I started learning how to do kerf cuts to make a rounded storage box. I knew that I could make the outside the flat side so the kerf cuts wouldn’t show, but I wanted to know how to fill in the kefir cuts on the inside. So, I researched how to do it and put together this article to explain it.
You fill kerf cuts by using epoxy/resin or glue. The best are those who have stuck well to wood, and you can use many specialty products. Depending on the project, you either need to screw or nail the wood into place first and then fill it, but you also use clamps.
Below I’ll give you a list of better glues, epoxies, and resins to use. And detailed instructions on how to hold your wood in a curve while you fill the cuts. So, read on to discover this and other helpful tips about working with kerf cuts.
At our Cucamonga Woodworking live online workshops we discuss bend and steaming wood at about the 5 minute mark of this video. You can also check out our other past workshops on Youtube Here(Link to Cucamonga Woodworking)
What should you fill kerf cuts with (best options)?
In my opinion, PVA glue mixed with sawdust is the best option. I’ve summarised in the table below:
| PVA glue (yellow glue) | Resin | |
| Shelf life | 1 to 10 years | 6 months to 1 year |
| Cost | $20 per lb (1 litre) | $40 per lb (1 litre) |
| Appearance | Good | Good |
You can use any wood glue mixed with sawdust or resins. PVA glue mixed with sawdust is the easiest for most folks since you’ll always have some around, and mixing it with sawdust makes it go a long way.
Also, resin’s shelf life is a lot shorter than PVA glue, which means if you have some leftover, you can use it for another project without it going bad. According to the Wood Whisperer, PVA glue lasts about 1 year, at least in an opened bottle.
But, it can last as long as 10 years. Resin, on the other hand, lasts about 6 months to a year in the bottle, according to Wood Epoxy World.
PVA glue is very cheap, and because you will normally need quite a lot of it, it is my favorite. But, epoxies are a lot thicker and are easier to apply. Resins are also good, but they can be quite pricey. Epoxies are also normally more expensive than using PVA glue.
A 32 oz bottle (1 liter) of resin that works well on wood costs about $40. Whereas the same amount of PVA glue only costs about $20. As you may be aware, PVA glue and yellow glue act the same. They have different names – yellow glue is PVA glue with an additive that makes it yellow.
My recommendation for the best PVA glue is Titebond III Ultimate Wood Glue, 8 oz.
And, my recommendation for the best resin for wood is Dr. Crafty Epoxy Wood Resin Kit – 1 gallon (Click on the link to check the current price on Amazon)
They also have a similar appearance to each other once they are dry. So, now that you have a good idea of what to fill kerf cuts with, I’ll include a step by step guide on exactly how to do it.
Whether you’re an experienced woodworker, carpenter, or joiner, or you don’t have any experience, this guide will work for you.
Step by step guide to filling kerf cuts
The hardest part about filling kerf cuts is getting the glue or resin into the cuts and holding the curve in place while the glue or resin dries. For this guide’s purposes, I’ll say glue, so I don’t have to say glue or resin each time. But, each of the steps works whether you’re using glue or resin to fill your kerf cuts.
Before executing the steps, it’s important to know that the order you do the steps in depends on the exact project you are working on, and you can interchange the two steps – holding the curve in place and filling it with glue.
1. Hold the curve in place
You need to hold the curve in place so that it doesn’t move around when the glue is still wet. You also want to secure the curve in place because, with really tight curves, the glue may not be strong enough to hold the curve in place once it dries.
Depending on your specific project, you will want to use screws, nails, or clamps to hold the curve’s shape. In most projects, you will be putting the curved piece of wood around a frame of some kind. So, you can also attach it to the frame using glue. Then once the glue has dried, you will fill in the kerf cuts.
The woodworking plans you are using will often have instructions for how to attach the kerfed wood to the other parts of the project. So, go ahead and follow those. If it’s something custom that you have put together, then you’ll want to use enough screws, nails, or glue to hold the curve in place before you fill in the kerf cuts.
In some project designs, you can also layout the kerf cut wood on a table, fill the kerf cuts with glue, and then clamp it into place while it dries.
2. Fill in the kerf cuts with glue
This can be quite easy and fast depending on the order in which you fill your kerf cuts. If you fill them with glue first and then clamp them or screw them into place, it’s straightforward and fast.
But, if the project’s requirements mean that you need to screw, nail, or clamp it into place first, then it is trickier to get the glue into the cuts. Either way, you can brush the glue or glue and sawdust mixture into the cuts. Then you’ll want to wait for it to dry.
You often need to apply glue twice to fill the cuts. Because it’s hard to get it perfect the first time. So, I recommend filling them as best you can once, waiting for it to dry. And then applying glue a second time to fill the cuts.
I wrote another article about how long it takes for wood glue to dry. You can read it by clicking here How Long Does It Take Wood Glue to Dry?
After all, that’s done, you may want to finish the kerf cuts to improve their appearance
Finishing the filled in kerf cuts
To finish the filled in kerf cuts you’ll want to:
- Sand down any excess glue or resin
- Glue a piece of paper backed veneer
But, you can also glue, nail, or screw the reverse side of another piece of kerf cut wood on top of it.
1. Sand down any excess glue or resin once it’s dry
You want the least amount of overflow as you can because you will need to sand down any parts that are sticking out. And with the curved surface of a kerf cut, you’ll need to do it all by hand.
2. Glue a piece of paper backed veneer to it
Paperbacked veneers have a shiny surface on one side and paper on the other. And they are by far the easiest option. The shiny side should face outwards and is the part you will see once you’ve glued it on top of the surface of the wood.
A drawback of a paper-backed veneer is that it isn’t natural wood. Which, in my opinion, looks a lot nicer. It depends on what you like, and how much time you need or want to spend finishing it.
3. Attach the reverse side of another kerf cut piece of wood to it
When you finish your project this way, both kerf cut surfaces will face each other. And both sides will have a nice wood finish. You can either fill in the kerf cuts of both or leave them unfilled because you won’t see the kerf cuts when they’re glued together. If you fill the kerf cuts, though, it will make it stronger.
And that sums up everything you need to know about filling kerf cuts.
Conclusion
You fill kerf cuts by holding the curve in place and then filling it with glue or resin. Wood glue is cheaper than resin, and both have a similar finish. If you hold the curve in place and then fill them, it can be more tricky than filling them with glue first and then holding the curve in place.
Each project is unique, and you should do it the way that makes the most sense for your specific project. And based on your experience.