We will soon be at the point of our sport sectional build where we will pour epoxy into the bow and stern. In addition to the structural support this may provide (I realize from prior posts that some debate this) we do plan to drill through-holes so that we can attach the ropes that help hold/carry the kayak. But the manual doesn’t really say what volume to use, only to pour a cup. What volume would you recommend? In addition, how have folks dealt with the heat generated by curing, which could be significant given the geometry there and the volume. Do you use ice packs? Cold wet towels? Bucket of cold water?
i am one who ascribes to the end-pours as not offering much structural value but more important as a way to be able to drill holes for ropes and not have that open into the hull.
i also do my end-pours before joining the deck to the hull…so i can control the process and only use the amount i need.
so my approach is to mark the holes and then use a little cardboard dam to isolate the area for the end pour with only about 1/2 " proud of the hole…and fill it with very thickened epoxy with woodflour. often this only requires a 1/4 to 1/2 a cup.
If you do an end pour I think the best bet is to just estimate the volume by eyeball. Keep the pour as small as possible - which will mean that you’ll want to judge how close to the bow you are comfortable with putting any through-hole for handle/loop placement - maybe 1.5 inches back from the end of the boat. I’m guessing about 1.5 cup volume. If you have microballoons, use as many as possible while keeping the mix still pourable. That helps keep the end pour a little lighter, and probably cooler during curing. I don’t think it will do any good to pre-chill the epoxy, I think a large bolume like this still generates a lot of internal heat no matter what temperature it starts out. Maybe you’d get a slower overall reaction and lower highest temperature during the cook-off - I’ve never experimented with that.
I did have trouble with the heat generated when I did my first end on my Shearwater Sport. And I think I overdid it with the volume on the pours - they could hve been smaller. For the second end I put the whole bow (or stern?) in a bucket of cool water (boat leaning up on garage or tree) which I continually swished around for 20 minutes or so after the pour. For weight and epoxy-cost considerations I’m now a proponent of glueing in a wood block during the build. The block doesn’t have to totally fill the tringle shape of the bow, just has to have ends that match the hull angles well at the selected location. Then you can drill through the block and coat the inside of the hole with epoxy. Lighter, cheaper and strong enough, although it does require the foresight to do this step prior to putting on the deck, and you’'re now beyond that point on your current build.
Thanks Howard and Jeff for weighing in. Since in this build the end pour is done after the kayak’s body is already constructed, I can’t use some of the techniques mentioned. The manual says to drill the holes 4” back from the tips and 1 1/4” from the deck. I put a piece of blue tape in the corresponding location in the pic below. I realize I don’t have to locate the hole in exactly that spot and can move it close to the tip if desired, but that’s what’s in the manual. In the pic I put a plastic cup in front to get a rough idea. I wouldn’t think I’d need that entire cup’s worth of epoxy—the cup holds 10 oz if filled to the brim.
Jeff, I wasn’t suggesting precooling the epoxy, I was thinking of using some cold wet towels wrapped around the tip to cool the wood (and epoxy by conduction) as it cures after pouring. I could also try the water bath technique (I got the idea for the towels by speaking to someone at CLC). Also, I don’t have any microballoons I only have the wood flower or cell-o-fill. Not sure how much the latter expands the volume, and it has to be runny enough to pour and settle.
I do like the idea of using a filler block/dutchman so if I do another build I’ll incorporate that approach.
Rob, yes as Howard says, a cup is a lot. When I did my wood duck 12 I used a lot of micro spheres to make it as light as possible while still having about a 150ml of fairly runny compound to pour.. it heats up quickly so a put the ends in a bucket of cold water though it still got super hot when it was setting. If you do use a bucket of water, I would put the end of the boat in a strong plastic bag in case there is a small leak, otherwise you’ll end up with a steaming foaming mess in the end, don’t ask how I know!
On my petrel play I used the dam method which was a lot more controllable.
