Best way to seal leak between 2 car boot panels?

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Car boot has been leaking and I’ve figured out where it’s getting in, which appears to be the seam between 2 panels in the tailgate roof (1 metal / 1 plastic). I’ve taped it up for now but need a long term fix, can anyone recommend anything to stick in the seam to seal it up? The metal panel is rigid but the plastic one has some flex, so it would need to be able to cope with that – would standard silicon sealant work?

Silicon would work, but you’ll need to make sure you’ve squirted it in any gap before cleaning it up. You can often get water tracking up and around the rubbers where it pops onto the door/boot surround. Is the plastic just a bit of trim though ?

I’ve just had a similar issue start, so following thread.

My tailgate is filling up with water, which then drains out through a hole at the top, into the boot, when it’s open.

How did you go about working out where your water was getting in?

Is the plastic just a bit of trim though ?

It’s fully integrated, it’s the part on the left of the tape on the pic. I don’t think there’s any tracking going on as I can see its coming through to the interior via 2 plastic fixers that seem to attach the plastic exterior bit to the metal part of the tailgate.

How did you go about working out where your water was getting in?

Took the interior trim off where it looked like it was coming from – was pretty obvious as it was wet – and then sprayed water on the exterior while I sat inside with a torch and looked for where it was getting through. Looks like there are 2 plastic fixers that attach the plastic exterior part to the metal part of the roof and that’s where it’s leaking, problem is it’s impossible to reach them to just apply silicon round them.

Sikaflex, the stuff used for sealing campervan roof windows etc. I think it’s available in black.

Any one of the modern adhesive, waterproof, gap fillers. OB1, The Works, X8 hybrid, sticks like, Fix All.
These are non hardening, go off underwater, allow a degree of movement.
You could try an all weather silicone first, or builder’s silicone. They are cheaper and almost as good.
Then pay more fpr the hybrids if the outdoor silicone fails

Sikaflex

Perfect, thanks – is it reasonably easy to clean up any overfill before it dries? From past experience redoing bathroom sealant I tend to be slightly cack-handed in applying it!

Sikaflex is the stuff I used to reseal the rear windows in my old pickup. Works great but it can get messy. If you’re really cack-handed then consider using a silicone profiling tool, such as https://www.toolstation.com/cramer-fugi-profiling-tool-set/p46602

I was going to suggest ‘Dum Dum’ – it’s what Landrover used for sealing the many Defender gaps but apparently it’s no longer available.

A quick Google suggests
https://www.frost.co.uk/eastwood-flexible-strip-caulk-dum-dum-replacement/

Is it leaking in because drain holes are blocked (somewhere)?

What about something from the marine industry. Might be a direction to think about given leaks are not thew done thing for boats

Really hard to trace at times. We bought a 10 year old Aygo just over a year ago, and my first job was stopping the leaks in the boot. Water tracks round the seals, so I siliconed the whole rubber boot seal, the high level brake light leaks, that got done, the bump stops leak, did them, and finally replaced all the rubber seals on the rear lights. Bne dry now.

My car let a shoot load of water in last winter for some reason, traced it to water tracking under seals/possible body gap. Out with the sealant – not bad as the car is 22 ! Bone dry again. Entry points for lighting wiring is a cause too.

If you are unsure, a puff of talc on the metal body panels beneith the trim can help trace it.

Is it leaking in because drain holes are blocked (somewhere)?

Entirely possible, it sits under a tree most of the time and the crap just builds up everywhere.

The caulk looks a good option as well, avoids the need to fanny about with silicon. I have got better at using it over time, but I generally end up with at least as much on me as I’ve used to do the gaps!

is it reasonably easy to clean up any overfill before it dries?

Best to use masking tape alongside the groove you’re filling, then there’s no cleaning up to do.

I’d use black sikaflex or one of the other polyurethane sealers such as stixall. It’s very sticky so you’ll want to mask both sides and cut the nozzle so the bead is not too wide.

Leave it in the house so it’s not too cold to dispense, if you can loosen the trim or get someone to flex it down slightly to help get it in the gap that would be good.

It’s the same as seam sealer and there is probably lots in your car already. Check if the one you buy is UV stable.

I’m assuming that it’s no longer in warranty? I’d be off to a body shop to see if the holes can be sealed.
External fillet of sealer is going to look very different to the exterior finish and the feathered edge might lift when you polish the car

External fillet of sealer is going to look very different

Yep, polyurethane like sikaflex picks up dirt to so it’ll ultimately look sh*t. It can be tooled clean with methyl hydrate etc that shouldn’t damage clearcoat.
I’d be trying to restore the seal around those fixings before bodging it though.

As above, rubber boot seals get tired and can leak. Friction fit seals can be removed and have their crimps tightened then refit. Or sealed up and this is where I’d draw the line at the application of goo, hidden away not between 2 exterior panels.

Have you had any body shop work done on the rear end?

Remove the spoiler via the fixings. Reapply with liberal dose of sealant round the fixings is how Its regularly done on the higher spec Aygos c1s and 108s with similar spoilers when they leak.

Spray bottle with white spirit and some cloths for cleanup. Not too messy if you mask tape also.

Bear in mind ambient temperature. I think needs to be warmish to cure the Sikaflex. It should say on tube. Could be your issue this time of year.

Also, once cured it would be on hell of a job to remove the Sikaflex and whatever it’s joining. Serious brute force and prying and scraping. I suspect risk you bend or snap plastic trim. So make sure you’re happy before it cures!

I’m assuming that it’s no longer in warranty? I’d be off to a body shop to see if the holes can be sealed.

Nope, 9 year old car that’s very much functional so aesthetics aren’t hugely important (as long as it doesn’t look awful).

Have you had any body shop work done on the rear end?

I did get lightly tapped by a lorry a few years back (at ~1 mph or something) and it went in for some work on that, possible it’s related but tbh it’s nearly 4 years since that now.

Remove the spoiler via the fixings.

Probably the best option and if I can find some diagrams that show how it fits then I’ll give it a go, but the workshop manual online wasn’t much help – don’t want to just yank it off!

Bear in mind ambient temperature. I think needs to be warmish to cure the Sikaflex. It should say on tube. Could be your issue this time of year.

Yeah, I also have a leaking porch window that’s patched up with gaffer tape just now while I wait for spring and temps where there’s a chance of getting a good seal!

How did you go about working out where your water was getting in?

If it’s a VW or something else of that group it’s not a leak it’s the screen wash hose popped off… Again.

Failing that clear the drain hole that’s currently blocked so it runs out constantly. Then you worry about the source.

Mine’s a Mazda, managed to find a video showing how to remove the spoiler for the hatchback model and it looks pretty similar inside to mine (estate), so will give that a go and then seal up the fixing points – thanks all!

Any hybrid polymer sealant

Eg CT1

https://www.ct1.com/videos/