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Morris Chair Joinery - Unibond 800 vs. Epoxy

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Forum topic by SeventyFix posted 03-03-2016 02:40 PM 332 views 0 times favorited 1 reply Add to Favorites Watch
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SeventyFix

50 posts in 977 days


03-03-2016 02:40 PM

Topic tags/keywords: epoxy west systems unibond 800 morris chair mortise tenon squeeze out clean

I am making two Morris chairs using plans and guidance from Marc Spagnuolo’s Wood Whisperer Guild website. I have finished gluing up 2 chair sides (I am making 2 chairs so I have 4 sides total). I was wondering if I could use Unibond 800 for the mortise and tenon joinery instead of epoxy. My rationale was that (1) I already had the Unibond 800 from the bent lamination steps, (2) I didn’t have epoxy or experience with it and it’s expensive and (3) it cleans up nicely with water. This topic was posted on another forum but I’m looking to assemble my build ideas and woodworking posts on this site so I wanted to share.

Choosing Epoxy

I finally decided to use West Systems epoxy over Unibond 800 for one reason: temperature. The people at Vacupress were very helpful and knowledgeable about the product and I bought the Unibond from them. They said that if a temperature of 80 degrees couldn’t be maintained, they would not recommend using Unibond 800 for mortise and tenon joinery. It’s currently winter, the chairs are fairly large (making a heating blanket difficult to use) and I cannot maintain that temperature. Come back in a few months, in Texas, and that wouldn’t be a problem. There’s no doubt that the water clean-up is a nice feature of Unibond. Yes, a respirator is required when mixing the product and there are associated safety concerns (you should research this and decide for yourself if that’s acceptable to you).

I did use the Unibond 800 to glue up the chair backs prior to coming to a final decision to use epoxy. I moved the chair backs into the house after the glue-up (for warmth) so I hope that the joints will stay strong. At the end of the day, it is what it is. I have to live with my decision so I’m hoping for the best. I’ll update this thread again if something disastrous happens when I first sit in the chairs.

Clear Hardener (West Systems 207)

I used regular fast-setting hardener on the first chair side and then ran out (it was given to me by a friend and there wasn’t that much left in the can). The fast setting hardener is quite dark – much darker than the cherry wood (this hardener may have also been several years old). 207 is clear. This makes squeeze out and mess far less noticeable. Squeeze out is an important consideration and should be avoided when possible. But I haven’t been able to achieve that yet. There is some play in the vertical slats during assembly. This results in epoxy getting onto surfaces where it shouldn’t be.

Squeeze Out

West Systems recommends that light adhesive squeeze out is desirable. Just like regular glue, it’s a sign that there’s plenty of glue in the joint. But cleaning up cured epoxy squeeze out is difficult as the material is quite hard. What to do? I have found that the wet epoxy cleans up fairly nicely with lacquer thinner. For this purpose, West Systems recommends either alcohol, lacquer thinner or acetone. I used lacquer thinner because that’s what I had in my shop.

My method is pretty simple. First I apply the mixed epoxy resin everywhere that requires it. Then I assemble the chair, being as gentle as possible, making a supreme effort to ensure that the epoxy stays where it’s supposed to be (i.e. touching a epoxy wetted tenon to the side of the chair, rather than carefully guiding in straight into the wet mortise). Once everything is assembled, I clamp the project to close all of the joints and everything fits tightly. I check all of the joints and make sure that everything is lined up the way that I like it. If not, I add clamps or adjust the existing clamps to get the fit that I’m trying to achieve.

Squeeze out is going to happen in two places. First, the vertical slats in the chair float between the upper and lower rails. This play can result in a slat coming out of the mortise by a small amount, carrying some unwanted epoxy with it. Second, epoxy applied to the top of the upper rail tends to squeeze out when the chair arm is clamped tightly to it.

Wet a rag with a good amount of lacquer thinner. Take a first pass and wipe up any excess epoxy. Fold the rag and vigorously scrub out the joint. Wet a second rag with a significant amount of lacquer thinner and wipe the area again. Don’t try to save rags – the objective is to clean up all of the errant epoxy.

I’m leaving everything in clamps for 24 hours and sanding the next day. Please note that I am NOT staining this project. Cherry wood darkens naturally with age. I’m not sure how much epoxy is actually getting absorbed into the wood fibers/pores and may inhibit stain penetration. I suggest testing this method out on scrap material first prior to using it on your finished project.

The epoxy does cure slower than TiteBond but don’t kid yourself, it’s starting to set up on my when I’m finishing the glue-up. I’m doing a complete dry assembly right before the glue-up so that I know for certain that everything fits and where everything goes (the vertical slats are numbered and fit to a specific mortise). I am taking every precaution that I can to achieve success. That said, I have to move quickly and accurately. Although the epoxy can be cleaned up, the objective is to not have to clean anything.

Conclusion

So far it’s going quite well. It’s not as stressful as I had originally thought. West Systems epoxy is provides several significant benefits for use on the Morris chair project :

• Epoxy has a longer open/working time than some wood glues
• Epoxy is tolerant of less than ideal conditions (temperature)
• Epoxy has gap-filling properties that help to strengthen less than perfectly fitting joints

The clear hardener (West Systems 207) is a good choice because it has a medium cure time and squeeze out isn’t as noticeable on the finished project. Squeeze out should be as tightly controlled as possible. Wet, uncured epoxy can be cleaned up using lacquer thinner, alcohol or acetone. Care should be taken when disposing rags soaked in organic solvents.

The epoxy does cure slower than TiteBond but don’t kid yourself, it’s starting to set up on me when I’m finishing the glue-up. I’m doing a complete dry assembly right before the glue-up so that I know for certain that everything fits and where everything goes (the vertical slats are numbered and fit to a specific mortise). I am taking every precaution that I can to achieve success. That said, I have to move quickly and accurately. Although the epoxy can be cleaned up, the objective is to not have to clean anything.


1 reply so far

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shipwright

7165 posts in 2259 days


#1 posted 03-03-2016 03:10 PM

You should really look into hide glues. You have big concerns about squeeze out and cleanup and with hide glues this is just not a problem as water cleanup is easy and it will not affect later finishes. Also, especially in the case of pieces like chairs, repairs are inevitable albeit not necessarily soon and the reversibility of hide glues makes the restoration much easier. As for open time, liquid hide glue (I would recommend Old Brown Glue) will give you all the time you need and of course if you should misfit on a glueup and not notice it until cured, it can be disassembled and redone.

I have used a lot of epoxy I’m my boat building career and am a big fan of it for structural gluing but would not recommend it for a chair for a couple of reasons. One is the complete lack of reversibility and the other is cleanup. I don’t much like the solvent cleanup you describe in the above text because the epoxy thinned by the cleaning solvent will be more capable of penetrating and sealing your wood fibre.

Lastly toxicity. UF glues are better IMHO than PVAs but do contain formaldehyde. Epoxies and their solvents are nasty as well. Animal protien glues are completely non toxic, in fact lots of kids used to eat one of them (fish glue) right out of the bottle back in grade one.

If you want a good intro to hide glues, I did a blog series a while ago. Specifically there is a video by Patrick Edwards in the first segment that I highly recommend. http://lumberjocks.com/shipwright/blog/series/5437

Maybe it’s too late for this project but you really should look into hide glues.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees. http://thecanadianschooloffrenchmarquetry.com/

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