3M 4200 vs 5200 Choosing the Right Marine Sealant
At a glance
For 3M 4200 vs 5200, 3M lists 5200 for permanent assembly of wood and fiberglass parts and Fast Cure 4200 for parts that may need to be taken apart later. Both are one part polyurethane sealants, and they differ in strength, cure speed and bond permanence.
- 5200 is 700 psi tensile strength with Shore A hardness 68, while Fast Cure 4200 is 180 psi with Shore A hardness 40.
- Fast Cure 4200 has a typical tack free time of 1 to 2 hours, while 5200 takes 12 hours at 73 F.
- Alcohol interferes with the cure of Fast Cure 4200, so avoid alcohol wipes as the last cleaning step.
Contents (10 sections)
The right tool for this job
Marine Sealant & Adhesive Caulk
Marine sealant and adhesive caulk for seams, portholes and repairs above or below the waterline once fully cured. Flexible bond, sandable and paintable, in several colors and sizes.
View productFor 3M 4200 vs 5200, the choice comes down to one question. Will this part ever need to come apart? 3M's data sheets list 5200 for permanent assembly of wood and fiberglass parts, and list Fast Cure 4200 for parts that may need to be disassembled later. Both are one part polyurethane sealants that cure with moisture, so the real differences are strength, cure speed and how permanent the bond is meant to be.
If a flexible waterproof seal is what the job needs, a marine sealant and adhesive caulk from Better Boat is a comparable option to look at alongside the 3M products below.
What Are 3M 4200 and 3M 5200?
3M's technical data describes Marine Adhesive Sealant Fast Cure 4200 as a fast curing, one part polyurethane that reacts with moisture to bond wood, gelcoat and fiberglass and seal joints and hardware above and below the waterline. 3M describes Marine Adhesive Sealant 5200 as a one part polyurethane that reacts with moisture to form strong, flexible bonds to wood, gelcoat and fiberglass and a watertight seal above and below the waterline.
So 5200 is a polyurethane, not a silicone. Picking the right one is less about finding the best product and more about matching the sealant to the job.
Which One Does 3M Recommend?
The two data sheets point at each other.
Pro tip. 3M does not recommend 5200 as a teak deck seam sealer, so check the data sheet limits before choosing it for deck work.
- 3M lists 5200 for permanent assembly of wood and fiberglass parts, and says to use 4200 when a non permanent bond is wanted.
- 3M lists Fast Cure 4200 as designed to allow disassembly of wood and fiberglass parts bonded together, and says to use 5200 when a permanent bond is wanted.
In practice, ask whether the part could need service, replacement or adjustment later. If the answer is yes, 3M's own guidance points to 4200. If the part is meant to stay put for good, 3M's guidance points to 5200.
3M 4200 vs 5200 Side by Side
This table uses 3M's typical values for Fast Cure 4200 and for 5200. 3M states that its figures are typical values only, not for specification purposes, and that adhesion should be tested on the actual substrate.
| Characteristic | 3M Fast Cure 4200 | 3M 5200 |
|---|---|---|
| Type | One part polyurethane | One part polyurethane |
| Typical tensile strength | 180 psi (ASTM D412) | 700 psi (ASTM D412) |
| Shore A hardness | 40 | 68 |
| Typical tack free time | 1 to 2 hours at 73 F and 50 percent relative humidity | 12 hours at 73 F (4 hours at 90 percent relative humidity) |
| Typical rate of cure | 3/16 inch (4 mm) per 24 hours at 73 F and 50 percent relative humidity | 1/8 inch (3 mm) per 5 days at 73 F |
| Temperature range | Minus 40 F to 190 F typical service | Minus 40 F to 190 F long term, not recommended above 190 F |
| 3M lists it for | Parts that may need to be disassembled | Permanent assembly |
3M 4200 and 5200 Cure Time
Both products cure by reacting with moisture, and 3M gives a typical tack free time and a typical rate of cure for each.
- 3M Fast Cure 4200 has a typical tack free time of 1 to 2 hours at 73 F and 50 percent relative humidity, and a typical cure rate of 3/16 inch (4 mm) per 24 hours under those conditions.
