Resealing visible sika like seals

[steve hill]

Having had some locker door seal leak problems on the van recently, I also checked the van edges for sealant wear. The van is a Roller Team 707 and is 7 years old, the joints around the van appear to be a white “Sika like” sealant on the outside but there may be a hidden soft mastic behind some of them. I note that the outer visible white sealant looks to be failing where visible in some areas.

My question is should this outer visible bit be stripped off and a new small layer of Sika 512 (or similar) be applied, some small repair areas have also been badly applied in the past. I know this is time consuming but feel it may be safer in the long run.

Ta

 

[Derek Uzzell]

The way in which coachbuilt motorhomes are constructed varies from converter to converter. For example, I beleive Auto-Trail builds the complete habitation ‘pod’ as an entity and then attaches it to the base-vehicle’s chassis, whereas it’s more common for the conversion procedure to begin with the habitation pod’s floor being attached to the chassis, the interior fiurnishings and walls then being screwed to the floot and the external body-panels and roof fitted last. This 2012 video shows the Roller Team factory choosing to use the latter ‘inside out’ approach.

 

 

It’s doubtful that Roller Team used two types of sealant (an inner soft mastic and an outer “Sika-like’ product) for your motorhome’s joints. It’s much more likely that a single constructional adhesive was employed (SIKA or Henkel products are often chosen) that glues the panels firmly together but has sufficient elasticity to cope with vibration, temperature changes, etc. There may be some ‘mechanical’ fixing (eg. metal brackets) but it’s the adhesive that does the lion’s share.

 

Up to you whether you remove and replace the white sealant that has weathered. If there are no signs of water ingress, there’s no imperative to do it immediately and It’s really not a task to be carried out in the open air during the winter. When you have the opportunity, you might want to ask a professional caravan/motorhome repairer to inspect the joints and see what their opinion is.

 

When George Collings used to edit MMM’s “Interchange” section, he occasionally used to suggest to avid DIYers “If you need to ask the question, the answer is usually “No”. ;-)

[Brian Kirby]

Very much agree with Derek. One further point is that after those side, floor, and roof panels you can see in the video are mated, corner mouldings (usually colour coated aluminium extrusions) are installed to cover and seal the actual panel joints.

 

These mouldings are laid on top of what should be two continuous beads of sealant (one for each panel) and are often additionally screwed down with a further flexible insert into the corner moulding to cover the screw heads. I didn't see that process on the video, 'though the corner mouldings were clearly apparent in views of the more complete vans.

 

So, all you are probably seeing on your van is some degradation of the tooled off edge of that bead of sealant. Providing the beads of sealant were properly applied, the corner moulding was correctly aligned, and the screws were not tightened to the point at which little to no sealant bed is left under the moulding, all the joint waterproofing is being done by the bed of sealant, and that sealant bed is protected from U/V radiation by the moulding.

 

There are many caveats there, and motorhomes are largely hand assembled, so it is not unknown for gaps in the sealant beads, for example, to result that will allow ingress to the panel edges themselves and over time, via wet wooden framing, to the interior. If that is what is happening, the only proper remedy is to get the van into a covered workshop, and carefully remove the whole corner moulding, plus all the old sealant, and then, once the underlying wood is sufficiently dry, apply new sealant beads and re-bed, and screw down, the corner moulding. Trying to re-seal those joints from the outside edges is at best a temporary bodge that is unlikely to last.

 

The further point is that sealants are complex, chemically engineered, products, and not all formulations are compatible with others. Unless you know whose sealant, of which formulation, was actually used on your van, there is the possibility that whatever you use may react unfavourably with what is already there, to the eventual detriment of one, or other, or both. Trigano/Roller Team should be able to advise what they use, and you could then contact the manufacturer's technical department for guidance on which of their DiY products would be compatible. It is likely to be some variant of modified silane polymer.

 

Finally, Sika has become a catch-all term for sealants (just as Hoover was for vacuum cleaners), but don't be fooled! Sika is a large Swiss chemicals manufacturing company that makes many products for many purposes, and you need the right product for the job. There is no such thing as "Sika" - despite the number of people who refer to "using Sika" for joint repairs.

 

If your van is regularly damp checked, and shows no signs of water ingress, you will be best advised not to intervene. If it is showing signs of ingress, especially if main panel joints are suspected, repair should be entrusted to a specialist.