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Epoxy dam for filling knots

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Forum topic by BuckeyeDennis posted 12-13-2019 04:01 PM 384 views 0 times favorited 9 replies Add to Favorites Watch
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BuckeyeDennis

67 posts in 307 days


12-13-2019 04:01 PM

Topic tags/keywords: knots epoxy dam turning

I’m turning a bowl that has a couple of punky/checked knots in it, and I want to stabilize the knots with tinted slow-cure epoxy while the bowl is at the rough-turned stage. I covered the outside of knot #1 with blue painter’s tape, and then filled the knot from the inside of the bowl. That went pretty well, and the knot soaked up epoxy like a sponge. I just kept adding epoxy until the knot wasn’t thirsty anymore.

When I removed the tape after the epoxy cured, I found that some of the epoxy had flowed through the larger checks all the way to the outside of the bowl, but that most of the knot’s outside surface still needed to be filled. And filling the outside of the knot was a pain. The bowl surface there is convex, so the epoxy wanted to keep running off of the knot. It took a whole lot of babysitting to get it filled.

Before tackling knot #2, I’m looking for a better way to control the epoxy. Making some sort of dam around the knot seems like a good way to do it. Then I can overfill with epoxy, let it penetrate at it’s own pace, and simply turn off any excess cured epoxy during finish turning.

Any advice on a good way to form an epoxy dam on a bowl? A ring of rope caulk is my leading idea right now, but I’m hoping that you experienced turners might be able to share some proven methods.

-- Dennis 'We are all faced with a series of great opportunities, brilliantly disguised as impossible situations.' Charles Swindoll


9 replies so far

View AZWoody's profile

AZWoody

1477 posts in 1832 days


#1 posted 12-13-2019 04:17 PM

I’ve seen people use silicon caulk so you’re on the right track thought-wise.

View Davevand's profile

Davevand

151 posts in 1445 days


#2 posted 12-13-2019 04:30 PM

I haven’t used it myself, but I see people use hot melt glue

View LesB's profile

LesB

2318 posts in 4051 days


#3 posted 12-13-2019 06:40 PM

Not a fan of messy epoxy for that purpose and where the knot material is still there but soft or loose. I use thick or medium thick CA glue. If there are gaps larger than 1/8” I pack them first with a matching color sawdust (collected with a orbital or belt sander). If the knot or filling is somewhat dense I first apply a coat of thin CA glue, immediately followed by the thicker glue. The thin glue acts to wick the thicker glue into the wood or sawdust. As you continue to turn the piece you may find pockets that did not fill and you will need to stop and fill them. I have used this method to completely fill missing knot holes and larger cracks with sawdust then the CA glue.

-- Les B, Oregon

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CaptainKlutz

2257 posts in 2103 days


#4 posted 12-13-2019 09:03 PM

Sorry I don’t turn much. But have used epoxy for many decades in laminating, and casting work.

Standard modeling clay works well as dam. Is usually reusable too.

Use tape a lot for small fill areas. Have used all kinds. Like the thick plastic box sealing tape best, as it removes in one piece, and doesn’t stick to adhesives. Run a circle around with 1/4-1/2” flap sticking up around the area to be filled.

Best Luck.

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

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BuckeyeDennis

67 posts in 307 days


#5 posted 12-14-2019 03:06 AM

Thanks for the feedback, guys. It looks like there’s a lot of ways to skin this cat. Hot glue dams never occurred to me, and I already had the stuff on hand. Probably a bit harder to remove than caulk or modeling clay, but I have no doubt that it would get ‘er done.

I’d be concerned about using silicone caulk, having recently painted some brand-new window sashes where it made the paint fisheye like crazy. But Google did find a few recommendations for using latex caulk to make epoxy dams. And one or two recommendations each for modeling clay and rope caulk.

Les, I do need to get up to speed on using CA glue. Back when dinosaurs roamed the earth and I was a youngster building and crashing RC airplanes, I used CA glue for quick-and-dirty crash fixes, and epoxy when I needed a bullet-proof permanent joint. But it seems that CA glue and techniques have come a long way in the intervening 40+ years.

As for epoxy being messy, for most of my life I would have agreed with you. But I bought some System Three epoxy for a windowsill rebuild last year, and took to heart their advice to use only disposable stuff for mixing and handling it. Party supplies are now my friends. Plastic cups for mixing, plastic spoons for measuring. Disposable wooden paint stirrers for troweling the stuff, and super-cheap disposable paintbrushes if I need to spread it.. My skin never comes into contact with the epoxy, and the few pennies worth of mixing tools go straight into the trash. So there’s no sticky glue cleanup whatsoever.

