The 9 Best Automotive Seam Sealers
Updated by · How we research
For floor pans, trunk seams and door jambs, nine one-part, brushable and two-part seam sealers compared by paint time and safety. The 3M Urethane 08367 leads. When users buy our independently chosen editorial recommendations, we may earn commissions to help fund the Wiki.
An RTV silicone is the wrong product for a body seam, since most paint won't stick to silicone. Seam sealer is a flexible, paintable paste laid over the joints in a car's sheet metal, such as floor pans, trunk seams and door jambs, to keep out water, salt and road noise. Restorers and collision shops apply it after metalwork and primer.
From the manual
- Paint after 30 minutes; once it's been on more than 24 hours, scuff it with a Scotch-Brite pad before painting. p. 2
- It works as a weld-through sealer, but only with squeeze-type resistance spot welders; 3M says to make test welds on scrap first. p. 3
- Keep it off acid etch primer: 3M says leftover acid can weaken the bond. p. 3
- Unopened cartridges keep 12 months at room temperature, and 3M sells it for professional use, not retail. pp. 2, 3
From the manual
- Sand bare metal with P180 grit, or scuff factory e-coat with a red pad, then clean with SEM Solve. p. 1
- Paint right away with most solvent-based paint, or within 24 hours without scuffing; SEM says to test compatibility first. p. 1
- Don't lay it over acid-based self-etching primer, or that primer over it; SEM warns of cracking and blistering. p. 1
- Wipe off excess with a little SEM Solve while it's still wet. p. 1
Compare the specs
Swipe the table sideways to see every column.
| Product | Type | Container | Paint after (minutes) | Bare metal OK (per maker) |
|---|---|---|---|---|
| 1. 3M Urethane 08367 | 1K urethane | 310 mL cartridge | 30 | Yes |
| 2. SEM 29392 | 1K silane polymer | 10.1 oz tube | 0 (solvent paint) | Yes |
| 3. 3M Dynatron 550 | Brushable caulk | 12 oz cartridge | 30 | Yes |
| 4. Eastwood 51655Z | Caulk-gun sealer | 300 mL cartridge | 60 | — |
| 5. Evercoat 365 | Brush-on | Quart can | 60 | Yes |
| 6. 3M 08308 | 2K epoxy | 200 mL dual cartridge | 15 | Not listed (primer, paint) |
| 7. SEM Dual-Mix 39387 | 2K epoxy, self-leveling | 7 oz dual cartridge | 15 | Non-flexing roof skins |
| 8. ACDelco 10-2013 | Solvent-based | 300 mL | — | — |
| 9. Transtar 4167 | 1K, ready to use | 11 oz cartridge | 30 | Yes |
Paint times are the makers' minimums. 3M's 08367 and SEM's 29392 can be painted for up to 24 hours without scuffing; SEM's 0 is for solvent paint, and it lists one hour for waterborne. SEM's Dual-Mix figures come from its 2016 product guide. A dash means the maker publishes no figure.
Sources
- 3M Urethane Seam Sealer technical data (PDF) Dynatron 550 product page 08308 product page
- SEM 29392 product page Complete guide to 1K seam sealers Seam sealer line page Product guide, 2016 (PDF)
- Eastwood 51655Z product page
- Evercoat 100365 product page
- ACDelco 10-2013 safety data sheet (PDF)
- Transtar Ultra Flex data sheet (PDF)
From the manual
- It's 30 to 35 percent toluene, rated highly flammable, and suspected of harming fertility or an unborn child. pp. 2, 3
- Use it outdoors or with good ventilation, away from sparks, and wear gloves and eye protection. p. 2
- The sheet lists Dominion Sure Seal of Ontario as the maker, ACDelco as distributor, and the color as white. p. 1
From the manual
- It skins in 3 minutes and takes paint in 30. Tool it with a putty stick dampened with Transtar's Acry Solvent. p. 1
- Rated for bare steel, galvanized, aluminum, primers and old paint; test plastics, and solvent-test aftermarket e-coat first. p. 1
- Transtar sells it only to trained painters, not the general public, and gives it a one-year shelf life. p. 1
Editor's Notes
November 5, 2026, by Ezvid Wiki Editors:
We read the makers' data sheets, procedure and safety sheets for these sealers and corrected several claims: the 3M 08367 is the black version and is approved for bare metal, the SEM 29392's paint window is 24 hours, not 48, and the Eastwood, Dual-Mix and Transtar timings now match their makers. We added a spec table, notes from the makers' data and safety sheets for four picks and a collision-shop owner's tip on purging two-part nozzles, and updated two older notes that no longer match the list.
