Wood for boats

Discussion in 'Watercraft' started by Jacob Peterson, May 14, 2009.

  1. Frank R

    Frank R Member

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    I did some quick research on thinning epoxy and using commercial epoxy sealers (which is epoxy thinned with a solvent). I found this very useful article at this link: http://www.seqair.com/skunkworks/Glues/WestSystem/Thinning/Thinning.html

    Here is an excerpt:

    "Water resistance of a piece of wood is not enhanced by deep penetration. Wrapping wood in plastic makes a pretty good waterproof seal without any penetration at all. Likewise, an epoxy coating on the surface is more water-resistant than a thinned epoxy coating that has penetrated deeply into the wood because, in most instances, the epoxy thinned with solvent is porous (emphasis added. I remember reading somewhere else that the solvent leaves little holes in the epoxy resin).

    [​IMG]
    Figure1. MEE of various combinations of thinned and unthinned epoxy at six weeks exposure to 100% humidity.

    The USDA Forest Products Laboratory developed the Moisture Exclusion Effectiveness (MEE) test. It is a measure of how much moisture is absorbed by wood when it is continuously exposed to 100% humidity. Higher numbers mean the wood has absorbed more moisture while lower numbers indicate less moisture is absorbed. You can see that epoxy with solvent added is not nearly as moisture resistant as un-thinned epoxy (Figure 1). However, if you need an epoxy coated surface that is less of a vapor barrier, thinning West System epoxy with solvent is a valid way to achieve this."

    I think I will avoid thinning the epoxy as I build my boat.
     
  2. Bob Triggs

    Bob Triggs Stop Killing Wild Steelhead!

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    If you thinned the epoxy yourself, using a proprietary solvent, and did nothing else over that penetrating epoxy application, you would indeed have a resultant "porous surface" and very little water resistance. In general thinned epoxy is not going to provide the same molecular structure, nor strength and water resistance, as normal epoxy mixes.

    Smiths Clear Penetrating Epoxy Sealer CPES ( or any other brand of factory thin epoxy mixes) is not merely thinned with solvent and sold that way. It is a thinner formulation than "normal" epoxy mixes. It is used as a first application sealer prior to subsequent applications of normally mixed epoxy. It does indeed penetrate wood and plywood surfaces, pores and joints very well. In use one wets and coats the surfaces repeatedly while the CPES mix is still watery thin.

    Usually then three to four following applications of normal mix epoxy are recommended,( this is prior to final over-painting or varnishing), to achieve a "water proof" status. You can think of the Clear Penetrating Epoxy Sealer as a "primer" to regular epoxy and it does enhance water resistant and waterproof qualities. Look up the previously recommended "Epoxy Hot Coating" method.

    I would not get the wood "as hot as possible". Simply warming the surface for a while is adequate. Very high temperatures accellerate epoxy curing times and can actually interfere with bonding and penetration. The result is an epoxy that may be weaker and brittler. A great old trick is to use a hot lamp or old electric blanket to warm the surfaces for an hour. Then remove the heat, apply the epoxy and then let it cool as it sets without additional heat. Note that epoxies require a nearly room temperature for adequate curing.

    Also take a look at www.woodenboatvb.com and see the Building/Repair Forum pages there.

    By the way, under a previous post: Dave Carnells work on the paint issue is fantastic and he is widely respected.
     
  3. Mark Moore

    Mark Moore Just a Member

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    Bob,

    Thanks for making that point. I was in a hurry with the post and certainly over simplified, I should have stated that the ambient air temperature in the room can be raised then lowered to create the reverse of out gassing. Rob White explained this thoroughly in Woodenboat and I have used it on occasion to great effect.

    I suspect that we are all postulating way over the aspirations of the original poster.
     
  4. nomlasder

    nomlasder Active Member

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    The use of a penetrating epoxy sealer only enhances the natural attributes of the wood. Wood wants to breathe. Locking it up completely with fiberglass or epoxy can have bad side affects. If there is any damage to the outer coating and moisture gets in, being "sealed" in will promote rot.
     
  5. Frank R

    Frank R Member

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    Thanks Bob, I was referring to the previous post about thinning your own epoxy. BTW: The rest of the article in the link is well worth reading.
     
  6. Frank R

    Frank R Member

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    Ummm, I don't want to step on any toes here, but there are some issues here that need to be discussed.

    Wood does not want to breathe, its dead. Applying anything to the surface is going to "lock it up" in some way. Whether it is oil, wax, varnish, paint, or epoxy. Epoxy sealer is no different in kind, only in degree.

    You do want to lock it up completely. This will reduce the rate at which water is absorbed into the wood. What you said about water getting in through a damaged area is true, but it is the mold spores and oxygen along with the water that causes rot. Using only a penetrating expoxy sealer would not help prevent this.

    Here are four excellent articles to read. They are by Dave Carnell who is "a retired chemical engineer who has been messing about in boats for well over 50 years":
    Waterproofing Wood
    Chemotherapy for Rot
    Latex Paint For Boats
    Epoxy Knowhow