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Thread: Urethane, dont do it ??

  1. #1
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    Default Urethane, dont do it ??

    Hi. Im ready to paint my Tirrik but I bought Ian Oughtred's book "clinker Plywood, Boat Building" in the section on painting all Ian has said under the heading urethane is "don't do it"!

    my day job often involves coating concrete with epoxies and urethanes. so im thinking epoxy perhaps a primer then a filling undercoat then a good two pack urethane. Does anyone know if this is the way to go and maybe why Ian Oughtred got so down on urethanes for his boat designs ?

    I don't expect the Tirrik to spend more than a day or two in water
    Last edited by Stray; 07-11-2018 at 12:28 AM.

  2. #2
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    Default Re: Urethane, dont do it ??

    My experience with trying to roll on a two pack urethane product was horrible. The fumes were beyond nasty, the working time was too short, and the results were disappointing. Leave that stuff to the pro's, with decent spray gear, a proper booth, and a forced air respirator.
    Personally, I will never go there again, unless the stuff is explicitly intended to be applied with a roller rather than sprayed. YMMV.

    Pete
    Don't underestimate the power of stupid people in large numbers!

  3. #3
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    Default Re: Urethane, dont do it ??

    thanks pete. I will investigate that issue. does sound like a problem

  4. #4
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    Default Re: Urethane, dont do it ??

    I use only 2 part urethanes (LP) on my the outside of my painted boats anymore.
    Both are epoxy strip plank.,but I would not hesitate to use it on ply.
    I can understand avoiding it for timber/carvel.
    Dunno what Ians problem is for his glued ply boats.
    It lasts longer and better.
    Sands better without gumming the disc when the time comes.
    Brushes as well as paint if the correct solvent is used.
    Charcoal mask.

  5. #5
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    Default Re: Urethane, dont do it ??

    +1 on Wzbang comments. I have used brushable 2 parts with good effect. It requires 2 people to apply. One person rolls (with the correct foam roller) and the other wipes out the air bubbles with a foam brush. The results are close to a perfect sprayed application.

    Of course prep is the key.

  6. #6
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    Default Re: Urethane, dont do it ??

    Quote Originally Posted by wizbang 13 View Post
    I use only 2 part urethanes (LP) on my the outside of my painted boats anymore.
    Both are epoxy strip plank.,but I would not hesitate to use it on ply.
    I can understand avoiding it for timber/carvel.
    Dunno what Ians problem is for his glued ply boats.
    It lasts longer and better.
    Sands better without gumming the disc when the time comes.
    Brushes as well as paint if the correct solvent is used.
    Charcoal mask.
    And yes... lots of ventilation - as the isocyanates are extremely toxic. One can roll & tip with a basic mask, but spraying releases much more guck - and should involve both lots of ventilation, and a supplied-air respirator.

    I'm curious why Ian eschews urethanes. Was he talking about mono-urethanes... or two-part urethanes? the quote wasn't clear. I'd have no problem recommending two-part urethanes for his glued-lapstrake, or other plywood/epoxy, designs.

    OK... I asked him. We'll see what he says.
    Last edited by David G; 07-11-2018 at 09:56 AM.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  7. #7
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    Default Re: Urethane, dont do it ??

    Heard back from Iain. He says he was referring to 'polyurethane'. Based, I'm guessing, on some bad experiences early - which put him off the whole notion.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  8. #8
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    Default Re: Urethane, dont do it ??

    It's my understanding that LPU paints' isocyanates get into the air only when they are sprayed. In that case, a supplied air respirator is the only way to be safe.
    When rolled or brushed, only the solvents get into the air and a proper resoirator is sufficient protection. With a proper organic vapor (i.e. charcoal) mask. you won't smell the solvents. If you do, change to fresh cartridges.

  9. #9
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    Default Re: Urethane, dont do it ??

    Thanks to all. Sounds like its a go for two part urethane. I have a good charcoal mask so will use that. Looks like Ian might update his next book to include its use. What i find with doing floors with urethane is that it has very good uv resistance and it has better scratch resistance to epoxy. With scratch resistance I believe it has something to do with giving a bit rather than being harder and scratching.

    I just watched a great video on Off Center Harbour where a boat painter rolled the material on with a short nap roller then tipped it off with a two inch brush.

    The trick he used was working right to left (right hander) he would load his roller and begin rolling about a foot and a half ahead of his wet edge rolling back to the wet edge. The rationale behind this was that he was not putting a paint loaded roller over the previously rolled and tipped wet edge and thus getting to much thickness in this area. this technique ensured a more even roll coat.