October 17, 2026, by Ezvid Wiki Editors:
Two of the old picks aren't body seam sealers at all. In all, three picks from the 2021 list no longer belonged. The J-B Weld 31919 listing now sells a high-temperature gasket maker, and the Permatex 81173 is an RTV silicone. Permatex itself says most paint won't stick to silicone, which is the opposite of what a body seam needs. We also dropped the 3M Flexiclear, a clear sealer for vinyl roofs and lamp seams that was close to selling out.
The SEM 29392, 3M Dynatron 550, Eastwood 51655Z, Evercoat 365 and Transtar 4167 stay. New to the list: the 3M Urethane 08367, a one-part sealer with well-documented paint times, the ACDelco 10-2013 that GM dealers use, and two two-part sealers, the 3M 08308 for tooled beads and the SEM Dual-Mix 39387 for flat roof seams. We looked at a couple of cheaper no-name cartridges too, but they came with no data sheets and mixed reports on how well they stick.
We found no lab tests of seam sealers. We relied on makers' pages, can labels and data sheets, a 3M safety data sheet, restorers' forum threads, owner feedback and recall databases. Several of these sealers carry industrial-use labels, and some contain a trace of isocyanate, so gloves and fresh air matter more than the brand.
Earlier notes
March 5, 2021, by Brett Dvoretz:
While you can find automotive seam sealers from a variety of companies, we recommend sticking with the best and most respected brands in the industry, which is exactly what you have here. It should be noted that there aren't a lot of changes made in the formulas and sealants available from year to year, and as such, no adjustments needed to be made to our recommendations at this time. The sealers you'll find here have been proven to perform, and perform well, which is why we continue to recommend them. If that changes for any reason, we will be quick to reflect this in our lineup. [2026 update: the 2026 refresh replaced three of these picks; see the note above.]
October 9, 2019, by Rafael Perez:
Removed Carborundum EZ Repair because of availability issues. Added the Eastwood 51655, the Permatex 81173, and the J-B Weld 31919.
The Eastwood 51655 is purpose made for sealing body seams and replacement floor pans. It has just the right consistency when cured to form a waterproof seal but keep everything in place. We included the Permatex and the J-B Weld because they can be used for metal seams but since they are RTV silicones, they come in handy for most silicone needs. [2026 update: both were dropped in 2026. Most paint won't stick to silicone, so it's the wrong choice for a body seam you plan to paint.] Keep in mind that these are not oil-resistant. Special oil-resistant silicone is needed for parts that are meant to come in contact with oils.
Auto repair can be dangerous and should only be performed by trained technicians to avoid personal injury or damage to equipment.
One-Part, Brushable Or Two-Part
They set faster and need a two-component gun and mixing nozzles.
Most seam work calls for a one-part (1K) sealer in a cartridge of about 10 ounces. It cures without a hardener, fits a caulking gun and stays flexible as panels move. The 3M Urethane 08367 is typical: paint after 30 to 45 minutes and a full cure in about a day. SEM notes that its one-part sealers stretch further than its two-part ones, so they suit seams that flex.
Brushable sealers are thinner. You paint them on with a stiff brush to copy the brush-stroke look many factories left on floors, trunks and jambs. Evercoat's brushable sealer comes in a quart can, while the 3M Dynatron 550 goes on from a cartridge and brushes out.
Two-part (2K) sealers mix a resin and a hardener in a dual cartridge. They set faster and need a two-component gun and mixing nozzles. Heavy-bodied versions hold a tooled bead on vertical seams. Self-leveling ones, like the SEM Dual-Mix line on SEM's seam sealer page, flow flat into roof ditches and other level seams that don't flex much. Kye Yeung, owner of the European Motor Car Works collision shop, said on a 2017 Society of Collision Repair Specialists video panel that "the biggest abuse I see" is skipping a test strip, as Repairer Driven News reported: run four to six inches from a new mixing nozzle onto cardboard first, or the bead on the car can fail because it never catalyzed.
Primer, Paint Windows And A Factory Look
Clean and degrease the seam first. Whether sealer can go on bare steel depends on the sealer. 3M's data sheet for the 08367 and SEM's 29392 page both approve properly prepared bare metal, while 3M lists its 08308 epoxy for a two-part primer or sanded paint, and SEM allows its self-leveling Dual-Mix on bare metal only on roof skins that don't flex. Restorers often put epoxy primer on any bare steel that will sit for more than a day. Keep acid-etch primer away from the 3M and SEM sealers, since both makers warn against direct contact, though Transtar rates its sealer for self-etching primer.
A sealer that skins in 15 minutes isn't cured. Paint too soon and the top coat can wrinkle or lose its grip, so follow the paint window on the label or data sheet rather than the skin time. The windows differ: SEM's one-part sealer takes solvent paint right away and for up to 24 hours without scuffing, while 3M's urethane needs 30 minutes and a scuff after 24 hours. To smooth the bead, makers name their own solvents, and sealer seller Berkland's guide suggests a spatula or rounded stick dipped in mineral spirits.
