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epoxy gluing tweak?

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Forum topic by harum posted 09-02-2018 01:35 AM 973 views 0 times favorited 22 replies Add to Favorites Watch
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harum

364 posts in 2065 days


09-02-2018 01:35 AM

Topic tags/keywords: epoxy curing time mortise tenon gluing

Even though my M&T joints are pretty tight (meaning they can be closed with hand pressure, but the gravity is not enough for the tenons to slide out of mortises), I decided to use epoxy for the four high stress joints in my bench for long term bond.

System Three General Purpose epoxy is relatively thin when freshly mixed and therefore is readily absorbed by the endgrain—which is great because it might be beneficial for the joint strength. On the other hand, curing time is an hour to several hours, which is slow enough for the epoxy to ooze out of the joints just by gravity.

Would it still develop full strength if I first prime the gluing surfaces with fresh epoxy for soaking, then wait until the epoxy starts getting thicker, and finally apply more thickened epoxy and close the joints without the danger of the epoxy leaking out?

Would appreciate any comment! Best wishes, h.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."


22 replies so far

View OnhillWW's profile

OnhillWW

184 posts in 1655 days


#1 posted 09-02-2018 03:00 AM

My 2C
I would dry fit each joint, then mask off the areas around the joint with blue painters tape or similar. Covering the entire area so that no wood is exposed at the joint. Then disassemble the joint. Mix the epoxy and if you think that end grain absorption is important – I don’t with a M&T joint – apply to end grain only and let sit for 5 minutes. While waiting I would thicken the mixed epoxy with very fine saw dust, powdered metal, or micro balloons( made for this purpose). Then liberally apply the epoxy to all joint surfaces, make the joint, secure with clamps etc. now wipe off squeeze out dampened with denatured alcohol. Quickly tape over the actual joint to help retain runout and let this cure. Epoxy will generate a bit of heat and can weaken the tape adhesive at the joint so make sure the tape extends an inch or so beyond the joint. Check the glue pot leftovers from time to time and when the epoxy is the consistency of tire tread or a bit harder remove the tape and trim squeeze out with sharp knives or chisels. Don’t get too fussy at this point just get the big stuff off as once it is fully cured it will be a lot more difficult.

-- Cheap is expensive! - my Dad

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shipwright

8320 posts in 3220 days


#2 posted 09-02-2018 05:13 AM

Read this blog.http://lumberjocks.com/shipwright/blog/series/4499
Thickening epoxy is done with thickeners like minifibres not with fillers like micro balloons and wood dust.
Good thickeners do not weaken the epoxy and will not sag when the cure warms the epoxy.
You should be able to do a clean job while the glue is wet and need minimal to no sanding and cleanup after cure.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese! http://thecanadianschooloffrenchmarquetry.com/

View harum's profile

harum

364 posts in 2065 days


#3 posted 09-02-2018 10:44 PM



Read this blog.http://lumberjocks.com/shipwright/blog/series/4499
Thickening epoxy is done with thickeners like minifibres not with fillers like micro balloons and wood dust.
Good thickeners do not weaken the epoxy and will not sag when the cure warms the epoxy.
You should be able to do a clean job while the glue is wet and need minimal to no sanding and cleanup after cure.

- shipwright

Thank you, Shipwright. A lot of useful tips in your blog. Remember to use thickeners, not fillers.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

View harum's profile

harum

364 posts in 2065 days


#4 posted 09-02-2018 10:51 PM



My 2C
I would dry fit each joint, then mask off the areas around the joint with blue painters tape or similar. Covering the entire area so that no wood is exposed at the joint. Then disassemble the joint. Mix the epoxy and if you think that end grain absorption is important – I don t with a M&T joint – apply to end grain only and let sit for 5 minutes. While waiting I would thicken the mixed epoxy with very fine saw dust, powdered metal, or micro balloons( made for this purpose). Then liberally apply the epoxy to all joint surfaces, make the joint, secure with clamps etc. now wipe off squeeze out dampened with denatured alcohol. Quickly tape over the actual joint to help retain runout and let this cure. Epoxy will generate a bit of heat and can weaken the tape adhesive at the joint so make sure the tape extends an inch or so beyond the joint. Check the glue pot leftovers from time to time and when the epoxy is the consistency of tire tread or a bit harder remove the tape and trim squeeze out with sharp knives or chisels. Don t get too fussy at this point just get the big stuff off as once it is fully cured it will be a lot more difficult.

- OnhillWW

If there’s really no benefit in extra soaking of the endgrain, then I should probably go with System Three T-88, which is much thicker compared to the General Purpose. As I said, there are no gaps in joinery to fill so far, so I thought pre-soaking would help get extra strength.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

View MrUnix's profile

MrUnix

7408 posts in 2621 days


#5 posted 09-02-2018 11:43 PM

While waiting I would thicken the mixed epoxy with very fine saw dust, powdered metal, or micro balloons( made for this purpose). Then liberally apply the epoxy to all joint surfaces, make the joint, secure with clamps etc…

I would take that advice with a grain of salt… most epoxy manufacturers recommend applying a thin coat of neat epoxy (no fillers or additives) to all surfaces first. Then – fillers are applied/mixed in the remainder of the epoxy and applied. The purpose is to initially allow maximum adhesion/soaking into the substrate, which fillers could inhibit.

Also, micro balloons (aka: glass microspheres) are not recommend for gluing applications. Its primary purpose is for use as a secondary bulking filler, typically for use in faring applications. (System 3 data sheet can be found here , West System 407 micro-balloons filler here). West System filler application chart can be found here.

