West System Epoxy Filler — Which one?

[Tom Bain]

I need to fill some relatively large voids in some punky-ish wood I’m using in a project. There is no structural requirement for the fill, it’s purely aesthetic. There are so many choices for fillers with the West system, I’m not sure which to use. I’m leaning toward the 407 or 410 fairing fillers since I will need to sand and finish the areas being filled, but if others have advice or experience with this, I’m all ears.

Thanks.

[Steve Jenkins]

Not sure if it really matters. I used sanding dust and it looked like the filler I have (don’t remember the number). I’ve also left it clear so you an see down into it. Sanded and finished fine

[Rick Whitehead]

I've used the colloidal silica before. We mixed it with the epoxy resin and black dye to fill knots and voids in walnut.It worked very well.
Rick

[Malcolm Schweizer]

I find 407 to have a very man-made look to it, ie the color isn’t natural looking. I have dyed it, but you still get specks of color in the fill. 410 is white if I’m thinking of the right one. I like to use wood flour and I dye it with either paint colorants, or the best black I’ve found is to break open an old printer cartridge and add the powder from it.

Beware that with West System and other structural epoxies the cure is exothermic and you can’t pour too much at a time or it gets hot. I would use a resin made for pours that doesn’t get as hot. The down side is long curing times, but longer cure times also means less bubbles and voids, as they have more time to float out.

*edit- the second paragraph is if you are just going to do a pour. Since you said it’s not structural, a pour would be the easiest. Fillers are to add strength or to make it easier to sand. You can just run it through the planer after pouring, so there isn’t a need for micro balloons.

[Thomas Colson]

I have gone through gallons of various manufacturers of epoxy filling thousands of BF of punky/bug eaten/cracked reclaimed barnwood. I started with West, and used both the fast (dried TOO FAST) and medium hardener. For the past 2 years I've been using whatever generic "Table Top Epoxy" ships for free next day with Prime on Amazon. They're all the same, albeit cost half as much as the West stuff. IMHO you don't need any fancy/expensive "fillers", generic epoxy will work. Disclaimer, I'm using black dye. What I've learned: It always takes me two "pours" to achieve a fill. I never attempt to entirely fill a void in the first pour, all it does is leave me with so much epoxy on the piece it destroys my planer blades. The issue is, especially with punky wood, and wood species, is I've found that especially dry, old wood drinks up that epoxy like I do beer at the end of a long weekend pouring epoxy. So my first pour is just to coat the insides of the void, let it dry, then the second pour to fill the void. I see a lot of the high-end live edge slab epoxy table guys do this on their YT channel. If you have really complicated geometry, you can use caulk or hot glue to make "dams", provided you can get rid of them without destroying the piece. I rarely do this, but when I do, it works great. I have also found that with the cheapo Amazon epoxy (70$/gal), I get a longer pot time and less bubbles than I was with the West. As for void prep, I use plenty of painters tape on the other side, cellophane tape will work as well, and I used compressed air to clean out the voids. For smaller voids, I use a thin stick to "drip" the epoxy in as to avoid getting epoxy all over the piece. I've had better luck with very rapidly waving a blow torch over the piece as opposed to a heat gun, which requires you to "wave" slower but puts more heat/time on the epoxy. For mixing, I use the highly calibrated system of "A sharpie line on a clear dixie cup" and I've never had any problems with incorrect ratios as long as I mix for 2 or so minutes. Epoxy is like purple PVC pipe primer, it runs uphill, so I also keep on hand (at 40$ a box now!) some latex gloves, and I cover my workbench with an old tarp. For liquid dye, you only need 4-5 drops per dixie cup, powdered dyes end up looking like....powdered dyes. For thick/big voids, if time is an issue, I'll fill the void up to about 1/8 below surface, let it get tacky, then do another smaller mix and fill the final 1/8th inch to avoid exothermic cracking. All depends on how much is in your dixie cup and shop temps, I have no formula for success other than a small pile of failed pours when I first started out. I've got a pretty good work flow going now, and the only thing I can think of is: I never mix more than 1/2 dixie cup at a time. If you end up with too much epoxy "proud" of your work surface, I hit it with a belt sander at 60 grit before sending it thru the planer or the drum sander. Also note that any sanding/planing with an epoxy filled piece, you need to be wearing mask/respirator, even with good dust collection.

[Scott Winners]

If you don't need structure strength I would avoid the #406 colloidal silica. It is great for strength where you need it. I find the silica leaves a white tint in the cured glue, the more silica I add the whiter it gets - and that stuff is really really bad on lung tissue. If you are going to fool with it you don't just want a respirator, you want a respirator with a really good seal all around and you want to leave the shop doors open for many may air turnovers before you take off the respirator.

I have only ever used wood flour/ fine sawdust for non structural fill, but you can't hardly shake a stick without finding a couple dozen folks raving about micro balloons.

[Tony Latham]

For filling knots, I use finally ground coffee. It helps make the grain wake up.

T

[andy bessette]

Glue in a fitted wood "plug".