Gluing Ipe in a Harsh Outdoor Environment

Resorcinol tops the list of recommended adhesives for an Ipe glue-up in an outdoor ocean-front location. October 13, 2010

This is probably the worst condition (challenge) in which I could ask for a glue to perform. We have pyramid shaped post caps made from Ipe that are being installed on an exterior deck in saltwater environment with southwest exposure. Can I use epoxy? If I do will it remain flexible? Will 3M 5200 work?

Forum Responses
(Adhesive Forum)
From contributor G:
Ipe is the worst. I have had the best luck with West System, but I have had issues too. Some form of joinery will help, but when Ipe wants to move, split or behave badly, nothing will stop it. Also remember that there are many sub-species that are marketed under the Ipe name. Some seem to be better than others. Roughing the glue joint with 60 grit sandpaper really helps.

From Jeff Pitcher, forum technical advisor:
The only adhesive that will work for your application is a resorcinol resin. Epoxy will result in delamination over time. The key is to use freshly machined Ipe and make sure your blades are extremely sharp to avoid burnishing the surface.

From contributor A:
I concur with Paul. You must sand with a fresh piece of 60-80 grit paper. This is actually true for most epoxy applications, but without a doubt Ipe doesn't bond well. 3M 5200 is the ultimate for paint grade applications. PL sells a very similar poly caulk/adhesive for about $5 a tube versus $12.

From contributor S:
Why glue up to get there? Why not start with a large enough piece of wood to make the caps? In this case, it eliminates the problem at hand and the potential future problems. Remember, there are two basic methods of woodworking: additive and subtractive. One adds pieces of wood to make something, the other subtracts wood to get what is needed.

From the original questioner:
Thanks to all for your responses. Contributor S I certainly would love to be able to make this in one piece but it would require 10/4 stock 10" wide. I have not found any supplier with Ipe in that size. We have made a fixture to cut all of the compound miters on the CNC with a spline to reinforce the joint. I think we will use the West System and then reinforce the underside as well with fiberglass mat in west resin. We are also planning on a 10% failure and making additional to compensate. I just hope it is enough.

From contributor A:
You do not use fiberglass mat with epoxy resin. Mat is only used with polyester resin, because you need a really wet saturated bond layer between cured layers of polyester. Epoxy bonds well to itself so no mat only cloth. What is the purpose of the epoxy/cloth on the bottom?

From the original questioner:
The G/Flex product is designed for this type of application - yes even wetting and bonding fiberglass tapes and fabrics. Why put it on the underside - why not? It is an additional mechanical bond to the underside which will aid in keeping the pieces together. If the joint does fail it will still provide some protection against water penetrating to the post.

From Gene Wengert, forum technical advisor:
The only adhesive I would suggest is Resourcinol. Note that epoxy will deteriorate with time, even if UV stabilized. Often epoxy fails because the joint has too much pressure prior to curing. Epoxy does not work well with a thin glue line. No adhesive will work well if the wood surface is oily, burnished, aged, or otherwise not suitable for gluing. For this reason, we often will hear about someone who claims that this glue or adhesive does not work well, but often the reason if surface preparation and not the adhesive.

From contributor A:
I am aware of the G/Flex resin system. It is more flexible, resilient. However, my last post was about fiberglass mat. It might be overkill for your application. Fiberglassing one side of a piece of wood could lead to cupping.

From the original questioner:
Gene, I was hoping you would respond. I've used resorcinol only once almost 20 years ago yet you and Jeff P. recommend it over the epoxy. Knowing that all epoxy is not created equal, do you have any brand specific knowledge of the G/flex for this application? All preparation of the wood has been followed to the letter. In addition the spline is not a tight fit knowing that this glue does better with thicker glue lines. We may make some with both types of glue for a comparison test.

From contributor C:
I was really surprised to hear the negativity about Ipe. It can be a challenge but has too many good points to write it off. Every stile and rail Ipe door I build gets through doweled as well as glued, no failures. 5200 is a fantastic glue and is flexible to boot. Try and design the glue line or joint into the design. Itís ok to use a wider glue, or caulk line. 5200 is has tenacious glue properties, and rarely fails. Clean the fresh cut surface with acetone and glue up or glue and hold into position and let dry thoroughly. Sand and finish as planned.

From contributor M:
If you are splining anyway, why not make a dovetail spline and forget about glue failure?