Epoxy for M&T joints for Mahogany Screen Door--first time user needs advice

[Todd Mason-Darnell]

I appreciate all of the great advice I have been getting on a number of projects.


I am building the first of 3 mahogany screen doors for the house. We like a more modernist look, so the door has 6 "stretchers" between the 2 rails, resulting in 5 smaller screened panels. I have done M&T joiner for everything and had planned on using Titebond 3, but now I am considering using epoxy as the glue for the joints. Aside from the great exterior properties, Some of my joints are a little looser than I would like and there are some gaps at the top of the tenons (i.e. some tenons are narrower than the mortise).

I have never used epoxy before, so I start researching on the internet and now I am confused. Most of the information I am finding is about stabilizing cracks or doing epoxy river tables

Some comments have said not to use epoxy on any structure joints. Seems weird to me, but is that true?

I have been looking at West Systems with the 206A hardner to get a longer open time....are there other recommendations?

I have seen some comments that if I using the epoxy as an adhesive, I need to add a thickening agent to the mix. True/false?

I am in Central Texas, with summer temps generally in excess of 100F, do I need to worry about the epoxy becoming brittle?

Any good reference sites?

Thanks

[Phil Gaudio]

System Three T-88 Epoxy is what you want. Long open time, excellent results.

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[Stewart Lang]

I've used epoxy on wood joinery with great success and I know many very experienced woodworkers who do the same.

The benefits are most obviously the incredibly long open time compared to regular glue. I've had some complicated glue-ups that need at least 45 mins and epoxy works beautifully for that application. Just as strong as wood glue. Seems to flow better too which helps it apply more evenly in joints in my mind. Just as strong too. Since it's not water-based it won't swell joints, and actually acts as a lubricator so you can run tight joints that go together better with epoxy than just dry. Lots of benefits to epoxy.

Only downside is cost really, and also the reason wood glue has such a strong stance in the glue-up world. Also I've heard to be a little careful when mixing to ensure the right ratio, however I've never once had an issue. I do use the West System's pumps though so that does all the work for me.

[Jim Becker]

System Three T-88 Epoxy is what you want. Long open time, excellent results.

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I agree with this recommendation. T-88 is a structural epoxy and designed for this kind of operation.

[John TenEyck]

Not all epoxies are structural adhesives, but several are. Go to Systems Three and West Systems websites. A wealth of info. at both. I've only used System Three's T-88 for the exterior doors I've made and can vouch that it's easy to work with and 5 years in all is well. You definitely do not want to use TB III for a structural joint that gets any direct sun on it. Even non structural joints that get stressed don't fair well.
Titebond Polyurethane glue would be another excellent choice and requires no mixing. The working time is not as long as T-88 but it doesn't require mixing and has equally impressive water resistance and high temperature strength.

Oh yeah, epoxy cleans up easily with plain white vinegar. Also, you don't want tight fitting joints with epoxy. An easy sliding fit is best.

John

[Jacob Mac]

I just used epoxy for the first time over the weekend. I was gluing up a bed that had 16 spindles on both the headboard and footboard, housed tenon's, and they were they were four different lengths. So it was very fiddly getting everything together.

I went with the west epoxy and the hardener you mentioned. With the pumps west supplied, the ratio for the two parts was easy. I did a little experimenting on Friday to see what it was like, but my experimenting showed it to be like any other glue up, just with a long open time.

I really liked it, and no way I could get the glue ups complete with parts swelling and a short open time. It is expensive, and I won't use it for every project, but I was really happy I used it this time around.

[Alex Zeller]

The only other downside to epoxy is it's not as easy to clean up as wood glue when wet.

[Jim Becker]

The only other downside to epoxy is it's not as easy to clean up as wood glue when wet.

White vinegar is your friend... :)

[mreza Salav]

I used west system for this 42"x96"x2.25" door out of Mahogany:
https://sawmillcreek.org/showthread.php?207022-Building-an-entry-door-(work-in-progress-)&highlight=

In our harsh climate (with +30C to -35C in winter) it is holding up pretty well after 6 years.

[andy bessette]

WEST System epoxy is virtually all I have used for wood glue for over 40 years. Nothing better. 206 hardener will be fine. Take time to cleanup excess squeeze-out before cure takes place. I like acetone for cleaning up.

[Scott Winners]

I have only ever used West system products. Besides long open time, you can mix some of your saw dust in it for color matching as well as thickening, and it has excellent gap filling properties.

When you think it is dry and fully cured, give it another 24 hours before you sand. Sanding green epoxy is hard work and hard on your lungs. Get a respirator.

[Gordon Stump]

Yup....T-88

[Mike Cutler]

System Three T-88 Epoxy is what you want. Long open time, excellent results.