- 3M 5200 has a typical tack free time of 12 hours at 73 F, or 4 hours at 90 percent relative humidity, and a typical cure rate of 1/8 inch (3 mm) per 5 days at 73 F.
Every 5200 figure on this page comes from the 3M Marine Adhesive Sealant 5200 data sheet. The 4200 figures come from the Fast Cure 4200 data sheet. Timing for any other version of either product is not covered here, so check the tube label and that version's own data sheet before planning around it.
Temperature matters too. 3M says not to apply 5200 below 40 F, on frost covered surfaces, or on surfaces above 100 F.
When 3M Lists 5200
3M lists 5200 for permanent assembly of wood and fiberglass parts, with a typical tensile strength of 700 psi. 3M lists 5200 for permanent assembly and says cured material can be removed mechanically.
The 5200 data sheet also lists limits worth knowing before a job starts.
- 3M does not recommend 5200 as a teak deck seam sealer.
- 3M does not recommend 5200 for glass, polycarbonate or acrylic windows that are not also mechanically fastened.
- Harsh chemicals such as teak cleaners, oxalic acid, gasoline and strong solvents may permanently soften it.
- Some one part solvent based marine paints may not cure on top of cured 5200, so 3M recommends testing paints first.
3M says cured 5200 can be removed mechanically with a knife, razor blade, piano wire or sanding device.
When 3M Lists Fast Cure 4200
3M lists Fast Cure 4200 as designed to allow disassembly of wood and fiberglass parts bonded together. Its typical tensile strength is 180 psi, Shore A hardness is 40 (softer than the 68 listed for 5200), and elongation at break is over 400 percent.
Which sealant fits the job
3M 5200
Use where 3M lists 5200
Fast Cure 4200
Use where 3M lists Fast Cure 4200
3M lists it for bonded parts that may need to be disassembled later. Always confirm the fit for your own boat against the product label.
Two application notes come straight from 3M. Alcohol interferes with the cure of Fast Cure 4200, so avoid alcohol wipes as the last cleaning step. Abrading the surface with 180 to 200 grit improves bond strength.
What Is Comparable to 3M 4200?
For jobs that call for a flexible waterproof seal, Better Boat Marine Sealant and Adhesive Caulk is a comparable option. It is made for boat, RV, auto and repair jobs where sealing and adhesion both matter, and it is designed for above and below waterline use once cured.
Before you pick a sealant
- Check which product 3M lists for your job
- Compare the cure time of 4200 and 5200
- Review what 3M recommends
- Read the application tips before opening the tube
- Bonds to fiberglass, gelcoat, plastic, metal, glass, ceramic, wood and more.
- The cured bond stays flexible and handles vibration, expansion and contraction.
- Cured sealant can be sanded and painted.
- Available in white, clear, black, gray and brown, in 10 oz and 3 oz tubes (not every color comes in both sizes, so check the listing).
For a closer look, see the 3M 4200 vs Better Boat Marine Sealant comparison. Follow the Better Boat product label for cure and application details.
Application Tips
Surface preparation affects adhesion. Surfaces should be clean, dry and free of old sealant, wax and grime before any bead goes down. Follow the product label or data sheet for the cleaner and the surface prep, since 3M notes that alcohol interferes with the cure of Fast Cure 4200.
Test adhesion on the actual substrate, as 3M advises, and keep the temperature limits above in mind. For step by step technique, see the Sealant Application Guide.
Frequently Asked Questions
What is the difference between 3M 5200 and 4200?
3M lists 5200 for permanent assembly and Fast Cure 4200 for parts that may need to be disassembled. On 3M's typical values, 5200 is 700 psi tensile strength with Shore A hardness 68, while Fast Cure 4200 is 180 psi with Shore A hardness 40. 5200 also cures more slowly.
What is 3M 4200 used for?
3M describes Fast Cure 4200 as a one part polyurethane that bonds wood, gelcoat and fiberglass and seals joints and hardware above and below the waterline. 3M lists it where bonded parts may need to be taken apart later.
What is 3M 5200 sealant?
It is a one part polyurethane marine adhesive sealant, not a silicone. 3M lists it for permanent assembly of wood and fiberglass parts and for a watertight seal above and below the waterline.
How long does 3M 4200 take to cure?
