pondliner under marble countertop?

15 Replies

Hello, I need a solution for making darn sure a bathroom vanity top is waterproof. It is in a small trailer. The main electrical box backs out under the vanity. The sink will be 2 feet away from it but I am still concerned in case of too much spillage on the countertop.

I have a nice piece of marble cut to fit the vanity. I am wondering if I can use pond liner under the marble or if it needs a completely stiff surface. The pond liner would be sitting on a rough plywood surface. The marble is about 4 feet by 16 1/2 inches and is 3/4 inch thick. Fairly heavy- I can't see it moving much once sliconed down, but I suppose the rubber pond liner might accentuate any vibration.

It's either that or hardiboard, but I'm not too keen on the hardiboard idea as a seal on the edges might fail over time.

Anyone know the answer on this one? Or have a better idea? And no, I can't move the electrical box.

First off,  yes you can move the Electrical box.  

What you mean is,  no it's not cost effective or a viable option etc.  .  . 

If it were me, I'd get a bit of pond liner and drape it over the box, that would protect it from water. Putting a pond liner under the vanity top will do absolutely nothing.   

@Lynn Harrison I am confused, are you concerned that water will permeate through the marble counter? I don't think that this will happen if it is a solid marble countertop. Skip the liner, install the sink and counter correctly, caulk all seems and you should never have a problem.

As the other poster mentioned you could take steps to waterproof the electrical panel too.

Good idea and I'll do that.

My thought was to put the pond liner over the vanity top and under the marble slab. Then curl the edges slightly to raise it above the marble on the back and sides and hide that with a backsplash. I'd like to do both but not sure if the PL is a good underlayment for the marble.

Oops, guess I was writing while you posted. No, my concern is that caulking eventually fails. Not usually much of a problem. Unless the leak is directly above the main.

I could use lexel insted of caulk but it's messy and could still fail.

Thanks guys. I found the answer- pretty sure I can. They make 100% rubber soundproofing mats for stone tiles that are 40mil. Pond liner is 45mil, and a 3/4 inch slab should be more stable than a marble tile. They make a latex mortar for the adhesive, so I'll use latex caulk. This is a small piece- 4 ft x 16 inches, yet heavy enough to not want to move much. So I think it will be fine.

Will this even pass an inspection?  Is all this new or was it already in the same spot and you are redoing it?

Re-doing it, it came like this. I didn't put that box there.!! Can't move it without rewiring 6 or so runs OR putting 6 junction boxes under there. Which would be worse. It had a formed plastic counter top before this which was cracked and not safe. Originally the plastic top was backsplash, counter and sink cast all together and not prone to get water anywhere.

I just found a good tile and stone forum and am going to ask them how to do this. I want to be sure the underlayment and caulking are compatible. Or find something that is.

There are water proof electrical boxes available that can be retro fitted over existing panels &/or boxes. Or if it's NOT to too much work you could simply replace the old box with a new completely sealed unit. This would be far more effective than your somewhat remote pond liner install as it would also ensure complete moisture protection from bathroom condensation. We have found the latter a major problem in many older panels/boxes whereby condensation alone caused heavy corrosion within the old unit.

I don't feel as if the liner is a great solution to your problem. You will still need penetrations in that liner for the faucet, sink or drain. the water getting in will have to go somewhere and eventually will find its way out through the penetrations.  A liner under the tile on a shower floor is one pc that goes several inches up the walls and the only penetration is at the drain  where the liner sits into the drain so any seepage finds its way into the drain. You can also have a leak where the water supply lines connect to the faucet, your liner will do nothing to stop that water...  Water and electric don't mix well so my recommendation would be to move the panel or at the very least use a box rated for outdoor use. Be safe, spend a few dollars, do it right and have peace of mind.

Pat L, thanks! I like the retrofit Idea very much, I'll look into that. Problem is I am not touching that box myself and in this remote rural area I can not get an electrician to work on a trailer's box. I don't trust a handyman to do the whole box either. Box looks fine though- no corrosion inside or out.

Robert, faucet hole leaks and supply lines are not a concern. The box is up off the floor and about 2 1/2 feet away from water junctions and where the sink will be.  I rebuilt the cabinet so that it has a slight slope away from the box on both planes- back and width. The supply lines are at floor level under the cabinet & I've used Jedd's idea of loosely skirting with good air flow in front of the back of the box with pond liner. 

Yes, basically I'm looking at the type of water barriers that showers have, and am going to ask a forum of professionals how to do that right, This is a trailer, not a house, and things are crammed up against each other- that's how they are built. I hope my next project is a house, trailers are a PITA.

Sounds good Lynn, good luck with the project and finding a house in the future

Regarding "The main electrical box backs out under the vanity." You need a licensed and experienced electrician. Your statement raises concerns about code violations and triggers 'red flags' for me. You need to make sure this is done correctly.

No kidding. Which is why I'm not touching it. This is a trailer, not a house. It was designed and built this way.

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