2 part or 1 part

[01somta]

What is the difference in a 2 part (lord fusor or similar) and a 1 part (fast n' firm or similar) seamler

[danbob67]

2 part seam sealer is alot better in my opinion the 2 part has a activator to actually harden it unlike a 1 part which kinda just air dries. the 1 parts seem to crack up in time to. comparing the two is like comparing base clear paint to lacquer

[67velle]

well said

[Alan Johnson]

2 part seam sealer is alot better in my opinion the 2 part has a activator to actually harden it unlike a 1 part which kinda just air dries. the 1 parts seem to crack up in time to. comparing the two is like comparing base clear paint to lacquer

Better depends on the intended use of the product. The 2 part sealers ( such as Fusor or Worth) are great for special applications. Both have a self leveling sealer for drip rails etc. The also have an expanding sealer to use in places like where the outer wheel well would meet the quarter panel. For these special areas the regular sealers can not provide the same results.
A good quality single part sealer (solvent base )has applications that the 2 part sealers can't compare to. I use a product from Rubber Seal that works very well. On exposed seams like door and trunk jambs you can use a light solvent to smooth the product by hand to give the seams a very finished look. On floor pans or other joints that are covered the product works well by brushing with a little solvent. The solvent base sealers take 8-12 hours to fully dry before applying paint.
A Urethane base sealer will not flow or smooth out as well in the exposed areas but also work fine where the finish isn't as important. These also dry faster than the solvent base sealers. The sealer should be applied when the parts or vehicle has been properly primed and finish sanded ready for paint. You never want to use a sealer over bare metal. I can post photos of this process if interested. Most of the sealers that I have seen that gave any problems were the older water based ones that were either used over bare metal or top coated before dry.