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Boat Forum / Building / October 2005nu2 woodworking - my epoxied wood is delaminating,..
ahoy, I epoxied some one inch strips of wood in slats to make up a little decorative rope bin which was intended to sit on deck but it warped and popped apart in about 3 days in a damp shop. Does everything have to be notched or biscuited or doweled and pinned or screwed? I thought epoxy was an invincible adhesive. I used left over strips of purple hart and mahogany and west system 105/205 in a dry room if that makes any difference. thanks as always. > ahoy, I epoxied some one inch strips of wood in slats to make up a > little decorative rope bin which was intended to sit on deck but it [quoted text clipped - 3 lines] > strips of purple hart and mahogany and west system 105/205 in a dry > room if that makes any difference. thanks as always. Purple heart and mahogany are oily woods that can be difficult to glue without careful preparation. Wiping the surfaces to be glued with a good solvent (acetone, lacquer thinner) will improve the bond. Also, did you apply a finish to the wood or leave it bare? If the latter, the expansion an contraction of the wood from getting wet, then drying can cause glue joint failures. >> ahoy, I epoxied some one inch strips of wood in slats to make up a >> little decorative rope bin which was intended to sit on deck but it [quoted text clipped - 10 lines] >expansion an contraction of the wood from getting wet, then drying can >cause glue joint failures. Yes, I wiped the contact surfaces with acetone. I had intended to varnish but found one of the 20 joints had failed after the first day. Over the next two days they all let go one by one. I've glued it (now with dowels) half a dozen times so far. It's never been outside yet. Thank you. >ahoy, I epoxied some one inch strips of wood in slats to make up a >little decorative rope bin which was intended to sit on deck but it [quoted text clipped - 3 lines] >strips of purple hart and mahogany and west system 105/205 in a dry >room if that makes any difference. thanks as always. There is epoxy and then there is epoxy. In other words there are various formulations of various quality for various purposes. Oak in particular has problems (the tanin in it). Unless the wood was epoxy coated the force of the wood warping exceeded the strength of the joint. Epoxy is an adhesive, it is not a miracle substance of unlimited strength. Squeeze too much out and the joint is weak. Have too thick of a layer and again the joint is weak. Some formulation are known to suffer from excessive creep, but those are intended for finishing not wooden joints. All epoxies soften at warm temperatures, the point depending on the formulation. But a dark hull on a sunny day can easily exceed that point. It is also waterpermiable. It doesn't let in much but it is not like a metal barrier, some moisture will go through epoxy, the amount and speed depending on the formula and the thickness. For very highly stressed wood to wood joints I would either use resorcinol or epoxy with the joint REINFORCED by fiberglass cloth. De lamination with epoxy is not uncommon when the wood is not completely and properly epoxy coated to control moisture. Epoxy resin is much stronger and less permeable than polyester resin, but again it is not a miracle substance. It has limitations just like any other material. JJ James Johnson remove the "dot" from after sail in email address to reply The problem wasn't the epoxy. The glued connection wasn't strong enough to resist the warping ...which can be quite strong I might add. You can either back the joint up with hardware or encapsulate the wood in epoxy so that it doesn't absorb moisture. With proper preparation of the wood(s) and proper mixing of the epoxy, the wood generally fails before the epoxy. In other words, when the joint gives way, you'll find all the epoxy and some torn away wood on one side and nothing but wood on the other side. The only time that I had an epoxy joint fail (other than doing tests), it failed right in the epoxy itself but it was a joint that I remembered may not have had the right resin/hardener ratio in it. My cheap bottle top pumps failed me when one went 'pop' and shot some air into the cup instead of epoxy. I tried to guess a corrective amount to squirt in and just took a risk. The epoxy was whitish and crystallized, brittle. NOT normal. The lesson there was to avoid guessing and to make sure the measured ratio is correct, then mix well. But in your case, it sounds like if the wood is not going to be encapsulated with epoxy (coat 3 times), then a mechanical back-up is in order. If you're not going to encapsulate, and especially if you'll put your project in a damp environment, then yes ..treat epoxy like any other glue and dowel it, or back it up with screws, or whatever. I've seen warping wood pull screws out ...nothing is invincible, even epoxy. Brian D >>ahoy, I epoxied some one inch strips of wood in slats to make up a >>little decorative rope bin which was intended to sit on deck but it [quoted text clipped - 43 lines] > James Johnson > remove the "dot" from after sail in email address to reply |
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