Kiln Dried Treated Wood for Cores

Discussion in 'Fiberglass and Composite Boat Building' started by LMB, Oct 28, 2010.

  1. LMB
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    LMB Junior Member

    Seeking opinions on what I have discovered to be a fairly new alternative for structural core materials in fiberglass boats. I know of several production boat builders who are now using treated/dried marine grade plywood in stringers, decks and transoms. I've used some recently in rebuilds.

    I've also just found a local source for treated/dried dimensional lumber like 2x8s. I'm considering this for a stringer material as well. I do have a few concerns, including possible problems the treatment could have resin/glass adhesion and cure. Also, the manufacturer lists the moisture content after drying at 19%. That sounds a little high to me, but the wood may continue to dry some over time.

    I welcome any thoughts on this and figure others might be interested as well.
     
  2. tunnels

    tunnels Previous Member

    Moisture needs to be lower than 19% and you can use i dehumidifyer to dry the wood if you have the time to do it !!
    Core ?? are you building a wooden boat with glass as a skin inside and out or a glass boat ??:confused:
     
  3. rxcomposite
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    rxcomposite Senior Member

    About 15% for any timber that is to be glued, bonded, or laminated over. LR Rules.
     
  4. apex1

    apex1 Guest

    12% - 15% to make a safe bet........the lower value is the superior!

    And the mentioned wood / ply cannot be used in boatbuilding in general. (assuming you refer to the "hardened" stuff, LMB)

    One cannot use wood with such moisture content and encapsulate it in FRP, it does not dry out later, it rots.

    Regards
    Richard
     
  5. PAR
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    PAR Yacht Designer/Builder

    The new treatment process used in the US is not especially comparable with good epoxy bonds. The old CCA wasn't so bad, but the new CA is not acceptable. Second is the quality of the materials given the PT suppliers. As a rule the construction grade PT plywood is about the worst junk plywood you can find. Yes, it's rated for continuous ground contact, but the panel construction, repairs, voids and other defects permitted in the panel, are just way outside the acceptable range for marine uses. This stuff is great if you're building a back porch over at your brother's house, but it has very limited usefulness in a boat.
     
  6. LMB
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    LMB Junior Member

    To be clear, the 19% moisture reference was only for the dimensional lumber. I'm not sure the moistuer content on the plywood but I do know it is specifically designed for fiberglass boat building applications and is being used by some major manufacturers.

    You have confirmed my concern that 19% would be too high. I'm am still curious how much that moisture content would decrease under good storage conditions and what the relative time frame would be. I know there are alot of factors at play here.

    I do like the idea of treated wood as an alternative to standard wood. Except for potential for rot I think wood has proven itself as a great material for reinforcing fiberglass boats. The treated wood looks like a "win-win" to me.
     
  7. PAR
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    PAR Yacht Designer/Builder

    LMB, what s the chemical treatment being used on this stuff? I'm under the impression that all PT products at CA.
     
  8. LMB
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    LMB Junior Member

    Par, the plywood I'm referring to is CCA treated Marine Grade Plywood. I'm not an expert on grades but I think its a B-C. One side is a little rough but the material is very flat and really looks pretty good. I think it's douglas fir and is probably available in other species and grades.

    The dimensional lumber I'm looking at is from another manufacturer and is CA treated. Between that and the moisture content I might have to rule it out, but I'm looking at all the options. I think the idea that all treated materials are 2nd grade junk is being challenged by the availability of select grades and species with various treatment and drying options.

    BTW, I'm using Poly and Vinylester in most applications. I know this is an epoxy biased forum - which is fine. I use and understand the merits of epoxy, it's just not a practical application in much of what I do. For me this is a business.
     
  9. apex1

    apex1 Guest

    As it is for PAR and me, amongst several others.

    There is no bias here!

    Regards
    Richard
     
  10. TeddyDiver
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    TeddyDiver Gollywobbler

    I don't know how compatible it's with poly and VE, but with epoxy wood treated with monoethyleneclycol is ok. It can be used only for encapsulated wood..
     

  11. PAR
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    PAR Yacht Designer/Builder

    CCA is fine for both resins systems, but CA tends to seal the pores and the tubule structure in the wood, which prevents both resin types (poly or epoxy) from getting a good grip. Considering poly's poor preformance in this regard generally, any additional disadvantage should be suspect.

    No PT treatments are not all junk, but the huge and vast majority of retail availability is. You can get some really nice stock PT'd, but you'll pay for it.

    My point with the plywood is most typically the panel construction is very poor and the APA regulations are voluntary, so many manufactures just build what they want and put whatever stamp on it that they want. For example, I'm now seeing 3 veneer 1/2" ply a lot. The minimum marine requirement would be 5. I've never seen construction grades that had good panel construction, even the very rare to find AA sheets. The BC sheets you're seeing are typical of construction grade material. The letter grades only the finish on the two exteior veneers. If you look closely at these sheets, they'll have over lapping internal veneers, huge voids, lots of repairs, surface defects (you can imagine what's inside out of sight). Placed along side a BS-1088 or 6566 sheet you'll quickly see why the "good stuff" cost more.

    You must be using a commercial account, because CCA isn't permitted to be sold retail any more. CCA is a better PT chemical and if the moisture level and panel construction are good enough, a perfectly good preventive treatment for both resin systems. If it's CA, you'll have adhesion issues. This was recently covered in Pro. Boat Builder magazine (within the last few years any way). If memory serves me, it was about the time the new CA treatments were about the hit the fan.
     
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