"Marc Levenson" wrote in message
...
| I see small bubbles in the finished results. Is this because I'm using #3
instead
| of #4? Is it because I'm holding the pieces by hand instead of using
mounted
| speed squares? Is it because I'm not using pins, but just wick the weldon
in to
| the joint?

Marc,
I had the same problem on my first two sumps. Your problem is twofold.
First, I've had much better luck with #4. Its slower cure time is much
easier to handle when we come to reason #2.
Reason #2 is, you're not using the pins method. I can safely say I've made
over 100 seams now, and without pins, they'll never come out bubble free.
The pins method, in conjunction with #4, can even make up for less than
perfect edge finishing. I've found that if I leave the joint soaking a
little longer before pulling the pins, that it doesn't necessarily have to
be a perfect edge. This won't help with imperfections any larger than about
1/64" (I've noticed this is how much the vertical piece "sinks into" the
horizontal piece in the joint after being softened by the solvent), but with
pins & #4, I can get a bubble free seam with edges straight off the table
saw (Ryobi 10" w/ DeWalt 80 tooth TC carbide). I watch closely for the first
minute or so after pulling the pins to see if any areas are starting to suck
air as the solvent shrinks away, and add a little solvent if needed.
On the last sump I did (75g sump for a 75g tank) out of the total 34' of
seams, I have about 3-4" of seam with bubbles, the rest is perfectly clear.
I mostly have trouble only with corners these days, perhaps it's because of
my construction order. I think I'll try a different sequence on the next
one.
As for the pins themselves, I've had too much trouble with actual pins, and
have switched to twist-ties with the paper stripped off. Pins seem to be too
heavy a guage, or maybe just the ones I was using were...anyways.
I'd be happy to come over and go through a couple of seams with you some
weekend, if you like.

Kev