Seam sealer or paint first?

[Bonnewagon]

When doing floorboards you need to seal the new welds and seams. I know they make special seam sealers just like the factory used. The factory only used spot welds so the seams were leak points without sealer. But I also like to paint the entire floor, trunk, anywhere water could accumulate and rust. I usually use POR-15 but I found another marine product called Rustlok that is also a moisture cured urethane. It used to be called Trailer Coat and my 1989 boat trailer looks brand new because I faithfully paint it with this stuff. I think it is better than the POR-15. My concern is what to use first. The urethanes dry so hard they need to be severely sanded to re-coat. The 3M seam sealer is also urethane but it says it is paintable. So do I use the seam sealer first, then paint? Or if I paint with urethane do I still need seam sealer? Will it even stick? I know that the POR-15 does not stick well to old hard seam sealer.

 

[pagrunt]

The factory seam sealer is painted over so I'ld roll with sealer then paint.

 

[melloelky]

The larger question should be whether the sealer you're using is direct to metal or not. That would be the deciding factor for my money.

 

[Bonnewagon]

First 3M says this : "High quality, single component formula adheres well to bare metal, primed metal and painted surfaces". Later, in the SDS sheet it says "Meant to be applied to primed or painted surfaces" and "Designed to be used over epoxy or urethane primed surfaces". Confusing to say the least. But it does say PAINTABLE so I'm guessing better to paint over the sealer rather than try to get it to stick to POR-15 or Rustlok?

 

[Clone TIE Pilot]

Most seam sealers including 2k epoxy sealants work best applied over painted metal. Most seam sealers need to be painted afterward to UV protect them.

 

[Longroof79]

I've noticed when stripping my doors of paint and seam sealer. I would notice rust forming under the seam sealer, especially when the seam sealer cracks from being hard and brittle over time thus allowing moisture to enter.. I would think some form of primer or rust neutralizer under the seam sealer would make sense.

 

[blk7gxn]

Seam sealer shrinks just a tad over time and in theory, flexes with the body of the car, yes it is flexible and gives, BUT may tend to roll a little on the edges leaving bare metal exposed. I personally would paint the surface first, this should in fact help with the bonding as well, and prevent any issues with rust in the future.

The factory does the "paint over the sealer" to save money. You cant spray paint on body panels and then pay employees money to stand around and wait for the paint to dry before installing the sealer, not feasible. I've learned that every driving force in a factory is to save money, and this is inclusive to cutting steps out of the assembly line procedures. Car manufacturer's make cars to make money, period, not caring about longevity.

 

[spidereyes455]

Mabey a good coat of paint worked into and around the seams first and then seam sealer finally another coat over everything including the seam sealer.
That's probably how I'd do it anyway.

 

[Bonnewagon]

Maybe a good coat of paint worked into and around the seams first and then seam sealer finally another coat over everything including the seam sealer.
That's probably how I'd do it anyway.

Jim you think like me! The key here would be to apply the sealer while the POR-15 or Rustlok is still tacky. The 3M urethane sealer and the urethane paints are all moisture cured and once the paints are dried they are a bear to sand to get some 'tooth'. Funny thing about the Rustlok. It is made by Pettit, is a marine rustproofing metals primer, and can be applied all the way down to 10 degrees F. Of course warmer is better but the POR needs WAY warmer and humid conditions.

 

[Clone TIE Pilot]

Seam sealer shrinks just a tad over time and in theory, flexes with the body of the car, yes it is flexible and gives, BUT may tend to roll a little on the edges leaving bare metal exposed. I personally would paint the surface first, this should in fact help with the bonding as well, and prevent any issues with rust in the future.

The factory does the "paint over the sealer" to save money. You cant spray paint on body panels and then pay employees money to stand around and wait for the paint to dry before installing the sealer, not feasible. I've learned that every driving force in a factory is to save money, and this is inclusive to cutting steps out of the assembly line procedures. Car manufacturer make cars to make money, period, not caring about longevity.

Good seam sealer is paintable in 15 minutes or less.