Advice on recovering a mess of polyester over plywood

Discussion in 'Fiberglass and Composite Boat Building' started by jwt, Jan 23, 2011.

  1. jwt
    Joined: Jan 2011
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    jwt New Member

    Hi.

    My first post here, spent a week searching back as far as 2005 looking for info on this.


    looking for guidance or opinions on reworking a bit of a mess.


    12M2 of 18mm marine plywood has been put down on a commercial fishing boat due to previous deck rotting out. Underneath was treated with what I believe to be a 2 part polyurethane

    an attempt to sheath with polyester and csm failed due to contamination from a diesel fired space heater emitting smoke and low temps resulting in de-lamination from the plywood. Possibly some moisture present as well.


    Customer does not require a smooth or glossy finish.


    My plan of attack on this is to ....

    remove the polyester/csm using a blades and hot air guns.

    Abrade the surface using 40 grit flappy wheels on a grinder until clean wood is found.

    Clean using acetone to remove any traces of contaminant

    Tent the area and try to maintain a temp of 10 degrees C (50 F)

    Caulk all gaps using TEC 7 (http://novatech.eu/index.php?st=products&prodkey=tec7&taal=en)
    In particular I'm thinking of using the Tec7 where the deck meets the gunnels to allow some flex rather than thickened epoxy as a putty????

    Apply epoxy using a fast hardener to cover me if the temperatures stay low and two layers of 280g/m (9 oz?) twill weave fabric.

    Makes sense?

    Things that worry me.

    Low temperatures, daytime temps are hanging around 5 to 8 degrees C.

    Contamination of the marine ply possibly polyester has soaked in a good bit, will I end up grinding a complete layer off the ply?

    Is two layers of 280g/m2 twill fabric enough, I have 390g/m2 (13 oz) twill in stock as well. Is it overkill?

    By my rough calculations 2 layers of 280g/m2 fabric over a 12m2 area will require 10 kilos of epoxy?

    Thoughts or comments welcome

    John
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Just noticed something: don't think I'd clean with acetone since it is hydroscopic and will leave the surface damp and perhaps allow the wood to absorp some of the moisture-defeating your purpose. Alcohol might be better....
     
  3. gonzo
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    gonzo Senior Member

    I've never had problems with acetone. Alcohol is hygroscopic too, that is why it is used to absorb water contamination in fuel.
     
  4. Doug Lord
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    Doug Lord Flight Ready

  5. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    Well, they say polyester won't stick to epoxy but epoxy will stick to polyester so you might be OK on the "Contamination of the marine ply possibly polyester has soaked in a good bit, will I end up grinding a complete layer off the ply?" question.
     
  6. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Defeats me why pulling the sheathing off isn't as easy as peeling a banana, unless the ply surface was scored to give a mechanical key.
     
  7. fiberglass jack
    Joined: Dec 2005
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    fiberglass jack Senior Member

    after you have grind the wood down and cleaned with acetone ( dudes a irishman he wont waste Alcohol Iam a mick myself from north co dublin ) try drilling a **** load of hole into the ply at a 45 degree angles them thickin up some resin with cabosil and milled fiber and fill in the holes as you lay down the glass this way you will get a good mechanical bond dont worry u wont weakin the ply wood only make it stronger
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Acetone will not harm anything, in fact it will dry things out to the contrary of some concerns. Remove the poly as best as you can, but don't get too anal about it if it's really well suck, just hit it with a 36 grit disk and get real aggressive about the tooth you put in the surface. Actually, 16 or 24 grit would be noticeably better.

    Epoxy will stick well to the polyester, so your major concern is temperature control for the cure and sufficient tooth for the epoxy to grab a hold of. Rig a tarp over the work, sealing it to the work or shop floor or ground. Place a space heater or two under it and leave it this way until you've got a good cure. Now you're probably suffering with winter's worst about now and so are we, but I've made epoxy cure in freezing weather with space heaters, the trick being they have to be under a good tarp, that is not letting in any cold air. I usually nail 2x4's to the shop floor or the ground outside to keep out drafts. They'll work like dogs at first, but once the air under the tarp is warm, they'll have an easier time of it.
     
  9. gonzo
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    gonzo Senior Member

    We use infrared lamps with good result. They call them "pig lamps" here.
     
