Bonding Fiamma 28f roof light to pvc

[trialsrider]

I've just noticed a watermark on my bathroom ceiling around the roof light. It is a Fiamma 28f crystal roof light. When I removed the flyscreen and lower part of the sandwich construction roof light I noticed the upper sandwich that is on top of the roof has clearly not adhered to the sealant the converter used. I spoke to him and he said he uses werth sealant on the roof lights. Does anybody know what these Fiamma roof lights are made of ? I've just ordered a new roof light and some sikaflex 522. However I notice sikaflex 522 ska 512 is not suitable for polypropylene. Does anybody know what this roof light is made from ? Or is there a release agent in the roof light plastic the converter simply hasn't bothered removing or keyed in the plastic. Any ideas ?

[Deneb]

The Fiamma 28 rooflight on my PVC was fitted by the converter using a non-setting bedding mastic. I removed and refitted it a couple of years ago to fit the turbo vent kit, and used Hodgsons Seamseal CV, a similar non-setting mastic sealant, and it is fine. The advantage of non-setting sealants is that it is a quick and simple job to remove existing sealant and thoroughly clean the roof and vent with white spirit before re-bedding if necessary at any time, whereas once Sika 522 has cured you can only remove it mechanically, with the risk of damage to the surfaces it has been applied to and possible difficulty in resealing them satisfactorily.

 

Probably OK if you assume the vent you are fitting is staying put for the life of the van, but what happens if it needs replacing due to damage or failure in use?

[Derek Uzzell]

If you GOOGLE-search on "fiamma vent 28 installation” you’ll retrieve several YouTube videos about this, and Fiamma’s own Vent 28 installations are also available.

 

https://www.johnscross.co.uk/templates/__custom/InstPDFS/VENT28TURBO28_2015.pdf

 

Fiama recommends SIKA LASTOMER-712 for sealing, but I think that Lastomer ‘number’ is no longer marketed. Sika Lastomer is a butyl sealant and used to be marketed in gunnable and tape form - nowadays I think the equivalent to 712 would be 710 that’s available in several colours.

 

The time-honured method for installing leisure-vehicle roolights would be to use a non-setting ‘mastic’ (often in tape form) as the primary seal between rooflight and roof, as this facilitates subsequent removal of the rooflight should this ever prove necessary.

 

The high bond-strength of a ‘constructional’ adhesive like Sikaflex 522 will glue the rooflight to the roof with a vengeance and getting it off later without damage occurring could be challenging. For tidiness, a cosmetic fillet of someting like Sikaflex 522 might finally be applied around the very edge of the rooflight and that’s what was done on the following link using Wurth Bond & Seal.

 

https://magnummotorhomes.co.uk/stage-12-fitting-the-rooflights/

 

I’m not sure if anyone will be able to advise on the plastic material a Fiamma Vent 28 is made from, but whatever it is it (and the roof) needs to scupulously cleaned before sealant is applied. Sika markets the “Cleaner P” cleaning agent

 

https://www.affixit.co.uk/sika-cleaner-p.html

 

but it’s not cheap and a kitchen degreaser like Cillit Bang might do the job on a one-off basis.

 

This 2015 forum thread discussed rooflight sealing

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/White-mastic-for-sealing-roof-vent-/38559/

[PJM]

To degrease just use plain old fashioned meths. Available from all good hardware stores and most chemists or supermarkets. A rag moistened with meths rubbed across the surfaces to be joined and then allowed to evaporate will do the trick. Depending on the level of contamination you may need to do a couple of passes.

[Deneb]

Meths is toxic, so use gloves and a face mask. Commercially available meths also has other substances added to it such as colourants and bittering agents, which may leave a residue that could affect bonding or paint application.

 

My goto degreaser is acetone. Available in bulk from hairdressing supplies shops, very low toxicity and evaporates to leave no residue whatsoever. The only caveat I would mention is, that whilst it has no effect on factory applied vehicle paint, if used on a surface that has been resprayed, due to accident repair for instance, it will dissolve the paint.

[trialsrider]

Thanks for everyone's input. Yes I think I'll go the two pronged method of inner butyl mastic with a sikaflex seal around the outer edge. I've got access to acetone so will clean with that.

[pepe63xnotuse]

Hi Trialsrider

I had a similar issue some years back when I fitted a couple of mushroom vents into the roof of our little Toyota festival/camping-van.

Although (I thought!) that I had thoroughly prep'd all of the surfaces("roughed-up" & cleaned with panel wipe),and used what I thought at the time was the right sealant/adhesive(sika 512?), it wasn't long before they were leaking.

As with yours, the sika hadn't "stuck" to the "plastic" of the vents at all.

Initially I put it down to the differing expansion rates of the materials ( a metal roof, sat exposed to direct sunlight etc)

But even a "test sticking" in the shed(using the off-cuts of roof) showed that the "plastic" vent just wasn't interested in staying stuck to the metal, using the sika I had.

 

I ended up just using what I thought was a "low-tech" *non setting bedding sealant from a local caravan spares place.

