pre finishing before glue up

[Tim Sherwood]

I'm building a chest of drawers with maple and walnut. With all those internal guides, dividers and parts, I would like to pre-finish many of the pieces. I usually mask off any glueable areas, like dadoes, before I spray one or two coats of de-waxed shellac. Is that really necessary? How much would shellac de-grade the holding power of a glue joint?

 

[Skymaster]

I mask also, to me it is the safest bet

 

[Matt Furjanic]

Do Mask. Shellac is one of the best wood sealers. Wood glue needs to penetrate the surface of the wood to ensure a good bond. Take a piece of scrap wood and shellac it. Then put some wood glue on the surface to dry. After drying, most of the wood glue will easily peel off, proving the point.

 

[Bill Clemmons]

Do Mask. Shellac is one of the best wood sealers. Wood glue needs to penetrate the surface of the wood to ensure a good bond. Take a piece of scrap wood and shellac it. Then put some wood glue on the surface to dry. After drying, most of the wood glue will easily peel off, proving the point.

+1 to Matt's point. The only time I don't mask is if I'm coloring wood w/ a water soluble dye.

 

[Newboy]

I try to finish anything I can prior to assembly. I mask the tenons.


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[golfdad]

Agrees with all of the above. I have stated to do a lot of finishing before assembly. I always tape connections. :icon_thum

 

[Graywolf]

When I work with the custom shop at Marsh, we always pre finish the interiors of the products before assembly. Masking off all joinery areas is common to insure a proper bond with the adhesive. On my personal projects I do the same, and I fined that the extra time masking off these areas to time well invested.

 

[Willemjm]

Is that really necessary? How much would shellac de-grade the holding power of a glue joint?

The holding power will be de-graded more than 95%.

Quote from the artice below:

"Effective mechanical interlocking takes place when adhesives penetrate beyond the surface debris and damaged fibers into sound wood two to six cells deep. Deeper penetration into the fine microstructure increases the surface area of contact between adhesive and wood for more effective mechanical interlocking. The most durable structural bonds to wood are believed to develop not only when an adhesive penetrates deeply into cell cavities, but also when an adhesive diffuses into cell walls to make molecular-level contact with the hemicellulosics and cellulosics of wood. If an adhesive penetrates deeply enough into sound wood and becomes rigid enough upon curing, the strength of the bond can be expected to exceed the strength of the wood"

http://www.woodweb.com/knowledge_base/fpl_pdfs/ch09.pdf

 

[Tim Sherwood]

Thanks to all of you. I was pretty sure this would be the case. But I'm always looking to a short cut I didn't know about.