filling knots and cracks with sawdust and epoxy vs. sawdust and wood glue?

[kooshball]

I have to fill some knots and cracks within knots on my walnut bed but I would like some advise on the best way to do it. Can I go for sawdust with wood glue or am I better off using epoxy?

Thanks,

 

[Bas]

I'd use 5 minute epoxy. I mix it with some coffee grounds to get a nice dark filling for the knotholes. Sawdust would work too, but may look unnatural in a knothole. The good thing about epoxy is that it won't creep like PVA glue and it's much harder.

 

[Tar Heel]

I have used walnut sanding dust (not sawdust) and CA with very good results.

 

[kooshball]

I'd use 5 minute epoxy. I mix it with some coffee grounds to get a nice dark filling for the knotholes. Sawdust would work too, but may look unnatural in a knothole. The good thing about epoxy is that it won't creep like PVA glue and it's much harder.

Any issues with yellowing of the epoxy?

 

[Bas]

I haven't seen any yellowing, but my woodworking experience with walnut is limited. Certainly nothing within 2 years. BTW, when filling a large knothole with epoxy, check the back and if it goes all the way through, put a piece of masking tape over it. Otherwise, you may attach the board to something permanently...

 

[Matt Furjanic]

Coffee Grounds! Why not! Now there's an idea...
I agree with Tar Heel on the sanding dust vs sawdust; although, on a knot sawdust would probably work okay.
Usually, on walnut, the knot is darker than the surrounding wood. I have had excellent results mixing in some ebony or wenge sanding dust in with the walnut dust to get a good color match.
Definitely go with the epoxy. Its harder, and doesn't shrink. You may have to use more than one application of epoxy, as it will sink into the wood and leave a depression on the first try. If so, you probably want to apply the second coat within a few hours (talking 5-min version); otherwise, after the first application fully cures, the second coat will not make a good bond with the first.
Hope this helps.
Matt...

 

[CarvedTones]

Epoxy will break down from exposure to light over time if there is no top coat of finish over it, but it doesn't require much to protect it. Just a little lacquer or varnish. Get it very near flat when you fill. A little "fudge factor" that seems like a good idea when you are filling it is a major pain to sand away later (DAMHIKT).

 

[Bas]

Epoxy will break down from exposure to light over time if there is no top coat of finish over it, but it doesn't require much to protect it. Just a little lacquer or varnish. Get it very near flat when you fill. A little "fudge factor" that seems like a good idea when you are filling it is a major pain to sand away later (DAMHIKT).

Sanding is definitely a pain. A block plane or scraper works quite well on epoxy. Just make sure you let it cure for 24 hours. It hardens within 5, but it will still be a little gummy on the inside.

 

[CarvedTones]

I get myself in trouble talking epoxy sometimes, but here I go again...

I had troubles with the quick stuff a while back. I tossed what I had and got some newer better packaged (not the syringes) Loc-Tite 5 minute stuff and have had good results with it. For void filling, 5 minutes is about how long it takes for a film to form on the top and it will not run after that if you made a decently thick slurry. In the instructions on the Loc-Tite, they refer to 5 minutes as the "set time" and 24 hours as the cure time. Using it as an adhesive, you have to be really careful about what "set" means. Put some pressure on it anytime in the first couple of hours and you can get some creep. I also have some 2:1 slower laminating epoxy I often use for void filling, but after getting some better 1:1 quick stuff, I have to recant on my earlier opinion (in other threads) about that offering any significant advantage. There are some 5 minute products out there that never get all that hard though, so just make sure it really is a decent epoxy.

 

[Bill Clemmons]

I just did exactly what you're talking about on some turned walnut legs for a table. I gathered some fine sanding dust from the piece and mixed it w/ epoxy. I use the 60 min. variety, but the 5 min. works just as well. I just prefer the longer working time. One of the keys I've found when filling voids w/ epoxy is to stir it VERY slowly. Otherwise you will create bubbles which will gradually rise to the top and be visible when it is cured.

Another way to color epoxy is with black tint. If you want to highlight or put emphasis on a spot, like a knot, add black artist tint. But again, stir slowly, as if you were moving in slow motion.

