For flexible bonding and sealing in a hot, humid, high-UV climate, MS polymer (modified silane) is low-hazard, primerless on many substrates, paintable and UV-stable, while polyurethane is strong, abrasion resistant and well proven but isocyanate based and sometimes UV sensitive. Pick MS polymer for weather exposure and easy handling, polyurethane for mechanical toughness. Confirm grade limits on the TDS.
MS polymer for safe, primerless, exposed work; polyurethane for higher tear and a longer working window. Values from the TaftGrip and TaftFlex TDS.
What are MS polymer and polyurethane, and why compare them?
MS polymer (modified silane) and polyurethane (PU) are the two main elastomeric chemistries for joints that need to flex and seal at the same time, such as transport bodies, construction joints and signage. Both are single-part, moisture-cure elastomers that stay rubbery after curing, so they absorb movement, vibration and thermal expansion instead of cracking like a rigid adhesive.
They differ in hazard profile and durability. MS polymer, for example TaftGrip, carries no isocyanates or solvents, is paintable, and is primerless on many common substrates with good weather and UV resistance. Polyurethane, such as Taftflex 6221 and Taftflex 6292, is strong, abrasion resistant and flexible, but is isocyanate based and some PUs are UV sensitive and may need a primer on certain surfaces. Confirm any grade limit on the TDS.
| Property | MS polymer (e.g. TaftGrip) | Polyurethane (e.g. Taftflex) |
|---|---|---|
| Chemistry and cure | Modified silane, single-part moisture cure | Single-part moisture-cure elastomer |
| UV and weather resistance | Good as a class, suits exposed joints | Variable; some grades UV sensitive, may need protection |
| Paintability | Paintable | Paintable |
| Primer need | Primerless on many common substrates | May need a primer on certain surfaces |
| Hazard profile | No isocyanates or solvents, low hazard | Isocyanate based, normal handling care |
| Flexibility and toughness | Flexible elastic seal and bond | Flexible, strong, abrasion resistant |
| Cured-elastomer tensile / tear (per ISO 37 / ASTM D412) | Confirm on TaftGrip TDS | 6221 tear >10 N/mm; 6292 tensile >0.25 MPa (per TDS) |
| Best use | Weather-exposed elastic sealing and bonding, easy handling | Joints needing mechanical toughness and abrasion resistance |
How do they behave in a hot, humid, high-UV climate?
Both chemistries cure by reacting with moisture, so a warm, humid tropical climate generally speeds the cure of each. That can shorten the working and skin time, so the working window should be confirmed on the TDS for local conditions rather than assumed. As a verified reference point, TaftGrip skins in about 5 to 10 minutes, reaches functional cure in about 24 hours and full cure in about 7 days, with a service range of about -40 to +90 C.
Outdoors, high year-round UV favours the more weather-stable chemistry. MS polymer is known as a class for good UV and weather resistance, which suits exposed joints. Some polyurethanes are UV sensitive and may discolour or degrade at the surface over time unless protected, which is one reason a topcoat or primer is sometimes specified. For coastal work, note that the verified water and salt-spray resistance of Taftflex 6292 is rated only average, and MightyLoc makes no marine or immersion claim for the Taftflex range.
Where does each chemistry win on strength and handling?
Polyurethane is the tougher mechanical performer as a class: strong, abrasion resistant and flexible, which is why it is widely used on transport, automotive and construction joints that take wear and load. As verified figures, Taftflex 6221 has a tear strength greater than 10 N/mm and Taftflex 6292 a tensile strength greater than 0.25 MPa, both per their TDS. Do not read one grade’s figure across the range; check each grade.
MS polymer wins on handling and finishing. It is primerless on many substrates, paintable, and low hazard because it contains no isocyanates or solvents, which simplifies storage, ventilation and worker protection on a busy production floor. It also bonds metal, glass, wood and many plastics while sealing the same joint. Polyurethane, being isocyanate based, calls for normal handling care. Both are paintable, so both can be overpainted to match a finish.
How to choose
- Start with exposure. For joints in full sun and weather, lean to MS polymer such as TaftGrip for its weather and UV stability, and protect any UV-sensitive polyurethane with a topcoat.
- Weigh the hazard profile. If you want no isocyanates or solvents for easier storage and ventilation, MS polymer is the lower-hazard choice; polyurethane is isocyanate based and needs normal handling care.
- Match the mechanical demand. For joints that abrade or carry wear, polyurethane such as Taftflex 6221 brings strength and abrasion resistance; verify the tear or tensile figure you need on the grade TDS.
- Check substrate and finishing. MS polymer is primerless on many substrates and paintable; if you choose polyurethane, confirm whether a primer is needed for your substrate. Both can be overpainted.
- Do not assume marine duty. For water or salt exposure, note Taftflex 6292 is rated only average for water and salt-spray, with no immersion claim; confirm suitability on the TDS library or contact MightyLoc for the right grade.
- Time the joint to the cure. Tropical heat and humidity tend to speed both chemistries; confirm working and skin time on the TDS, and see the construction industry page for typical joint examples.
Frequently asked questions
For weather-exposed joints in strong sun, MS polymer such as TaftGrip is usually the safer pick because it has good UV and weather resistance as a class. Some polyurethanes are UV sensitive and may need a topcoat or primer. Confirm the exposure rating for your chosen grade on its TDS.
Polyurethane is the tougher mechanical performer as a class: strong, abrasion resistant and flexible. Verified figures include Taftflex 6221 tear strength greater than 10 N/mm and Taftflex 6292 tensile greater than 0.25 MPa, per their TDS. MS polymer is flexible and seals well but is chosen more for handling and weather than peak toughness.
MS polymer such as TaftGrip is primerless on many common substrates, which simplifies application. Some polyurethanes can need a primer on certain surfaces, so the primer question depends on the substrate and grade. Always check the primer and surface-preparation notes on the relevant TDS before you bond.
MS polymer contains no isocyanates or solvents, so it is the lower-hazard option for storage, ventilation and worker protection. Polyurethane is isocyanate based and needs normal handling care, including appropriate ventilation and protective equipment. Follow the safety data sheet for the exact product you use.
MightyLoc makes no marine or immersion claim for the Taftflex polyurethane range. The verified water and salt-spray resistance of Taftflex 6292 is rated only average. For any water-exposed or coastal joint, confirm suitability on the TDS or contact MightyLoc for the right grade rather than assuming immersion duty.