Namrups
10-14-2021, 11:43 AM
My name is Scott Pregont and I have been following the forum’s and build’s for a while. I have seen discussions about sealing the aluminum panels to the space frame. I would like to educate everyone, especially anyone just starting a build, about sealants.
I have worked for Momentive Performance Materials (formally GE Silicones) for 34 years. This is my opinion based on that 34 year history.
Disclaimer: I am in no way trying to sell anyone on a particular manufacturer of sealant. This is a discussion on what sealants are and how they work in this application. It applies to all manufactures of sealants.
The Basics:
There are two basic types of sealants. Polyurethanes and Silicones.
Polyurethanes:
Pros: Good initial adhesion
Easy cleanup – soap and water
Fast cure
Low cost
Easily available
Cons: Not good under extreme temperature conditions/swings
Does not have good flexibility over time. Will eventually dry out and crack
May lose adhesive bond over time
Silicones:
Pro’s: Excellent adhesion to bare aluminum and painted/powder coated surfaces
Stays flexible under extreme temperature conditions/swings (Hot and/or cold)
Will not dry out over time
Excellent adhesive strength
Easily available
Cons: Does not cleanup well
Slower cure
Expensive
I would not recommend using a polyurethane for this application at all. With the extreme temperature conditions under the hood a polyurethane will eventually fail. Silicone is the way to go.
BUT ALL SILICONES ARE NOT THE SAME!!!! Every silicone manufacturer has different types of silicones for different applications. I will use the “GE” brand found in Home Depot or Lowes as examples given my experience with them. What I say will also hold true to other silicone manufactures as well. I will try to explain this without getting into to much chemistry.
A sealant like GE’s Window sealant is an Acetoxy based sealant. What this means is that when this sealant cures it gives of acetic acid as a byproduct. Acetic acid is very corrosive. You don’t want to use this sealant for this application. You can tell when you open a tube of this sealant as it will clear out your sinus’s and make your eyes water.
A sealant like GE’s Tub and Tile sealant is a neutral cure chemistry and a better choice for this application. It is not acetoxy based and does not give off acetic acid as a byproduct. It is easy to work with, does not give off strong fumes that force you out of the garage and cures within 24 hours.
Neatness counts when using silicones. Get a good caulking gun. There is usually a metal seal inside the nozzle that needs to be pierced. Use a 6 penny nail, coat hanger, etc to pierce it. You should only cut the nozzle at the point that will accept what ever you use. Cutting to far back on the nozzle will create a much larger dispensed bead which will be harder to work with and have a tendency to create a mess.
Ahh the mess. No, silicones do not clean up like polyurethanes. Soap and water doesn’t work. DO NOT LET THE SILICONE CURE BEFORE TRYING TO CLEAN IT UP! The best thing to do if you have a situation is to wipe it up immediately! It may take more than one wipe to get it up depending on how much it there. After wiping up the bulk if the material, use acetone to wipe the area clean. This would include your hands. If your concerned about getting acetone on your skin (Acetone was the main substance of fingernail polish remover!) use neoprene gloves. Just be careful not to get material on your glove and then spread it elsewhere. Change gloves frequently. If the silicone cures you can not remove it, even with a razor blade. There will always be a very thin film left which paint will not stick to.
Surface Prep: Before applying the silicone you should clean the surface with Acetone or Toluene. IPA (rubbing alcohol) will not dissolve any grease or oil that may be on the surface. (Including the oils from your skin) Acetone and Toluene will. There is no need to ruff up the surface.
Side note: Loctite manufactures an Oxime catalyzed silicone sealant. It is excellent for this application. It is not easily available and is expensive. I’m not sure if it is carried at HD or Lowes. It may be available on their web site. If your looking for “the best”, IMO that would be it.
Final thoughts. I hope this clarifies for everyone there’s more to it than just “use a silicone sealant”. Again, this was just to educate folks. If you built your car using a polyurethane I’m sure your car is not going to all of a sudden fall apart. Just be aware that if you see a leak in the foot box it might be due to the polyurethane drying out and cracking.