Also, as some others have pointed, definitely plan on two applications. The first one will settle into the void and leave a depression. I use a scraper to remove the excess around the spot, and try to do it just before the epoxy hardens completely, but cured enough that it won't pull out of the void. Its a little easier.

HTH, Bill Clemmons

 

[Gofor]

I use the 5 min loctite epoxy and walnut sawdust. I have found it is easiest to tape close to the defect (blue masking tape or cellophane packing tape both work well) and fill level to the tape surface. After about 15 - 20 minutes, remove the tape, and it will be soft enough to pare with a sharp chisel flat with the surface. This will greatly reduce the sanding/scraping, which are a pain.

Pics of how I do it are here: http://www.ncwoodworker.net/pp/showgallery.php?cat=1349. They will give you an idea of what it will look like.

Go

 

[Bas]

Coffee Grounds! Why not! Now there's an idea...

Cocoa powder makes for a terrific medium brown. Not kidding. I haven't gotten into using Paprika yet, or Curry, but I'm sure one day I'll need a special color....

 

[kooshball]

Who has the oldest knot filled with coffee? I am curious as to how this will age (fading, reacting to epoxy, etc) although if you have a good UV resisant top-coat it should all be ok with the fading.

 

[Jeff]

My main complaint with some of the epoxies from the big box stores is that it's hard to measure them out for the exact 1:1 mixture (eyeball it?). The smaller tubes with the self mixing nozzle/head work well, but you only get two (2) nozzles which can't be cleaned (supposedly acetone or ethanol will work if used right away). For small projects like filling knots you'll have a bunch of leftover epoxy resin and hardener in the dual syringe tubes, but no nozzles to dispense and mix it . Cost effective? :icon_scra

The chemical reaction which creates epoxy only happens when the resin and hardener are mixed so the commonly held theory that either component "gets old" sitting on the shelf is hogwash. Store it as recommended by the manufacturer and it should last for years.

West System epoxy is a little pricier, but you've got a lot of options from resins, hardeners, open time, cure time, fillers, etc. For starters the #105 resin (1 qt) and #205 hardener (1 pt) is an economical choice that'll give you a lot of epoxy for your buck. The metering pumps ($13 for the set) are designed to dispense the precise amounts of resin/hardener each time you use them. No need to clean them either, but they can be cleaned and stored away if you wish. Check out the West website for loads of useful information on product selection and applications.

http://www.westsystem.com/ss/

ccasion1

 

[Glennbear]

My main complaint with some of the epoxies from the big box stores is that it's hard to measure them out for the exact 1:1 mixture (eyeball it?). The smaller tubes with the self mixing nozzle/head work well, but you only get two (2) nozzles which can't be cleaned (supposedly acetone or ethanol will work if used right away). For small projects like filling knots you'll have a bunch of leftover epoxy resin and hardener in the dual syringe tubes, but no nozzles to dispense and mix it . Cost effective? :icon_scra

The chemical reaction which creates epoxy only happens when the resin and hardener are mixed so the commonly held theory that either component "gets old" sitting on the shelf is hogwash. Store it as recommended by the manufacturer and it should last for years.

West System epoxy is a little pricier, but you've got a lot of options from resins, hardeners, open time, cure time, fillers, etc. For starters the #105 resin (1 qt) and #205 hardener (1 pt) is an economical choice that'll give you a lot of epoxy for your buck. The metering pumps ($13 for the set) are designed to dispense the precise amounts of resin/hardener each time you use them. No need to clean them either, but they can be cleaned and stored away if you wish. Check out the West website for loads of useful information on product selection and applications.

http://www.westsystem.com/ss/

ccasion1

Thanks for posting this Jeff, my first major woodworking project was a tack box for my daughter to take to equine college. The plans recommended West system for joinery and it worked out well. :wsmile:

 

[CarvedTones]

The chemical reaction which creates epoxy only happens when the resin and hardener are mixed so the commonly held theory that either component "gets old" sitting on the shelf is hogwash. Store it as recommended by the manufacturer and it should last for years.

