Re: Glueing up a chair
- From: "Bob S" <spam@xxxxxxxx>
- Date: Fri, 02 Dec 2005 02:16:24 GMT
"DonkeyHody" <spammetts@xxxxxxxxxxxxx> wrote in message
news:1133487013.028869.275130@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
> Bob S wrote:
>> Myth Buster #77:
>>
>> Poly glue certainly does foam out and it does expand - but - the
>> expansion
>> is nothing but weak walled bubbles (look closely) and does not add any
>> measurable strength to the joint whatsoever. Gap filling is best done
>> with
>> epoxy type adhesives. This myth has been covered in a number of articles
>> in
>> the woodworking mags in the past and is easily researched.
>>
> Bob,
> I've read those articles too, and I've used more than one bottle of
> poly glue. I understand that the expanded glue has very little tensile
> or shear strength, but it certainly fills the inevitable voids in a
> joint that has worked loose. These joints typically have good contact
> on part of their mating surfaces and the poly will grab very well
> there. I believe the expanded part helps keep the joint from wiggling,
> which adds strength.
>
> I completely disassembled and reglued six 1950's era kitchen chairs for
> a friend who weighs over 250# They've been in daily use by his family
> for five years years since then. I asked him a few months ago how they
> were holding up. He said they are all still tight with nary a loose
> rung anywhere.
>
> Have you ever tried it in this application?
Never have used poly on gluing any old chairs back together, only hide glue
and epoxy and then only when needed for a hidden repair, like a partially
broken dowel. I have used poly on a number of other applications and know
full well that the expanded foam has little strength. If the gap is a wide
as the thickness of a business card - then you're better off with epoxy.
I'm not saying the joint will alway's fail (depends on a number of
variables) but the recommendations are to not to use poly for gap filling if
joint strength is an issue. The walls of the bubbles have minimal strength.
Poly's strenght comes from the bonding action and by wetting the wood prior
to applying the poly, it allows the poly to be forced into cell structure of
the wood when the parts are pressed together and the curing starts.
Obviously your chairs must have had good tight fitting joints if they have
not failed in 5 years. Do an experiment and drill a hole in some wood and
then sand down a piece of dowel so it's undersized and has a gap all around
when placed in the hole. Mist the wood, apply the poly and clamp. Now do
the same again but be sure the dowel is a snug fit in the hole. Make the
dowels long enough so you can get your hand on them to wiggle and pull them
and break the joint. Which one do you think will fail first? Do a 3rd
hole, undersize the dowel again and use epoxy this time (even the 5 min
variety will work for this experiment).
Bob S.
.
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