Silicone sealant problem.

[Druk]

About five years ago I replaced one of the roof hatches in the caravan. It's approx 300 x 300 and made from an ABS type plastic and is held to the roof by an internal frame screwed up into it on four corners. The sealant used at the time was Evo-Stik No-Nails which I've successfully used in many other applications.

This seal failed spectacularly during a nighttime thunderstorm at Coniston eek: and was temporarily repaired by a bead of silicone sealant around the edge.

This has also now failed and i have to take the hatch out to re-seal it properly.

1. What is the best sealant to use on a plastic/painted metal interface? If silicone then which one?

2. Would I be better spacing the hatch off the roof with (say) 3-4mm spacers and gunning the sealant into the gap rather than have most of it squoze out by the clamping action of the internal frame?

What say you?



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[Deleted member 113659]

Derek, is the sealant to be applied internally or externally? If the latter then a mastic would be better IMO.

 

[Druk]

The flange is on the caravan roof Ant and sometimes subjected to water puddling if the 'van is level. I'm thinking of this maybe...

Sika Sikaflex EBT+ All-Weather Sealant Grey 300ml | Weatherproof Sealants | Screwfix.com

 

[Deleted member 113659]

That'll be better than the 'No Nails' that you used because no nails is an adhesive not a sealant although it did the job for a while it gets hard and non flexible once cured (especially once exposed to extremes in weather.)

Go for the Sika Derek. Great brand.


Look at the 3rd review on screwfix.

 

[BTB 500]

They are normally bedded on non-setting mastic, AFAIK.

I think there's going to be enough movement and flexing (plus thermal expansion/contraction etc.) to eventually cause a 'set' sealant to separate. It's not easy to bond to smooth plastic ... for pipes etc. they rely on a solvent weld cement that melts the surface layer.

 

[Druk]

That'll be better than the 'No Nails' that you used because no nails is an adhesive not a sealant although it did the job for a while it gets hard and non flexible once cured (especially once exposed to extremes in weather.)

Go for the Sika Derek. Great brand.


Look at the 3rd review on screwfix.

Did read that one thanks but wondered about BTB's comment below about the plastic 'bond'

They are normally bedded on non-setting mastic, AFAIK.

I think there's going to be enough movement and flexing (plus thermal expansion/contraction etc.) to eventually cause a 'set' sealant to separate. It's not easy to bond to smooth plastic ... for pipes etc. they rely on a solvent weld cement that melts the surface layer.

Which is why I thought about raising the plastic flange away from the actual roof slightly so any sealant would provide a small dam to water getting past the seal. I'm going up later to the storage site to take the hatch out and then I'll determine which side of the old sealant has failed. Plastic or paint.

Where would I get/what type mastic if that proves to be the best solution?




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[Deleted member 113659]

There's a product called 'Lead Seal' that is great on smooth surfaces and remain highly flexible in all weathers. The last time you used No nails it lasted five years so if you use something that remain flexible it will last longer Anyhow's.

It seems the mastics of old aren't as widely available anymore. Mostly silicone based produces nowadays.

 

[grober]

These folks might be worth a visit?
Home

 

[Druk]

These folks might be worth a visit?
Home

I'll give them a go, might be a fun day out if nothing else . Last time I was up that road -visiting Glamis- I nearly got done for speeding. Blooming radar van in a lay-by near Dundee.

 

[grober]

Step-By-Step Guide To Re-Sealing Your Caravan Window - Without A Hitch | Without A Hitch

One thing to note is the use of a solvent to prepare the surface. The artcle cites methylated spirit but i have also heard of toluene or ethyl alcohol being used. I suspect this is to remove traces of ABS monomer which may have migrated to the surface over time weakening adhesion??

 

[PobodY]

I'd guess it's more about removing any oils from the surface so that the silicone can get a good bond.

