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

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Forum topic by tmasondarnell posted 10-12-2020 06:10 PM 684 views 1 time favorited 16 replies Add to Favorites Watch
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tmasondarnell

141 posts in 2709 days


10-12-2020 06:10 PM

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


16 replies so far

View eflanders's profile

eflanders

329 posts in 2770 days


#1 posted 10-12-2020 06:46 PM

IMO Using any type of an adhesive is not a good idea for gap filling. Instead of trying to use the glue to fill the gaps, why not use some wood slivers? An old handyman trick for loose screw holes is to fill the hole with a combination of match sticks or toothpicks and glue. Assuming of course there isn’t a gap greater than an 1/16”. Just take a knife and shave off an properly sized sliver of mahogany to fill the gap between the mortise and tenon. I have used TBIII for door construction for years with good results.

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bondogaposis

5898 posts in 3271 days


#2 posted 10-12-2020 06:51 PM

I’ve always used T88, it is pretty thick at room temperature.

-- Bondo Gaposis

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Fred Hargis

6581 posts in 3413 days


#3 posted 10-12-2020 07:00 PM

I have done what you asked and it worked fine, as I recall I used a Loctite product most recently. I’ve never added a thickener, but that may depend on just how loose those joints are. But your question about heat (and maybe the thickener) could be asked of West themselves, they have a technical support line (866-937-8797) and they may help you with which package would be meet your needs. But do consider what eflanders said about wood slivers to tighten the joints, it works very well…though I would personally stay with the epoxy as an adhesive.

-- Our village hasn't lost it's idiot, he was elected to congress.

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pottz

12402 posts in 1904 days


#4 posted 10-12-2020 07:01 PM

i agree with eflanders,glues are not for filling gaps.i did a mahogany screen door a while back,it’s on my projects page.i used the domino for the tenons and titebond III glue and have had no issues.

-- working with my hands is a joy,it gives me a sense of fulfillment,somthing so many seek and so few find.-SAM MALOOF.

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SMP

2905 posts in 825 days


#5 posted 10-12-2020 07:14 PM

How much narrower are the tenons? I’d rather use the epoxy and fiberglass tape to wrap the tenon to be able to sand it to the right thickness than trying to use it as a gap filler.

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Rich

6169 posts in 1509 days


#6 posted 10-12-2020 08:04 PM

There’s nothing wrong with having mortises longer than the tenons. It’s the glue on the cheeks that makes the joint strong. In fact, giving yourself a little wiggle room aligning the joint is a good thing. Even with dominos, you cut all but one of the mortises a couple of millimeters longer than the domino itself for easy glue-up.

If the tenon isn’t a good fit for the width of the mortise, that’s a problem. You can glue on some shims, and then mill to the correct dimension. You only need the shims on the cheeks of the tenon.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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BigMig

518 posts in 3533 days


#7 posted 10-12-2020 09:56 PM

I’m with BondoG – if the tenon is too thin for the mortise, then shim it. Don’t expect glue to fill gaps and make the best joint. It’ll work, but I don’t think it’ll be as strong. And especially if it’s not a through tenon – it will work great and nobody will EVER see it.

-- Mike from Lansdowne, PA

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Madmark2

1829 posts in 1508 days


#8 posted 10-12-2020 10:03 PM

After the epoxy is set, pin the joints.

-- The hump with the stump and the pump!

View Aj2's profile

Aj2

3505 posts in 2718 days


#9 posted 10-12-2020 10:40 PM

I would also fix the tenon thickness if they were soo loose it gives you pause.
For heaves sake 6 stretchers is going to give you a lot of strength. The top and bottom ones are the most important.
Using epoxy is ok in my book but shouldn’t be a crutch for lofty work.
It’s going to be a stressful glue up hope you make a good plan.

