Whoops! I used the wrong silicone sealant.

June 1, 2009 3:00 AM

I used silicone sealant in a situation where it will be immersed in water. On later inspection of the tube, it says, 'not suitable for permanent immersion'. What will happen to it?

I used it when attaching the outlet to a domestic water tank, and some of the silicone is inside the tank, around the internal seal part.

The seal is good without the silicone, I used silicone to make sure it would be super extra watertight.

This water is not being consumed, it's for garden watering and toilet flushing.

The silicone in question is a 'roof and gutter sealant'. Why is one silicone suitable for immersion, and not another?

posted by tomble to home & garden (8 comments total)

I'm sure you will get better answers, but the silicone will probably start degrading in the water, lose adhesion etc, and end up in the tank.

Is the tank pressurized, or is the outlet of the tank hooked up to the suction side of a pump? If the seal is ok without the silicone, then it should be fine. How is the outlet attached to the tank? Screwed connection? Is it easy to get to if there is a leak in the future? I would just leave it, and deal with it then (if ever).
posted by defcom1 at 3:08 AM on June 1

It's a suction pump setup, the outlet is at the base of the tank next to the pump. The outlet is tube, threaded on the outside with a flat disc section which fits on the inside of the tank.

In layers from the inside out, it would look like - metal base of outlet, rubber seal, plastic tank, metal nut holding on the outside, with a blob of silicone smooshed through those layers.
posted by tomble at 3:12 AM on June 1

If you left yourself a good, solid bead of caulk then you can probably expect it to hold up for a good while before it begins to break down. It is a clear / opaque caulk, right? It's not black and tar-y?
posted by Glendale at 3:13 AM on June 1

The seal is good without the silicone, I used silicone to make sure it would be super extra watertight.

FWIW, it's generally a bad idea to "improve" connections this way. If the seal isn't designed to use silicone, then adding silicone is more likely to cause problems than to make it "super extra" anything.
posted by jon1270 at 4:32 AM on June 1 [1 favorite has favorites]

Yup, I agree with jon1270, you may have set yourself up for a problem with the silicone smooched through your gasket. It's supposed to seal by compressing the rubber between the inside flange and the inside tank wall, using the threads on the outside to squish the rubber, if I understand the description correctly.

I would just leave it, it's not under much pressure (just the static head of the tank). It may start to leak sometime in the future. It will be a drip. You will have to deal with it then, probably by disassembling the mess and getting a new gasket. I would probably advise against tightening in the future if it does start to drip, you may do damage by overtightening things. Just open and replace. Note - this could take a while to happen. Months, years even.
posted by defcom1 at 5:52 AM on June 1

Could you post a picture of the setup, or link to the type of part that you used? Is it threaded? As jon1270 mentioned, you may be working against yourself here. Teflon thread tape may be all that's necessary, if that.
posted by odinsdream at 6:27 AM on June 1

tomble posted "What will happen to it?"

This is going to depend on what it was adulterated with. Best thing to do is phone the customer service line of the company (it's usually on the tube) and enquire. I've almost always found product support lines for this kind of stuff very helpful.
posted by Mitheral at 9:05 AM on June 1

Followup : The tank has been sitting, full, for a couple of months now thanks to some decent rain, and there's no sign of a leak. Phew!
posted by tomble at 12:03 AM on September 14