Does epoxy swell wood like water??

Discussion in 'Materials' started by Skua, Aug 18, 2020.

  1. Skua
    Joined: Apr 2013
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    Skua Senior Member

    I am wanting to use epoxy on the wood framing around the entrance door to the cabin.The door itself is aluminium, and will be set into the bulkhead entrance. Obviously the metal frame will be installed using a sealer, but water usually finds a way. So i wish to prep the wood with a couple coats of epoxy, but am wondering if I need additional clearances foe swelling?

    Thanks
     
  2. fallguy
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    fallguy Senior Member

    You need clearances for the thickness of the coatings. Epoxy does not swell wood like water will. Epoxy coatings will often run on a long vertical. I would try to allow 1.5-2mm clearances prior to coating if the door allows it.

    You can keep working the coating back up until gelation to deal with drips. I like to keep a foam brush handy to grab drips.

    Sanding the wood with 40-60 grit paper is a good way to take it down a bit if it is really tight.
     
  3. Blueknarr
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    Blueknarr Senior Member

    All liquids will cause wood to swell. The viscosity of the epoxy will determine how much swelling will occur. However,it will only be minimal raising of the wood's grain .

    As fallguy said the nessicary clearance is greater than the swelling.
     
  4. Will Gilmore
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    Will Gilmore Senior Member

    Epoxy will swell wood of you fail to add the hardener. It takes time for water to swell wood, epoxy, even longer because of its viscosity. By the time it has penetrated the cellular structure enough to swell the wood, it should have hardened and sealed the area it covers.

    -Will (Dragonfly)
     
    Last edited: Aug 18, 2020
  5. upchurchmr
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    upchurchmr Senior Member

    I can't believe that answer from Blueknarr.

    No swelling.

    Get a copy of "The Gougeon Brothers on Boat construction" if you want a real answer.
    Free download: https://www.westsystem.com/wp-content/uploads/GougeonBook-061205-1.pdf

    Epoxy doesn't penetrate the wood to any realistic extent. Only the cut outer fibers.
    No matter want West System name stands for.
     
  6. missinginaction
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    missinginaction Senior Member

    I've coated a lot of wood. I've never seen any appreciable swelling. Nothing that I've noticed anyway. I've fit things pretty tight sometimes. You can get some raising of the grain on the initial epoxy coat on some plywoods, but you can knock that down in a couple of minutes with some 120 grit paper. If I were the OP, I'd apply three fairly thin coats around the door frame, paying particular attention to the end grain. Apply each coat before the prior coat has fully cured. Once the third and last coat is past the tacky stage you can apply some sealer (I'd use clear silicone) and install the door frame. Pay special attention to the screws that attach the frame. I like to pre-drill the holes and dip each screw in a 1 oz. mixing cup with some silicone in it. You're going to leave a little play for the sealer anyway, right? You'll be fine. Just asking the question shows that you're taking more care with the installation than 99.9% of commercial contractors.
     
    Will Gilmore likes this.
  7. Blueknarr
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    Blueknarr Senior Member

    Raised grain is swelled up wood fibers. It is the hardening of the resin which prevents them from laying back down. All resin systems will raise grain. The longer the resin stays liquid the greater the grain will raised by swelling.

    Wood can be swelled with out changing dimensions
     
  8. Skua
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    Skua Senior Member

    Thank you everyone!
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    :eek: How so ?
     
  10. Blueknarr
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    Blueknarr Senior Member

    Somehow the first part of my previous post was lost to the ether world.

    Here it is again.

    The liquid of a paint or resin inters the wood's surface fibers, causing them to swell and raise away from their normal position. The resin hardens preventing them from returning to their original place.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    That is called "raising the nap", I believe.
     
  12. fallguy
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    fallguy Senior Member

    Epoxy doesn't swell the wood as much as water because water molecules are smaller and penetrate deeper and since epoxy is more viscous than water; it leaves a film that may oftentimes or at least in a couple of coats; exceed the dimension of the swollen wood.

    Here is some google scholaring for you. My experiences are real world.

    https://www.fpl.fs.fed.us/documnts/pdf2011/fpl_2011_masoodi002.pdf
     

  13. Skua
    Joined: Apr 2013
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    Skua Senior Member

    "Just asking the question shows that you're taking more care with the installation than 99.9% of commercial contractors."

    But, there is a need to produce a product with an appropriate profit margin in a timely manner. I'm into my 7th year of what started as a gas tank replacement. I'm hopeing to finish before I'm dead, lol. But thank you for the kind words.
     
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