Silicone vs other caulks

**rootusrootus** · 12-03-2022, 11:55 AM

So, Grand Design uses Trempro 645 to seal the RV. Conventional wisdom is generally that silicone is inferior (for external use at least) for various reasons, like weathering, cracking, UV resistance, difficulty applying new caulk where old caulk is, etc. Is there any reason why in this case it would actually be superior? Did GD choose this caulk because it saves them on manufacturing costs despite creating extra work for customers down the road, or is it actually superior objectively? I.e. should customers go buy a tube of TremPro 645 or a tube of ProFlex instead?

This is one of those things I thought I knew the answer to, but GD has me second guessing.

**FlyStar** · 12-03-2022, 01:25 PM

I too have this same question. Lately tried LEXEL which seems to work OK. But, not sure what is best. I hope this thread can be more definitive that the ones regarding what size truck to use. Ha.

**MoonShadow_1911** · 12-03-2022, 01:49 PM

Originally Posted by FlyStar

I too have this same question. Lately tried LEXEL which seems to work OK. But, not sure what is best. I hope this thread can be more definitive that the ones regarding what size truck to use. Ha.

I've used Lexel for years with great results. Someone, on a different thread, recommended Marine caulk.

**Riverbug** · 12-03-2022, 04:08 PM

The marine caulk mention was probably me. I try not to get on my high horse about it but it's a challenge. I just don't know why silicone has a place in this industry. I'd rather do it once and be done for several years. I have refurbished and modified boats and travel trailers, and maintained a couple of motorhomes. Adhesive caulking will out-perform silicone every time. Marine caulk is adhesive caulk which can withstand below water line conditions. I have used it on RV's as well as boats. I re-caulked my boat's through-hull fittings last year after 17 years - under the waterline.

After week 2 with my 2022 GD, I had to go on the roof because there was a damp spot in the corner of the ceiling above the entry door. As is very typical, the caulking along the metal trim and roof membrane had already cracked. In the rear, the self-leveling caulk could already be peeled up along the edges.

Normally, I would remove all the existing caulking first but I wasn't in a position to take that much time. I just ran a thick bead of adhesive caulk (I always have marine caulk) and smoothed it out with my fingers making sure the edges had good contact with the membrane and the metal trim, but directly over the top of their previously installed caulk. (I should mention that I did clean it well first.) This stuff sticks, even to the existing caulk - but not silicone. 1.5 years later and no cracking anywhere. I would like to take the rig to RV Roof Install and have a proper roof put on. But in the event I don't do that in the next year, I will take the time to clean off the old stuff and redo it all.

Some will argue not using appropriate recommended "compatible" (yeah right) products will void the warranty. My philosophy is that I'm up there because their inferior product or application isn't holding up after week 2 so why would I want to maintain that for the next year or however many for a warranty? I won't have to worry about water leaks if it is sealed properly. The only warranty work I would bring it in for on the roof is when those bubbles all over start billowing in the wind due to inferior application of the roof membrane. If they try to tell me the caulk I used along the edges or around any fittings voids the warranty for the middle of the roof membrane billowing in the wind, well I'd like to understand that logic. Anyway, they can keep their warranty if that's the case. I'll spend the money to get something done right myself.

Dismounting the high horse now...

**MoonShadow_1911** · 12-03-2022, 04:14 PM

Originally Posted by Riverbug

The marine caulk mention was probably me. I try not to get on my high horse about it but it's a challenge. I just don't know why silicone has a place in this industry. I'd rather do it once and be done for several years. I have refurbished and modified boats and travel trailers, and maintained a couple of motorhomes. Adhesive caulking will out-perform silicone every time. Marine caulk is adhesive caulk which can withstand below water line conditions. I have used it on RV's as well as boats. I re-caulked my boat's through-hull fittings last year after 17 years - under the waterline.

After week 2 with my 2022 GD, I had to go on the roof because there was a damp spot in the corner of the ceiling above the entry door. As is very typical, the caulking along the metal trim and roof membrane had already cracked. In the rear, the self-leveling caulk could already be peeled up along the edges.

Normally, I would remove all the existing caulking first but I wasn't in a position to take that much time. I just ran a thick bead of adhesive caulk (I always have marine caulk) and smoothed it out with my fingers making sure the edges had good contact with the membrane and the metal trim, but directly over the top of their previously installed caulk. (I should mention that I did clean it well first.) This stuff sticks, even to the existing caulk - but not silicone. 1.5 years later and no cracking anywhere. I would like to take the rig to RV Roof Install and have a proper roof put on. But in the event I don't do that in the next year, I will take the time to clean off the old stuff and redo it all.