Keep silicone away from the job. Permatex says most paint won't stick to its silicone, and paint maker BASF lists silicones among the contaminants that cause craters, or fisheyes, in fresh paint. Match the sealer color to what's already under the car: gray, beige, white and black all show up on factory seams.
Safety: Isocyanates, Solvents And Gloves
Seam sealers are shop chemicals, and several here are labeled for professional, industrial or occupational use. 3M's safety data sheet for its gray urethane sealer lists xylene, ethylbenzene and a residual isocyanate below 1 percent. It warns that the sealer may cause skin allergies or asthma-like symptoms, recommends polymer laminate gloves, with nitrile over them for dexterity, and calls for a respirator if ventilation is poor.
Solvent-heavy sealers bring a fire risk too. The safety sheet for the ACDelco 10-2013 lists 30 to 35 percent toluene and rates it highly flammable, so keep sparks and flames away. Two-part sealers add a hardener, so treat the mixing nozzle and any leftover material with the same care.
Don't grind or weld through cured sealer without good ventilation. SEM marks only some of its sealers as resistance weldable, and Eastwood says its cartridge sealer isn't a weld-through product. Web searches of the U.S. Consumer Product Safety Commission's sites, including SaferProducts.gov, and of Health Canada's recall site turned up no recalls of these sealers.
How we researched this
We compared 19 seam sealers and sealants and kept nine. For those, we read 3M's technical data sheet and 2015 safety data sheet for the 08367 and its 2024 sheet for the gray version, SEM's 1K seam-sealing procedure sheet, Transtar's Ultra Flex data sheet, and the safety sheets for the 3M 08308 and ACDelco 10-2013, plus a GM service bulletin that names the ACDelco compound. We found no data sheet for the Eastwood 51655Z, Evercoat 365 or 3M Dynatron 550, so their timings come from the makers' product pages, as do the SEM Dual-Mix 39387's, along with SEM's 2016 product guide. Web searches of the CPSC and Health Canada recall sites in November 2026 found no recalls of these sealers.
Sources (25)
- Urethane Seam Sealer 08367
- Urethane Seam Sealer technical data, June 2020 (PDF)
- Safety data sheet, 08367 black, 2015 (PDF)
- Safety data sheet, urethane seam sealer 08361/08362 (PDF)
- Dynatron 550 seam sealer
- Heavy-Bodied Seam Sealer 08308
- Safety data sheet, 08306/08308 (PDF)
- 1K Seam Sealer 29392
- 1K seam sealing procedure (PDF)
- Seam sealers
- Complete guide to 1K seam sealers
- Product guide, 2016 (PDF)
- Dual-Mix Forever Warranty
- Autobody seam sealer cartridge, black
- Brushable Seam Sealer, quart (100365)
- 10-2013 safety data sheet (PDF)
- GM bulletin naming P/N 12378500
- Ultra Flex seam sealer data sheet (PDF)
- Permatex: black silicone adhesive sealant
- BASF: craters and fisheyes in automotive paint
- Berkland: how to apply seam sealer
- Repairer Driven News: SCRS video on seam sealers, June 6, 2017
- Camaros.net: seam sealer recommendations
- U.S. Consumer Product Safety Commission: SaferProducts.gov
- Health Canada: recalls and safety alerts
Frequently asked questions
What is automotive seam sealer made of?
It depends on the type. 3M's 08367 is a moisture-curing urethane whose safety data sheet lists urethane polymer, PVC, xylene and a little isocyanate. SEM's one-part sealers use modified silane polymers, and the ACDelco compound is solvent-based. Two-part sealers such as the 3M 08308 and SEM Dual-Mix are epoxies with a separate hardener.
What's the difference between 1K and 2K seam sealer?
A 1K sealer is one part, cures without a hardener and fits a standard caulking gun. A 2K sealer mixes a resin with a hardener from a dual cartridge, sets faster and needs a two-component gun.
Can you paint over seam sealer?
Yes, if it's labeled paintable, but wait for the paint window on the label or data sheet, not just the skin time. Paint over uncured sealer can wrinkle or lose adhesion.
Can seam sealer go on bare metal?
Some makers approve it: 3M for its 08367 urethane and SEM for its 29392, on properly prepared metal. 3M lists its 08308 epoxy for primed or sanded painted surfaces. Priming bare steel that will sit for a day or more is still the safer habit.
Can I use silicone instead of seam sealer?
Not on body seams you plan to paint. Permatex says most paint won't stick to silicone, and BASF lists silicones among the contaminants that cause fisheyes in fresh paint.
Should I brush seam sealer or run a bead?
Run a bead from a caulking gun to fill gaps and joints. Brush a brushable sealer when you want to copy the brush-mark texture many factories used. Heavy-bodied sealers can be tooled to match shaped factory beads.
