Last year we redecorated the house. Round the windows where they meet the sills I siliconed and have noticed on all the windows that it has cracked. I applied it and used some washing up liquid to smooth it out. Looked great at the time but looks awful now. Obviously I have done something wrong but what?
Thanks in advance
Also I used Unibond gear. As I need to redo this what is the best silicone to use? Thanks
Its common to use an acrylic-based frame sealant which is more durable than silicone. Commonly available in white and brown. Also, don't be sparing - be prepared to use several tubes. Good prices from toolstation on acrylic sealant. I'm just waiting for the temps to increase to fit some windows. The foam an sealant all says use in 5C plus, but probably 3C would OK using sealant stored indoors. Hope that helps, Simon.
In what way does it look awful? Is it untidy -, discoloured, or what?
Ben, can you post a photo somewhere that we can look at ? Simon.
I take it that acrylic sealants can be overpainted unlike normal silicone ?
Just noticed that Toolstation have "Forever Sealant" which claims to stay white with no mould for 10 years ...anyone used that in a bathroom situation ?
It has cracked and shrunk.
You need to use a Low Modulus Neutral Cure Silicone ... such as Unibond frame sealant
Ben,
Could I ask what size of mastic bead you applied?
The reason for asking is that the thinner the bead, the more likely it is to crack.
Could I also ask if the windows are painted or UPVc?
Again the reason for this is if the windows were painted, silicone mastic will not generally accept a painted finish causing the paint to crack a flake off. In this case, painters caulking should be used as this can successfully be over-painted once 'dried' - this can also be used in very small cavities without cracking and should be tooled flush with the surface.
*DO* *NOT* use this as water barrier between the frames and wall [1].If the windows are UPVc, then remove all the old mastic, clean off the joints and then re-mastic with as thick a bead as possible for the circumstances and *lightly* tool it of with a wetted finger (water only, [do not lick your finger] and use a thin surgical glove to protect the hand) - or use a propriety tool for the job.
As for using "washing-up liquid to smooth it" - I wouldn't advise this as it
*may* cause problems with the silicone, unlikely, but it is possible. And it will certainly cause problems if you have over-painted the silicone by causing an even greater lack of adhesion between the two surfaces, causing the problems that you are experiencing. [1] This is not waterproof and it will certainly break down and allow water ingress if the frames are exposed to very heavy weather conditions over a period of time.Hope this is of some help.
Cash
It was wooden sill against PVC windows and granted, yes, I did apply a small bead thinking it would look better. Also in the downstairs loo where I did put on a thick line it hasnt cracked. Will do it better next time and go to Screwfix for the sealant. Thanks again everyone
Thanks for the feedback Ben, and the best of luck on the repair.
Cash
Use right product for right job ... smooth with a a tool or finger dipped in water with a few drops of washing up liquid.
For frames I use Neutral Cure Low Modulus .....this can cope with the expansion caused by sunlight. Something such as "Unibond Frame Silicone Sealant" ... cheap enough is screwfix.
Neutral cure has far better 'stickability' than acetyl cure in this type of application.
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