I’m in the process of building my first one-piece paddle (walnut) and I fear I made the handle a little too thin. Am I worrying too much or should I look into laminating the grip or adding a flexible wrap (I’m thinking leather) to widen it? Or is there another option I’m not thinking of? The paddle is a gift for my sister. The wood blank was 1-1/8” thick, and the grip now is 5/8“ thick and 3-5/8” wide.

See attached images.

You might need to thin it further to flatten it out and add a layer on each side. I would not add anything like leather.

It it were me, I would just add a thin strip along the top edge then round it off. Making it square enough to add a layer is going to be a pain. You might want to use a plane or a saw to get a straight edge to work with. Keep in mind that it doesn't need to be square to the shaft, a slight angle would be easier for the transition. Then you just shape the added material and have a nice rounded end to hold on to.

I did something similar with my paddle, but used different color wood to make it pop a bit.

I've seen commercially available paddles that had a piece glued on to make the handle thicker.

Is your sister more likely to use this paddle on the water or hang it with pride on the wall? If it won't get used a lot I would probably leave it as is. One of my favorite paddles (to look at) is walnut but I rarely use it because it is a bit on the heavy side.

If I really wanted to fatten up that grip I guess I would go ahead and laminate. Probably not too challenging for someone with the skill to make this in the first place!

A1t2o, if I’m following what you’re saying, instead of laminating the two sides/faces of the handle you would essentially square the top off and laminate that with say a 1” wide strip? That would be a bit easier compared to the former since there’s only one face to glue. Probably won’t be as strong but it would likely not fail.

HikePaddleBike: "A1t2o, if I’m following what you’re saying, instead of laminating the two sides/faces of the handle you would essentially square the top off and laminate that with say a 1” wide strip? That would be a bit easier compared to the former since there’s only one face to glue. Probably won’t be as strong but it would likely not fail. "

I've made a few paddles, and my kids have all made their own. I'd maybe laminate on both sides as opposed to the top. Depending on what adhesive you use, it may pop off eventually as it would receive a lot of push/pull during it's life. Just my hunch.
The first paddle I made was a-single piece black walnut, really loved making that one. It was too heavy, so it sits on our mantle. I then tried laminating, experimenting with different kinds of woods to reduce weight. I've cracked the shaft of two of them. a laminated handle piece has fallen off the grip of my son's. Decided to try a carbon paddle...and oh man, I don't think I'll ever go back...but building those paddles was fun!

HikePaddleBike: "A1t2o, if I’m following what you’re saying, instead of laminating the two sides/faces of the handle you would essentially square the top off and laminate that with say a 1” wide strip? That would be a bit easier compared to the former since there’s only one face to glue. Probably won’t be as strong but it would likely not fail. "

No I would laminate the sides, but I'm saying that you don't have to have the laminate at exactly 90 degrees to the shaft. To add the laminate you need a close to perfectly flat surface or there will be gaps between the layers that can become obvious when you start shaping the wood. What I was saying is that instead of trying to flatten the handle as it is now to prep it for the laminate layer, it would be easier to take it to a table or miter saw and cut a corner off on each side.

It doesn't need to be a sharp angle, but you would want the same angle on both faces so it is symmetrical. Looking at the second image you attached, the line of the cut would be from near the center at the top of the handle to the outer edge at the bottom of the handle. See image below. I think that this will look much nicer when you are finished due to the lines it will make on the handle. As long as it is symmetrical, it will be a great feature.