For the application described, where there is no real need to fill gaps, neat epoxy should work just fine without anything else needed IMO. And yes, you can let it sit until it’s just about cured to a solid gel state, and it will still work as usual and eventually cure to 100% strength. Applying the thin first coat neat will aid in adhesion of the more solid secondary coat.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View shipwright's profile

shipwright

8320 posts in 3220 days


#6 posted 09-03-2018 01:36 AM

Ive never pre-coated surfaces and I always use thickeners for ease of application. As long as the thickeners aren’t overdone the epoxy will penetrate just fine.
Never had a boat come apart yet. .... or a bathtub.
That said there are lots of ways that work. Epoxy is very forgiving stuff.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese! http://thecanadianschooloffrenchmarquetry.com/

View ArtMann's profile

ArtMann

1399 posts in 1238 days


#7 posted 09-03-2018 04:08 AM

System Three, which I have used a lot, recommends wood flour as a thickener to hold plywood seams together when building “stitch and glue” boats. That is about as demanding as it gets. Are you saying that is not a good idea?

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runswithscissors

3052 posts in 2447 days


#8 posted 09-03-2018 04:19 AM

Pygmy Kayaks (kit boats from Port Townsend, WA) supply System III, and wood flour (sanding dust) with their kits. One time I did not align a joint properly, so removed the wires and tried to correct the misalignment. The only way I could separate the joint was by sawing it apart with a very fine toothed saw.

Incidentally, some designers specify that the wires are to stay in place on a stitch and glue boat. I think this is a bad mistake. They provide zero strength to the joint (especially after being sanded flush), and make it impossible to apply a smooth fillet with glass tape on the inside of the joint. It is very easy to snip the wires and pull them out. Any stubborn ones can be briefly heated with a soldering iron and pulled. Why do it the hard way?

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View shipwright's profile

shipwright

8320 posts in 3220 days


#9 posted 09-03-2018 04:38 AM

Wood flour is OK, and cheap but IMHO minifibres are a lot better.
As I said lots of things work.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese! http://thecanadianschooloffrenchmarquetry.com/

View MrUnix's profile

MrUnix

7408 posts in 2621 days


#10 posted 09-03-2018 05:03 AM

Wood flour is OK, and cheap but IMHO minifibres are a lot better.
As I said lots of things work.
- shipwright

+1. I use microfibers when gluing up laminated sailboat tillers and have never had one come apart yet.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View splintergroup's profile

splintergroup

2730 posts in 1645 days


#11 posted 09-03-2018 02:19 PM

I use S3 epoxy fairly often for M&T joints when I need the 30 minutes of open time to get everything assembled and aligned. Leaking is an issue and the tape idea works well, but what works best for me is to apply a border of wax (Waxilit or paste wax) around the assembled joint , working into the corers with a Q-tip. You can also apply an amount to the faces of the tendon shoulders to act as a sealant to keep the epoxy in place.

The epoxy pops off the waxed surfaces with a sharp chisel after it has cured.

The wax is easily removed with a mineral spirit wetted rag (and Q-tips), using a fresh rag surface for each wipe.

View Planeman40's profile

Planeman40

1420 posts in 3183 days


#12 posted 09-03-2018 03:36 PM

Why use epoxy?

I keep seeing epoxy being used as a woodworking glue. Other than a gap-filling ability, I personally don’t see the advantage of epoxy over other glues like Titebond for wood. Once a wood glue bond is stronger than the wood itself you get no advantage of an even stronger bond. Please ‘splain this to me.

-- Always remember: It is a mathematical certainty that half the people in this country are below average in intelligence!

View harum's profile

harum

364 posts in 2065 days


#13 posted 09-03-2018 06:18 PM


Why use epoxy?
...
...
Please splain this to me.

- Planeman40

Well, they say that initially and for some time Titebond glues may be as strong as epoxies.

Please note that all those numerous glue stress tests are done at most within a couple of weeks after glue-ups. However, long term resistance to seasonal wood movement is not addressed, which is #1 concern. They say Titebond glues “eventually” fail at cross-grain and face-to-end grain glue-ups due to wood movement.

I don’t know though how long this “eventually” is. Three years, ten, fifty? Probably, depends on the environment.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

View harum's profile

harum

364 posts in 2065 days


#14 posted 09-03-2018 06:21 PM



I use S3 epoxy fairly often for M&T joints when I need the 30 minutes of open time to get everything assembled and aligned. Leaking is an issue and the tape idea works well, but what works best for me is to apply a border of wax (Waxilit or paste wax) around the assembled joint , working into the corers with a Q-tip. You can also apply an amount to the faces of the tendon shoulders to act as a sealant to keep the epoxy in place.

The epoxy pops off the waxed surfaces with a sharp chisel after it has cured.

The wax is easily removed with a mineral spirit wetted rag (and Q-tips), using a fresh rag surface for each wipe.

- splintergroup

Appreciate the tips, Splintergroup! Yes, I will need at least 30-40 mins for the final glue-up, which is another reason for using epoxy.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

View harum's profile

harum

364 posts in 2065 days


#15 posted 09-03-2018 06:24 PM


...
For the application described, where there is no real need to fill gaps, neat epoxy should work just fine without anything else needed IMO. And yes, you can let it sit until it s just about cured to a solid gel state, and it will still work as usual and eventually cure to 100% strength. Applying the thin first coat neat will aid in adhesion of the more solid secondary coat.

Cheers,
Brad

- MrUnix

Thanks for sharing your experience, Brad. Looks like my plan might work.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

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