For paint-grade furniture and cabinets (ply and 1″-by, no MDF), lately I have found myself priming many of the pieces before assembly to make the final painting easier. Then I glue the cabs together with yellow glue. On some pieces that are completely protected on the inside, I have even been putting on a glossy finish coat before assembly.
It struck me that maybe I am diminishing the strength of my glue joints with this practice. Does anyone have any good knowledge or practical experience?
Rick
Replies
I prefinish as much as possible. I cut my dados, rabbets and other joints after two coats of finish, assemble, then final coat(s).
Chuck S
If you are applying the glue over the top of the finish you are definitely not getting the glue joint you want.( That is the way I am reading you post)
The glue will only adhere to the painted surfaces, if at all.
"Yellow" glue needs to penetrate the wood fibers in order to achieve a bond.
Woodworking glue is formulated to adhere to wood. Have you ever noticed how easy it is to scrape excess glue off painted surfaces compared to bare wood?
When you pre-prime, you introduce two potential problems: 1. does the primer adhere to wood as well as glue does? 2. Will glue adhere well to primer?
When you glue over a topcoat you introduce two more problems: 1. topcoat-primer adhesion and 2. glue-topcoat adhesion. Then there is the problem of the paint/primer not attaining full cure until after days or weeks of exposure to air. If the topcoat is not cured, it will be weak; if cured, it should be hard and slick, making adhesion of anything to it a difficult proposition unless you sand it first, in which case you have to paint again...
The bonding agent in latex primer is nearly the same thing as your glue is.
I have primed before glue-ups too.
But I tend to doubt the value of top coats first. I would want them totally cured hard and dry, then sanded to give tooth instead of glossy and soft
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"The bonding agent in latex primer is nearly the same thing as your glue is."In the case of PVA (polyvinyl acetate) primer, but that stuff is used only for drywall. Waterbase primers for wood are based on latex or acrylic latex emulsion resins that are far more water resistant than PVA. I don't know if their adhesive properties are as strong as PVA or not, but it is likely that adhesion of glue to any primer film will be less than to bare wood.
The test would be to break such a glue joint; good glue will not fail before the wood does. Glue on painted surfaces would probably fail at the glue/paint interface or by delamination of the paint film.
BruceT
after reading all this through, I have to agree with you, but for practical puposes, I don't see a need to lose slepp over it for the boxes. panels and stiles in doors yes, but the boxes have dodoes and dovetails and fasteners also, so it is not just the glue holding.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
"...I have to agree with you, but for practical purposes..."Hey, no fair ignoring theoretical best practices for what is just plain PRACTICAL! :)
BruceT
Is it called "Paint glue"?
No, its wood glue.
Glue goes on wood. MASK the joinery if you must pre-finish.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations
Thanks to all. My suspicion prompted the initial question, and I think I got several real decent ideas. Glad I asked.
Rick
After 30+ yrs of woodworking and such, if and when that little voice says " hmm, is this OK?" it usually isn't ...LOLSpheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations
That's the same one that says "Ah sheet, this is gonna hurt..."
What about Roo Glue? It is a yellow glud..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I use Gorilla glue sometimes, even on wood. Gorilla glue sticks to paint, gorillas, humans, heck I even glued the side back on my swiss army knife with it.But it is better to glue to the wood than primer. yup.
I cannot get Gorilla glue to work properly on wood projects. There is just too much foaming and expanding going on.
Rick
I only use it on construction projects. It makes too big of a mess for finish work. I have no problem with it sticking to wood though.