  10. michael pierzga
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    michael pierzga Senior Member

    "Clean using acetone to remove any traces of contaminant"
    Be wise with acetone...other than being a toxic nightmare acetone is a solvent. It will dissolve any contaminates and drive them into the wood. If possible wash the bare wood with simple soap and water and float the contaminate away. If not possible to wash with water use the double wipe technique...one worker wetting out and wiping with acetone and a 3m pad and another directly behind wiping again with a rag. In general I hate using solvents like acetone.

    As to layup schedule, the local guys are sheathing a new ply deck on a tour boat...looks like 12oz fabic . I notice that in order to lay the continuous 20 meter long bow to stern piece of fabric , with joints only on center line foredeck and aft, they first covered the deck with a sheet of polyfilm so that they could slide , position and trim the long sheet of fabric without disturbing the weave by catching wood grain. They then sliced and slid out the poly sheet, section at a time, as they laminated from mid deck forward and aft. ....
     
  11. mark775

    mark775 Guest

    I won't get into the acetone vs. water debate but I will say that infra-red lamps have caused more than one fire and at least four deaths in my town. Trying to avoid an open flame when using acetone or other highly flammable material, knock over an infrared lamp - instant explosion and fire.
     
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Again Michael, you should stick with what you know. An acetone bath over cured polyester will not drive anything into the wood. One of three things will happen to "surface contaminates": they will be diluted, if not dissolved by the acetone, then evaporate out with the acetone; they will be attracted to the acetone and carried out by the evaporating acetone (in fact, a great water to get moisture out of wood is an acetone bath for this very reason); or they will be unaffected, which is precisely what will happen in this case, as the acetone will not do crap to the cured polyester, unless left on it for months at a time.

    Again, any traces of polyester left after the grinding and cleaning is done, will be little more then particulates or toothed substrate in the subsequent epoxy coatings.

    Water and soap would be the last thing to introduce to this surface Michael.
     
  13. jwt
    Joined: Jan 2011
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    jwt New Member

    Thanks for the replies.

    Have removed all of the polyester. Sanded the marine ply with 40 grit flappy paddles on the grinder and topped off with 40 grit on a belt sander used at 45 degrees to the grain and again at 135 degrees to the grain to give a solid keyed surface.

    I'll wipe the surface with a clean rag soaked in acetone rotating the rag regularly and changing rags often. Then leave the acetone evaporate over night and epoxy in the morning.

    For clarity the contaminants I was worried about are in the top layer of ply underneath the poly so basically it was...

    polyester/csm GRP
    some weird oily substance mixed with uncured polyester I think
    Possibly water and unburned hydrocarbons
    Top layer of ply


    Now its whatever stuff was contaminating the wood originally which I am now 99 percent sure was unburned diesel from a space heater that nicely misted the wood with diesel and diesel smoke. Well that and some size 12 boots walking hydraulic fluid around the deck before I arrived on the scene :rolleyes:

    I've attacked the ply aggressively with the 40 grit wheel on the grinder and although I haven't removed a complete layer of the ply I'm happy I've taken off 0.5mm at least .

    So it'll be heat control to worry about, the infra-red heaters allow me to pre heat the wood on an area I'll soon be glassing and subsequently heat the epoxy once down.

    I'm shying away from any diesel or kerosene based space heaters, even if they appear to burn cleanly they seem to cause issues in a tented environment with the exhaust gasses condensing on your substrate. West Systems specifically recommend not using them. And after what I've just gone through I'm feeling pretty anti space heaters at the moment :D


    So.

    Will 2 layers of 280g/ms twill weave fabric in an epoxy resin bonded to 18mm marine ply with a clean and well keyed surface provide some decent wear characteristics?

    John
     

  14. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I'm not sure if you actually mean twill weave, but two layers of 10 ounce (280 g) is pretty good but not the most you can do. A bottom layer of 280 with a top layer of 140 Xynole (4 ounce) will be far better then two layers of conventional cloth. You'll use more resin, but it's much tougher result. The twill weaves are usually reserved for "show" laminates.

    Instead of those types of space heaters, I've had great success with the electric, oil filled versions of these. They can't catch things on fire, they can be tipped over without regard and generally are a lot safer to work with.
    [​IMG]
    I have 4 of these things and they work great.
     
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