Is epoxy a good selection for filling knot holes in soft maple? If so, is there a specific product, e.g. marine epoxy, or brand of epoxy that works best for wood applications? After milling up stock, I’ve found several knots that are almost the full width of the piece and in one case, almost full depth as well. This is for a workbench top so these can be placed strategically in the laminations to limit any loss in stiffness but I’d like to repair these areas to minimize that. Thanks, Brett
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Replies
Brett,
Normally, for filling knots I use a 5-minute epoxy, but for a workbench, I don't know if that's the best answer. I don't know about all epoxies, but some dry to a ceramic-like hardness. And that can't be kind to a plane blade which might be an issue when resurfacing the bench. Maybe just cut out the knot? Let's see what everyone else has to say...
My first thought would be to cut the knot out square and glue in a patch rather than filling it with a non wood material.
Check out this web site for pro level info
http://www.systemthree.com/index_2.asp
Generally regular (not quick curing )epoxy is stronger.
I have had no problem with epoxy too hard to plane. If there are strengthening filler/fibers added to the epoxy then there may be an issue.
Epoxy is just plastic, hardened oil, not too hard to plane. Some body correct me if I am wrong.
Here is another web site with excellent info ( see " How To Use " ) and excellent epoxy.
http://www.westsystem.com/ss/
Good epoxy is costly but long shelf life if not mixed.
System 3 epoxy, which is readily available at Woodcraft and online, is a very good epoxy to use for this application. I have built many rustic tables with "character" in the wood, and have filled many, many knotholes and checks with their epoxy. It works really well, and doesn't crack later. I'm looking (right now) at a coffee table I built 4 years ago with bookmatched crotch cherry, and the epoxy I used to fill all the crevices is invisible.
It would work well for you, and add some structural strength. Make sure when you do your glue up that you stagger the knots in your lamination for the benchtop so spread the weak points individually around the benchtop.
Also, the epoxy planes and scrapes very well without issue. I would plan on scraping it with card scraper if I were you, as it won't be showing anyway.
Jeff
About a year ago I built a wood stripped kayak and shot up the learning curve on epoxy. I use West System, which may be purchased many places, for me purchased at West Marine. I learned the most about filler to use by talking to a marine fishing fighting chair manufacturer. West System has many different fillers depending on what characteristics you want. I would use the standard 105 resin with a long working time hardener (207 I believe) and collocial silicia as the filler. Meter out the number of pumps you need for resin and hardener an mix together per instructions (2 or 3 minutes of mixing), then add the filler mixed with fine sawdust (mix another 3 minutes) until it reaches the consistency of peanut butter. After glue up prior to drying wipe off the squeezed out epoxy with alcohol (acetone is dangerous to people). You should be fine. Working the epoxy is like a hardwood. Even with sawdust, the color will not be as light as the wood. Also, if you use the fast hardener (205 or 206) the glue line will be much darker.
Given the amount of time it takes to make a workbench top, and the number of years it should last, I would hesitate to use a piece with a near full thickness near full width knot. Even with epoxy filler, it strikes me as a butt joint, which I wouldn't want in the middle of a bench top. Just my opinion.
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