Both Dow-Corning Chemical and GE have long
made silicone sealants suitable for aquarium
use. Dow's brand is DAP. In 2000, GE repackaged its Stock #012 clear silicone "Household
Sealant" (in the familiar blue and white tube) as
#012A, relabeling it "Window and Door"
and disclaiming responsibility by labeling
it "not for aquarium use," doubtless
because they can't control how we clueless
spazzes use the product. Fair enough, in
this litigious society. The repackaging caused
ripples among aquarists, but RJ reported
his discussion with a GE consumer relations
representative in an excellent Jan 2001 post
to the killietalk newsgroup. The gist of it: it's the same old sealant.
There are still some lingering fears about
possible long-term low-grade toxicity from
possible anti-mildew agents. Reservations
about whether a silicone sealant is non-toxic
should be clarified: the silicone elastomer
itself is inert and non-toxic. Silicone sealants
for certain non-aquarium uses have anti-mildew
additives (arsenic, etc.) that are designed to release long-term low-grade toxicity.
Read the packaging. Conversely, you can be
absolutely sure, when you see a premium-price
aquarium sealant packaged as "for aquarium
use," that it's only being marketed--
and not custom-manufactured-- for aquarium hobbyists.
For a secure bond, use alcohol or a non-oily
solvent to clean the surface free of dust
and lint, soap residue (you shouldn't be
using soaps to clean a tank anyway), detergents,
or oil and grease (including what may be
left by a fingerprint). The surface must
be dry.
As the silicone elastomer cures, acetic acid
is formed by contact with atmospheric moisture.
A curing time of 48 hours is minimal. There
should be no hint of vinegary acetic acid
smell. Though silicone has bonded after 48
hours, it continues to gain strength. Optimum
strength hasn't developed until about a week
has elapsed.
Long after they have cured, silicone sealants
continue to absorb water and swell. Make
allowance for expansion when you're sealing
rocks together, for example, so that the
sealant doesn't start to show later.
