Which Silicone Sealant To Use?

[jesmond]

niece bought a house last year and is finally getting through the work it needed and is now planning "summer" jobs, my question is, the sealant on the upvc windows are grubby and she wants to take it all off and re-seal and as there are lots of different sealants, which is the best or the correct one, indoor part is what it is for, tia

[The Builder]

Here's one of the good ones, Jes ...................

http://www.screwfix.com/p/dow-corning-796-upvc-silicone-sealant-brilliant-white-310ml/40004

Glazing silicone. Low modulus.

The low modulus simply means it's more flexible.

[Zacs-Master]

Builder, what do you recommend to remove old silicone?

[The Builder]

Awful job, Zacs. There are chemical "silicone eaters" on the market. In my experience, they are not terribly effective on a thick silicone bead. Rather like paint stripper on thick coats of paint.

I tend to strip of the greatest thickness mechanically, with Stanley knives, blades etc.

Then, chemical to remove the final traces. I'd be interested to see if others have found better methods.

[jesmond]

hi builder have looked at that one and not sure if I can read "outdoor" on the label unless you can tell me otherwise, and in answer to Zacs-Master, I think she will use good old fashioned elbow grease!!!!!!

[Zacs-Master]

Thanks.

[The Builder]

Jes, you'll notice on the Screwfix page, it mentions "weather sealing". It's not like sanitary silicone. That has to restrict itself to "indoors" for obvious reasons.

Any glazing sealant that doesn't work externally wouldn't be very useful ;o))))

[jomifl]

If you want to find a solvent to remove the traces left after mechanical removal the website in the following link may be of help. Just look for the least compatible solvent that is readily available, non toxic and cheap.
Paraffin works well on silicone rubber.

http://www.coleparmer.co.uk/Chemical-Resistance

[trt]

To remove old silicone, I found the easiest way is to buy a largish hook, file the end to nearly a point, so you can get behind the silicone, and drag down.

[jesmond]

thanx all

[KARL]

There are purpose-shaped scrapers made of hard plastic to cut away silicone. They have the advantage of being hard enough to cut the silicone but not so hard as to score wood, PVC, etc. to which the silicone was applied. The one I have used to a limited extent is V-shaped to form something like a corner cap strip which is cut at about 45 degrees so the cut forms a point at the apex of the strip (difficult to describe but I hope it can be understood). This "working end" is quite short and fitted to a handle (well, all formed in one piece of plastic). It does work but getting the last little bits away can be tricky but then if it sticks well enough one may decide to just put the new silicone on top.

[woofgang]

Speaking as a jolly bodger, I would have to be sure that my re seal will be waterproof before i started messing with window sealant. has she tried cleaning the existing sealant?

[jesmond]

not sure of that woofgang but I know she thoroughly cleaned the house, including the windows just before Christmas and the black that is on the sealant didn't budge

[woofgang]

that sounds like mould that is actually in the sealant. Sometimes rubbing over with milton mixed with washing up liquid (use gloves) will bleach the black off. you need to not slosh it around though as it will bleach most things it touches. rinse off with a cloth wrung out in clean water after about 10 to 15 minutes.

[woofgang]

That’s quite unusual actually. is it inside or outside? if inside, does she have a damp problem?

[jesmond]

not damp. probably just a build up of dirt or the dirt has possibly got on it before sealant has hardened/dried