Tightbond Creep

[John Hartman]

Ron Nossaman wrote:
> 
>> You will also find the same information in "Understanding Wood" and 
>> the "wood Handbook".
> 
> 
> I don't find it in Understanding Wood. Must be looking in the wrong 
> place. I did find mention of "tends to yield under continued stress" in 
> the Wood Handbook, with no differentiation made between white and yellow 
> PVA. There is a considerable and obvious difference between the two, as 
> anyone familiar with both knows. It also mentions crosslinkable PVA, 
> which would be the Titebond II equivalents, with no mention of creep 
> whatsoever.
> 
> I'd still like to find some real information on this for my own 
> education, if nothing else, should anyone happen across it somewhere.
> 
> Ron N
> 


Ron,

I know you will not finds this in the least conclusive but if you get 
your hands on Technical Bulletin No. 1512 you will find a few charts. On 
page 73 there it a chart of side to side joints with various glues. The 
samples are subjected to repeating cycles of 65-30 and 90-30 RH. The PVA 
glue start out fine but after 36 months it slip in both cases. It is at 
the bottom of the list in the 90-30 RH test after only 12 months. Hide 
glue is near the top of the list in both tests.

 From page 23
"Probable the most serious limitation in the use of these adhesives 
(PVA)in woodworking is the lack of resistance to continuously applied 
loads."

I would relate some personal experience but that would mean nothing to 
you. One thing seems clear at least to me: PVA is not a structural 
adhesive because of its cold flow. It never truly hardens like many 
other woodworking glues - urea resin, resorcinol, phenol-resorcinol to 
name a few. Hide glue is only kept off the list of structural adhesives 
because is is not water resistant - in every other way it meets the 
criteria.

John Hartman RPT

John Hartman Pianos
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Rebuilding Steinway and Mason & Hamlin
Grand Pianos Since 1979

Piano Technicians Journal
Journal Illustrator/Contributing Editor
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