Sikaflex 252 Vs 221: What’s the Difference?
Sikaflex 252 is tough to dispense, being very thick. I’m not using the nozzle, which makes it a bit easier. For securing my solar panels to my RV rubber roof, I chose it. At the same time, 221 is more suitable for faster sealing jobs like HVAC and windows. 252 has superior longevity but 221 can be painted over.
Sikaflex 252 Vs 221: Specs & Uses
⏰Full Cure Time
Sikaflex 252: 24-48 hours
Sikaflex 221: 24 hours
🆚Key Advantages
Sikaflex 252: Exceptional strength and vibration dampening, very flexible, excellent UV resistance
Sikaflex 221: Faster tack free time, good flexibility, paintable
🛠️Common Uses
Sikaflex 252 can be used to bond automotive and electronic parts; bathroom fixtures and industrial equipment; useful in applications where vibration is a concern, such as automotive and heavy equipment manufacturing.
Sikaflex 221 is good for windows, doors, and furniture; can be painted over for applications where the adhesive needs to be concealed or matched to a specific color.
Technical Info
Sikaflex 252 has better tensile strength. It is a clear choice for manufacturing trucks and trailers to equipment as it can withstand high dynamic stress. Sikaflex 221 is a high-quality adhesive sealant with a non-sag and multipurpose formula that offers better results on the surface.
My Hands-on Test of Sikaflex 252
✅Mounting Solar Panels
I’ve used Sikaflex 252 to secure flexible solar panels to my Airstream’s fiberglass roof. The adhesive forms an incredibly strong bond between the aluminum framing of the panels and the fiberglass surface.
Before application, I simply rough up the bonding area on the fiberglass by sanding to allow for maximum adhesion.
Attaching a C-channel
Another project where Sikaflex 252 came in handy was attaching a c-channel to the side of my conversion van for an awning installation. I followed the recommendation of warming the product slightly in the oven to make it flow easier from the tube. I also used painter’s tape to create boundaries for the adhesive.
Once applied, I secured everything in place with sheet metal screws. The end result looked professional, and I’ve tested it in strong winds without any issues. It’s held up really well. Yes, it’s a bit pricey, but the quality is worth it.
Securing Solar Panels to RV Roof
For securing my solar panels to my RV rubber roof, I used Sikaflex 252 along with 3M 5200 (You can see my test here: 3M 4200 Vs. 5200). I was concerned about the adhesive integrity when driving at high speeds, but I checked and everything was still secure.
3M 4200 Vs. 5200: Sanded Caulking, Best Below-Waterline, Roof Sealing and RV Maintenance
The application was easy, although the adhesive is quite thick and bright white. One of the best things about it is that it’s highly waterproof, which is essential for outdoor installations. I even used it to secure my 8×10 junction box to the roof, saving me from having to drill holes.
It’s tough to dispense, being very thick. I’m not using the nozzle, which makes it a bit easier. Lots of surface prep, cleaning off the white coating that the previous owner applied, sanding and cleaning the gel coat with lacquer thinner, and sanding the aluminum bases. The 252 cleans up with lacquer thinner.
Holding Power
Speaking of holding power, I can’t praise this adhesive enough. It did an exceptional job, providing a tight and reliable hold. The panels have stayed in place without any issues, and the overall installation looks clean and professional.
It’s truly a testament to the quality of this adhesive.
For mounting brackets or mounts, I combine Sikaflex 252 with 3M VHB tape. I use the VHB for the contact surface between the bracket and roof, then seal around the bracket with Sikaflex 252 to protect the VHB tape from weather exposure.
3M VHB Vs. Gorilla Tape: Mounting Lightweight Objects in Humid Environments
For below freezing temperatures like sealing a freezer unit, Sikaflex 252 remains effective as long as the surfaces are properly prepared – cleaned and roughed up before application. Just allow the full 24 hour cure time.
While it can be used for vertical applications without sagging, I would not recommend it for consistently overhead applications. For those, a self-leveling product like Sikaflex 521 FC would be better suited.
While pricier than some alternatives like Sikaflex 221, the extra strength and performance of 252 is worth it for heavy duty bonding applications. Its versatility makes it a staple that I always keep on hand in my RV and for outdoor projects.
Sikaflex 227 Vs. Sikaflex 221: Stick to Aluminum, Seals Leaks & Fill Auto Cracks
❌Cons: Sikaflex 252
I had some trouble applying the adhesive because the tip had a very large opening, and it was difficult to apply a fine line. The thick consistency of the adhesive also meant that a good heavy-duty caulk gun was necessary. I learned the hard way that once I started the tube, even though I put a nail in the end and taped it up, it still set up in the tube, so I had to start a new tube. It’s important to plan your work properly because this adhesive is pricey.
💬 FAQ of Sikaflex 252
Q: Is Sikaflex 252 suitable for bonding PVC plastic to a painted metal van roof when mounting flexible solar panels?
A: I used it on a houseboat roof to attach metal clips for solar panels, and it’s incredibly strong stuff! It has withstood the winter with strong winds and heavy rains.
Q: Can I use Sikaflex 252 inside my cargo van to reduce noise? The label does not specify whether it is for interior or exterior use like the Sika 221.
A: No, it is not suitable for reducing noise inside a cargo van.
Q: Is it easy to remove this adhesive if I need to replace my solar panels in a few years?