443092

Exactly!!
Admittingly the OP referenced loose joints, and T-88 is designed to fill gaps.

To the OP
Epoxy is not difficult to use, and is used in zillions of wood working applications world wide,every day. Many, many of them high stress structural joints. There are though, many formulations that have different properties, for different applications. For the application you have detailed, you need a "gap filling" structural epoxy, and T-88 is a one and done product. It is very easy, and forgiving to use, and easy to get. You don't need "micro balloons", or wood flour. The thixotropic, or thickening agent, is already in the resin when you buy it.
Epoxy is not "glue". You don't need pressure on the clamps for it to work, and in most cases, to much clamping pressure is the cause of an epoxied joint failure. You need only enough clamping pressure to hold the pieces in alignment. You're not looking for "squeezeout". Epoxy does require an initial "cure time", usually 12-24 hours before the joint can be stressed, and it may take up to a week for 100% strength. The initial cure will be about 80% of strength in the first 24 hours.
If you want to prove it to yourself, cut an M&T joint to fit more loosely that it should. Apply the T-88 epoxy and set the joint up in a vise so that only gravity is holding the tenon piece in the mortared piece. Align them with blue painters tape and come back the next morning. That joint is not coming apart.
Most epoxies available to the general consumer have a shelf life measured in years, so don't be worried that it will "go bad" if you buy the bigger kits. ;)

[Stan Calow]

I started using epoxy for M/T joints because I've rarely had a good tight joint. I've used T-88 for several years with inside and outside projects. I start I have a oak bench with all the joinery done with T-88 and its held up for several years in the extreme cold and the extreme heat. One advantage is that its a bit slick, as opposed to PVA glue which can start swelling the wood and making it a tight fit in assembly.

[Neil Gaskin]

I'll go against the grain a bit and support West Systems. You can use an additive to increase strength, workability, or filling depending on what you use.

https://www.westsystem.com/filler-selection-guide/

[Melvin Feng]

It looks like I'm the odd one out. I haven't used T-88 before, the epoxy that I keep on hand is primarily total boat, both the high performance, and recently their penetrating epoxy. I also have some 5 minute for quick fixes too, but I only use that when I have to.

What I like about the high performance, is that you can use it for general filling cracks and finishing, but then also add silica to it to use it as an adhesive. I've done this a number of times now, and I've enjoyed using it. I can't claim any strength numbers, but I have used it for installing dutchman to stabilize cracks, and for wedged through mortise and tenons. It definitely helped fill up slight gaps. I use this epoxy enough that I now have the gallon kit with the pumps, and I use it most often to fill in cracks on lumber that I am processing that I've chainsaw milled.

If you don't foresee yourself using epoxy for much else though, it wouldn't make sense to get something like the high performance, and it would be better to just get the purpose made adhesive epoxy.

[John Powers]

Jamestown distributors sells boat stuff. They have a product called I think Thixo. Epoxy in a caulking gun tube. Nozzle mixes part a and b. It’s thickened. About $18.00 a tube. Be aware the tube is only half filled. I’ve used it on a kayak. For only one job you won’t have to buy pumps and have leftover crystallizing in the garage. I think West has a similar product. You can buy spare nozzles. Check it out.

[Scott Bernstein]

I use mostly wood glue for my projects, however I have also made several larger pieces of furniture with epoxy for glue-up. I have used T-88, most recently on a solid Ash dining table. The table top is constructed with five Ash boards 12/4 thick and 6-8" wide, and 8 feet long. The solid Ash legs are integrated directly into the top with large "bridle" or "finger joints" which span the thickness of the table. No apron. I used the epoxy to glue the edges of the boards together along with several 14mm dominos for strength and alignment, and also of course on the bridle joints on the legs. The T-88 worked great; I find it to be a little thicker and less runny than the West Systems or Total Boat (but you can add thickeners to any of them). The long open time for the epoxy was critical for this particular project since it took so long to apply to all the mating surfaces. I do find the T-88 takes a long time to completely cure...really several days until it feels rock-hard. But there is no need to clamp it for that long. The epoxy is also great for filling small gaps and irregularities in the joints, without compromising strength.

This table is in our dining room, very close to a large window on one side and our wood stove on the other - so it is subject to a lot of changes in humidity and temperature over the seasons. I built it 2 years ago and have not seen any degradation or separation of the joints. I don't know how much this table weighs but it's a lot! Hopefully it will hold up for many years.

Scott

[Jim Becker]

Melvin, Total Boat products are very good...they are just not as well known, but that's changing as they are supporting some 'Tubers like Tim Sway to get the word out around both adhesives and their finishing products, many that have good application in general woodworking.