(*Hodgson. Seamseal CV. Non Drying Bedding sealant"- is what it says on the tube) and then "squidged" them on,using the inner trim fixings to sandwich/retain them in place. It was certainly a messy product to use, and far harder to achieve a tidy finish, also I wasn't overly confident it was going to work...but eight plus years later and they're dry and secure!

 

But ours certainly required the physical/mechanical fixings of the inner trim to "sandwich" and retain it though....

 

(There was/is a forum member Globebuster (I think?) who is very helpful and knowledgable about adhesives and the likes, as I believe he is involved in building boats?)

 

[trialsrider]

pepe63 - 2021-04-10 1:48 PM

 

Hi Trialsrider

I had a similar issue some years back when I fitted a couple of mushroom vents into the roof of our little Toyota festival/camping-van.

Although (I thought!) that I had thoroughly prep'd all of the surfaces("roughed-up" & cleaned with panel wipe),and used what I thought at the time was the right sealant/adhesive(sika 512?), it wasn't long before they were leaking.

As with yours, the sika hadn't "stuck" to the "plastic" of the vents at all.

Initially I put it down to the differing expansion rates of the materials ( a metal roof, sat exposed to direct sunlight etc)

But even a "test sticking" in the shed(using the off-cuts of roof) showed that the "plastic" vent just wasn't interested in staying stuck to the metal, using the sika I had.

 

I ended up just using what I thought was a "low-tech" *non setting bedding sealant from a local caravan spares place.

(*Hodgson. Seamseal CV. Non Drying Bedding sealant"- is what it says on the tube) and then "squidged" them on,using the inner trim fixings to sandwich/retain them in place. It was certainly a messy product to use, and far harder to achieve a tidy finish, also I wasn't overly confident it was going to work...but eight plus years later and they're dry and secure!

 

But ours certainly required the physical/mechanical fixings of the inner trim to "sandwich" and retain it though....

 

(There was/is a forum member Globebuster (I think?) who is very helpful and knowledgable about adhesives and the likes, as I believe he is involved in building boats?)

Thanks for that. I've just ordered sika 710 butyl sealant. Thanks Derek for the info. I'm going to gun it in and if I can tool it neat enough I'll just use that. I get a good finish with silicone gunning as my friend used to fit windows and taught me well.

 

I've also just ordered from road trippin these plastic inserts which fit into the corrugation on the roof. You then ultimately have a flat roof once these are fixed in place. I will sikaflex 522 these in situ and then just butyl the rest.

 

Sadly I don't think there is anything I can do with the water mark on the ceiling. Just glad I noticed it.

[rajohno]

I used this Mastic strip when fitting 1 new and resealing the 2 other rooflights on my MH been through 80-90mph winds and heavy rainstorms (I live on 180m away from a cliff edge!) without any issues.

https://www.towsure.com/mastic-sealing-strip-5-metres-32mm-width?gclid=Cj0KCQjw5MLrBRClARIsAPG0WGwP5Vmeh2GNfh89PVZWDSm6i-m4o4Vx0e9udi_rxw2p1cqAQJNVD84aAv4sEALw_wcB

[trialsrider]

Does anybody have any suggestions how thick (depth) a seal of the butyl sika 710 I should be trying to achieve. I'm going to use spacers so that when it sandwiches together it doesn't all squeeze out. My previous fitting of a solar panel confirms the roof is convex so this needs to be considered too. I see the butyl tape comes in a variety of depths.

[Derek Uzzell]

This is another earlier forum thread about sealing a motorhome rooflight.

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Sealant-for-the-roof/46990/

 

There is a 2-page section in John Wickersham’s book “Build Your Own Motorcaravan” that covers fitting a Remis roof window, but John chose to use ‘ribbon sealant’ for bedding the unit and Sikaflex-252 round the edges for extra waterproofing.

 

I recall discussing minimum joint thickness with a SIKA rep years ago. I don’t remember what minimum was specified, but it was emphasised that too narrow a joint must be avoided.

 

Road Trippin advertises Soudal Butyrub for windw/vent installations

 

https://www.roadtrippin.co.uk/Soudal-Butyrub

 

and Soudal’s technical data sheet for that product includes the following guidance

 

Joint dimensions

Min. width for joints: 5 mm

Max. width for joints: 20 mm

Min. depth for joints: 5 mm

Recommendation sealing jobs: joint width = joint depth. Use PE backer rods before applying the sealant in large joints to avoid 3- point adhesion.

 

Road Trippin has advice on their ebay advert for the ‘spacers’ you are ging to use

 

https://tinyurl.com/482xtea6

 

Apparently they employ butyl tape on the roof vent and a bead of sealant around the edge, but you could ask then for guidance on joint thickness when using sealant from a gun.

 

(As the roof is convex where the Fiamma vent is, I think you’ll need to play this by eye, erring on the side of an over-thick joint.)

[trialsrider]

Derek Uzzell - 2021-04-12 9:07 AM

 

This is another earlier forum thread about sealing a motorhome rooflight.

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Sealant-for-the-roof/46990/

 

There is a 2-page section in John Wickersham’s book “Build Your Own Motorcaravan” that covers fitting a Remis roof window, but John chose to use ‘ribbon sealant’ for bedding the unit and Sikaflex-252 round the edges for extra waterproofing.

