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    Default Re: 2 Part vs. 1 Part Polyurethane Paint?

    Nice post saildan
    1982 Baja 16ss

  9. #9
    Captain erikgreen's Avatar
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    Default Re: 2 Part vs. 1 Part Polyurethane Paint?

    Yes, good info.

    Not to nitpick, but epoxy and most urethane based paints don't have a catalyst, but rather the two parts form the eventual coating completely, IE they combine. Some other two part systems are the same.

    Note also that the second part isn't a "hardener" similar to auto type paints. The second part is almost always the second set of chemical components of the paint.

    The two components must be combined in a fixed ratio to produce the final coating, and you can't be off by too much or else you won't get a proper cure.

    Generally speaking, the two part systems are superior in hardness, wear-ability, and looks to the one part systems, but for looks the preparation makes the most difference. Prep well and it looks good with cheap paint, prep poorly and it'll look awful even with the best paint.

    They're expensive, yes. Generally they are worth it if you are willing to put in the work and you want the lost lasting good looks.

    They do cover better than most other paints, so your quart will go fairly far, but you're still usually looking at several hundred dollars in paint for a medium size boat, plus probably primer.

    The boat will look nice though... many high end yachts are painted with a super quality paint called a linear aliphatic polyurethane that is harder, shinier, and more durable than gelcoat. Gelcoat is used because it's cheap and you can mold it, not because it's the best performance coating

    Erik
    Sea Ray SRV-210 - Winter refit
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  10. #10
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    Default Re: 2 Part vs. 1 Part Polyurethane Paint?

    Quote Originally Posted by erikgreen View Post
    Yes, good info.

    Not to nitpick, but epoxy and most urethane based paints don't have a catalyst, but rather the two parts form the eventual coating completely, IE they combine. Some other two part systems are the same.

    Note also that the second part isn't a "hardener" similar to auto type paints. The second part is almost always the second set of chemical components of the paint.
    Ummmm - yes and no - really, coatings are a recombinant whose linking in the final application stage is promoted by a catalyst.

    The combining you talk about requires heat. The catalyst a "base" is brought together with a "metal" and when they come in contact they react to create the heat necessary. In the presence of the heat the two plastic elements chemically combine in the final step of their "polymerization" to become a single solid (the paint we see).

    In manufacturing, creating a polyurethane product, like a foam billet, is an all at once reaction, but in the case of paint the components are being carried out into the field before the final combining reaction takes place.

    Anyway I thought keeping it easy to conceptualize was better than quoting DOW or Union Carbide -

    Excerpt from Wikipedia on Polyurethane's makeup and how different recombinations are used in different products - just in case you want the pizza with everything.
    The most important aliphatic and cycloaliphatic isocyanates are 1,6-hexamethylene diisocyanate (HDI), 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI), and 4,4'-diisocyanato dicyclohexylmethane (H12MDI). They are used to produce light stable, non-yellowing polyurethane coatings and elastomers. Because of their toxicity, aliphatic isocyanate monomers are converted into prepolymers, biurets, dimers, and trimers for commercial use. HDI adducts are used extensively for weather and abrasion resistant coatings and lacquers. IPDI is used in the manufacture of coatings, elastomeric adhesives and sealants. H12MDI prepolymers are used to produce high performance coatings and elastomers with optical clarity and hydrolysis resistance. Other aliphatic isocyanates include cyclohexane diisocyanate (CHDI), tetramethylxylene diisocyanate (TMXDI), and 1,3-bis(isocyanatomethyl)cyclohexane (H6XDI).

    Polyurethane catalysts can be classified into two broad categories, amine compounds and organometallic complexes. They can be further classified as to their specificity, balance, and relative power or efficiency. Traditional amine catalysts have been tertiary amines such as triethylenediamine (TEDA, also known as 1,4-diazabicyclo[2.2.2]octane or DABCO, an Air Products's trade mark), dimethylcyclohexylamine (DMCHA), and dimethylethanolamine (DMEA). Tertiary amine catalysts are selected based on whether they drive the urethane (polyol+isocyanate, or gel) reaction, the urea (water+isocyanate, or blow) reaction, or the isocyanate trimerization reaction. Since most tertiary amine catalysts will drive all three reactions to some extent, they are also selected based on how much they favor one reaction over another. For example, tetramethylbutanediamine (TMBDA) preferentially drives the gel reaction over the blow reaction. On the other hand, both pentamethyldipropylenetriamine and N-(3-dimethylaminopropyl)-N,N-diisopropanolamine balance the blow and gel reactions, although the former is more potent than the later on a weight basis. 1,3,5-(tris(3-dimethylamino)propyl)-hexahydro-s-triazine is a trimerization catalyst that also strongly drives the blow reaction. Molecular structure gives some clue to the strength and selectivity of the catalyst. Blow catalysts generally have an ether linkage two carbons away from a tertiary nitrogen. Examples include bis-(2-dimethylaminoethyl)ether (also known as A-99, formerly a Union Carbide product), and N-ethylmorpholine. Strong gel catalysts contain alkyl-substituted nitrogens, such as triethylamine (TEA), 1,8-diazabicyclo[5.4.0]undecene-7 (DBU), and pentamethyldiethylenetriamine (PMDETA). Weaker gel catalysts contain ring-substituted nitrogens, such as benzyldimethylamine (BDMA). Trimerization catalysts contain the triazine structure, or are quaternary ammonium salts. Two trends have emerged since the late 1980s. The requirement to fill large, complex tooling with increasing production rates has led to the use of blocked catalysts to delay front end reactivity while maintaining back end cure. In the United States, acid- and quaternary ammonium salt-blocked TEDA and bis-(2-dimethylaminoethyl)ether are common blocked catalysts used in molded flexible foam and microcellular integral skin foam applications. Increasing aesthetic and environmental awareness has led to the use of non-fugitive catalysts for vehicle interior and furnishing applications in order to reduce odor, fogging, and the staining of vinyl coverings. Catalysts that contain a hydroxyl group or an active amino hydrogen, such as N,N,N'-trimethyl-N'-hydroxyethyl-bis(aminoethyl)ether and N'-(3-(dimethylamino)propyl)-N,N-dimethyl-1,3-propanediamine that react into the polymer matrix can replace traditional catalysts in these applications.[18][19]