 

[Dickie Fix]

Sikaflex 512 is the standard stuff for caravans. I've used it for ages and never had any problems - just make sure everything is clean before applying. Here's a useful link to a Sikaflex how-to (sorry for the Google bit, can't work out how to give a simple link) : https://www.google.co.uk/url?sa=t&r...an.pdf&usg=AFQjCNG_Bv-PSIp2vUVUtgQsZ7XazwB-gQ

 

[grober]

Reading that pdf on the SikaFlex 512 the Sika remover 208 has the following ingredients from its safety data
Hydrocarbons, C9-C10, n-alkanes, isoalkanes, cyclics, <2% aromatics so neat petrol might do at a pinch??

 

[Chrishazle]

For re-sealing round our shower, I was told that new silicone will not adhere to old silcone, so after the traditional Stanley knife for getting the majority of the old silicon off, you need to use a silicon remover to get the rest off before applying new silicon. Did that last time I resealed the shower, and it seems to have worked.

 

[LTD]

I'm surprised you haven't considered fitting a Mercedes glass sunroof with rubber seal.

 

[Druk]

Reading that pdf on the SikaFlex 512 the Sika remover 208 has the following ingredients from its safety data
Hydrocarbons, C9-C10, n-alkanes, isoalkanes, cyclics, <2% aromatics so neat petrol might do at a pinch??

Just bought in a new supply of Panelwipe so might give that a try. Too wet this affty to get the hatch out so might try tomorrow.

For re-sealing round our shower, I was told that new silicone will not adhere to old silcone, so after the traditional Stanley knife for getting the majority of the old silicon off, you need to use a silicon remover to get the rest off before applying new silicon. Did that last time I resealed the shower, and it seems to have worked.

Good idea Chris, I even got some in the store.

 

[Dickie Fix]

Reading that pdf on the SikaFlex 512 the Sika remover 208 has the following ingredients from its safety data
Hydrocarbons, C9-C10, n-alkanes, isoalkanes, cyclics, <2% aromatics so neat petrol might do at a pinch??

I used isopropyl alcohol (IPA). Bought a litre off fleabay for a few quid. Very useful stuff to have around.

 

[D-18]

I used this stuff on my cast-iron guttering (house not caravan!) and it worked well. Apparently it is capable of being used underwater so ideal for the Lake District or Scotland

Geocel The Works Sealant & Adhesive Clear 290ml | Weatherproof Sealants | Screwfix.com

 

[optimusprime]

Wish i had a pound for every one of these i had fitted in the past ..My job was to seal the caravan before it went to its new owner The leak you talk about is common, after a few years, the movement of the caravan panels crack the seals ;.or sealant .And also the roof light, or vent would split on the roof , through old age, and heat from the sun . .So removal was the only wayto go . along with replacment And yes as post 3 said .Sikaflex is the only sealant i used .Made for all the caravan builders .Other sealant will harden and crack .But the roof cassette will need full removal to seal it right . One thing if the roof light is old then check out the plastic weld holding both the top parts together, they will be upermost looking from the top ..The plastic weld cracks in the area that both the handles are fitted to .

 

[Druk]

Wish i had a pound for every one of these i had fitted in the past ..My job was to seal the caravan before it went to its new owner The leak you talk about is common, after a few years, the movement of the caravan panels crack the seals ;.or sealant .And also the roof light, or vent would split on the roof , through old age, and heat from the sun . .So removal was the only wayto go . along with replacment And yes as post 3 said .Sikaflex is the only sealant i used .Made for all the caravan builders .Other sealant will harden and crack .But the roof cassette will need full removal to seal it right . One thing if the roof light is old then check out the plastic weld holding both the top parts together, they will be upermost looking from the top ..The plastic weld cracks in the area that both the handles are fitted to .

Thanks for this. The hatch was new maybe four or five years ago and was fitted as replacement for a broken Dometic aircon unit that was going to be too expensive to fix. I'm aware of the problem you suggest regarding the plastic weld holding the two top parts together and have done an excellent repair to both those fitted using plastic weld glue. (like Airfix stuff but runnier). This new hatch is of a different design to that type. I'm pretty sure it will just be the flange seal that's gone but, yes, the thing will now come out completely for a fix.