 

I recall discussing minimum joint thickness with a SIKA rep years ago. I don’t remember what minimum was specified, but it was emphasised that too narrow a joint must be avoided.

 

Road Trippin advertises Soudal Butyrub for windw/vent installations

 

https://www.roadtrippin.co.uk/Soudal-Butyrub

 

and Soudal’s technical data sheet for that product includes the following guidance

 

Joint dimensions

Min. width for joints: 5 mm

Max. width for joints: 20 mm

Min. depth for joints: 5 mm

Recommendation sealing jobs: joint width = joint depth. Use PE backer rods before applying the sealant in large joints to avoid 3- point adhesion.

 

Road Trippin has advice on their ebay advert for the ‘spacers’ you are ging to use

 

https://tinyurl.com/482xtea6

 

Apparently they employ butyl tape on the roof vent and a bead of sealant around the edge, but you could ask then for guidance on joint thickness when using sealant from a gun.

 

(As the roof is convex where the Fiamma vent is, I think you’ll need to play this by eye, erring on the side of an over-thick joint.)

Thanks for the info Derek. Yes I've just had a email back from road trippin and they stipulate a minimum of 2mm. I'll use my double glazing spacers to achieve this. The screws certainly had enough length in them to accommodate this increased height in the sandwich.

[Derek Uzzell]

The advice in an ancient SIKA document about sealing using Sikaflex-512 Caravan said

 

Do not squeeze all the Sikaflex®-512 Caravan out of the joint. If necessary, use spacers. Optimum thickness is 2mm.

 

Adapter frames are marketed by Dometic to facilitate fitting a Heki Midi, Mini or Micro rooflight to Boxer/Ducato/Relay X250/X290 panel vans. The Heki Micro has a similar 28cm ‘footprint' to a Fiamma Vent 28, but it’s anybody’s guess whether the Dometic frame (advert here)

 

https://www.genesis-sporthomes.com/roof-hatches-accessories/dometic-adapter-frame

 

would be suitable when installing the Fiamma product.

 

Your spacers should be just as effective.

[trialsrider]

Finally finished the roof vent. I fitted the spacers with sikaflex 522 to make the corrugations flat. Used the sikalaster 710 to bond the vent to the roof. The sikalaster is the most unworkable and untoolable compound I have ever worked with. It is like dough mixed with Shi* !! The attached photo shows the finished vent but this was my second attempt. The first attempt I tried to tool the sikalaster and absolutely ruined it. Had to pull everything off and reclean. It took 3 hours to clean it all off again. That is why the sealant has not been tooled in the photo. Second attempt I used much less sikalaster 710. The Fiamma vent it appears is actually designed to be flush with the roof with no gap. This is why there is a suggested torque setting for the screws. The vent mating surface with the roof has a recessed groove which when filled with sealant forms a inner gasket between roof and vent.

 

So my question is, does it need an additional sealant around the outside. I was going to gun sikaflex 522 around the outside and tool it neatly as I did the spacers. But I'm tempted just to leave it as it is. This is how Fiamma say to do it. Furthermore the vent is made of polypropylene and sikaflex 522 says it is unsuitable to bond to polypropylene. Shall I just leave it how it is ? It has squeezed out on every edge so it's definitely sealed.

 

[Deneb]

All of the roof vents on my van are sealed with copious amounts of non-setting bedding mastic, which has not been tooled at all. It looks a little unsightly, but as I can't see the roof in normal use it doesn't bother me at all. On the Facebook group for our vans, another owner said they had contacted the converter and asked if they could tidy up the mastic as it looked unsightly. The reply was that they could if the owner really wished, but they've found the approach that they use much less likely to result in any leaks down the line. I copied their approach when I refitted my vent, just laying some masking taper around the roof aperture about 15mm away from the edges of the vent moulding before dropping it in place so that I could remove any mastic that had spread too far. But I didn't tool it afterwards. I can understand the desire to make the joint look neat on a flat roof where a smooth sealant line will help any water flow around the edges of the vent, but on a PVC body with the ridges and gullies that can hold standing water and not allow it to flow around, I favour the more is better approach.

[trialsrider]

Thanks for the response. I think I'll just leave it as it is then.

 

Deneb - 2021-04-19 9:12 AM

 

All of the roof vents on my van are sealed with copious amounts of non-setting bedding mastic, which has not been tooled at all. It looks a little unsightly, but as I can't see the roof in normal use it doesn't bother me at all. On the Facebook group for our vans, another owner said they had contacted the converter and asked if they could tidy up the mastic as it looked unsightly. The reply was that they could if the owner really wished, but they've found the approach that they use much less likely to result in any leaks down the line. I copied their approach when I refitted my vent, just laying some masking taper around the roof aperture about 15mm away from the edges of the vent moulding before dropping it in place so that I could remove any mastic that had spread too far. But I didn't tool it afterwards. I can understand the desire to make the joint look neat on a flat roof where a smooth sealant line will help any water flow around the edges of the vent, but on a PVC body with the ridges and gullies that can hold standing water and not allow it to flow around, I favour the more is better approach.