Some will argue not using appropriate recommended "compatible" (yeah right) products will void the warranty. My philosophy is that I'm up there because their inferior product or application isn't holding up after week 2 so why would I want to maintain that for the next year or however many for a warranty? I won't have to worry about water leaks if it is sealed properly. The only warranty work I would bring it in for on the roof is when those bubbles all over start billowing in the wind due to inferior application of the roof membrane. If they try to tell me the caulk I used along the edges or around any fittings voids the warranty for the middle of the roof membrane billowing in the wind, well I'd like to understand that logic. Anyway, they can keep their warranty if that's the case. I'll spend the money to get something done right myself.

Dismounting the high horse now...

Lol! Don't fall off! (Coming from an old rodeo bareback bronc rider!)

Thanks for the detailed information. I do believe it was you who mentioned it on the other thread. I'm seek some out for the next reseal this coming spring. It would be nice but to have to do it every year.

So people reading this thread can find the info here, what brand would you recommend?

**Riverbug** · 12-03-2022, 04:38 PM

Originally Posted by MoonShadow_1911

Lol! Don't fall off! (Coming from an old rodeo bareback bronc rider!)

Thanks for the detailed information. I do believe it was you who mentioned it on the other thread. I'm seek some out for the next reseal this coming spring. It would be nice but to have to do it every year.

So people reading this thread can find the info here, what brand would you recommend?

Haha! A real bronc rider?! You have courage that I don't! I did however ride our pig named Butterball and got thrown many times into the soft "mud" and whatever else many years ago.

Over the years I've found that any of marine caulks hold up well. Primarily look for marine adhesive sealant or caulk. 3M is the go-to for many people. You can get a 3M 4000 UV Marine Adhesive Sealant and not question its reliability. I don't recommend 3M 5200 only because it is nearly impossible to remove if needed. 4000 is also very difficult, but strong holding. I've also used Loctite Marine, Bostik Marine, and others.

The difference between this type and silicone is that it is harder to clean up and harder to smooth nicely. It's not as forgiving as silicone. On the roof, it doesn't matter. When doing windows and other things, cut the tip no bigger than needed, go slowly, and try to keep the need to smooth and remove the excess to a minimum. It just makes it easier. Wet your finger when smoothing. A damp rag, maybe some Goof Off will help cleaning up where needed. But once it is on, if sealed well, you won't have to mess with it for a long time.

Hope that helps.

**rootusrootus** · 12-03-2022, 04:54 PM

When I did my side cameras, which replace a running light, I removed the existing sealant -- came right off with mineral spirits, totally clean, which made me think it was unlikely to be silicone. I used clear 2300 MHRV (ProFlex, same thing) when installing the camera/lights. Worked great, though I have been told that some people find the ProFlex sealant hard to work with. I just sacrifice my finger cleanliness and smooth it just like caulk, works fine. Messy.

But after a discussion elsewhere, I decided to find out what GD actually uses so I emailed them a couple days ago. That's where the TremPro 645 info comes from. I was surprised because it sure didn't resist mineral spirits like I would have expected from a typical silicone based sealant.

**Riverbug** · 12-03-2022, 05:01 PM

Originally Posted by rootusrootus

When I did my side cameras, which replace a running light, I removed the existing sealant -- came right off with mineral spirits, totally clean, which made me think it was unlikely to be silicone. I used clear 2300 MHRV (ProFlex, same thing) when installing the camera/lights. Worked great, though I have been told that some people find the ProFlex sealant hard to work with. I just sacrifice my finger cleanliness and smooth it just like caulk, works fine. Messy.

But after a discussion elsewhere, I decided to find out what GD actually uses so I emailed them a couple days ago. That's where the TremPro 645 info comes from. I was surprised because it sure didn't resist mineral spirits like I would have expected from a typical silicone based sealant.

I believe Geocell is considered an adhesive sealant but they have a number of products so not sure specifically about the 2300 MHRV, I would assume so.

**Redapple63** · 12-03-2022, 06:25 PM

Originally Posted by Riverbug

I believe Geocell is considered an adhesive sealant but they have a number of products so not sure specifically about the 2300 MHRV, I would assume so.

Geocel 2300 is a Tripolymer Elastomeric sealant per their website.

Back in Septemberi had a screw blackout where the front cap attaches to the side and pushed out the seal. I cleaned it real well and applied the Geocel 2300 to that area. Worked great. Didn’t use the clear though, I used the opaque.

Bill

**Capt Bob** · 12-03-2022, 08:42 PM

Originally Posted by Riverbug

You can get a 3M 4000 UV Marine Adhesive Sealant and not question its reliability. I don't recommend 3M 5200 only because it is nearly impossible to remove if needed. 4000 is also very difficult, but strong holding.

I'll second that. Use it on our boat for just about everything. Replaced the fuel tank 12 years ago and sealed the hatch cover with 4000. It stay white and cleans up with Simple Green. 5200 has its use but it yellows. Nothing on your RV that needs that kind of holding power. 4000 can be removed mechanically (think scraping). Expensive (relatively speaking) but worth it.