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More about bonding agents
I am having my 1969
single story
So. Calif. house restuccod and the Sub wants to use a cement type glue
to glue (Crete-Weld) over the old painted stucco. I have been told that
sandblasting the old stucco is vital for a good bond, he feels that he
can get away without sandblasting the old stucco and just applying the
glue product directly over the old painted stucco. Can you please
comment
on this issue?
I got sued when a house we did this
way
popped off 4 years later. Jobs we did 10
years ago are now popping off. Weld
crete
dissolves in water. Stucco
isn't waterproof, and is porous. Water will
eventually
dissolve the weld crete.
It may last longer in Southern California
due
to the lack of humidity, but I doubt much longer.
I just redid a patch (for free) I did
on
a friend's house 9 years ago that was popping off. The way
weld-crete,
plaster weld and euco weld work, the surface dissolves
with the wet plaster (or cement mortar).
After
the mortar sets, it all dries together
forming a chemical bond. This works fine
for
indoor plaster with a warning
on the can not to be used in wet areas.
Trust
me here. It has cost me a lot of
money and embarrasment.
Weld-crete, plaster weld and euco weld say
right
on the bucket not intended for
wet areas such as showers. The outside of a
house
gets wet, too. These bonding
agents work fine for interior plastering,
but
fail when used for exterior stucco.
We have torn off loose stucco on buildings
done
this way. It makes me sick to
ride by buildings we did 10-15 years ago
that
have loose stucco and maybe some
band-aid patches. I didn't know any better.
Acrylic bonding agents work great for
stucco
on unpainted porous surfaces
such as concrete, old stucco (unpainted),
etc.
They are used in swimming
pools. The directions on the bucket says
mix
with mortar and not paint on first.
The acrylic mortar mix can be troweled on
or
even painted on with a brush, and
left rough for the application of a brown
coat
or just a finish coat.Examples of these are Acryl60, Flexcon or
Milestone.
I worked with an old plasterer years ago
who
showed me how to bond cement
mortar to concrete using a Portland cement
paste.
Pure portand(no sand) is
mixed with water and painted on. First the
concrete
is wet down. Second,
the cement paste is painted on leaving the
surface
rough. The paste sets instantly
when it hits the concrete, and then starts
to
dry. A scratch coat of mortar must
be troweled on before it dries. One
plasterer
can paint a small section at a time,
and then scratch mortar on right away, or
one
can go ahead painting and the other
scratching(applying mortar.
This method was used in swimming pools
years
ago, and is still used in foreign
countries. I saw this done when I was in
Mexico.
Thick stucco ceilings were applied
to concrete slabs with no failure. If they
trust
it on a ceiling, I trust it, too.
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