pepe63xnotuse Posted March 14, 2012 Share Posted March 14, 2012 Sorry..just a quickie...Does Sika' 512 "skin over" or does it always remain "tacky"?(..and in doing so,going "grubby" quick?) Having just washed the van,I've noticed that the large seam that runs across the roof is starting to look a bit ropey... So I'm looking to arm myself with a couple of tubes of decent sealant,with a view to chamfering out the original mastic when the weather's looking good enough... Thanks.... C Link to comment Share on other sites More sharing options...
ips Posted March 14, 2012 Share Posted March 14, 2012 The data sheet for this product states that it can be "sanded" and cures on contact with atmosphere so one assumes the answer is yes it does go hard. Link to comment Share on other sites More sharing options...
Rayjsj Posted March 14, 2012 Share Posted March 14, 2012 No, it doesn't remain 'Tacky' once out of the tube (and sometimes in It ! ) it sets hard, but gives a good waterproof seal, and an 'unbreakable' bond, I swear by the stuff, Just be careful of 'Shelf life', buy them with a good long date before they need using. As it will set hard in the tube. It gives a good 'White' seal line which doesn't go 'Yellow'. just don't use it where you want to 'take something apart again' in the near future. It stays flexible for moving joints. Good stuff. Ray Link to comment Share on other sites More sharing options...
pepe63xnotuse Posted March 14, 2012 Author Share Posted March 14, 2012 Thanks for the reply ips... ..but "..can be sanded.." ?..I think I must be thinking of the wrong one then, 'cause I thought it stayed flexible... :-S Edit: Sorry Ray,I missed your post...It sounds like it is the stuff I'm after then ;-) Thanks for the tip about checking the "shelf life".. Link to comment Share on other sites More sharing options...
ips Posted March 14, 2012 Share Posted March 14, 2012 Have a look at the pdf link below (you may need to copy and paste it into google search) for all sika marine products should find a suitable one in there. Sikaflex® Marine Handbook www.bluemoment.com/downloads/sikaflexmarinehandbook.pdf Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 14, 2012 Share Posted March 14, 2012 I suggest you follow this link, and consult Sika direct for their recommendation http://tinyurl.com/77h63uc If the existing sealant is in any way similar to the current range of modified polyurethane sealants, you will have a horrible job trying to remove it/cut it back. They are highly elastic, and extremely tough, and you will, IMO, be liable to damage the existing surfaces in the attempt. I would not do anything to it unless it is absolutely necessary. If the existing sealant is of older type (assuming an '83 van this is possible), and it is now breaking down, you will need to remove the lot back to clean surfaces and start again, unless you can discover the formulation. Compatibility with more recent sealants cannot be guaranteed unless you know the natures of both, and the last thing you want on a roof is chemical incompatibility causing breakdown in the joints between dissimilar products. Might an alternative be to apply a protective tape over the joint? I don't think this will be a job than can safely be completed in a day (it may, it may not) and it would be unwise, IMO, to attempt unless the van is under cover. You may find, once you start, that you have to do more work than you are anticipating. Have you tried contacting Chausson to see if they can tell you what sealants they used for these models? Link to comment Share on other sites More sharing options...
pepe63xnotuse Posted March 14, 2012 Author Share Posted March 14, 2012 Thanks for the input chaps... I have already ordered a couple of tubes of the Sikaflex 512 (from Caravanstuff4u)...so I'll see how I get on with that... The seam in question,is the join between the(low profile)cab and the main roof section.It's about 5/8-3/4" wide and appears quite "deep".. I've had a bit of a trial "poke about" with one of the "suspect" bits... I've cut two small chamfers into the original bead(along the back and front),and refilled the resulting "gulleys" with beads of White Evo-stick All weather sealant,that I had knocking about(..this WILL get replaced..honest..) Brian..The "83" is the model number(it's an '08) but funny you saying about tape..I had considered that but I thought it may look a bit of a bodge..and as it isn't leaking,tape may give the impression that it had been and look like a rushed repair.... Having said that,depending how tidy my first method ends up(with the sika'),I may also look at bonding a neat 3" strip of upvc moulding over the top as well.It would be easier to produce a neat bead against and make a much tidier job.. ..like the 75mm D section listed here: https://www.angelplastics.co.uk/Products_Sub.asp?PP=445&PCT=1&U=444&N=window_trims.gif (..obviously leavings slight gaps at the ends,to allow water run off...) Having said that,maybe a bit belt'n'braces... Link to comment Share on other sites More sharing options...
