Silicone on old Silicone

[Muse2k8]

Just something brought up over on the plumbing forum. Seemed to be a mix of opinions on whether or not you could add silicone over old silicone, usually to cover cracked sealant etc.

As such I did an experiment to get a did definitive answer.



The first bed was put down and given nearly 48 hours to cure.



After that a new bead was added, firmly pressed to the older silicone and with a decent bed behind it to simulate filling a gap or what have you.

Again this was allowed to dry fully before testing.

On testing the new bead was pulled at to see how easily it came off. Remember that these were new beads and clean unlike silicone that might have been down for years!

And the result?



It came away effortlessly.

So obviously without teaching how to suck eggs, hopefully this will help someone or anyone in the future with either DIY or indeed professional jobs.

Cheers

 

[Muse2k8]

Actually surprised nobody has posted and called me a liar or anything lol

 

[John Benton]

The camera never lies (hhmmmm, Photoshop, who said that) :lol:

 

[steveb]

i can vouch for muse2k3 the thread was spread over several days while he conducted his experiment here is a link

can you apply silicone over silicone?

 

[swanman]

No Remove old silicone first

Much neater job just takes a little more time

Come on lads dont be lazy:8:

 

[Topshop]

The only problem I see with your experiment is that how often do you not force the first or second silicone in a joint with your finger or tool. From what I can see in your experiment you only laid the second one on top wth no smoothing to force it together.

Either way I think the biggest danger of not removing old silicone is that the old may not be adhered to the surface well anymore and to put new on top may not fix the old failure. Plus often there are science experiments growing on the old silicone which make the old stuff look like butt.

Leaving excess silicone behind only makes silicone fail. I always remove as much excess silicone as I can with a razor - the excess peels later causing the joint to fail.

 

[Muse2k8]

Haha now now John

Cheers Steve!

 

[AliGage]

In much the same way as we answer "can you tile over tiles?" Professionalism says no. But good to have the theory and science behind it.

 

[Muse2k8]

The only problem I see with your experiment is that how often do you not force the first or second silicone in a joint with your finger or tool. From what I can see in your experiment you only laid the second one on top wth no smoothing to force it together.

Either way I think the biggest danger of not removing old silicone is that the old may not be adhered to the surface well anymore and to put new on top may not fix the old failure. Plus often there are science experiments growing on the old silicone which make the old stuff look like butt.

Leaving excess silicone behind only makes silicone fail. I always remove as much excess silicone as I can with a razor - the excess peels later causing the joint to fail.

The bit of silicone attached to the other was pushed hard into it then given some bulk afterwards to try simulate it being pushed into joint. But seems that once its cured nothing is going to stick. And yeah your right for old silicone there's other worlds living on it!!!