Would it make sense to break it up into two pours for each end? Pour half the amount, wait for it to cure sufficiently to cool off (an hour maybe?), then pour the second half? I would imagine the second pour would bond nicely to the first.
To keep weight down, I used micro balloons to thicken my end pour epoxy. It lightens it up and worked well, but when adding them, they are easily dispersed into the air. Even with a mask on I was uncomfortable using them. Just another data point.
Well, I don’t have microballoons but with all the talk about their utility maybe I should bite the bullet and get some. I see I can order some on Amazon for about $20 and they’ll be here in a few days.
there are some other ways to do this…that i will put out there. all have been tried by me.
an approach that you can use that doesn’t use more epoxy than you need and can be done at this step is:
pre-drill your hole before epoxying the tip. make sure to drill the hole a 1/4 inch more diameter than the final hole you expect…so if you want the final hole to be 1/2 inch then you drill a 3/4 inch hole. i put a pilot hole on each side using 1/8 inch bit then use a 3/4 inch spade bit from each side in…avoid going all the way through the other side to keep it all nice and neat. you can also put blue tape or tape down prior to drilling to help keep the edges clean. note spade bits tend to give the cleanest hole becuase they don’t screw into the wood in an uncontrolled fashion.
once the hole is made, perch the boat so that it is bow (or stern) down…depending on the end you are working on.
get clear packing tape to cover one side of the hole
create a thick epoxy mixture with wood flour (so that it matches the wood). by thick, i mean mayonaise like that will almost hold its shape.
with a popsicle stick or other tool, now fill in / push the epoxy in from the open side. you do this until you see it fill/cover the othe side where you had the clear packing tape.
pack in another table spoon of epoxy/woodflour mix once you have the hole filled from each side…and then tape the open side to hold it in place.
once it is cured/hardened…drill you 1/2 inch hole (so you have a 1/8 perimeter of epoxy) from each side…meet in the middle.
sand your hole smooth with a piece of 150 grit sanpaper wrapped around a dowel that will fit in the hole.
9 inspect the hole and check for any opening into the inside of the hull. if there is an opening, just make some more thick epoxy and push it into your opening. and repeat step 8.
Now you have a perfect drill, fill, drill hole with no more epoxy than you need. i would avoid the microballoons in this step becuase it won’t make that much difference in weight…and microballoon color is not a good match with wood color. but if you are painting and you want to play with it, go ahead and buy some. its great to have around.
Thanks Howard, very creative approach. I think we’ll try just pouring some amount of epoxy mix and putting some cold wet towels around the tips.
I ended up getting a quart of microballoons from Amazon for $15 so will try adding some though not sure how much to add (google’s AI says it can expand volume by about 30% when adding about equal volumes of epoxy and microballoons).
i would just highlight that in practice it doesn’t ‘expand’. it simply displaces. so if i had 1 cubic inch of epoxy and mixed in the maximum recommended micro balloons, i would have 1.3 cubic inch volume of ‘putty’. since the micro balloons, practically weigh nothing, the cubic inch of ‘micro balloon’ putty weighs only about 66% of what a similar volume of straight epoxy would weigh.
all that said, the best way to keep the weight down is to keep the epoxy use to a minimum. its heavy stuff even with micro balloons mixed in.
if you look at your picture of the cup over the tip, the other thing to remember is the volume you need to fill is only the internal volume so you get to subtract the thickness of the material and the internal fillet along the bottom of the hull that is already there…
its deceptive how small the volume is if you only go as far back as you need to - i shoot for 1/4 inch over the back edge of the hole i expect to drill…and even when doing my end-pour with the deck off, i inevitably toss quite a bit of what i mixed
Yes, good points Howard on the volume taken up by the wood and fillets, it’s not small. One trick I saw somewhere here on a prior thread was to take a stick (e.g. a thin dowel) long enough to reach the tip, measure to the hatch opening, then after pouring a certain amount, look down into the hatch and see how far the stick goes before it hits the epoxy, and see where it now reaches the hatch opening. I might try that.