Guest 1footinthegrave Posted March 14, 2012 Share Posted March 14, 2012 Brian is right I would try to find out what your dealing with. On my van a mixture of sealants have been used, some resembling plumbers mate ( on the Heki roof light), and others that I guess are Sikaflex or something similar, why that should be I'm not sure though. I should add that Sika skins over to form a very tough "rubberised" type of product that cures all the way through, unlike the "plumbers mate" type stuff used on my Heki, but it does look dirty, unlike the Sikaflex where used on other parts of my van. It would be a good idea for Sikaflex to supply their product in a smaller tube for us folk that do a bit of tidying up, most of mine went in the bin as when I opened it despite trying to reseal the tube against air it had cured well into the tube around six months later. :-( Link to comment Share on other sites More sharing options...
crinklystarfish Posted March 14, 2012 Share Posted March 14, 2012 You'll be fine digging the old stuff out and using 512 as a replacement. It's a bit odd that the original stuff has started to look 'iffy' so soon though. I'm wondering whether there's a bit of torsional stress at work causing the mouldings to move against each other. Even if it is, 512 is the best solution as it'll move around a lot before it shears from a surface. You will need to make sure the surfaces to be treated are uber-clean so make sure give them a wipe with thinners or a proprietary cleaner before going at it with the Sikaflex. Once in there you will need to be quick but it can be easily shaped with spit-on-a-finger and any excess can be removed with white spirit. If you do go for a moulded section to finish beware that 512 won't stick to some PVC and polypropylene type plastics. To be honest though, if you do a neat job of application, you won't need a capping. Link to comment Share on other sites More sharing options...
Rayjsj Posted March 14, 2012 Share Posted March 14, 2012 C, Sounds like you are 'sorted', just as an aside, I attatched a Fiamma Wind deflector to the roof of my old Autosleeper, to stop the front rooflight from blowing open in transit, using just Sikaflex 512, with no screws, because I didn't want to compromise the 'Watertightness' of the roof. Six years later, the deflector was still there as strongly attached as when I first fitted it. And still a nice white seal, so it must have some 'anti-fungicide' in the mix as well. Hope the repair goes well. I have to agree with ' 1 foot' though, i must have thrown away more than I have actually used over the years. Once opened, it slowly cures right through the tube, within a couple of months it's Solid. no matter how hard I try to 're-seal' the tube. Ray PS I also sealed a crack in my Back Box with it. Link to comment Share on other sites More sharing options...
flicka Posted March 14, 2012 Share Posted March 14, 2012 Brian Kirby - 2012-03-14 4:06 PM I suggest you follow this link, and consult Sika direct for their recommendation http://tinyurl.com/77h63uc If the existing sealant is in any way similar to the current range of modified polyurethane sealants, you will have a horrible job trying to remove it/cut it back. They are highly elastic, and extremely tough, and you will, IMO, be liable to damage the existing surfaces in the attempt. I would not do anything to it unless it is absolutely necessary. If the existing sealant is of older type (assuming an '83 van this is possible), and it is now breaking down, you will need to remove the lot back to clean surfaces and start again, unless you can discover the formulation. Compatibility with more recent sealants cannot be guaranteed unless you know the natures of both, and the last thing you want on a roof is chemical incompatibility causing breakdown in the joints between dissimilar products. Might an alternative be to apply a protective tape over the joint? I don't think this will be a job than can safely be completed in a day (it may, it may not) and it would be unwise, IMO, to attempt unless the van is under cover. You may find, once you start, that you have to do more work than you are anticipating. Have you tried contacting Chausson to see if they can tell you what sealants they used for these models? Whilst it's best to be safe than sorry, I think Brian may have mistaken the 83 as being the van was manufactured in 1983 (rather than it being part of the Model No. ) From memory, this model was introduced in 2005/6, so less likelyhood is that the Sealants will have changed. Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 15, 2012 Share Posted March 15, 2012 pepe63 - 2012-03-14 5:03 PM....................Brian..The "83" is the model number(it's an '08) but funny you saying about tape.................... If this is an '08 van, why are you piking about with it? Does it not have a water ingress warranty that is still in force? If you poke about with these joints you will invalidate the warranty. Sealants of this generation, in themselves, generally have an expected life of around 25 years. Most fail earlier because they are poorly applied, or because the joints are poorly designed. There should be no question of your roof joint beginning to fail after only 3 - 4 years. If it is, it will be because the material itself was defective when applied, or because it has been contaminated since application. If you can be confident contamination is not the cause, then it seems defective sealant is at least possible. I think you really need to get to the bottom of what this is, before you inadvertently cause a problem you don't yet have! Surely, there must be other similar joints, for example between rear wall and roof, and between side rails and roof, that will have been sealed in the same way with similar sealant. Do these other joints not join at some location with the one you think defective. If what you do results in an incompatibility between the sealants they will not bond, leaving gaps at the ends, through water will penetrate. However, my main point remains that sealant failure after so brief a time is pretty much unthinkable with modern sealants, unless the stuff itself was duff, or it has begun breaking down as a result of a reaction to a contaminant. Link to comment Share on other sites More sharing options...
