I had essentially this same problem but in reverse. The preform I got
needed a spillway lip and it did not, and one that had a lip I wanted
without. I bought a cheap half barrel liner and used it for the
material I needed to alter the two preforms. Do not rely on silicone
alone. I owuld install a stainless steel pop rivet or two or some
stainless stovebolts to help keep the alteration in place and rely on
the silicone to seal it. ONce a siliconed piece starts to let go its
history, and a fastener or two in it helps prevent that. While
silicone will work, not all silicone is created equal........so take
that into account......What I prefer anymore over silicone is the new
polyurethane sealants. They work great, and are available in caulking
gun tubes n various colors as well. PL is a brand with good rating, as
is Wooster.........

I know a lot of foks do not know how to do it, but to be honest the
best route is plstic welding the parts how you want them, and thats
exactly what I do any more....no sealanrts and the p lastic the
preforms are ,made out of are especially well suited for hot air
welding process. You can get a hot air plastic welder from Harbor
freight for under $40 but you still need a compressed air source, but
a little practice on scrap plastics and in no time you can weld or
should I say fuse up all kinds pf plastic. The plastics used in
preforms do not solvent weld,, and they are slick and even with
scuffing do not allow a real good adhesive or sealant joint. HOt air
welding does. Even altering plastic buckets, 55 gal drums etc is all
possible with a hot air welding outfit. I added 2" threads to a
barrels bottom side by using bungs from a drums top, welded onto
position on the sides, and elimimnated a bulkhead fitting or trying to
get down inside the barrel as it has the top intact on it for the
application I needed it for......You can even hot air weld PVC
pipe....and its amazing what you can construct out of pieces of PVC
and a hot air welder.........You can make some amazing plant holders
out of larger PVC pipe, and weld on brackets and leggs. PVC welding
is a bit more tricky but sitll doable. I have made special adapters
and fittings by this method and its as strong as a molded fitting
would be. Its all within the doable range of most any home owner, and
any small cheap compressor will work as it does not require a lot of
air, but just a low psi and low air flow to operate. You can buy
plastic or PVC and other types of filler rods for these welders or the
best is small scraps of the same material your welding up...... A
couple of old plastic buckets or plastic pieces and a few hours
practice will get you into the hang of it and you'll be doing it like
a pro in no time, Its easy to do!

PS another good method to get sealants etc to stick better on preform
type plastics is to heat the area after scuffing it with a piece of
coarse sandpaper........sosunds counter produictive but plastic as
such oxidizes quickly, a hand held torch or hot air gun applied to
it, burns off that oxidation and makes the surface a little bit more
suitable for adhesion.Just apply heat to the point the surface gets a
shiney waxy look to it and stop, allow to cool to touch and apply
sealant.




On Sat, 30 Apr 2005 20:12:41 -0400, "RichToyBox"
wrote:

===The plastic that the preformed ponds is made from can be heat formed, so
===taking a propane torch and warming, not to hot and burning, bend the lip up
===to the level that you want. You can also take a piece of stainless and bend
===it to fit, place silicone tank seal around the edges betweem the tank and
===stainless sheet, and bolt it through the liner. You may be able to effect a
===seal with greatstuff foam, which a lot of people use for waterfall mortar.


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Put some color in your cheeks...garden naked!