Resealing a Seam in a Caravan

Which product should you use to reseal a seam on a caravan roof?

Selleys SolarFlex is ideal for this application. There is one condition attached, and it decides whether the job works: if a silicone sealant has been used previously, it could prevent the SolarFlex from bonding properly, so you will need to completely remove or scrape off the silicone before applying it. Selleys Sealant Remover can be used to help remove the silicone.

That caveat is not a formality. On a painted aluminium caravan roof with a PVC beading strip down the centreline and an unknown white sealant along its edges, getting the old material off is most of the work, and it is where the repair is won or lost.

Why old silicone has to come off completely

Cured silicone is one of the hardest surfaces in construction to bond to. It is deliberately low-energy — that is what makes it shed water and resist dirt — and almost nothing adheres to it, including fresh silicone.

So a new sealant applied over an old silicone bead is not bonded to the roof. It is bonded to a layer of old material that is itself letting go, and it will fail along that interface, usually within a season. On a roof where the leak only shows up in heavy rain, that failure is invisible until water is inside the van again.

There is a second point specific to hybrid and polyurethane sealants: their technical data sheets state they should not be applied in the presence of curing silicone, because the cure can be affected. Old cured silicone is not the same as curing silicone, but the general principle holds — get the previous product off and start from the substrate.

What SolarFlex is, and why it suits a caravan roof

SolarFlex is a silyl modified polymer (SMP) sealant built on Sil-X technology, and Selleys describes it as more durable than conventional polyurethane sealants. It is formulated for demanding exterior applications, including caravan roof seams and solar panel bonding.

Property	Selleys SolarFlex
Technology	Moisture-curing silyl modified polymer (Sil-X)
Colours and packs	White and grey in 445g cartridge and 600mL sausage; black in 445g cartridge
Tooling time (23°C, 50% RH)	Approx. 30 minutes
Skin time (23°C, 50% RH)	Greater than 2 hours
Cure rate (23°C, 50% RH)	Approx. 2.5mm / 24 hours
Service temperature	0°C to 70°C
Movement capability	±25% (ISO 9047)
Elongation at break	Greater than 400%
Elastic recovery	Approx. 70% (ISO 7389)
Standards	ISO 11600 Type F Class 25LM; meets GBCA VOC limits
Storage	Cool, dry, below 30°C; use within 6 months of opening

Indicative data only, not intended for the preparation of specifications.

What those figures mean on a roof that puddles

The long skin time — over 2 hours — is a genuine advantage here. A centreline seam runs the whole length of the van. With 30 minutes of tooling time you can gun a long run and come back to tool it properly, rather than working in half-metre sections and leaving joins in the bead. Joins are weak points, and on a seam that ponds water they are the first place to leak.

It can be applied to damp or wet substrates without primer. That does not mean sealing in the rain, but it does mean a roof that is not perfectly bone dry is workable — useful in a job where you are often chasing weather.

±25% movement capability and over 400% elongation matter on a caravan, which flexes on the road far more than a house does. Elastic recovery of around 70% means the bead returns towards its original shape after being stretched, rather than staying deformed.

Service temperature 0°C to 70°C. A white roof in Australian summer sun sits at the upper end of that. It is within range, but it is a reason not to leave the sealant cartridge itself on the roof while you work.

Cure at 2.5mm per 24 hours. A bead pressed into a seam and tooled to a few millimetres deep needs a day or two before it is fully cured. Selleys notes SolarFlex cures well at temperatures above 5°C, with better extrudability and faster cure in warmer conditions.

Removing the old sealant

1. Work on a cool, overcast day if you can. Handling sealant on a hot metal roof is unpleasant and the product skins faster than the figures suggest.
2. Cut and scrape as much of the old bead away as physically comes off, leaving only a very thin residual layer — less than 5mm depth is what Sealant Remover is designed to work on.
3. Spread a layer of Sealant Remover at least 5mm thick evenly over what remains, and leave it at least 10 minutes. A second application may be needed.
4. Work a scraper backwards and forwards to lift the softened material off.
5. Clean the residue and your tools immediately with mineral turpentine.
6. Check the whole seam by eye and by fingernail. Anything rubbery still in the joint is a future leak.

Keep the remover off the PVC beading. Sealant Remover is not suitable for rubber, EPDM or polycarbonate, and the data sheet warns that it may affect some surfaces and that compatibility should be tested before use. On a beading strip whose exact material you cannot confirm, test an out-of-sight section first and be prepared to remove the old sealant from it mechanically instead.

