BillB Posted March 21, 2016 Report Share Posted March 21, 2016 For the gunwales on my Moccasin boats, I cut pieces to make the 3/4 inch square strips then scarf the pieces together with un thickened epoxy to achieve the desired length. When new, the joint is a visible line but over time the line becomes a line you can see and feel. The joint appears to be pulling apart lengthwise, could this be epoxy creep or am I doing something wrong? This time I have pinned the join with a dowel through the scarf joint in an effort to prevent this creeping. Anyone else experience this problem? Bill Update see attached image The dowel is not in previous gunwales but I am going to try it on this one. Quote Link to comment Share on other sites More sharing options...
Hirilonde Posted March 21, 2016 Report Share Posted March 21, 2016 The gunwales of my Lapwing are made of 3' pieces of teak scarfed and glued with epoxy, but using wood flour and some colloidal silica (B&B blend) as filler. I clamped the pieces together with just finger clamps to avoid excess squeeze out. I can only conclude that your joints are starved of epoxy due to no thickening and maybe over-clamping? I don't have any clever fix ideas. Pictures might help. Quote Link to comment Share on other sites More sharing options...
PAR Posted March 22, 2016 Report Share Posted March 22, 2016 Epoxy doesn't really creep. There is some shrinkage, but the amount is so little it's hard to measure, compaired to many other adhesives. It's hard to tell what's going on with your rails, though I'd bet Dave may be on the right track. How much surface area is inside the joint, on the is 3/4" square stock, an 8:1 scarf? What were your thickening materials and was the end grain wetted out prior to the thickened goo application? Quote Link to comment Share on other sites More sharing options...
Action Tiger Posted March 22, 2016 Report Share Posted March 22, 2016 I will defer to the above about the actual adhering, they are both undoubtedly more experienced than I. If the seam is bugging you, though, I have a fix. You can use a thin bladed handsaw to cut through the joint, as if you were "kerfing" a joint together (which, you kinda are). Now, you make a tape dam, mix up a good, thinnish slurry, and force it into the kerf you just cut. Easy, peasy, and good as new. Quote Link to comment Share on other sites More sharing options...
Hirilonde Posted March 23, 2016 Report Share Posted March 23, 2016 If the seam is bugging you, though, I have a fix. You can use a thin bladed handsaw to cut through the joint, as if you were "kerfing" a joint together (which, you kinda are). Now, you make a tape dam, mix up a good, thinnish slurry, and force it into the kerf you just cut. The gunwale is bent and under strain. If you cut a kerf at the seam the gunwale will distort as the tension is released. Quote Link to comment Share on other sites More sharing options...
PAR Posted March 23, 2016 Report Share Posted March 23, 2016 I've used this method (Action's description) to make repairs on "loaded" pieces and you do need to arrange some clamping, so it doesn't explode when you make the cut. Quote Link to comment Share on other sites More sharing options...
Action Tiger Posted March 23, 2016 Report Share Posted March 23, 2016 I've done it on canoes. My wife and I tried for about ten years to wear out several canoes, and every river within one tank of gas... I have repaired boats in situ many times. The gunwale will indeed pull some kind of stunt, but I was assuming (uh-oh) the gunwale is firmly attached to the hull side and there is some other furniture to hold the boat shape. If the gap opens too much, you can clamp a batten around the outside after re-smoodging the new little slice. Maybe not super easy, but super easy for anyone who built their own boat. Quote Link to comment Share on other sites More sharing options...
PAR Posted March 23, 2016 Report Share Posted March 23, 2016 That's the way I do it, I use a sacrificial batten (1x2) for the initial part of the cut, then replace it with another, sliding the saw behind the new batten, to finish the cut. This batten will hold the now severed rail pieces, until you go her up. I usually cover the restraining batten with clear plastic packaging tape, so when it's goo time, I don't have to remove anything and the batten doesn't stick. Quote Link to comment Share on other sites More sharing options...
BillB Posted March 23, 2016 Author Report Share Posted March 23, 2016 I have experienced this with both thickened and un thickened epoxy. The gunwales are attached to the hull with thickened epoxy and show no sign of separation. The scarf joints are 8:1. and are staggered on the hull. You may have hit upon the problem as starved, due to over clamping. There is no crack at the join, it is as though the two pieces are pulling apart and the epoxy is stretching but not cracking. I refinished my boats every two years and can easily return the gunwales to their new condition. It is just the fact that it is happening that puzzles me. Quote Link to comment Share on other sites More sharing options...