For Fast Cure 4200, 3M gives a typical tack free time of 1 to 2 hours and a typical cure rate of 3/16 inch (4 mm) per 24 hours, both at 73 F and 50 percent relative humidity.
How long does 3M 5200 take to cure?
3M gives 5200 a typical tack free time of 12 hours at 73 F, or 4 hours at 90 percent relative humidity, and a typical cure rate of 1/8 inch (3 mm) per 5 days at 73 F. These figures are for the 5200 data sheet only, so check the label of the exact version you buy.
What is comparable to 3M 4200?
Better Boat Marine Sealant and Adhesive Caulk is a flexible alternative that bonds and waterproofs above and below the waterline once cured. Check the product label for the job at hand.
3M 4200 marine sealant
3M describes Marine Adhesive Sealant Fast Cure 4200 as a fast curing, one part polyurethane that reacts with moisture to bond wood, gelcoat and fiberglass and seal joints and hardware above and below the waterline. 3M's data sheet lists it for bonded parts that may need to be taken apart later. 3M states its figures are typical values only, so adhesion should be tested on the actual substrate.
3M marine adhesive sealant 4200
For Fast Cure 4200, 3M gives a typical tack free time of 1 to 2 hours and a typical cure rate of 3/16 inch (4 mm) per 24 hours, both at 73 F and 50 percent relative humidity. 3M notes that alcohol interferes with the cure and that abrading with 180 to 200 grit improves bond strength. For a flexible waterproof seal on seams, portholes and repairs, Better Boat Marine Sealant & Adhesive Caulk is a comparable option, and its label covers cure and application.
3M marine sealant 4200
3M's typical values for Fast Cure 4200 are 180 psi tensile strength, Shore A hardness 40 and elongation at break over 400 percent. Typical service temperature is minus 40 F to 190 F. These are typical values only and not for specification purposes, so check the product label and test on the actual substrate.
3M marine adhesive sealant 5200
3M describes Marine Adhesive Sealant 5200 as a one part polyurethane that reacts with moisture to form strong, flexible bonds to wood, gelcoat and fiberglass and a watertight seal above and below the waterline. 3M lists it for permanent assembly and says to use 4200 when a non permanent bond is wanted. Typical tack free time is 12 hours at 73 F, and typical cure rate is 1/8 inch (3 mm) per 5 days at 73 F.
Marine grade 5200 sealant
3M sells 5200 as a Marine Adhesive Sealant, a one part polyurethane listed for a watertight seal above and below the waterline. 3M does not recommend it as a teak deck seam sealer or for glass, polycarbonate or acrylic windows that are not also mechanically fastened. Cured 5200 can be removed mechanically with a knife, razor blade, piano wire or sanding device, so it suits parts meant to stay put.
3M 4200 marine adhesive sealant
3M's data sheet lists Fast Cure 4200 where bonded wood and fiberglass parts may need to come apart later, and lists 5200 for permanent assembly. On 3M's typical values, 4200 is 180 psi with Shore A hardness 40, while 5200 is 700 psi with Shore A hardness 68. Asking whether the part could need service or replacement later is the simplest way to choose between them.
What to Buy for This Job
- Better Boat Marine Sealant & Adhesive Caulk for a flexible waterproof seal on seams, portholes and repairs, in colors and sizes to match the job.
Before any sealant job, check the manufacturer's data sheet and label for your exact product and conditions.
What to buy for this job
- Marine Sealant & Adhesive Caulk. When a seam, porthole or fitting needs a flexible sealed repair.
- Butyl Tape RV and Boat Window Seal Sealant. When sealing windows, vents or gaps without a caulk tube.
- Boat Transom Drain Plug Kit. When replacing a transom drain plug housing and sealing it.
Quick quiz
Tap a question to see the answer.
Which 3M sealant is listed for parts that may need to be disassembled later?
Fast Cure 4200 is the one 3M lists for bonded parts that may need to be taken apart later. Marine Sealant & Adhesive Caulk
What does tack free time tell you about a sealant?
3M lists a typical tack free time of 1 to 2 hours for Fast Cure 4200 and 12 hours for 5200, both at 73 F.
What should you avoid as the last cleaning step before using Fast Cure 4200?
Alcohol wipes, because alcohol interferes with the cure of Fast Cure 4200.
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