Good Luck

-- Aj

View Jeff Vicenzi's profile

Jeff Vicenzi

42 posts in 309 days


#10 posted 10-16-2020 01:01 AM

The glue with the best gap filling properties is urea formaldehyde glues. These are good with gaps up to about 0.02”. Urea formaldehyde glues that contain furfuryl alcohol, such as Unibond 800, have the best gap filling properties. Other nice features are a very long working time (~ 1 hour) and they are very water resistant. Popular woodworking april 2018 has a good review of glues

View Aj2's profile

Aj2

3505 posts in 2718 days


#11 posted 10-16-2020 02:17 AM



The glue with the best gap filling properties is urea formaldehyde glues. These are good with gaps up to about 0.02”. Urea formaldehyde glues that contain furfuryl alcohol, such as Unibond 800, have the best gap filling properties. Other nice features are a very long working time (~ 1 hour) and they are very water resistant. Popular woodworking april 2018 has a good review of glues

- Jeff Vicenzi

You left out one important point. It’s pretty toxic stuff. Epoxy isn’t that good to breathe also but I think plastic resin glues are far worse . Always good to mention wear a respirator with plastic resin glues.

-- Aj

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Jeff Vicenzi

42 posts in 309 days


#12 posted 10-19-2020 01:09 PM

Good point AJ. I always wear a respirator with 3M 6005 cartridges specifically designed for formaldehyde vapors, and turn on my exhaust ventilation when using Unibond 800. But the good news is Unibond 800 was recently reformulated, greatly reducing formaldehyde content. It has no noticeable odor and cleans up easily with water. Overall I find it pretty user friendly, but yes, more toxic than typical PVA wood glues. I bought it mostly for veneer work, but it also works great for general woodworking, and I specifically pull it out when I have a complex glue up where the long working time makes a big difference. One thing to keep in mind with epoxy is it is actually not very strong with very tight, gap free joints; it actually needs some gap for strength (strange but true). I avoid epoxy for that reason.

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Robert

4157 posts in 2400 days


#13 posted 10-19-2020 01:38 PM

Exactly how loose are the joints? ;-)) IMO its always a good idea to pin tenons on doors.

Epoxy is a good choice and will fill those little gaps in the joints.

I use the product you’re looking at all the time. Unless the joints are pretty tight, I usually use thickener, either wood flour or the West microfiber thickener.

I recommend taping along all the joint seams prior to gluing, as epoxy can be difficult to clean up.

-- Everything is a prototype thats why its one of a kind!!

View PBWilson1970's profile

PBWilson1970

142 posts in 313 days


#14 posted 10-19-2020 02:09 PM

I’ve used West Systems epoxy on a good number of projects (knife handles, tricky glue ups where I needed extra open time, pore filling) and they have a fantastic customer service department and top quality products.

They also have four products that are made specifically for gap filling (#403, 404, 405, 406) and is one of the few adhesives that will have sufficient strength as it fills gaps. Their customer service will steer you in the right direction as to which one will work best for your door. Don’t fear gaps with this stuff, although I can’t say the same for some of the 5-minute epoxies you can find at the big box stores. It’s really not the same stuff at all.

-- I love the smell of sawdust in the morning.

View Sark's profile

Sark

352 posts in 1280 days


#15 posted 10-19-2020 03:20 PM

I use West System epoxy a lot. Along with the basic epoxy/hardener liquids, you buy/add different powered additives to modify the basic epoxy properties ( viscosity, strength, sandability) to get the results you want. The high strength additives result in a structural bond that will be stronger than the wood you are bonding. It’s also completely waterproof, will handle the heat just fine. Note that’s its used a lot to make and repair boats, and that’s a really demanding application.

Another huge advantage of West, is that it hardens slowly. And for complicated glue-ups that’s really an incredibly nice feature if you aren’t in a huge hurry. I glue up in the afternoon, and the next day it’s ready to go. Expoxy is a great gap filler glue. The more elegant solution (as suggested above) is to shim out the tenons, but the epoxy will certainly do the job.

The main disadvantage to West, is the cost. I bought a 1/2 gal a couple of years ago, and have used about half of it. But it’s nice to have lying around. It’s what I use for all my exterior projects.

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