pepe63xnotuse Posted March 15, 2012 Author Share Posted March 15, 2012 Hi Brian.. Just to clarify,the sealant itself,hasn't started to degarde or fail(it's still flexible and where it's sticking,it's stuck!),it's just that whilst washing it,I noticed that that there was a couple of spots where a "feathered edge" could be rubbed back with my thumb..and although it didn't expose the joint,it came it bit close to it for my liking...... (..This is the only seam on the roof,as the roof section is designed as a one-piece "cap"...) ...and although the van still has a valid water ingress warranty,personally I'd rather spend a little time and do this myself(properly)rather than risk and be forever wondering if it'd had,some rushed and bodged, "...just slap some sealant on that Chausson will ya...the chap's coming for it in a bit.. ", type of repair... ;-) Link to comment Share on other sites More sharing options...
crinklystarfish Posted March 15, 2012 Share Posted March 15, 2012 That kind of sealant ‘failure’ is not that uncommon and where it’s feathered it doesn’t take much to lift an edge. It’s often better to‘build’ the edge a bit and this can be done by employing masking tape, working up to the edge and then removing the tape. It has to be done fairly rapidly though or the Sikaflex will start to go off and ‘pull’ with the tape. If you remove the tape in such a way that any ‘pulled’ sealant falls back over the seam you have just laid then you can quickly blend this in with the old spittyfinger technique. It can get messy though so be a bit careful until you are confident with the product. Absolutely agree regarding the anxieties of having it done ‘professionally’. It might be done right, or it might be a slap job using an inferior trade product (there are many about). Link to comment Share on other sites More sharing options...
Dr Dave Posted March 15, 2012 Share Posted March 15, 2012 I've been on the roof of our Chausson recently to fit the solar panel. And the join between the roof and the low profile front cab GRP section is not just a sealant join it has a plastic cover over the joint, so it looks like it was sealed and then a cover bedded into the sealant and possibly screwed as well to provide some support, i am surprised at a deep sealant only joint on this vulnerable area. Hope you sort it out. Dave Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 15, 2012 Share Posted March 15, 2012 This very much depends on the design of the joint, which you can see and I can't! :-) However, if the joint has been done properly, the overcab moulding and the roof moulding will come together with a downstand edge on both. The two downstands will be gapped off each other by say 3 - 6 mm, so that there is an allowance for thermal movement of (mainly, because it is the larger part) the roof moulding. In an ideal world a backing cord (usually a polyurethane foam cord) is inserted into the gap, to a controlled depth, and this dictates the depth of the sealant bead. The joint is then filled down to the backing cord. Again, in an ideal world, the sealant should not stick to the backing cord, and a bond breaker should be used to prevent this. My impression is that few converters go to these lengths and merely fill the gap to whatever depth from the gun. This is daft, because the sealants themselves are highly sophisticated compounds, capable of out-lasting most vans (probably except Crinkly's :-)) if properly used. The ideal depth of sealant will vary a bit depending on its manufacturer's recommendations, but is unlikely to exceed its width, and is often only half its width. This is how it gains its elasticity. The sealant sticks to the sides of the joint only, so that as the adjoining panels expand and contract, the sealant bead is either stretched or compressed. If it is too deep relative to its width its depth restricts its ability form a "waist" as it is stretched, and this can cause a stress greater than its adhesion to the adjoining surfaces. So, it will start to pull away from the sides. Having filled the joint as required, it will usually be smoothed off flush using a wet-wipe of some sort, and in the absence of a tape mask along the sides, this will produce the feathering you can see. The feathering is best left undisturbed, even if its adhesion is not that strong, as rolling it back loosens the edges of the sealant joint. However, with a good joint, this is more likely to be untidy than