A: Sikaflex-252 has an incredibly strong grip and is one of the few adhesives designed to hold aluminum to other materials (aside from plastic). It peels off plastic easily, but I wouldn’t recommend using it on anything you may want to remove later. If you decide to use it, I suggest using a pneumatic caulk gun, unless you know someone who can crush bowling balls with their hands. It’s extremely difficult to apply with a manual caulk gun.
Q: Can I use Sikaflex 252 to attach a flexible solar panel to the roof of my motorhome?
A: Yes, absolutely! This is exactly what I used for the same purpose.
Q: Will Sikaflex 252 bond an aluminum L-bracket to a steel van roof better than 3M VHB tape
?
A: It probably would work if you could get the surface clean enough. I used it to bond solar panel mounts on a rubber roof after cleaning and prepping it. It also seals cracks very well. You might want to read my article on 3M VHB Vs. Gorilla Tape as well.
3 reviews
📣🔥 Share it to easily keep track of the answers!
Leave a Reply
My Hands-on Test of Sikaflex 221
This marine-grade polyurethane sealant has become my go-to for all sorts of projects, from sealing my Winnebago Adventurer’s windshield to the aluminum frame, to fixing leaks around my Kohler Highline toilet and Jacuzzi bathtub at home.
✅Incredibly Versatile
What makes Sikaflex 221 so special? First off, it’s incredibly versatile – wood, metals, glass, plastics like ABS, you name it. I’ve even used it to seal seams on my Old Town Predator MX inflatable kayak and rubber stair nosings to coin mats without any issues.
The adhesion is outstanding and it cures to a flexible, rubber-like consistency that can handle extreme temperature changes and movement without cracking or coming loose.
Secured with Sikaflex 221 and Sikaflex EBT+ when I ran out, worked just as well)
Speaking of flexibility, it’s ideal for sealing dynamic joints like between an RV and its awning. While it’s not identical to Sikaflex 291, the 221 provides enough flex to handle that kind of application. Just be sure to properly prep surfaces first by removing any old sealant or silicone.
Sikaflex 291 Vs. 3m 5200 Vs. Sikaflex 292i: 1-Part Polyurethane to Leaky Port Windows, Pool Tiles & Submerged PVC Pipe Coupling
Incredibly Strong With Good Flexibility
I’ve also mounted 2×3’s to the cargo van floor as part of the sub-floor structure, and the adhesive is incredibly strong with good flexibility. I also used it to install a fan on the roof of my van.
After laying down three beads around the perimeter of the mounting bracket, the adhesive held everything in place with just tape for clamps. I was able to continue the installation after letting it set for about an hour.
What I love about Sikaflex 221 is that it’s safe to use with drinkable water storage, making it ideal for sealing various direct-contact-with-weather areas along with a potable water tank. It’s flexible, so it won’t crack, and it doesn’t peel. However, cutting it with a blade requires some effort.
Bonded to the Fiberglass
In addition, I had to put a shelf into a fiberglass headliner with Sikaflex 221 and an epoxy adhesive for fiberglass 
. Guess what? I bonded 2×3 boards directly to the fiberglass, then screwed the shelf into those boards. The shelf hangs from those boards, and that was four years ago. Nothing has moved at all, even while bouncing up and down on some rough roads with the shelf fully loaded. It’s still as solid as the day I put it up.
❌Cons
It is easy to use, but it can stain, so it’s important to wear the proper protection, including gloves. Although I couldn’t find it at HD and Lowes, I finally found it here, and I would assume it’s a decent price, but I just don’t have anything to compare it to. I would definitely buy it again and have it.
💬 FAQ of Sikaflex 221
Q: Would Sikaflex work as a sealant on the ABS fitting that inserts into the RV poly holding tank outlet and has a hose clamp?
A: While Sikaflex 221 is often used on RV roofs, it may not be suitable for this specific application. It is important to ensure that the material is compatible with the surfaces and substances involved. Additionally, Sikaflex 221 may crack over time due to expansion and contraction, so regular inspection and maintenance are necessary to prevent leaks.
Q: Can Sikaflex be used to bond a window
into an aluminum U-channel on an RV? Is it removable if needed?
A: Yes, Sikaflex 221 is suitable for sealing RV windshields to aluminum and fiberglass. It is easy to remove before it cures but extremely difficult to remove once it has fully cured.
I’m Ronald Stevens, a Mechanical Engineer obsessed with adhesives, glue, and all things sticky! My passion began in childhood when I’d always be the one playing with glue during arts and crafts. And I’d spend hours researching and experimenting. Happy reading, and remember: stick with the best, and you’ll never be stuck in a mess!
Can I use Sikaflex 252 to glue down solar panel mounts on my RV's rubber roof?
I also have a rubber roof on my Challenger, and to ensure that my solar panels wouldn't fly off on the freeway, I removed the rubber coating where I wanted to place the glue-on mounts. I was concerned that the mounts would pull the rubber off if the panels had enough lift under them. Additionally, I screwed down the corner…Read More
I also have a rubber roof on my Challenger, and to ensure that my solar panels wouldn’t fly off on the freeway, I removed the rubber coating where I wanted to place the glue-on mounts. I was concerned that the mounts would pull the rubber off if the panels had enough lift under them. Additionally, I screwed down the corner mounts and sealed the holes. I read about a guy who lost his panels on the freeway – what a mess he got himself into! So exercise sound judgment and remember that overkill won’t hurt.
Show Less
None of these is recommended to be used in open to atmosphere or sun areas as none of these is UV resistant.