I am wondering what is the best gutter sealant ? And also best way to clean and prepare for the sealant? Lastly, what temp/climate conditions are best to apply the sealant for best results?

My husband is a retired carpenter. He say gutterlap is the best, but is difficult to find. He could only get it a quality lumber yard, like Great Central. There is also NP1 that you can get from any masonary/brick yard. Expensive but works really well. If you have to clean the joints must let them dry thoroughly, then apply the gutterlap or NP1 with a caulking gun. He has had good luck with them.. hope this helps... wouldn't try to do this until the outside temp gets pretty warm...

There are several products out there but I personally like the BioSeal product by GE. It costs about $6 a tube but will not shrink like other sealers do. Also, you want to wait until the gutter is completely dry and the weather is warm - over 65 degrees. I don't bother with any prep as you will be sealing the gutter seam from the inside - not the outside.

You can also opt for a roof tar type sealant but it only comes in black. That stuff works great as well.

Redid my roof edges last year and put up gutters on my home. What a production. I did find that in the areas that I did not use the BioSeal product my seams are now leaking. I'll have to redo them with the BioSeal stuff as the other silicone sealer shrank in the extreme cold this winter on me.

I use this many times.

Aluminum Butyl Caulk White 10.1 oz # GE15180 by GE Silicones

The warmer the better. Read directions on caulk you get for that.


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All of you so far provided good advice, I have had similar experiences using products specified as metal flashing/roofing sealants. I agree that to date even these products failed when used during cold weather season. The best luck I had sealing seam slices (inside the aluminum gutter) in using karanak/blackjack/similar modified wet weather tars now selling on the market. The only problem is that eventually karanak shrinks and cracks over a few seasons especially with seasonal weather expansion situations. I am a little skeptical about the GE bioseal in that it has a self life ( will dry even if unopened after a year or so and also being bio degradeble, I have my doubts as to the sealants long term performance too. PL and OSI make a tenacious sealnts but didn't see the particular sealant in homedepot yet. The reason why all this concern is that I am going to bid on a gutter leak repair job. The work calls for a 36ft ext. ladder and the industrial gutter was put together to follow the circular (half moon) arcitech design of the building. This means I'll be doing about 30 seams and really must find the best so I can assure quality workmanship. Perhaps margar has the best solution.. Is this like clay sticky strips you press into the seam on a warm dry day? Perhaps This is the best for a four season region? Thanks again for the replies! Hope I am helping here too.. I like karanak tar when you know you can't thoroughly clean older gutters to the metal.

The GE BioSeal is not biodegradeable. In places where I used this on my gutter system it did not fail due to the extreme cold. In places where I used other silicone sealants those places failed. In places where I used the BlackJack, that did not fail.

I will have to try GE bio seal along with the other recommendations others here provided. I certainly appreciate the professional help.

We use this product on vintage Airstream trailers and boat restorations. A local building supply company can get it for you or you could order it here.

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