So anyway, in the interest of time (while waiting for Cricket to vet this, my very first forum topic on LJ), I went ahead and filled the backside of knot #2 the labor-intensive way. But I do have several more blanks from the same apple tree, so I’ll likely be revisiting this soon.

Modeling clay and rope caulk both seem pretty ideal for making epoxy dams. Easy to form, no waiting for it to dry, and easy to remove. In the interest of science, I’ll try both of them on my next knotty bowl, and report back with my findings.

-- Dennis 'We are all faced with a series of great opportunities, brilliantly disguised as impossible situations.' Charles Swindoll

View Underdog's profile

Underdog

1438 posts in 2644 days


#6 posted 12-14-2019 12:32 PM

I was doing a commission job for a guy who had done some rather rough glue-ups for me. If I remember right he needed 8 newel posts. As I was turning them, I came across several pretty badly splintered spots where he hadn’t trued up the wood before gluing- he’d attempted to use bondo to patch things up. So I wound up prying off several pieces and gluing them back in place with 5 minute epoxy, which also led to voids that needed filled up. So what I did was use blue painters tape to make a dam on the outside to keep the epoxy from running down the side of the partially turned newel post.

It worked fairly well, but I wasn’t completely happy with it. At least there weren’t big voids and splintered out bits… and it was structurally sound at that point. Since it was to be painted it wasn’t a big deal, but it’s not the way I like to do things.

My problem is that the epoxy always has air bubbles in it and looks like crap. Of course it may be the cheapo five minute epoxy I use.

You apparently use the spendy stuff?

-- Jim, Georgia, USA

View Lazyman's profile

Lazyman

4535 posts in 1996 days


#7 posted 12-14-2019 01:16 PM

I’ve used plumber putty for a dam. Just clean off any residue with mineral spirits. For cracks and knots that go all the way through, I like the aluminum duct tape to seal the other side. I works much better than masking tape IMO. If the wood is smooth enough, you can use it for a dam too but any rough areas may leak.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View BuckeyeDennis's profile

BuckeyeDennis

67 posts in 307 days


#8 posted 12-14-2019 01:57 PM


I was doing a commission job for a guy who had done some rather rough glue-ups for me. If I remember right he needed 8 newel posts. As I was turning them, I came across several pretty badly splintered spots where he hadn t trued up the wood before gluing- he d attempted to use bondo to patch things up. So I wound up prying off several pieces and gluing them back in place with 5 minute epoxy, which also led to voids that needed filled up. So what I did was use blue painters tape to make a dam on the outside to keep the epoxy from running down the side of the partially turned newel post.

It worked fairly well, but I wasn t completely happy with it. At least there weren t big voids and splintered out bits… and it was structurally sound at that point. Since it was to be painted it wasn t a big deal, but it s not the way I like to do things.

My problem is that the epoxy always has air bubbles in it and looks like crap. Of course it may be the cheapo five minute epoxy I use.

You apparently use the spendy stuff?

- Underdog

I’ve been using System Three general-purpose epoxy that I had left over from a windowsill repair project. Woodcraft sells a 1-1/2 pint kit for $38, so the price per ounce is less than tubes of five-minute epoxy. I have the #2 medium-cure hardener, which gives at least half an hour of working time at room temperature. And the stuff is a whole lot thinner than 5-minute epoxy, so it soaks into punky wood and wicks into cracks & crevices very nicely.

The long open time and low viscosity gives air bubbles plenty of time to rise to the surface. Once there, you can just wave a heat gun over them, and they pop/disappear in seconds.

-- Dennis 'We are all faced with a series of great opportunities, brilliantly disguised as impossible situations.' Charles Swindoll

View wildwoodbybrianjohns's profile (online now)

wildwoodbybrianjohns

712 posts in 156 days


#9 posted 12-14-2019 02:26 PM

Plumbers putty sounds like a really good idea.

Caulk, latex or silicone, is commonly used for damns, but it can get into the wood or smear, and to remove it well it has to be more or less cured.

Red sheathing tape for vapour barriers is the best if and when using any type of tape, its what the epoxy pros use.

-- Wildwood by Brian Johns: If you tell the truth, you dont have to remember anything (S. Clemens) Edit: Now where is that darn pencil/ tape measure!

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