Waterproofing a working water fountain basin... with roof cement (tar)

[zailabouni]

I think I made a huge mistake. I built a working water fountain for a production of Jack Frost. I built the basin with a 3/4" plywood base and and the sides with 1/4" masonite. Everything fits together very tightly. First I caulked the seems and then made what I'm affraid is a huge error. I was going to coat it in Red Gaurd (a liquid latex water proofer used as a water barrier under tile in wet locations) However I was on a budget and at almost $40 /gl, I got the bright idea to use a roof cement tar product for $9 a gallon. Problem is, I applied it a little thick, and after a week, much of it is still not cured. Sticky to the touch. My question's are:

1) will it still hold water if the tar is not fully cured? It is only a two week run and I do not plan on emptying it until strike

2) is the tar going to leech chemicals into the water that will change the water's color?

3) will the above mentioned chemicals cause a problem with my pump? ( a cheap 1/10 hp sumbmersible pump)

4) any ideas to speed the curing process?

5) is it to late to just coat over the tar with a liquid latex or epdm product?

6) can you dim a pump? I already have a T diverting half the water's force back into the basin, but in testing it in a bucket, it was still a little too powerful. And I would love to have proportional control of the pressure through my light board.

Any ideas would be very helpful, tech week starts on Monday!

And on a different note... The fountain is "frozen" the whole show until the end, when the water turns on. I was thinking of hitting it with a light green gel (lee 245) from above, but not sure if it will give me the "spring" effect I'm going for. Thoughts? Thanks

 

[Les]

1) will it still hold water if the tar is not fully cured? It is only a two week run and I do not plan on emptying it until strike

You should be fine. See if you can get it to spread as thin as possible, and make sure there are no voids or bubbles.

2) is the tar going to leech chemicals into the water that will change the water's color?

Since tar is petroleum based, it shouldn't have the ability to change the water's color. The black tint of the tar at the bottom of the pond may make the water appear dark, though.

3) will the above mentioned chemicals cause a problem with my pump? ( a cheap 1/10 hp sumbmersible pump)

Maybe. Certain rubber parts can be degraded by petroleum products, but for a short run I'd just keep an eye on it and expect to throw this away after the show (unless it still works, of course) .

4) any ideas to speed the curing process?

I don't think there is a safe way to do this, but it probably doesn't need to be cured to be waterproof.

5) is it to late to just coat over the tar with a liquid latex or epdm product?

Latex will not stick to oil. I'd leave it.

6) can you dim a pump? I already have a T diverting half the water's force back into the basin, but in testing it in a bucket, it was still a little too powerful. And I would love to have proportional control of the pressure through my light board.

You can't dim a pump. Maybe you could transition to a larger outlet pipe in order to relieve some of the pressure? Maybe add a few loops in the tube as well (just some thoughts - haven't tested this).

---

In the future, might I suggest Drylok. The latex versions are available at most home improvement retailers, and it is less than $10 per quart (good for about 60sf as it is a little thicker than regular paint. It can also be tinted to light colors (no more than 2oz of colorant per gallon), and it is rated for underwater applications such as this. IIRC, a gallon was under $30.

I'm sorry about your tar issue. I've done similar things in the past while trying to make a pond for an outdoor reptile habitat. I used some DAP ready-mixed concrete patch to fill some voids (with the intention of going over it with Drylok) and the patch never quite dried - ending up rubbery instead. I'm still scraping the stuff off. The Drylok on the other hand is amazing, except for the unstable patch work underneath portions of it!

 

[zailabouni]

Thanks. Makes a lot of sense. I will leave it be. I can't use a larger outlet to releive pressure, but I will try to replace the T with a cross and a ball valve on one side, that should give me the adjustability I will need to fine tune the pressure. I appreciate the advice.

 

[lwinters630]

Tar is flammable and if it is thick it will not cure, it will just skin. Plywood covered with a cement base ROCI from TEC Roll-On Crack Isolation Membrane | TEC Specialty would have been water and fire proof. Use fiber mesh in corners and seams. If you scrape all the tar off or as much as possible the ROCI will possible cover it.

The tar will put a oil slick on the water.

Depending on the pump, it may be able to be dimmed, or put the ball valve on the output side. Don't block the intake side it will over heat. Most inductive motors can be reduced to a trickle.

 

[Van]

You've already got a couple good answers there but I have to throw a couple more out there as well. Most likely you don't have to worry about an oil slick on your water. Unless it was really old tar or had been sitting for a very long time. You are going to have residual tar smell, however, as I'm assuming it goes higher than your water on the sides. Do not try to speed up it's curing.
You could top coat the tar with a coating of an elastomeric compound such as Snow Roof. However it will be a pain to get it to cover properly as the materialwill want to pool on top of the petroleum product. What it would wind up doing is creating a latex shell on top of the tar. Tar would remain mushy underneath the shell but the shell would be elastic so unless someone was walking around in spike heels in your fountain it would be fine.
In the past I have had the most luck simply building my fountains then lining them with EDPM from Home Depot or Lowes., I'm more concerned that your fountain is going to self destruct when filled. 1/4" Masonite ?!? I hope to heck you have a lot of reinforcement framing. Remember that " All the world 'round, a Pint is a pound" that's 8 pounds a gallon, or 1 gram per square centimeter < you do the math, or rather, I hope you already have calculated the load.>

 

[zailabouni]

thanks for thought. Yes there is quite a bit of framing, the masonite was just to make a smooth curve. Since most of the show the fountain is suppose to be "frozen", I simply decided to line the basin with 6mil plasic. I then cut a piece of plexi to set the pump on to give it a solid base and to keep the intake from sucking in the plastic. We had our first dress rehearsal tonight and am happy to say everything worked very well. But i do appreciate the advice for next time. Suffice to say, I will not be using tar for anything ever again.

 

[zailabouni]

Oh, And I rolled the dice and hooked the pump to a dimmer channel. I worked well. No problems with the pump or dimmer.