    Organometallic compounds based on mercury, lead, tin (dibutyltin dilaurate), bismuth (bismuth octanoate), and zinc are used as polyurethane catalysts. Mercury carboxylates, such as phenylmercuric neodeconate, are particularly effective catalysts for polyurethane elastomer, coating and sealant applications, since they are very highly selective towards the polyol+isocyanate reaction. Mercury catalysts can be used at low levels to give systems a long pot life while still giving excellent back-end cure. Lead catalysts are used in highly reactive rigid spray foam insulation applications, since they maintain their potency in low-temperature and high-humidity conditions. Due to their toxicity and the necessity to dispose of mercury and lead catalysts and catalyzed material as hazardous waste in the United States, formulators have been searching for suitable replacements. Since the 1990s, bismuth and zinc carboxylates have been used as alternatives but have short comings of their own. In elastomer applications, long pot life systems do not build green strength as fast as mercury catalyzed systems. In spray foam applications, bismuth and zinc do not drive the front end fast enough in cold weather conditions and must be otherwise augmented to replace lead. Alkyl tin carboxylates, oxides and mercaptides oxides are used in all types of polyurethane applications. For example, dibutyltin dilaurate is a standard catalyst for polyurethane adhesives and sealants, dioctyltin mercaptide is used in microcellular elastomer applications, and dibutyltin oxide is used in polyurethane paint and coating applications. Tin mercaptides are used in formulations that contain water, as tin carboxylates are susceptible to degradation from hydrolysis

  11. #11
    Captain erikgreen's Avatar
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    Default Re: 2 Part vs. 1 Part Polyurethane Paint?

    Quote Originally Posted by saildan View Post
    Ummmm - yes and no - really, coatings are a recombinant whose linking in the final application stage is promoted by a catalyst.

    The combining you talk about requires heat. The catalyst a "base" is brought together with a "metal" and when they come in contact they react to create the heat necessary. In the presence of the heat the two plastic elements chemically combine in the final step of their "polymerization" to become a single solid (the paint we see).
    Well, the reaction can be accelerated (or "promoted") by a catalyst, but the second can of the paint that you're adding isn't a catalyst (or isn't just a catalyst).

    Linear polyurethane coatings like Perfection (which is an acrylic polyurethane) form their final coating by combining isocyanate and polyol (alcohol with multiple hydroxl groups) compounds which are dissolved in a solvent. More solvent (reducer) may be added at use time, and so can an accelerator (probably a catalyst or a chemical to generate heat, as you say).

    When combined and applied, the solvent evaporates and the isocyanate and alcohol compounds polymerize and leave behind the polymer coating with the inert ingredients embedded in it, specifically pigments, anti-UV agents and the like.

    Anyway... one of the two cans you mix from is the isocyanate compounds, and one of them is the polyol compounds, and both of them contain pigments, solvents, etc.


    Erik
    "Chemistry is Fun"

    Edit: I just realized I completely skipped my point there. Two part polyurethanes don't *have* to have a catalyst. They react in each other's presence, that's why they come in two parts. You can add a catalyst to speed things up....
    Sea Ray SRV-210 - Winter refit
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  12. #12
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    Default Re: 2 Part vs. 1 Part Polyurethane Paint?

    Quote Originally Posted by erikgreen View Post
    Well, the reaction can be accelerated (or "promoted") by a catalyst, but the second can of the paint that you're adding isn't a catalyst (or isn't just a catalyst).
    It would take longer to fully cure without the induced heat than most people are willing to wait.



    Quote Originally Posted by erikgreen View Post
    Linear polyurethane coatings like Perfection (which is an acrylic polyurethane) form their final coating by combining isocyanate and polyol (alcohol with multiple hydroxl groups) compounds which are dissolved in a solvent. More solvent (reducer) may be added at use time, and so can an accelerator (probably a catalyst or a chemical to generate heat, as you say).
    Right, more than one process is at work simultaneously.



    Quote Originally Posted by erikgreen View Post
    When combined and applied, the solvent evaporates and the isocyanate and alcohol compounds polymerize and leave behind the polymer coating with the inert ingredients embedded in it, specifically pigments, anti-UV agents and the like.
    That would be the polymerization process. One of the chemical reactions. The one that creates the coating we are looking for.



    Quote Originally Posted by erikgreen View Post
    Anyway... one of the two cans you mix from is the isocyanate compounds, and one of them is the polyol compounds, and both of them contain pigments, solvents, etc.

    I just realized I completely skipped my point there. Two part polyurethanes don't *have* to have a catalyst. They react in each other's presence, that's why they come in two parts. You can add a catalyst to speed things up...
    Right again, if it were only the catalytic element it would be measured in drops not pints. But, it's also good to keep the two polymer components separate until just before use so we get two cans of goo rather than one can and one eyedropper of catalyst.


    True - polyurethane doesn't need any catalyst but you wouldn't want to wait that long for it to cure. Notice in all the manufacturer literature an accelerating catalyst is used.

    So, what's true in an absolute sense isn't always desirable in the functional application.

    .

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