Applying the new bead

1. Make sure the surfaces are clean and free of dust, oil and the remains of the old sealant.
2. Cut the nozzle to the bead width you want and load the cartridge or sausage into a suitable gun.
3. Gun the sealant along the seam, pushing it into the joint rather than laying it over the top. A bead sitting on the surface has almost no depth of bond.
4. Tool it within about 30 minutes, working it into the joint and leaving a smooth, slightly convex face that sheds water rather than holding it.
5. Leave it to cure. Keep the van under cover if you can, and off the road, while the bead cures through.

On the puddling itself

Water pooling around the beading is what the original question identified as the cause, and it is the right diagnosis. A sealant that is fully bonded and correctly tooled will hold against standing water, but standing water finds every weakness there is, and it will find any gap you leave.

So the finish matters more than usual here: no pinholes, no joins mid-run, no thin section where the bead crosses a fixing, and a profile that sheds rather than collects. Where the van must sit level when occupied and puddling cannot be avoided, that quality of finish is the whole defence.

Safety: a full roof seam is the largest quantity of solvent any of these jobs asks for

The removal is where the classified product is. Selleys Sealant Remover is classified as hazardous with the signal word Danger, Poison Schedule S5, and is more than 60% petroleum naphtha:

• H304 — may be fatal if swallowed and enters airways (aspiration hazard, Category 1)
• H226 — flammable liquid and vapour; Dangerous Goods Class 3, UN 1133, Packing Group II
• H336 — may cause drowsiness or dizziness
• H315 — causes skin irritation

Scale. The method above is a layer at least 5mm thick along the full length of a centreline seam, left at least ten minutes, with a second application likely. That is far more of this product than a shower recess or a kitchen joint ever needs, spread across a surface with no containment at all.

Heat. This page already tells you to work on a cool, overcast day because the sealant skins faster on hot metal. The same instruction is a flammability control. A Class 3 Packing Group II liquid spread across a steel roof in the sun evaporates much faster than it does indoors, and the vapour is heavier than air — it runs off the roof and collects at ground level. That is where a caravan keeps its gas bottles, its fridge flue and its hot water vent. Turn the gas off at the bottle before any solvent goes on the roof, and keep the tub itself out of direct sun.

Posture. You are prone or kneeling with your face close to the work, often under an awning where there is no airflow. H336 drowsiness at roof height is a fall risk. Work in the open, take breaks off the roof, and do not do this job alone.

H304 and the caravan. Never decant the paste into a drink bottle or an unlabelled jar — a van with a fridge and a water tank is exactly the setting where that goes wrong. Lid on between applications, stored out of reach and out of the sun. If any is swallowed, do not induce vomiting — that is the mechanism that gets a light hydrocarbon into the lungs. Rinse the mouth, give water and seek medical advice immediately. Nitrile gloves and eye protection throughout — you are scraping toward yourself on a slope.

The control that matters most is already in step 2. Cut and scrape as much of the old bead away as physically comes off, leaving only a thin residual film — the remover is designed to work on less than 5mm. The less you leave, the less solvent ends up on the roof. The mineral turpentine in step 5 is flammable in its own right, and so is the metho some people reach for.

Poisons Information Centre — 131 126 in Australia, 0800 764 766 in New Zealand.

Common questions about resealing a caravan roof seam

Can I just run new sealant over the old?

No. If the previous product was a silicone it will prevent the new sealant bonding. Remove it completely first.

How do I tell whether the old sealant is silicone?

You often cannot tell by looking, which is why the safe assumption on an unknown white sealant is that it might be, and to remove it either way.

Which colour SolarFlex for a white roof?

White, available in a 445g cartridge and a 600mL sausage.

Is SolarFlex paintable?

Yes, it is listed as paintable, along with being mould resistant, non-bubbling and non-slumping.

Can I apply it if the roof is slightly damp?

It can be applied to damp or wet substrates without a primer. It still needs to be clean.

How long before the van can go back out in the rain?

Skin time is over 2 hours and the bead cures at about 2.5mm per 24 hours, faster in warm conditions. Give it time, and remember cure slows below 5°C.

Will Sealant Remover damage the paint?

The data sheet says the product may affect some surfaces and that compatibility should be tested before use, and that it should not be left on acrylic-painted surfaces for extended periods. Test first and do not leave it sitting.

What about the joints elsewhere on the van?

See the best sealant for caravan joints, and sealing leaking aluminium roof panelling for panel joints specifically.

Is there a general caravan guide?

Yes — how to make over your caravan.