Which Sealant, Adhesive or Caulk to Use? Depends on the Application.

[ckent323]

There are many threads on various repairs we make to our campers and often suggestions on Adhesives, Sealants and Caulks are made.

Frequently there is little or no discussion of the appropriate sealant, adhesive or caulk based on the materials involved or the specific application (e.g. roof leaks, window sealing or fasteners, Aluminum, Steel, etc).

Consider that there are literally many dozens if not hundreds of different sealants, adhesives or caulks.

Why so many, are they performing similar jobs? The short answer is no.

Besides the fact that there are numerous different manufacturers of adhesives, sealants and caulk, digging in a bit we find that each manufacturer may have numerous different products each designed for a specific application and/or material.

Aside from brand differences (or similarities) and marketing claims there is a lot of chemical and structural engineering behind these products so it makes sense to learn a bit about selecting the appropriate product for your application and materials.

Here are some informative links that may help sort all this out relative to RVs (the subject is much larger when considering buildings and other applications!):


https://www.practical-sailor.com/boat-maintenance/the-great-stickup-practical-sailor-tests-marine-adhesives-caulks-and-sealants?fbclid=IwAR3oUg0zZ2Z3OUhybFsCnsSgtZjTSYkhSPdLAkf8dXspnuj3_JE-_0DYD_s


https://www.thervgeeks.com/rv-caulk/


https://askthervengineer.com/my-favorite-rv-caulks-and-sealants-not-just-another-schmoozy-amazon-list/



and a serious read on adhesives and sealants (pdf document)


https://users.fs.cvut.cz/libor.benes/vyuka/lepeni/Handbook%20of%20Adhesives%20and%20Sealants.pdf



I hope this is incentive to dig further before simply being overwhelmed by all the choices at Home Depot, Lowes, Ace, Menards, McGuckin, OSH, West Marine, Autozone, O'Reilleys or whatever and just using something because of brand identity or someone said that is what they use (for who knows what reason or application).


Wishing all successful sticking and sealing wherever you may do it.





Craig

 

[craig333]

Thanks Craig. I'll definitely read up on it. Not that joe schmuck uses 9930 isn't useful information. Sometimes I wonder if I haven't just gotten lucky in my choice of sealants.

 

[craig333]

Wow, I wonder if the butyl tape I have is eternabond. Kind of explains why my fan has so many screws. I use silicone on the inside of screw holes but that's about it.

 

[TacomaAustin]

A "dear previous owner" of my camper used clear silicone sealant on the "outside" of my roof screws - with extra slathers of this goop around the base of the roof vent.

I'm sure that the "DPO" meant well - but I would have used a polyurethane sealant - which is at least paintable.

 

[DavidGraves]

Hi Craig....

That's your story and you're sticking with it ?

DG

 

[kmcintyre]

Nice, thanks. It's interesting because over the years, I've had discussions with both ATC and FWC about what products to use for various applications. I have to say, they both have different opinions but in the end, I'd use what they say they use....

 

[mobilelists]

OK, so what would be best for sealing the gap around a large battery cable going though a hole in aluminum? Nice to have it slightly flexible, not silicone and it would be pretty much shielded from UV.

Thanks for any suggestions.

 

[ckent323]

mobilelists,

If going from inside to outside (or vise versa) in roof or side of camper:

1) Buy a rubber grommet large enough for the cable to pass through to go over the sharp Aluminum edges
2) Push the cable through
3) If on roof and this is for solar I would use an entry gland over the rubber grommet
4) Seal with 3M 4300 or equivalent if on roof. If on side the rubber grommet may fit tight enough.


Here is one source of rubber grommets. I got mine from my local Ace Hardware.

https://www.amazon.com/Hard-Find-Fastener-014973176501-Grommets/dp/B00P4JIBG2/ref=asc_df_B00P4JIBG2/?tag=hyprod-20&linkCode=df0&hvadid=242007132876&hvpos=&hvnetw=g&hvrand=12039828869408433088&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9031757&hvtargid=pla-445975661509&th=1

I hope this is helpful,

Craig

 

[mobilelists]

Craig,

Thanks for the sound advice. I am an idiot...I have a couple rubber grommets that will fit perfectly sitting in my shop. I will use them tomorrow.

The battery cables enter on the side wall and are somewhat protected. This is just additional protection.

Pat

 

[EcoVntr]

[SIZE=12pt]Hello other Wanderers.... Continuing with the discussion of exterior sealants [forward bumpers and filling screw holes] and exterior trim screws [rusting and replacement].[/SIZE]


[SIZE=12pt]Screws - Trim:[/SIZE]

• [SIZE=12pt]I have noticed exterior trim screws starting rust [either the head of the crew and/or the threaded area] and was curious if anyone has a link to replace the trim screws with the original #8 x 3/4" or the next size up for those that no longer tighten up [#6 3/4"]. [/SIZE]
• [SIZE=12pt]After reading some other threads on screw metal types, still not clear if stainless will be an issue? Or, should the replacement be a zinc coating?[/SIZE]
• [SIZE=12pt]Polyurethane sealant for sealing the screw holes? has anyone done this for the trim screw holes on the exterior of the FWC? Just dab on the screw threads or dab into the FWS trim hole?[/SIZE]

[SIZE=12pt]Polyurethane sealant:[/SIZE]

• [SIZE=12pt]After seeing the trim screws rusting, is water trickling in from the exterior trim edges? Has anyone placed a bead of the sealant along the vertical and horizontal edges of the trim edges?[/SIZE]
• [SIZE=12pt]Forward bumper OLD sealant has dried and pulled away from the rubber bumpers that rest against the truck bed. Any luck with the sealant adhering to the rubber and aluminum siding of the FWC?[/SIZE]
• [SIZE=12pt]I’ll continue to read through the sealant types to figure out what I might need.[/SIZE]

[SIZE=12pt]Thanks for any input on the items above.[/SIZE]

[SIZE=12pt]Images:[/SIZE]

 

[ckent323]

EcoVntr,

First, I am not a materials expert or metallurgist. However, I am a long term owner of an ocean going sailboat as well as an FWC Camper. I also have considerable experience from my 45+ year career in aerospace painting and bonding parts and assemblies for use in Aircraft and in Space.

