Silicone sealant - shelf life and failure mode

[Steve Walker]

Hi all -

Fitted a stainless steel 'sit-on' kitchen sink onto a cheap B&Q base unit yesterday. Instructions said to bed it on silicone sealant. I used a tube of trade Evode window silicone, which had been around for years but unopened. Tube says quick-skinning, high-adhesion, low-modulus, so it seemed ideal.

I noticed at the time that there was no vinegary smell, and 24 hrs later the surface hasn't skinned (in dry area, room temp). So I'm thinking now, was it out-of-date and if so what does that mean? I'd always assumed that if left for too long it would cure inside the tube, but this stuff seems to have lost it's mojo.

Can some kind expert tell me what happens to silicone sealant if it's left unused for too long?

TIA!

[Grunff]

Old acetate-cure silicone will either not cure or take a very long time to cure. If you've seen no skinning after 24 hours, I'd be very surprised if you ever see any :-(

[Steve Walker]

Oh, bugger.... The pipework's all installed, and it'll be an evil job to take it back off again (especially now it's 'buttered' with sticky sealant round the edges). Never mind, it's only a 'bed' of 1-2mm so I'll scrape out what I can and 'repoint' with new sealant. The mechanical fit is already reinforced with small L brackets inside the base unit, so it's not going to move around. Thank heaven I wasn't fitting a window frame or bath though!

Thanks for the info re sealant, Grunff.

[John Schmitt]

I'll try and read up on it. Normally the problem with old silicone is that it self catalyses and goes solid. However, to get back to the actual problem, get the old stuff off with methylated spirits and paper towels or rags, disposable is the only way to deal with the stuff. Make sure you get to squeaky clean and redo with new stuff. Rather like epoxy glue, look around for other jobs to do in the same session.

John Schmitt

[Steve Walker]

Thanks John - I'd also assumed that if it was still runny, it was still OK. Now scraping out the uncured sealant with matchsticks & rag - it's fun all the way..... :o)

[Nigel Molesworth]

Best of luck, I found that it left a film that was impossible to remove. I wonder if silicone remover would work?

[Steve Walker]

Mmm, yep. Just like paint that never dries. Fortunately it's not an exposed position or requiring mechanical strength - I can just bodge over it. Very lucky it wasn't a door frame or similar.

Yeah, I'll try that. Meths just washed over it like water.... :o(

Cheers Nigel!

[Peter]

Try acetone (nail varnish remover), but be careful to keep it away from any plastic/acrylics