problematic. The alternative often used in motorhomes is to lap two sheets with a sealant bedding sandwiched between them. These joints are often then finished off with an extruded cover strip bedded on further sealant and screwed down through both sheets into the timber frame below, with a PVC tape inserted into the cover strip to hide the screw heads. To get a good seal around the screws, they have to be inserted before the sealant cures, and the tendency is to over-tighten the screws so that the sealant bedding between the sheets is reduced to virtually zero thickness. Any movement between the sheets (thermal or body flexing) then over-stresses the bedding, and it shears. This is a cheap and nasty solution, but it is quite common, especially where the roof sheet is aluminium and the overcab and rear panel are GRP, so forming a downstand on the aly is beyond the competence of the converter. It can work, but only reliably so if a spacer is inserted between the sheets to prevent the screws over-thinning the sealant bedding. It is because I don't know what yours is, that I am urging caution. If the Sika you have is not compatible with the material Chausson used (possible, though I think probably unlikely), it may begin to break down in the presence of the existing, or may itself attack the existing. To eliminate that possibility, you will need to remove all traces of the existing, or verify that the existing is fully compatible with the Sika. I had to repair a badly made sealant joint (locally incomplete adhesion on one side of the joint) on our van, and needed to remove a "Teroson" modified polyurethane sealant. This is similar in formulation to the Sika, curing by airborne humidity. The stuff could not be peeled out (except where the joint was badly made), because of its adhesion, and it was capable of stretching by about 600% before failing in tension. It invariably snapped before its adhesion failed. Once cured it behaves exactly like rubber. In the end, I just had to cut out as much as possible, but did have exactly the same product to re-make the joint. I was assured that the new would bond fully to the old (which was in any case only just over a year old), and this seems to have been the case. However, it was a total pig of a job! Link to comment Share on other sites More sharing options...
crinklystarfish Posted March 15, 2012 Share Posted March 15, 2012 Gosh Mr K, if only converters made 'em that way! I was talking to a horsebox converter the other day who knocks out £150,000+ boxes and he just looked at me gormlessly when I asked him how he spaced out his joints to ensure a suitable thickness of adhesive. He also uses a cheap Sika substitute saving himself the princely sum of about £100 per build. Given the thermal, torsional, climatic, vibration induced and any number of other stresses that joints are under I guess the occasional re-bedding of a duff one shouldn't be seen as too much of a hardship, even if it can be a pain to make a decent job of it. I'm sure your research regarding compatibility of products is on a very sound footing but would venture that the 512 winging its way to the OP will stick to anything any mainstream euro manufacturer has built in the past decade or so. Link to comment Share on other sites More sharing options...
pepe63xnotuse Posted March 15, 2012 Author Share Posted March 15, 2012 crinklystarfish - 2012-03-15 7:46 PM ...but would venture that the 512 winging its way to the OP will stick to anything any mainstream euro manufacturer has built in the past decade or so Well lets hope so eh..because it arrived this mornin'..! ;-) Interesting to hear that Dr Dave's Chausson has a cover moulding over the seam,similar to what I was considering... Link to comment Share on other sites More sharing options...
pepe63xnotuse Posted March 20, 2012 Author Share Posted March 20, 2012 Just to finish this off... ..I had a productive afternoon,as I've managed to cut out and rebead the joint in question and bond on a 60mm upvc cover moulding!..I'm really pleased with the result... ;-) ..while I was at it,I tidied up the beads on all the roof lights and TV aerial(...cutting away the "snotty" bits and rebeading..) ..and I had just finished the last vent,when the Sika' tube ran out...it couldn't have worked out better.. Thanks for all the advice and input... ;-) Link to comment Share on other sites More sharing options...
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