[TxCajun]

Seam seal the rain gutter using 3M Self-Leveling Seam Sealer, 08307, 200 mL Cartridge.

After a lot of reading on the forum about people's experiences with various products for the rain gutter seam sealer, I decided to use the 3M Self-Leveling Seam Sealer, 08307.

Several people said that they were able to borrow the special cartridge gun for this from a paint supplier or a body shop, but I was unable to find a loaner or rental. I ended up buying the 08307 cartridge on eBay for $37.50 and the 3M 08571 Manual Applicator for $57. I figure when I am done with the applicator gun I'll sell it for $15 or $20 less than I paid for it and consider that a “rental” fee.

I had already cleaned up and primed the rain gutter as per the instructions, and I elevated the front of the truck so that the side gutters were horizontal/level. I put some cable ties in the rain gutter drains at the four corners to keep the sealer from running through those holes. And I also put some 3M Masking Tape on the roof side of the gutter, about 3/16” from the bottom of the gutter, in order to keep stray sealant off of the roof.

I installed the cartridge in the applicator and primed the mixing tube per the instructions. At about 75 degrees F in my shop, the 08307 seam sealer is about the same viscosity as honey or a thin syrup. It was easy to pump the material out of the applicator gun, and it flowed very nicely in to the rain gutter channel. This material sets up relatively quickly; it has a nozzle dwell time of 6 minutes, a working time of 8 minutes, and can be painted after 15 minutes. The 3M instructions say to “Extrude sealer onto surface, being sure to keep end of mixing nozzle submerged in the seam sealer to reduce the possibility of entrapping air in the product.” I worked my way around the gutter doing this, and got a nice bubble-free flow.

A couple things I learned:

1) I used a good quality 3M masking tape to mask around the gutter, but this tears easily if some of the sealing material “sets up” on it before you remove the tape. I found some online video showing the use of 3M vinyl masking tape (like the tape used for fine lines), and I think that would work better for ease of removal.

2) I was working by myself, but I think it would be better if someone could follow you around and start removing the masking tape at the 8 minute point, because by the time you get all the way around the perimeter of the roof, the material is already setting up in the area where you started. This makes the tape removal a bit more difficult.

3) Some people said that they used a different sealer on the gutter area that angles upwards from behind the doors on the sides to the rear of the roof due to the “flow” of this sealer. However, I found that since this sealer sets up so quickly, I could use a “paddle” to scoop or slide the material back up the slope as it began to set up, and very quickly it was stiff enough to not flow down the sloped gutter, but still sufficiently thin to cure as a smooth surface. The “paddle” was just a rectangular piece of plastic material (probably polyethylene) that I cut from a margarine container. The "paddle" is the green thing in one of the pictures.

4) The cable ties that I stuck in the gutter drains helped to keep the sealer from running out, but the drains will take a little more work with an exacto-knife or Dremel tool to open them back up completely.

5) I tried to apply the sealant no more than 1/8 thickness. (As someone else said in the forum, it is a sealant not a gutter-filler.) If you can stay within this thickness, you should be able to seal the gutter all the way around the roof with maybe 20% to 30% of the material in the cartridge left over.