How to Seal your Van
Sealants and adhesives … is more always better?
Keeping water and dust out of your van is essential for keeping it in good condition and John Hughes did some research into the best products to use on your pride and joy.
A while ago I came across a caravan that looked like someone had taken a brickie's trowel and applied silicone 30mm thick at every sealing point on the roof. I am not talking about a thin film 30mm wide - I mean it was 30mm thick sitting on top of the roof. It got me thinking, is more always better?
I kicked this question around with a couple of my colleagues at Caravan World and it triggered a bunch of other questions. Is the stuff used all over caravans actually silicone or is it something else? To what extent do these products act as adhesives versus sealants? What processes are important to optimise sealing and bonding? How do substrates work in conjunction with sealants and adhesives? Should sealants be replaced over time?
It's such an important topic because we suspect water ingress is the most common cause of the demise of a caravan. And we have to throw in dust ingress as potentially one of the most annoying things you can deal with in a caravan. With the help of some industry experts, we have a crack at answering these questions. It may help you in researching buying a new caravan or considering the requirements of maintaining an existing one. We do have to admit though, it is tricky to see whether a manufacturer has done a good job of sealing and bonding as the bulk of the work is ‘covered up’ when the van goes together.
Bonding and Sealing
There are some parts of the van that are not generally intended to be disassembled and others that will need to be over time. The wall, floor and roof panels on a van are full of holes that have things inserted in them - windows, vents and plumbing to name a few. Obviously, we want a seal to prevent water and dust from leaking between the fitting/appliance and the hole. Things such as vents or air conditioners are prone to failing over time and need replacing. Therefore, we need to be able to remove them. This is where it is important that the sealing method used must have a limited bond strength otherwise it is never going to come out. We also have other instances where structural adhesion is critical, such as how the floor is attached to the chassis or how the roof is attached to the walls. In these instances, the adhesives applied are so strong, that I have seen repair jobs where you try to pull apart the materials, and the walls or the roof will break before the adhesive yields.
Using the Correct Products and Using the Correctly
We had a chat with Chris Bogos, Head Chemist, and Heather Felosvary, Technical Representative from HB Fuller to learn more. HB Fuller is a leading adhesives and sealant supplier to the RV industry and construction/manufacturing.
JH: I talk to a lot of caravan manufacturers who tell me there are a surprisingly large number of tubes of sealant/adhesives that go into making a van. Just how many is it?
CB: Some manufacturers dispense adhesive from larger packs known as sausages but if we talk in cartridges, the same size you would buy at the hardware, it is quite typical for 100 – 200 cartridges to be used in building one van.
JH: I have seen some vans with heaps of exposed sealant applied at sealing points. Does laying it on thick help?
CB: No, you are looking for a bond and or seal between the two joining surfaces and a thin skin on the joint area where it is exposed to the environment. If the sealant is whacked on thick in the exposed area, it’s a clue that there is some form of shortcoming in the sealing process, and they are overcompensating with sealant.
JH: What are the top few products you supply in the RV industry?
HF: We have two core products. One is a 100 per cent silicone known as FulaSeal Pro 300 and another which is a hybrid silicone/urethane product known as FulaFlex 650FC. The 100 per cent silicone product is designed as a sealant and does not have the same bonding adhesion properties as the hybrid product. Limited bonding is good because it means that the seal can be mechanically broken if necessary to replace a hatch or alike. The 100 per cent silicone product has another advantage of attracting less dust.
Using HB Fuller 100 silicone product
Conversely, it’s easy to understand the pros and cons of the hybrid product. It has superior bond strength while maintaining excellent sealing properties making it the product of choice for applications such as adhering panels to frames. Its downside is when its exposed it tends to attract dust. Its not a functional problem but is just hard to clean. So, our really simple rule of thumb is if you can see it use 100 per cent silicone, if it's hidden use the hybrid product.
JH: So, it’s important not to get the products mixed up on the assembly line?
