When I fill in cracks or larger voids, I use a black epoxy.
Then I come back after first sanding grits and fill the little microvoids from bubbles or whatever I can spot that appears, or I missed prior.
My struggle is to fill these usually proves to be very difficult. It usually takes me multiple attempts and resanding to complete them.
I’ve tried black hot glue pressed down, black CA glue, and black epoxy, I’ve did the glue and dust, but that doesn’t work so well on epoxy and black wax crayons.
I’ve tried pressing, brushing, heating, and poking it all in to try and persuade it to get in the little voids, but it just doesn’t like to go.
The only other thing I know to do is to drill them bigger and fill them again with epoxy, basically.
My issue with this is with voids that aren’t in the epoxy to begin with. I would have to make a tapered scrap of wood, tamp it in, cut it, and then sand it.
And it’s just generally a lot of work to do 20 times once for each little microdefect.
I hope you guys can give me more ideas to try, tricks, products, or techniques.
It’s been getting on my nerves lately and can delay my projects at a very unenjoyable stage.
Replies
I've used a heat gun or small butane torch to heat up the epoxy. This is supposed to make the bubbles surface and disappear from the surface of the layer that is curing. Sounds like you tried that already.
Also, if the cracks, etc. are deep multiple, thinner layers of epoxy should help eliminate the bubbles. Then, if any bubbles remain, pouring a thin layer over the top of the whole crack or void and scraping or sanding it off should yield a smooth surface without voids.
I don't use epoxy much but did some natural edge tables last year and worked with System Three (epoxy company). They sell a variety of epoxies made for different types of work. They had an epoxy that is made for deep fills which was intended to eliminate the bubbles. They also did say that their general purpose epoxy could be used on any fills, even deep ones, but it should be done in multiple thinner layers to avoid significant generation of heat when curing and to eliminate the bubble problem.
Though I'm no expert, my tables turned out well without any voids or bubbles. I don't think it's advisable to just fill small voids. That works with wood filler, but I don't believe, given what I know about epoxy, that it works well with epoxy. I would just
pour a final thin layer over the top and sand it off instead. Others, more experienced than I am, might disagree.
I've never used deep-pour stuff as I have yet to do a project requiring that much epoxy. My pours are an inch or 1.5 deep at most and pretty skinny.
Does deep-pour stuff not make any bubbles compared to tabletop or regular?
Could I try using deep pour for the little voids?
My only issue is that I was under the impression that deep-pour stuff takes a really, really long time to cure, and I can't delay a project for a week because of a micro void.
Overfill sightly and use the torch like grbmds suggests, then put a fold in the back of a single edge razor to curve the blade and use it as a scaper to get the hump flat before sanding. With luck your surface bubbles will be above the surface and scrape off.
I use a clear two part epoxy and add powered graphite to make it black. It is rather fluid and easily gets into cracks. If the crack runs thru the board, I tape the backside to prevent bleed out. I do not see bubbles like I did with the epoxy I got from HD or Lowes. Mix it, add the powder, dab it on the void. Then keep filling the area until no more goes into the void. Works well for me.
Hmmm. I always pop bubbles with a torch.
I also slightly overfill and pop as suggested. I don't go too far—maybe 1/8 high, 3/16 at most.
I use West System 105a epoxy and powder to get black.
I'll have a tiny little bubble here and there. It adds up over the whole project.
It seems unavoidable to me to have some of these. Am I wrong about that? Do I need to try a different epoxy, then?
It's certainly not a cheapo brand, and I like it besides this. I don't know if the epoxy is to blame here. Good rep.
The thin final layer would do nothing but waste the expensive epoxy, as I would have the same issue as when I dab it on the little bubble voids.
It just doesn't fall into the hole. It's like the surface tension is just preventing it, even when I poke the heck out of it and heat it up.
I'm talking about small voids. 1/32 1/16 even smaller.
Can you overheat the epoxy? I haven't tried leaving the torch on for multiple seconds for fear of scorching the wood or ruining the epoxy itself, but that might thin it more. I can run some tests with that and report back.
System Three customer support indicated that 2" thick pieces would be a candidate for their Mirror Cast or River Cast, but wasn't necessary if I did a 2" pour in 3 steps or possibly 2. It's almost impossible to get it perfect in one pour anyway. I've never heard of epoxy that takes a week to cure (might just be my inexperience).
I found that dry colorants work well. In fact, a professional furniture make who does quite a bit of natural edge work suggested I use fine sawdust from the piece I'm working with to create the color. That worked really well for me. The color blends in well with the surrounding wood. No "micro" voids similar to those you describe.
I doubt that trying to fill them would be successful as you've found out. There just isn't enough surface area to hold the epoxy in those tiny holes. I tried a few and was not successful. I just ended up making sure that my pours exceeded the surface of the wood enough that, when I sanded the eposy flush with the surface there were no voids.
As for heating the epoxy, a torch works well, but I have found that a heat gun works just as well or better (a heat gun though, not a hair dryer).
I would suggest that you contact customer support from whatever brand of epoxy you are using and ask them what they would suggest. If their customer support won't respond or give a good answer, maybe try a different brand. There are a number of them. I was very satisfied with System Three, but can't tell you whether they are more expensive than others (but of course cheap isn't always best).
I use a heat gun and it works really well, I use masking tape around the crack that allows me to overfill and I pre-heat the epoxy so it is watery when I fill and the bubbles have already escaped.
Good idea about the heat gun you and grb mentioned. I have a great heat gun i dont know why i never though of using that instead of the torch.
I have a feeling if i can get it watery like you said it might just do the trick.
Ill report back soon.
I was running into similar problems filling voids in bowls and table tops. Like you, I hit the resin with a torch, then switched to a heat gun for fear of scorching. I'd leave the piece to cure confident that all the bubbles were gone only to find new ones as I worked my way through final sanding. What has helped tremendously is to preseal the void by "painting" it with resin as best I can. Can't always get all of the crack sealed before filling, and it does add a second step, but as best as I can figure, some of the bubbles are formed by air coming out of the wood. You don't need to let the preseal dry completely, tacky is good enough. Same with pouring in layers. Hope this helps. I feel your pain.
That's really clever
Thanks Ben, wish I could take full credit.
I always preseal the main larger voids but never considered presealing the micro ones.
I will try getting it water thin with a heat gun and try to preseal the smaller ones too.
Im feeling confident with these new tips. thanks guys.
....but as best as I can figure, some of the bubbles are formed by air coming out of the wood....
In the Chesapeake Light Craft book that came with my dory kit it mentions that a way to minimize this is to put the epoxy on as the day is cooling down, not as the day is heating up. That way air in the wood is contracting, not expanding and making new bubbles.
Okay, so reporting back here. I tried what was mentioned about heating the epoxy up until its very warm and water thin with a heat gun.
I did this on some end grain splitting cracks that would normally give me a ton of trouble with micro voids.
I'm happy to say it worked like a charm. I stood there and popped bubbles for about 20 minutes, then came back a few times for the next couple of hours to pop them with a torch. When I cross-cut the excess off, there was not a single micro void.
I could see that the air was bubbling out a ton with that warm epoxy—much more than normal. I'm sure the wood being warmed up also caused this.
To me, this also confirms I should be presealing any void that is possibly large enough to do so. Not only the main pour edges.
These particular ones weren't big enough, but they were these deep, lengthwise cracks that released tons of air. really good test scenario.
Gulfstar, I very much appreciate your specific tip. You and thehistorydude are spot on.
Thanks everyone for your suggestions.
I'm feeling great about this moving forward now.