The following text was edited on 3/23/2024 to add additional information.

In order for a galvanic action to occur there needs to be two dissimilar metals in contact with each other as well as a dielectric material present, typically water or water vapor of some kind (rain, fog, condensation, etc).

Here is a link with a discussion of galvanic corrosion that may be useful. Note the diagram showing how to use dissimilar metals and minimize corrosion risk.

https://galvatech2000.com/understanding-galvanic-corrosion/?lang=en


In general, Stainless Steel and Aluminum have a potential difference large enough to be concerned about galvanic corrosion of the Aluminum, particularly in the presence of salt water (or salt water vapor) but even with rain or fog to lesser extent, corrosion just takes longer to happen. After all Stainless steel is much closer to Steel on the galvanic chart than it is to to Aluminum

Important note: As with other metals there are a variety of alloys or types of Stainless Steels. I believe only two alloys of Stainless have very low amounts of carbon and are considered non-ferrous and applicable to making screws and other parts useful on our campers. Those are type 304 and type 316. Either will work on our campers. Type 316 is preferred by boaters due to its excellent resistance to salt water induced corrosion. Type 304 is a slightly cheaper alternative. Now the mystery of why Stainless BBQ grills and other items made out of Stainless show signs of rusting when left outside in the rain is solved, they are not made of 304 or 316 Stainless.

If you look to buy something and it says Stainless Steel but it does not say it is 304 or 316 then it most likely isn't. Always be sure to ask.

Now it is fair to ask if other types of Stainless will work instead of 304 or 316. If you employ the strategy to minimize galvanic corrosion by employing the techniques in the link above then probably it is OK - but be sure you also understand the strength needed for the application as the strength varies among alloys. I think it would be appropriate to ask a metals expert at one to the metal suppliers online if a particular type of Stainless would work in the specific application location and conditions (outside, near the coast, rainy whatever) that you intend to use it.

In the end you may just want to use less expensive and likely stronger carbon steel fasteners while employing the corrosion mitigation approaches outlined at the link (a coating of paint or a coating of Zinc works too if you can avoid scratching the coating off of the treds and the fastener head when installing the fastener). ;-)

https://www.ryerson.com/resource/the-gauge/ferrous-and-non-ferrous-metals-whats-the-difference

https://www.ryerson.com/resource/the-gauge/what-is-stainless-steel


All of this winds up protecting the Aluminum from degrading. But if the main issue is just the fasteners rusting then the protective coating on the fasteners is either getting removed somehow or is not adhering properly to the surface of the fastener resulting in the fastener rusting. If the coating has pinholes or is too thin water can get between the coating and the steel body of the fastener and then corrosion happens. Similarly if the surfaces of the fasteners are not properly prepared and cleaned then the paint or protective coating may not stick adequately or fail prematurely allowing water to react with the steel. Stainless fasteners may solve the rusting problem but if they are not painted or used in a way to mitigate galvanic reaction then you may wind up with the Aluminum parts corroding.

Relative to sealants and painting:

The single best tip I can give for for sealants and paints - always prepare the surface in accordance with the manufacturers instructions and clean with acetone and/ or alcohol then prime as recommended for the paint or sealant you are using. Polyurethanes stick well to properly prepared surfaces.

In the space business we bond a lot of things together and we clean the surfaces to bright metal then often clean with acetone, deionized water (a strong solvent) or distilled water followed by alcohol since good high purity alcohol does not leave a residue when it evaporates whereas Acetone often does.

How do we know the surface is clean enough? It is referred to as a water break free surface. If you drop a drop of water on the cleaned surface the drop will spread out (literally instantly flash over) and wet the entire clean part of the surface and will not bead up. If the water beads up anywhere then that part of the surface is not clean enough and needs more cleaning. This level of clean does not last long, maybe 30 min to an hour at best, because the surface will soon oxidize (rate depends on the material cleaned).

Paint and adhesive bonds on properly prepared surfaces are very strong and it is not unusual when a good bod is tested to the limit of failure to see some of the substrate material the adhesive is applied to is pulled out with the adhesive.

Of course we do not need this level of clean to do bonding on our campers (although it would do no harm) but the understanding and knowledge that a good clean properly prepared surface maximizes bond strength and longevity is important.

Most paints and adhesive bonds fail prematurely because the substrate was not properly prepared and or cleaned.

I hope this is helpful.

Craig

 

[Vic Harder]

whoa, super cool Kent. That description of "clean enough" is wild.... thanks for sharing!

 

[craig333]

I really had an opportunity to see how proper prep works on my Jeep. I coated the bed in a rubbery type product (can't recall the name anymore) and prepped it exactly as instructed. Some pretty toxic solvents as I recall. I had some leftover and continued to coat unprepped surfaces. The bed you can't chisel the stuff off. The unprepped portions while it held well for years has peeled of and or peels off easily.

I hate prepping surfaces. Its boring and time consuming. Sure is worth it though

 

[EcoVntr]

Ckent323,

Thank you for the detail reply to my posting. Once the weather warms up in the garage, guess I will make sure to follow the prepping / clean instructions. Lots info to wade through.

Hope to replace the screws as needed and seal up opening in siding and front bumpers.

Thanks for the replies.