Silicone sealant not sticking to uPVC

[DoctorNick]

Hello all,

I was sure that I would find an answer to this on the web somewhere (quite possibly on this site). However, so far I have not.

Silicone sealant is nowadays used universally to seal around uPVC doors, windows, etc. However, certainly when I have used it, no matter how carefully I prepare the surface of the uPVC, after some months one can see that the silicone has become deadhered to the surface and there is a very narrow gap. This of course can let in moisture, which defeats the whole purpose of sealing it.

I always clean the uPVC with alcohol and then dry it before applying the silicone since I am sure that there is often a very thin layer of grease or something else on the uPVC surface. However, despite the silicone sticking well initially and showing no sign at all of having a problem adhering to the uPVC, after a few months careful examination shows a very small gap.

If this sounds like it is just me being inept, I would like to point out that the same issue has happened around many of the windows and doors in our house that were professionally fitted before we moved in (I think that they are Everest doors and windows).

Does anyone have a solution to this problem? I am wondering whether I need to roughen up the area that will be sealed using fine sand paper. Trouble with this is that if one is not careful one could damage the surface of the uPVC and shorten the life of the product.

Any thoughts / solutions most gratefully received.

Cheers,

Nick.

 

[and1c]

Nick,
I would suggest NOT to roughen up the edge of the UPVC...the lifted edge that often happens with silicone sealant does not mean that the inner/main part of the bead has also seperated from the UPVC surface.

As you will find if you start to try and remove the silicone (eg, it won't peel off in one smooth run)

The best way to ensure that the silicone bonds well to the UPVC is to mask the frame up leaving some extra space over the size of the bead (to be sure you get full coverage) and then use a relatively strong mix of PVA adhesive all around the frame. (5:1 *WaterVA* will do nicely)

Let this dry and if your feeling really fussy give it another coat

Once dried use a decent quality silicone sealant (not budget stuff) and provided yoy lay the silicone beading correctly....you will have given it the best chance of a solid bond

 

[wms]

Doc the problem with silicone pealing and not sticking is when the wrong type of silicon is used you should use low modulus neutral cure. for sticking trims up and perimeter sealing , if you use any thing with an assatoxic cure the assatones (fumes) cause the silicone to de laminate. and de bond. if you use low mod as described, other than making sure its clean and dry you do not need to do any other prepping etc. hope this helps.

 

[DoctorNick]

Hello guys,

Thanks for the suggestions. I have always just bought general purpose silicone sealant (usually from Wickes). I was not aware that there were these different types. However, some googling showed my ignorance. Screwfix have low mod neutral silicone on special offer at the moment, so I will pop along and get some.

Cheers,

Nick.

 

[DoctorNick]

Hi DortechDirect, etc,

Gosh, this thread was originally from 5 years ago and reminds me of how long we have now been in our "new" house. Hence, maybe it is time to give an update.

Good advice re the pro silicone, so worth knowing. I did go and get some neutral cure low modulus silicone from Screwfix as per wms' suggestion. I cut out the sections of original silicon that had unstuck (in some cases this was all around the window, but in others it was just a section). I then cleaned it well with ethanol and let that dry. Finally, I applied the new silicon and made sure I formed it into the joint to make a nice neat (as neat as I could!) bead. How did it do? Well, five years on, no sign of coming unstuck yet! Looks fine and still making a perfect seal.

Thanks again to all who replied and I hope this thread will help others in a similar situation. As so often is the case, its just having the right "tool" for the job.