Pianotech

"I have hesitated so far to join the fray in the vigorous debate on glues. But I know a bit about PVC-E and PVA glues, as my formal training and former employment was as a Ph.D. polymer chemist, with a specialization in latex/emulsion materials and industrial gelatin (effectively hide glue).

Both PVA and PVC-E glues are emulsion/latex glues which are milky in appearance until they dry, because they are a water-based suspension of very fine polymer particles that scatter light just like the suspended fat/protein droplets in milk.  Both can be thinned with water, and both can penetrate into wood pores and fibers.  The particles in both glues coalesce irreversibly when dried into a layer of water-insoluble plastic. Neither PVA or PVC-E glue is water-soluble after that point, and in my experience, neither can be easily cleaned off of wood surfaces.

The properties of the dried glues are very different.  PVC-E (poly (vinyl chloride)) is softer and more rubbery, and more hydrophobic or water repellent, while PVA (poly (vinyl acetate)) is harder and stiffer, with a more wettable surface and a greater tendency to absorb a little water and become a little softer.  Thick bulk layers of PVC-E can sometimes be peeled or scraped off, because it is softer.  And thick bulk layers of PVA glue can be swollen and softened by soaking in water (PVC-E with long! soaking) to aid removal.  But neither is "soluble" in the same way hide glues are, and a thin surface layer or the material impregnated in the pores of wood or fabric is effectively impossible to remove.

Most woodworkers who have used both PVA and hide glues have seen how a spilled or oozed PVA glue usually creates a later finish defect, even if it is wiped off the surface immediately with a wet cloth, or even if the surface was lightly sanded after drying.  Hide glue drips that are wiped off are much less likely to create a defect.  Because the PVA penetrates quickly and dries irreversibly, it remains in the wood pores and shows up during finishing, while hide glue is much more removable and more forgiving.

Hot hide glue will 'wet' cured PVA glue surfaces better than cured PVC-E surfaces, and will adhere to some degree, but in my experience not as well as to a wood surface that hasn't been contaminated with PVA glue."

Joe D. If you reread the Sobo MSDS I think you will find that is PolyVinyl Acetate Copolymer Emulsion, PCV-E I believe. PVA is PolyVinly Acetate which is a different formulation which is the basis for many wood glues such as Titebond. All of which is my opinion based on my research into the matter.  

Thanks for catching that, I don't do abbreviations well and should spell everything out. I posted an edited version as well as a version I tried to edit and messed up. Still learning after all these years.

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Dale Probst
Registered Piano Technician
Wichita Falls TX
dale@wardprobst.com
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Original Message:
Sent: 03-14-2011 14:26
From: Paul Bruesch
Subject: PCV-E and PVA

Dale,

Do you mean PVC-E? Or is PCV-E yet another beast?
Not meaning to pick nits (which is my nature, at times) but hoping for a year-round, locally-accessible product.

All,
Any clamping recommendation for PVC-E? e.g. Titebond requires tight clamping for 1/2 hour, epoxy not so much.

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Paul Bruesch
Stillwater, MN

Original Message:
<snip>
Joe D. If you reread the Sobo MSDS I think you will find that is PolyVinyl Acetate Copolymer Emulsion, PCV-E I believe. PVA is PolyVinly Acetate which is a different formulation which is the basis for many wood glues such as Titebond. All of which is my opinion based on my research into the matter.  
</snip>