I absolutely agree about the resin with one big if - if it is 100% epoxy resins (a little inert filler is okay), but I respectfully disagree about being able to make such a broad statement about hardeners. I have had some hardeners (RAKA medium is an example) that do seem to last and last and others, WEST being one, that don't keep as well. There seems to be some volatile stuff in the mix and I am not sure if the hardener breaks down or if something evaporates or condenses enough to throw the ratio off, but the better hardeners that give you the hard clear surface seem to have a shorter shelf life.

 

[magellan44]

This post comes in time for me, I'll be building a few interior doors and after looking over the stock that I'll be using I have found that I'll need to fill a few larger voids. A few go the entire way through the stock. I remember filling a few like this years ago in fact it's been that long that I think I used 5 minute epoxy but really can't be sure. I had good results and I remember passing the pieces through the planer without damaging the knives as I remember. Has anyone passed the stock through their planer since filling the voids or do you just pare the excess off when the material is at finished thickness?

 

[scsmith42]

Speaking of tinting.... one neat trick that I learned from Gary Conklin (NCTurner) is to use charcoal briquette dust for a black tint in CA or epoxy. Charcoal usually does not fade either, and it is cheap and available.

Don Patterson showed me the West System Epoxy; clearly it is one of the best options available.

 

[Jeff]

I absolutely agree about the resin with one big if - if it is 100% epoxy resins (a little inert filler is okay), but I respectfully disagree about being able to make such a broad statement about hardeners. I have had some hardeners (RAKA medium is an example) that do seem to last and last and others, WEST being one, that don't keep as well. There seems to be some volatile stuff in the mix and I am not sure if the hardener breaks down or if something evaporates or condenses enough to throw the ratio off, but the better hardeners that give you the hard clear surface seem to have a shorter shelf life.

Andy,

I can't disagree with your experience. I'm just starting to use some West epoxy instead of the Loc-Tite product from Lowes. What was the time-frame over which you noticed the apparent degradation of the hardener? What observation led you to conclude that something about it was funky? :dontknow:

The West specs claim a shelf-life of years for both resin and hardener "when stored in sealed containers". Sounds like "sealed containers" is the operative statement.

http://www.sterndrives.com/supplies/epoxyresin02.html

I've emailed the West folks about how to reseal the containers and thoroughly clean the dispensing pumps between uses. I'll post that info when I get it. We aren't boatbuilding here, so we probably only need a tablespoon or two at a time for a one-off use. Probably need to reseal the containers in between uses.

BAS recommended paring the epoxy before it fully hardens and then using a card scraper for smoothing. +1 on that. It planes fine without tearing up the blades! :icon_cheers

 

[CarvedTones]

Oddly enough, I have recently started to form a better opinion of the Loc-Tite stuff since getting some in the 2 separate bottles. It is a lot easier to get a 1:1 mix accurately for small jobs, sometimes eyeballing a couple of nickel sized puddles (they seem to have purposefully thickened the hardener so it is about the same) and sometimes using whatever small vessel is handy, like a twist off top from a water bottle (throughly dried, of course) or anything else it is easy/cheap to grab 2 of.

For larger jobs, I still have a fair amount of a different epoxy and some 2:1 hardener. That is not West; I will get to that in a minute. Anyway, the more recently acquired admittedly somewhat cheap epoxy and hardener seems to have some ammonia in the hardener and while it worked fine when new it has definitely degraded. It is a thin hardener to make the epoxy easier to spread over a wide area for sealing. I also have a little bit of the RAKA medium hardener I mentioned earlier that is probably 10 years old and still works fine.

My experience with West is mostly from quite a while back in boating repairs. West was pretty much the only brand I ever found in boating equipment stores (this was pre-internet, I am talking about walk in stores in Atlanta around 1980 and in Denver during the 80s). I would get the smallish kit for repairing dings and on a couple of occassions had to get the larger one to apply a little tape. After two or three seasons, the hardener would darken and thicken and the mix would stay tacky for several days and always felt soft even after it seemed to be dry.