# Is Sikoflex 521 the best for the job?



## Borisd0 (Jan 3, 2006)

A few years ago the rear roof vent in the MH developed a leak.

I removed it, cleaned both surfaces well with meths and resealed it with Sikoflex 521.

It started leaking again, I ordered a new tube of Silkoflex and this morning set about removing the vent. With a blunt kitchen knife it came away quite easily. The sealant had stuck perfectly to the roof but parted from the plastic vent frame cleanly without any sealant adhering to it. It looked as if Sikoflex did not stick to plastic frame at all. At the moment work has stopped with a temporary solution while I pause for thought. 

Is this the wrong sealant?
Did the plastic need priming?

Any suggestions gratefully received.


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## Pudsey_Bear (Sep 25, 2008)

I'm having similar difficulties with plastic not liking any of the sealants I've tried, I'm advised that CT1 is the one to go for, and get the spray to go with it as it gets rid of the old crap, and you also use it to smooth the CT1, there's video on you tube.


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## Borisd0 (Jan 3, 2006)

Looks impressive Kev, has anyone used it?


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## Pudsey_Bear (Sep 25, 2008)

I haven't seen anyone using it, but it''s been recommended on the self build site and on here a few times, Sika is good, as is Stixall, but onto "some" plastics seems to be problematic.


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## Melly (Jul 5, 2007)

Milliput is an epoxy putty which may do the job.
Not tried it myself but a google search does have good reviews.


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## Brian-the-Snail (Dec 1, 2011)

I have used Ct1 but not on the van, I used it to seal a leaking joint on my plastic guttering at home and it works well. As Kev says use the spray to condition the surface before use.

Clive


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## Borisd0 (Jan 3, 2006)

Has anyone used Carafax IDL 99, apparently it is used extensively in caravan construction. It is a non setting mastic. In many areas around my MH (10 years old) the original sealant is still soft and non setting. 

The roof vent needs to be sealed to the roof, it is not required to be stuck to it with an adhesive. My experience with Sikoflex 521 is that is remains flexible but dries and losses its sticking power.

I wonder if a non drying mastic might be better.
Just a thought.


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## mentaliss (Oct 23, 2012)

Borisd0 said:


> A few years ago the rear roof vent in the MH developed a leak.
> 
> I removed it, cleaned both surfaces well with meths and resealed it with Sikoflex 521.
> 
> ...


 I have been using Tec7 for two years, (latest generation of the M7 developed silicone polymers)* and I can confirm it will stick plastics to plastics and just about any metal and I also use their Tec Adhesive remover/ cleaner, specially designed to use in conjunction with the Tec7. CI is good but in my opinion the TEC7 product is currently the best out there....no I don't work for them!*


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