Comments/questions welcome.
I have worked for Momentive Performance Materials (formally GE Silicones) for 34 years. This is my opinion based on that 34 year history.
Disclaimer: I am in no way trying to sell anyone on a particular manufacturer of sealant. This is a discussion on what sealants are and how they work in this application. It applies to all manufactures of sealants.
The Basics:
There are two basic types of sealants. Polyurethanes and Silicones.
Polyurethanes:
Pros: Good initial adhesion
Easy cleanup – soap and water
Fast cure
Low cost
Easily available
Cons: Not good under extreme temperature conditions/swings
Does not have good flexibility over time. Will eventually dry out and crack
May lose adhesive bond over time
Silicones:
Pro’s: Excellent adhesion to bare aluminum and painted/powder coated surfaces
Stays flexible under extreme temperature conditions/swings (Hot and/or cold)
Will not dry out over time
Excellent adhesive strength
Easily available
Cons: Does not cleanup well
Slower cure
Expensive
I would not recommend using a polyurethane for this application at all. With the extreme temperature conditions under the hood a polyurethane will eventually fail. Silicone is the way to go.
BUT ALL SILICONES ARE NOT THE SAME!!!! Every silicone manufacturer has different types of silicones for different applications. I will use the “GE” brand found in Home Depot or Lowes as examples given my experience with them. What I say will also hold true to other silicone manufactures as well. I will try to explain this without getting into to much chemistry.
A sealant like GE’s Window sealant is an Acetoxy based sealant. What this means is that when this sealant cures it gives of acetic acid as a byproduct. Acetic acid is very corrosive. You don’t want to use this sealant for this application. You can tell when you open a tube of this sealant as it will clear out your sinus’s and make your eyes water.
A sealant like GE’s Tub and Tile sealant is a neutral cure chemistry and a better choice for this application. It is not acetoxy based and does not give off acetic acid as a byproduct. It is easy to work with, does not give off strong fumes that force you out of the garage and cures within 24 hours.
Neatness counts when using silicones. Get a good caulking gun. There is usually a metal seal inside the nozzle that needs to be pierced. Use a 6 penny nail, coat hanger, etc to pierce it. You should only cut the nozzle at the point that will accept what ever you use. Cutting to far back on the nozzle will create a much larger dispensed bead which will be harder to work with and have a tendency to create a mess.
Ahh the mess. No, silicones do not clean up like polyurethanes. Soap and water doesn’t work. DO NOT LET THE SILICONE CURE BEFORE TRYING TO CLEAN IT UP! The best thing to do if you have a situation is to wipe it up immediately! It may take more than one wipe to get it up depending on how much it there. After wiping up the bulk if the material, use acetone to wipe the area clean. This would include your hands. If your concerned about getting acetone on your skin (Acetone was the main substance of fingernail polish remover!) use neoprene gloves. Just be careful not to get material on your glove and then spread it elsewhere. Change gloves frequently. If the silicone cures you can not remove it, even with a razor blade. There will always be a very thin film left which paint will not stick to.
Surface Prep: Before applying the silicone you should clean the surface with Acetone or Toluene. IPA (rubbing alcohol) will not dissolve any grease or oil that may be on the surface. (Including the oils from your skin) Acetone and Toluene will. There is no need to ruff up the surface.
Side note: Loctite manufactures an Oxime catalyzed silicone sealant. It is excellent for this application. It is not easily available and is expensive. I’m not sure if it is carried at HD or Lowes. It may be available on their web site. If your looking for “the best”, IMO that would be it.
Final thoughts. I hope this clarifies for everyone there’s more to it than just “use a silicone sealant”. Again, this was just to educate folks. If you built your car using a polyurethane I’m sure your car is not going to all of a sudden fall apart. Just be aware that if you see a leak in the foot box it might be due to the polyurethane drying out and cracking.
Comments/questions welcome.