    I live in brisbane Australia so temperature wise I might take the advice of asking someone to help roll while I tip it off. thinking this might end up with less brush lines. Good time of the year to do this as its winter here.

    Anyhow always amazed at how helpful you guys are. seems to be a generous culture. Sometimes we get a bit to much one upmanship over here rather than advice, probably a bit the same everywhere but im sure there is a culture of "doing a good job" in the states

    Ive been finishing the tirrik off as bought an unfinished boat. Will get some photos up soon. not perfect but better than it was. ive filled the rough scarf joints, epoxy coving and fiberglass tape etc. want a strong boat that looks ok to.

    Kind Regards Brendan
    Last edited by Stray; 07-11-2018 at 06:10 PM.

  10. #10
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    Default Re: Urethane, dont do it ??

    I actually think regular old one-part polyurethane gets a bad rap and never having witnessed any of the supposed horrible things it is supposed to be prone to, I kind of wonder where this information is coming from. We have an old cherry dining table that we inherited from my folks. My mother put polyurethane varnish on it way back when and it has seen hard use. She cut out the pieces for my sister's prom dress on it and my sister is now 68 years old. It still has the same polyurethane varnish on it today and though it's a bit duller, it would probably polish up fine with a little polishing compound. I've used Minwax polyurethane on several things, like my gun cabinet, and it is holding up fine. I used polyurethane floor enamel on the inside of several canoes over the years, some of which were done more than 40 years ago and still look OK, and my Old Town Guide has it on the outside. If somebody could tell me when this stuff is supposed to self-destruct it would help with my future planning.

    cabinet.jpg

    guide2-001.jpg

  11. #11
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    Default Re: Urethane, dont do it ??

    Nice gun collection Tod, the Canoo looks awesome. Quite like those solid colours with the timber. Opting for an off white with cream sail on the Tirrik at this stage. Hope to paint this weekend so better decide soon.

    In the seamless flooring industry one pack urethane is thought to be premium. Called moisture cure urethane. combines with water in the air to harden. Resealing the drum becomes a bit of an issue if using on smaller jobs after a while it can start to gel up in the drum. Moisture cure is more chemically inert than water based urethanes offering better resistance to tyre compound migration and various other issues such as spilt oil etc. Of course its dearer than water based urethane so price wise it only gets used on jobs where they want to pay more for longevity.

    There is a newer material called polyaspartic which is a branch of chemistry from a material called polyurea. its pretty impressive stuff on floors and ive always wondered about using it on boats actually. Citadel, a company in the states makes a single pack polyurea suitable for floors. It has more chemical hook points than epoxy. it sets up pretty quickly though so better to use primers such as epoxy first. Need to be super organised to use it. generally we have small containers with part A and part B ready to just combine and mix. We have a designated mix person who keeps the small batches up to the blokes on the rollers. its tough as though. really tough and has flexibility. comes in around 40 dollars per Litre. might not have the gloss level of a urethane though. Bit of a segway but interesting

    https://www.youtube.com/watch?v=2mJQta-c2B4



    they use the polyurea on tanks sprayed thickly from a proportioning pump gun with heated lines. very impressive stuff ive used it on a large water tank a high rise we sprayed some on a piece of cardboard a 1/4 of an inch thick. dries in seconds and is crosslinked so you can bend it in half, they spray this stuff on humbies for bomb proofing the floor. Absorbs the impact.

    I don't propose to know that much about the actual chemistry thats getting pretty sophisticated these days. Be interested to know if single pack urethane boat paint uses moisture cure chemistry, Sorting the paint out tomorrow and painting this weekend. Im getting prices from a couple of paint shops today. will consider single pack to cheers

    Brendan
    Last edited by Stray; 07-11-2018 at 08:22 PM.

  12. #12
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    Default Re: Urethane, dont do it ??

    I think there may be some confusion about what finish is being discussed. Todd is apparently discussing polyurethane bright finish which many, including me, have excellent results with. LPU is two part urethane such as Awlgrip which I consider the current king of painted finishes for long term life and gloss retention. It is toxic and calls for precautions as already outlined. I'd not use it inside in any method without a proper mask or positive pressure air hood. Sprayed, roll and tipped or brushed if all done properly give fine results. It is very expensive and calls for several expensive associated components and knowledge that takes a bit of a learning curve. Getting all that together with inevitable wasted material for a small boat may not be cost effective. All worth it though if you want the best results. Of all the finishes, LPU is the most unforgiving of poor preparation because it is so thin and any imperfections will telegraph through. Other urethane paint like Easypoxy or Brightsides are not really epoxy and have a distressing tendency to mildew badly, in my experience.
    Tom L

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    Default Re: Urethane, dont do it ??

