Vortex: How Eliminate Mulm Traps?/Polyurethane Foam

[MikeM]

There are spots under the pipes leading in and out of my vortex that gather mulm. I was thinking that the polyurethane foam used to bind together rocks around ponds might work to fill the gaps so there would be no place for settlement to gather. However, the directions do not say whether the stuff can be submerged, do not say if it has to be fully cured before being submerged, whether it has to be fully cured to be fish-safe .... in fact, it does not say much at all, except to wear old gloves & clothes when applying it!

Anyone have experience with Polyurethane foam in a submerged location??

[mulberryjen]

Have used foam to seal around large rocks that form waterfall platform. It is sprayed under leading edge of rock & attached to liner to keep water from running underneath rock. Also platform actually 3 large flat rocks puzzle-peiced together with black foam. Point being, the foam is actually submerged at all times.

Have used the yellow and silver types sold as foam insulation, as well as the black kind marketed for use around ponds. Seems to be about the same stuff. Surface of liner & rocks had to be completely dry for the foam to properly bond in my experience. Did not use any scientific method to determine proper cure time - seems like it was at least 45 min. or so each time. Would simply push on it to see if it was firm and stick a nail in it to see if it came out dry without any tacky foam stuck to it (like you do with brownies & a toothpick )

There is a bit of an oily skim that washes off of it when water first runs over it. Maybe fill unit partially with water and drain and refill fresh to remove it. Sections where I did not trim off the shiny surface skin seem to hold up against the water & UV, while cut areas deteriorate over a season or 2. Have no science about possible breakdown in water so my idea is:

What about creating a soft dam with liner material with a hole to fit around pipe? You could slit one end of it to put it into place over the pipe and secure it to the inside wall of the vortex and outside of pipe with marine sealant. Maybe use foam behind it to give it structure and liner will keep it from reacting with water. (Just a top of the head thought)