CB: Correct. It boils down to 100 per cent silicone used in the wrong place may not stick enough and hybrid products in the wrong place may stick too well.
JH: What are other important disciplines?
HF: Surface preparation is probably the most important step in ensuring a good outcome. It is critical that the substrates are thoroughly cleaned before applying sealants/adhesives. Using a cleaner such as isopropyl alcohol is best practice for removing any contaminants such as oil. Working some distance away from high dust environments such as CNC machines is also important.
CB: Another example of more is not always better - product applied too thick will have a hard time curing and not reach its full bond strength.
CB: It is important for the caravan manufacturer to be aware of the product ‘open time’. It’s the maximum time between applying the adhesive to one surface and ensuring it comes into contact with the other surface. If you wait too long the adhesive will form a skin and a proper bond will not take place.
JH: What advice would you give DIYers doing maintenance and repairs?
CB: It’s definitely critical to keep an eye on seals regularly. If you see deterioration such as peeling, cracking or shrinking do something about it. However, if it aint broke don’t fix it. Disturbing a good seal and trying to create a new one can potentially create an ingress point.
HF: If it is necessary to redo a seal, one of the most important things to know is there is no point trying to apply silicone on top of silicone because it simply won’t adhere. Therefore, existing silicone must be thoroughly removed prior to resealing. Scraping with a plastic tool is generally the best approach being careful not to damage exposed surfaces.
Panels
We also thought it would be interesting to have a chat with Gretel Hornsey, Technical Sales from ProBond, one of the major suppliers of aluminium sheeting to the RV industry. After all, it is their products to which adhesives and sealants are applied.
JH: What’s your take on sealant and adhesives as a substrate supplier?
GH: PROBOND aluminium composite panels need to be bonded to frames using an MS Polymer (modified silicone also known as hybrid silicone), with an elasticity of 50 per cent or greater. The key reason for this is that the adhesive needs to have bonding strength with sufficient flexibility to move with the panel when it expands and contracts. A normal silicone comes into play when creating a seal on the H moulds. We strongly recommend sealing along the exterior of the join (H mould), to prevent water ingress as this can lead to corrosion. For those who may not know H moulds are aluminium profiles shaped like an H that our sheets slip into to create a joint. The sheets need to be cut to a length to enable a 3mm gap inside the joint so that they can expand and contract. If the sheets expand and have nowhere to go, they can either buckle or the adhesive bond can shear causing it to come away from the frame.
H mould is used for join panels
To simplify the process for caravan manufacturers, PROBOND is about to launch an H-mould that has small internal rubber inserts at intervals to allow for expansion. They will also be colour matched to our panels for a clean look.
Applying sealing on the exterior of H mould
Corners
As the name suggests, corner moulds create the join/seal where surfaces meet at 90 degrees such as where the walls and roof connect. The traditional method for achieving this is with an aluminium profile shaped like a J and known as a J mould. The J mould is held in place and sealed with a hybrid silicone plus secured with screws. The screw holes are a potential water ingress point over time. Some more contemporary van manufacturers place complete faith in the adhesive and use large corner caps also usually made of aluminium without any fasteners.
J mould is used for joining corners
The Wrap
Suppliers to the RV manufacturing industry make available great products to bond and seal components. When van builders use the right products in the right way at the right time, the results are fantastic. The challenge as a consumer (and journalists for that matter) is it is often not easy to see if this has been done well once the van has been built. What you can do however is ask lots of questions of the manufacturer and if you get a chance take a factory tour and observe with a critical eye.
IF IN DOUBT, CONSULT A PROFESSIONAL
Improper maintenance can lead to injury, death or property damage. Maintenance work of this nature should only be undertaken by people with suitable competence. Information provided is general in nature, not comprehensive and should only be taken as a guide. Individual discretion must be exercised and persons undertaking described tasks do so completely at their own risk. Publishers and creators of this content accept no responsibility for loss or damage.