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Permalink Reply by mlwebb on April 30, 2011 at 10:13am

T-88 should work great-it is made for structural joints.  (I really like the stuff).

Apply to both surfaces liberally, let set for 20-30 minutes, apply another coat and assemble.

Alternately, let 1st coat dry, sand lightly and apply next coat and assemble.

http://www.systemthree.com/reslibrary/tds/T-88_TDS.pdf

Michael

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Permalink Reply by Eric Loudenslager on April 30, 2011 at 2:48pm

I'm not clear on what you are proposing to do.  Sealing open end grain...like the exposed edge along the sheer?  Or are you going to use the T-88 as an adhesive to attach two pieces of wood?  Are these going to butt jointed or scarfed?

If you are using as an adhesive you should coat the end grain with unthickened epoxy, let it cure, and then use the T-88.  I did this recently to scarf eastern ash for replacement gunnels on a Mad River Canoe.  I used T-88, combined with the silver tip laminating resin.  Apply the silver tip, recoat as it gets soaked into the end grain, let it cure.  Sand with 80 grit the next day, then apply T-88 and clamp with modest pressure.  You do not want to starve the joint of glue. 

I would not use wood flour mixed with laminating resin as the adhesive for a scarf joint.  I would use the T-88. Others however might choose the woodflour mix.  That is typically used a fillet in stitch and glue.  As for coating the end grain when making a joint, I just coat it once.  Twice would be fine, three times seems like overkill. 

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Permalink Reply by Dave Z on April 30, 2011 at 3:11pm

Eric,

 

Please explain why you wouldn't recommend using wood flour and epoxy to glue a scarf joint. 

I've used wood flour and epoxy on at least 20 scarf joints in plywood, dimensional lumber, softwood and hardwoods with never a failure. 

 

Dave

 

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Permalink Reply by Eric Loudenslager on April 30, 2011 at 3:22pm

Dave,

 

No reason not to use the wood flour, I just use either T-88 or Gel Magic 'cause I've got it on hand.  No dusty fillers to add to the base epoxy. 

 

As is evident in lots of post to wbp, there are many ways to accomplish the same task, and most work fine.  Just personal preference.

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Permalink Reply by Andrew on April 30, 2011 at 3:43pm

The deed is done so there is no real turning back.

I am scarph joining some solid pieces to use as chines and gunnels etc.

What I did was put on 2 layers of T-88 with about 30 minutes between coats. When I started to put the pieces together a lot of the T-88 was squeezing out and I had some gapsin myjoiny so I mixed up anoth batch with HW flour and spread it on.

I will probably us the Silvertip to soak the ends of the plywood on the scarph and the do the joint with either T-88 or thickened Silver Tip.

Thanks for the tips guys.

Andrew

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Permalink Reply by Dave Z on April 30, 2011 at 4:44pm

Got it Eric.  I've not used the T-88 product-  glad it works well for you.

 

 

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Permalink Reply by Lawrence E. Long on May 1, 2011 at 3:35am

Andrew:

Call System 3.  When I asked about using Silver Tip for making scafs  they said it was for "laminating"  and did not reccomend it for use as a structural  adhesive.  When asked what they call laminating he said laying down fabrics.  Possibly they have changed opionions  from a year or so ago.

Good Luck

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Permalink Reply by Eric Loudenslager on May 1, 2011 at 9:30am

To clarify.  I primarily use System 3 products.  When I scarf pieces of wood - either dimensional lumber or plywood - I coat the open scarf with epoxy and let it cure before applying epoxy adhesive and then clamping the wood together.  I use silvertip laminating epoxy to soak into the open wood.  Then I use either T-88 or Gel Magic as the adhesive.  Silvertip Laminating epoxy, or any other epoxy that is thin enough to wet out fiberglass cloth does not have sufficient gap filling qualities to make an adequate adhesive.

 

The System 3 literature does not specifically address coating joints with non-adhesive epoxy before using either T-88 or Gel Magic (that I have found at least).  

 

Most epoxy construction guides I have read, and builders that use RAKA, or WEST, or MAS typically apply the coating (laminating) epoxy to the open wood, let it start to cure (or let it completely cure). Then they make a batch of the coating epoxy and thicken it with wood dust, or silica thickener, or even chopped glass, and then use this thickened version of the coating epoxy as the adhesive.

 

That is the approach I have always used.  Since I have the Silvertip resin I used it, and have had no failures.

 

Check with System 3, see if they believe pre-coating joints prior to the use of T-88 or Gel Magic is unnecessary.  I may have been making more work for myself than required.

 

I have followed System 3 advice and pre-coated plywood panels with Silvertip before laminating fiberglass to avoid starving the glass/wood joint with excellent results.

 

I also really like the System 3 products.

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