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. But what about 221? It is NSF approved for use in drinking water systems and food production operations.
Sikaflex 252 Vs 221: Specs & Uses
Sikaflex 252 is better for applications requiring very high strength, flexibility, and UV resistance like metal bonding. 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 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
I was even able to use a power washer to clean the channels under the panels without any sign of degradation.
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. 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.
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.
❌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.
📝 My Hands-on Test of Sikaflex 221
✅Pros: Sikaflex 221
The application process is easy, and it gives a nice look.
Used 25mm wood to fit the 25mm insulation. Weight applied overnight to stop them bowing. They have secured very nicely, ain’t coming off for no one
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.
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 windowinto 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.
Q: Is Sikaflex suitable for filling in concrete floor cracks? Will it self-level?
A: While Sikaflex 221 may hold up on concrete, it is not designed to self-level. It is important to select the appropriate sealant for the specific application.
Q: Is Sikaflex the best sealant to use on windows in a manufactured home?
A: Sikaflex 221 has been successfully used to seal windows in Elite Motorhomes, and my father-in-law has never experienced any leaks or product failures. However, it is important to ensure that the material is compatible with the surfaces and substances involved.
Q: Will Sikaflex adhere to a surface cleaned with isopropyl alcohol that has residual spots of previous silicone caulk?
A: While Sikaflex 221 is very sticky and may bond to the surface, it is important to thoroughly clean the surface and remove any residual caulk before application. Masking is also recommended to avoid unwanted cleanup from other surfaces.
Q: Can Sikaflex be used to glue and seal vinyl shower walls?
A: Yes, Sikaflex 221 can be used for this application. It is important to ensure that it is marine grade and compatible with the specific surfaces involved. You might also consider ones I recommended in adhesive for shower wall panels.
Q: Will Sikaflex bond a rubber stair nose to a rubber coin mat?
A: Yes, Sikaflex 221 is suitable for bonding a wide variety of substrates, including rubber. It is designed to create permanent elastic seals with high adhesive strength.
Q: Can Sikaflex be used to seal seams in rubber gym flooring?
A: While Sikaflex 221 may work for this application, the grey Sikaflex sealant may be a better option as it is designed to be more flexible. The black Sikaflex adhesive may settle flatter.
Q: Can mineral spirits be used to prep the surface before applying Sikaflex?
A: While some solvents may be used to prep surfaces before application, it is important to follow the instructions and recommendations provided by Sikaflex to ensure proper adhesion. Additionally, appropriate safety measures should be taken when working with solvents.