# how to determine which polyurethane varnish is safe



## nipzie (Nov 24, 2008)

I'd like to seal a concrete background with this stuff, preferably a satin finish in a spray can for ease of coating, though a cheaper route would be to use a can of varnish and just grab a dollar store spray bottle and just use that to spray it on, assuming the solvents don't dissolve the bottle in my hands. What are some ways to determine which ones are safe? I know people have used them, and I also found out some have a potentially poisonous anti bacterial additive, but which one have people used here, and with what results? Once under water it should be virtually impossible to see it, and outdoor grade varnish should be used, so I've read. Another advantage would be taking the roughness out of the surface lest anyfish decide to flash, but still retaining the rough rock look. People have used it to seal driftwood, how has it stood up underwater?

Anyone have any input?


----------



## Mcdaphnia (Dec 16, 2003)

All rated for use as boat finishes would be non-toxic and resist turning a translucent white from absorbing water.


----------



## bntbrl (Apr 23, 2009)

This is interesting and could have some other uses. Im going to checkinto this stuff. Im fairly new to the concrete backgrounds. *** been using coconut coir for years for SA tanks. I want to try my hand at concrete backgrounds now.


----------



## nipzie (Nov 24, 2008)

interesting, thanks mcdaphnia. Anyone know of any other ones that might be readily available from HD or Lowes?


----------



## nipzie (Nov 24, 2008)

Does anyone know about varathane? it is an acrylic based polyurethane finish, not a varnish. Wonder what the difference is.


----------



## nipzie (Nov 24, 2008)

I think I might have found something. Seen Quikrete natural looking waterproofer in lowes and did some googling. Also it is fairly thin so I can use a spray bottle to apply it, as I wanted

here is the link: [/url]http://aquaticpredators.com/forums/index.php?showtopic=27956&st=40


----------



## D-007 (Jan 3, 2008)

Wow, that is interesting indeed. Keep us up to date if you do use it and how it fairs in the tank. I also wonder how well it would work as the inside coating for a plywood tank :fish:


----------



## nipzie (Nov 24, 2008)

it's very absorbant, so I would think it would absorb into the wood. There was a 1 800 number on the bottle that I wrote down so I'll call the company and ask. At least I know someone has used it in a tank for this purpose before.

Mcdaphnia, spar varnish is used for boats, is that what you were referring to?


----------



## nipzie (Nov 24, 2008)

Apparently quikcrete does not make any product that holds up when permanently submerged. According to the company anyway. On with the search
[/code]


----------



## nipzie (Nov 24, 2008)

According to all manufacturers and the guy at the boat store, all varnishes will flake off eventually underwater. The timeline was never given, but even though polyurethane has been used it is not a reliable coating. That would leave epoxy for a hard durable finish. I believe I am going to use xypex high n' dry mixed with pigment for the colour coat now and colour over the finish again.


----------