BillB Posted March 23, 2016 Author Report Share Posted March 23, 2016 I agree, the epoxy doesn't creep the joined surfaces do, when under stress and over time. Epoxy we use on boats is stronger than the wood it is joining and I have never had an epoxy join fail, but have had the wood fail leaving wood still attached to the epoxy. Quote Link to comment Share on other sites More sharing options...
BillB Posted March 24, 2016 Author Report Share Posted March 24, 2016 Here is a link to more information about epoxy creep HTTP://www.adhesivestoolkit.com/Docs?test?Durability%20Design%20and%20Testing%20-%20Creep.xtp It looks like you can't connect from here, so have to copy and paste the link in your browser. Quote Link to comment Share on other sites More sharing options...
Chick Ludwig Posted March 24, 2016 Report Share Posted March 24, 2016 i couldn't copy and paste either. Quote Link to comment Share on other sites More sharing options...
BillB Posted March 27, 2016 Author Report Share Posted March 27, 2016 attached is an image of the search results for epoxy creep. the link shown will take you to the data. Quote Link to comment Share on other sites More sharing options...
PAR Posted March 27, 2016 Report Share Posted March 27, 2016 Cut and paste the chart showing epoxy creep and compare it to PVA or other adhesives. You'll see what I mean. Quote Link to comment Share on other sites More sharing options...
Don Silsbe Posted May 28, 2016 Report Share Posted May 28, 2016 Bill, I don't know about you, but when they call me an Epoxy Creep, I wear it with a badge of honor. Quote Link to comment Share on other sites More sharing options...
PAR Posted May 29, 2016 Report Share Posted May 29, 2016 If you didn't wipe your gooey paws on your shirt, you wouldn't have badges, honorable or not . . . 1 Quote Link to comment Share on other sites More sharing options...
Howard Posted May 30, 2016 Report Share Posted May 30, 2016 Is it possible the wood used wasn't as dry when you glued it up as it is now and the wood shrank over time as it dried out to equilibrium? I've had stuff pull apart before when the epoxy wasn't fully cured before it was loaded (slow cure epoxy+cold temps+loaded joint=movement). It may look hard, and you can't dent it with a thumbnail, but it is not ready to handle a heavy load. The same thing could happen if your mix ratio was bad, as it may never cure right or be slow to do so, remain gummy for too long and allow movement of a heavily loaded joint. Quote Link to comment Share on other sites More sharing options...
Don Silsbe Posted June 4, 2016 Report Share Posted June 4, 2016 I've also wondered about epoxied boats left out in the hot sun. If heat is how we remove stubborn wires, you gotta wonder... Quote Link to comment Share on other sites More sharing options...
Docpal Posted June 4, 2016 Report Share Posted June 4, 2016 Heat is also how we fully cure epoxy too though. It IS a thermosetting polymer.... Quote Link to comment Share on other sites More sharing options...
PAR Posted June 4, 2016 Report Share Posted June 4, 2016 Heat is a byproduct of the chemical reaction and not all epoxies are thermolytic, at least compaired to the ones most use. Most of the marine epoxy we use are fine up to about 150 degrees, where clear and noticeable distortion can occur. It doesn't melt, but does lose about 40% of its physical attributes above these temperatures. In the real world, if you paint your deck or cabin top black and if you happen to live in Florida or Texas, you might see some ripples appear, maybe some seams or grain lines show up out of nowhere and bonded down and highly stressed pieces will distort under load. These piece will not just suddenly release, though when cool, loaded items may retain some of the distortion, particularly is cooled quickly (boarding wave for example). This said, heat can be used to accelerate the chemical reaction. For every 20 degrees above the mid 70's, you'll half the cure times. I'm currently "cooking" a boat part in a homemade oven at 130 degrees. This slow cure epoxy usually takes a full 24 hours to cure (16 or more to sand), when in the mid 70's but I can start sanding after 6 hours, by post curing the goo. The benefit is I can use a slow hardener, so I have plenty of time to setup, apply and work the goo, but I can cook it off so I can continue working on it the same day. Quote Link to comment Share on other sites More sharing options...
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