Replies to This Discussion

Permalink Reply by lhedrick on April 13, 2011 at 7:13pm

You want to use the epoxy.  5200 might work, it bonds to anything but I have never heard of anyone using it to join scarfed plywood.

 

Place the joint on a flat surface covered with plastic.  This will prevent any epoxy from bonding the work to the work table.  

 

Mix the epoxy and brush it on each side of the end grain of the plywood.  Let is soak in and apply more. Do this about 3 times so you get a good saturation.  Next mix some ground fiberglass or silica into some mixed epoxy until it's as thick as tooth paste.  Brush it all over the joint on each side.  

 

Place the sheets on top of each other.   Double check your alighment. Clamp the sheets down so they can't move.  Add a piece of plastic on top of the joint.  Next put a flat board on top of the plastic and then put weight on top.  Paints cans, bucket of water, car battery, what ever you have.   You don't want to clamp it so tight that you force all the epoxy out of the joint.

 

Let is sit for 12  hours.

 

 

• ▶ Reply

Permalink Reply by Lawrence E. Long on April 13, 2011 at 7:19pm

Daniel:  DON'T use 5200.  Mix up your epoxy without any filler.  Coat both surfaces of the scarf.  let it soak in- the end grains will absorb the epoxy and look "dull".  Recoat both sides so that they are "glossy" all over.  Then add filler- cabosil and milled fibers to get the consistency of cold honey or runny peanut butter. Recoat both surfaces and then join the scarf.  Don't forget to use waxpaper/visqueen to keep from gluing the mess to you floor/work bench.  Use lots or weight- toolboxes/concrete blocks et to get around 1  psi over the entire scarf.Use a  strip of 1/2 "PW or a piece of 1 by 6 and make . Anchor the sheets and align them so they don't move around while the glue sets up.

Others may have a better way but this works for me .  Good Luck 

• ▶ Reply

Permalink Reply by Eric Loudenslager on April 13, 2011 at 7:39pm

Daniel,

 

You should take a look at the building instructions at the Montana River Boats site.  Sandy has made instructions and plans available that describe scarfing, glassing, etc.  Worth looking at what ever boat you are going to build.  Also, do an internet search for scarfing plywood.  There is a good explanation and pictures at a stitch-and-glue building site.  

 

As others have suggested, epoxy is the adhesive of choice.  You want to use unthickened laminating (coating) epoxy on the scarf, let it get to at least the setting up stage, and then use thickened epoxy or an epoxy adhesive like System 3 T88 or gel magic, put the panels together, clamp them, let them set-up.  Do not over clamp the epoxy or you will glue starve the joint.  The unthickened laminating epoxy serves to soak into the wood.  Thickened epoxy and epoxy adhesive will not soak into the wood and can produce a starved joint.  

 

Also, check out the Raka site where they sell epoxy and have a manual.  System 3 also has a guide/manual with all kinds of useful information and tricks.  You can download it from their website.  While some of the information is specific to their products, most info is general to epoxy used in composite construction.

• ▶ Reply

Permalink Reply by Russell Turpin on April 13, 2011 at 7:47pm

good advise from the previous posts.... no 5200.... not for scarf joints

 

a good resource for epoxy techniques.....system three epoxies web site...the epoxy book

 

http://www.systemthree.com/reslibrary/literature/The_Epoxy_Book.pdf

 

 

 

 

 

 

• ▶ Reply

Permalink Reply by Daniel Martin Romano on April 13, 2011 at 8:00pm

So happy that everyone else knows this stuff so well.  Thanks.

• ▶ Reply

Permalink Reply by Dave Z on April 13, 2011 at 8:12pm

use wax paper from the kitchen on y0our work surface and on top of your scarf for squeeze out.

use lots of epoxy.  tis better to have too much and scrape it off than to have a starved joint.

 

• ▶ Reply