On Mon, 10 Jun 2013 01:01:54 +0200, nestork
wrote:


;3075965 Wrote:

So what is your problem with PVA as a concrete bonding agent?


I don't have a problem with either PVA or PMMA as a concrete bonding
agent.

There are hundreds of different kinds of polyvinyl acetate resins used
to make paints, primers, adhesives and other products that I can't think
of right now.

What I'm saying is that PVA resins that are used to make wood glue will
re-emulsify if they stay wet for a long time. That's important so that
you can repair wood furniture by taking the joints apart with moisture.

PVA resins that are used to make concrete bonding agents need to
ultimately form a solid that's completely unaffected by moisture.
That's important in a concrete bonding agent because most concrete is
outdoors, and the repair could stay wet for a long time from rain, flood
or snow melt. You don't want your concrete repairs coming apart because
the glue used to glue the new concrete to the old is dissolving
(kinda).
The high Ph of the concrete apparently has an effect on the
crosslinking of the PVA resin making it more water resistant than when
it is used solo as a wood glue.
It's common to use white wood glue in brick mortar when repointing
bricks because the only moisture the bricks high up on an exterior wall
are every going to see is the occasional rain. But, at the other end of
the spectrum, you'd never use a white wood glue to repair a concrete
swimming pool or concrete underground sewer pipe because that
environment will be wet for long periods, and the wood glue used to glue
the new concrete to the old is going to come apart, causing the repair
to fail.
But the PVA is IN the concrete, not used as a glue between the
concrete -the hydrating of the lime in the portland cement combined
with the PVA resin apparently has a different effect.
It's in those situations where the concrete repair could stay
wet for a long time that you'd be better off using a concrete bonding
agent than a wood glue. And, it's all because the concrete bonding
agent will ultimately form a solid that's unaffected by moisture,

Which APPARENTLY is what happens when PVA resin is combined with
portland cement. An old construction worker next door has used
bondfast in concrete as a bonding agent for decades with good results
on porches and garage floors - and also in foundation parging.
-
whereas the wood glue will always re-emulsify in water if it stays wet
enough for long enough. And, that's true no matter how long the
furniture has been dry.