    I agree with Tom. Polyurethane varnish is fine inside but useless under the sun. You don't need to roll and tip Awlgrip as long as you have the right foam roller. Unfortunately I haven't been able to find good rollers anywhere in Australia! I ordered a bunch from the US though and they work really well with Awlgrip. There must be some available here but I just haven't been able to find any. Don't be misled by claims that rollers are suitable for use with solvents - they generally aren't and just collapse.

    Rick

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    Default Re: Urethane, dont do it ??

    hi rick. your right I think. ive had a lot of issues with rollers. rubbish usually. We sometimes wrap tape around them first then unwind it pulling out loose hairs. I am putting down a solid colour but there is some varnish work. What do you suggest for the clear varnish. I have not got to working out what to use yet

  15. #15
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    Default Re: Urethane, dont do it ??

    ive noticed that i get mildew on everything that is not epoxied atm. wonder why at times. do you think its the ultra smooth and dense surface ? or amine blush ?

  16. #16
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    Default Re: Urethane, dont do it ??

    Quote Originally Posted by Stray View Post
    hi rick. your right I think. ive had a lot of issues with rollers. rubbish usually. We sometimes wrap tape around them first then unwind it pulling out loose hairs. I am putting down a solid colour but there is some varnish work. What do you suggest for the clear varnish. I have not got to working out what to use yet
    I just use a brush for varnish.

    The rollers I recommend for Awlgrip are not hair rollers, they're foam. But they're not ordinary foam - I'll let you know when I remember the brand. American, starts with C, I think, and the company makes very good badger brushes .... Corona, that's it. Look them up and see if you can get them here. Otherwise, call Awlgrip and ask them what foam rollers they recommend.

    Rick

  17. #17
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    Default Re: Urethane, dont do it ??

    Plus one for Corona brushes. My good brushes are all Corona.

  18. #18
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    Default

    I have used Interlux Brightside, a one party polyurethane, for years. It's pretty good, but a little picky about surface prep on multiple coats or repainting (get all the gloss off the undercoat). Use it mainly for the deck, as repairs are easy.
    I have also used their two part, Perfection, on topsides. It is a very good product, IMO. Rolls and tips easily, if you good with a brush, that works well also. Seems to last a long time.

    I have not put it on bare plywood, but have on epoxy.

  19. #19
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    Default Re: Urethane, dont do it ??

    Stray
    Re: Urethane, dont do it ??
    ive noticed that i get mildew on everything that is not epoxied atm. wonder why at times. do you think its the ultra smooth and dense surface ? or amine blush ?




    my interior is painted with brightsides polyurethane and it is beautiful and quite durable,
    but i am having a huge problem with mildew on every surface within months of scrubbing it back clean...
    i am thinking of switching paints (latex??) or maybe trying a biocide additive ??

    the boat gets plenty of ventilation; maybe too much, since it seems to be the moist salt air that starts things off

  20. #20
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    Default Re: Urethane, dont do it ??

    I think your on to something for sure, Might sound a minor point but i prefer to be sailing than cleaning off mildew.

  21. #21
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    Default Re: Urethane, dont do it ??

    Just a semi educated guess here but mildew wise im definitely thinking two pack. reasoning is crosslinking and less open carbon chains on the surface for mildew to get a hold on. I think it might be better than latex with a biocide

  22. #22
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    Default Re: Urethane, dont do it ??

    There is enough salt residue in the air to form a mildew-friendly film on surfaces like that, as well as on sails, upholstery, etc.

  23. #23
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    Default Re: Urethane, dont do it ??

    Looks like soap and water

    sail made yesterday. (Balanced lug rig) Left the extra reef point out (thanks Todd) went for the first reef and the top one only,

    Ive got an issue though. The original builder made the mast for for the gunter rig. My problem is that the mast looks about ten inches short now as the boom is two foot from the base of the mast at this intersection. (gunnels are two inches less), Mast is raked which will steal some of the extra height under boom aft. Taking grandies out so will somehow lift the boom to the correct height.

    for some reason he put a stainless rod in the top of the mast. presumably to strengthen the top to take the standing rigging. I was wondering about using this to dowel ten or twelve inches of extra mast on the top.Will send photos in ten but does anyone know if epoxying a mast extension on is doable apart from scarfing which I can also do if necessary

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