by TFH Magazine on May 25, 2011 at 12:10 pm
By Bill Brissette
I wanted to write a note about using silicone with expanded PVC. Expanded PVC is a great material because of its light weight, easy machinability, and smooth, food-safe surface. Unfortunately, its surface is one of its downfalls as well: While it is readily glued to itself with PVC cement for plumbing, silicone has a hard time sticking to the surface.
After writing the latest installment of “Adventures in Aquascaping” and setting the tank up for a week of rinsing, the cork island in the center of the tank floated up and away. The silicone had stuck just fine to the cork, but not to the surface of the PVC. At least, it did not stick well enough to overcome the buoyancy of the cork. The other parts of the hardscape seem fine, especially where I used a lot of silicone, and where it is above the waterline. But this was a major setback that could have been avoided.
I would like to experiment with a few glues to be able to tell you the best one for this particular application, but I think an expanding polyurethane foam glue may be more suitable than the silicone in places where it is not visible.
One thing is for sure though, and that is that the porous center of the expanded PVC sheet is far more receptive to bonding than the smooth surface is.
To repair the float-away island, I plan on fully drying the insert and using the random orbital sander to roughen and gouge the surface of the PVC where it will be reglued so the glue has a chance to grab hold. Then, when I return to my rinsing phase, I plan on loading up the submerged cork parts with stone, so that their buoyancy doesn’t defeat the bond prior to planting. Simply adding weight during this phase, will emulate the substrate that will weigh things down once the tank has been planted.
In future projects, I will be sure to really roughen all surfaces that are to be glued, to avoid this problem.