How To Caulk Fiberglass RVs

caulking-on-rvsHow is it that I’ve written 349 posts (not including picture, video, and brief unplanned updates) and never done a post on caulking before now? Maybe it’s because I’ve thought of caulking as a relatively easy chore once I figured it out for myself. Which was the first time I needed to fix a leak – immediately after I bought my Casita home – and had a lot of other things on my plate at the same time.

But thinking back now, there definitely was some apprehension before the first time I attempted to fix a leak on my home-on-wheels. It’s been a while since I’ve done a how-to post, and as there isn’t much else exciting to talk about right now (work, work work) this is as good a time as any.

So, as regular readers know, my RV is a 17′ Casita, a molded fiberglass trailer that looks and behaves like two boat hulls joined together. It doesn’t have four walls and a ceiling with seams joining them like more traditional RVs, instead it has two large fiberglass pieces held together with a metal band and rivets, but there are still more seams that need occasional caulking than you’d think. The A/C and roof vents, the grey and black tank vents, the stove and refrigerator vents, the windows, outdoor accessible storage cubies, the battery compartment, the outdoor light fixtures, and of most recent note – the door. Said door seam started leaking a week ago when a bout of rain came though, so last Saturday on my only day off in a nine day stint (urp) that’s what I spent my precious few daylight hours doing.

First off, it’s a good idea to get up on a ladder and check your RV’s seams and/or rivets twice a year even if you don’t have anything leaking, so that you can catch problem areas before they become a leak. Having done so myself, there were a couple other things I had put on the list of things to caulk. All told, the top of the door, two rivet snap caps, 75% of one of my storage cubbies, one corner of my Fantastic Fan vent, and the top of one of my outdoor light fixtures were on the list of things to caulk on Saturday. That might sound like a lot, but with set up and take down included it was only about an hour and a half, not bad at all. Here’s what you’ll need:

*Note, all the projects I’ve done using this method have been relatively minor. If you need to redo a whole roof or replace a window or door, this isn’t the guide for you.

  • Caulk of your choice. If you’re a newbie, search online for “caulking” and whatever brand your RV is, and see what other people use. I use ProFlex, which is made specifically for RVs and can be found at Camping World and other RV supply stores. In many cases though, silicone will do just fine too.
  • A caulking tool, to squeeze the caulk out with. I got mine at Lowe’s, it was pretty cheap.
  • Caulk caps if desired, to save the leftover caulk when you’re done (in my experience, it’ll last up to three weeks when capped before drying out).
  • A scissors.
  • Gloves (optional).
  • Scraping tools, for getting the old caulk off. I picked up a set that had two plastic tools, one for corners, and one for flat surfaces. They work just fine, but for heavy duty jobs I sometimes wish I had a metal razor to cut big chunks off.
  • Spirits. As in paint thinner or turpentine, not the kind you drink (I promise it’s not so scary or frustrating as to require alcohol). You’ll also want old rags and/or paper towel.
  • Soap and water. It’ll have two uses actually.
  • A ladder, if the area you’re caulking is higher up.

And now, for the process.

  1. Move your RV outside or to a well ventilated area. First step is removing the old caulk. Take your scraping tools and get to work getting as much of the old caulk up as possible. The better job you do with this, the better a seal you’ll be able to get with the new stuff.
  2. After the old caulk is cleared away, clean the area. Use the turpentine or paint thinner first, this’ll remove most of the residue left behind by the old caulk. The soap and water comes second to remove the spirits, and any dirt. Rinse well afterward to get rid of any traces of soap.
  3. Use the scissors to cut the tip off of your caulk tube at the desired width (you should see several widths marked on the plastic), you’ll want to cut the tip at a diagonal to make placing the bead of caulk easier. If you’re not sure how wide of a bead you’ll need, underestimate. It’s easy enough to cute the tip off more later to make the bead of caulk wider, but impossible to go the other way.
  4. Use the little metal rod on the caulk tool to puncture the seal in the caulk tube several times, now the clock is ticking and your caulk is drying out, so hopefully you have everything else out and ready. Put on the gloves if desired and load the caulk into the caulk gun. Pulling the trigger forces caulk out through the plastic tip, the harder you squeeze the faster it’ll come out.
  5. Caulking is something of an art form. You’ll get better at it the more you do it, but the basic idea is to start at one end of the line you want to caulk, and glide the caulk tool across the seam to the other. If you have a gap, or it doesn’t look as smooth as you like, you can dip a finger into your soap water (that’ll keep the caulk from adhering to it as much) and run your finger along the line to smooth it out. The good thing is, this is a relatively risk-free job. If you botch the caulking up horribly, all you have to do is wait for it to dry, and using your caulk scrapers to take it off and start over. Don’t worry too much about making it perfect, even if you don’t have the area immaculately clean or weren’t able to get all the old caulk up, what you’re doing now will still buy you a good deal of time. The very first caulking job I did on my RV over two and a half years ago is still holding up, even if it’s not professionally precise.
  6. When you finish one area, move on to the next, until all seams are done. A paper towel will clean the tip off of the caulk between areas so that you have a clean start. When you’re completely done, clean the tip off again, and pull back on the caulking gun plunger to release the caulk tube. Put your caulk cap on. All that’s left to do now is cleanup. Congratulations, by learning how to caulk yourself, you’ve saved a wad of money on having a repair place do it for you!

One other quick thing about aesthetics. If you’re really worried about getting caulk where it shouldn’t go, you can use masking tape to make a sort of guide along the edges of where you’re planning to caulk. I don’t do this myself, but I know others who have. If you decide to use masking tape, you’ll want to put it on after the cleaning stage and before you open your caulk.

Good luck! Any questions, comments, or tips you’d like to share about caulking? You know what to do, leave a comment below.

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  1. Paul Dahl on November 15, 2014 at 2:41 pm

    Just a recommendation, silicone is not a good idea for RV caulking. If you need to re-caulk at a later date and use a different kind of caulk (ie: Dicor), it will not stick to it, no matter how carefully you clean out the old silicone. Also silicone is about the only surface that Eternabond will not stick to if you try to place it over silicone for a permanent fix.

    • Becky on November 15, 2014 at 6:49 pm

      Plein and Paul,

      There are differing factions on silicone. It’s what the Casita factory uses and I can say from experience that you can put other caulk over and it’ll hold, I’ve been doing it for years. Little House Customs also uses silicone – the number one place Casita owners go for mods and fixes. Larry explained to me once why silicone wasn’t as bad as people say for RVs but I forget the details now. I stick with Proflex because it’s specifically for RVs, but I no longer feel like silicone is as horrible as some say.

      • Lee on November 30, 2014 at 10:20 pm

        I have always been a believer in silicone sealant but now I’m not so sure. I just purchased a Camco vent cover for my Fantastic fan roof vent that was installed at the factory. It had a thick bead of silicone sealant all the way around it and I had to trim it so the new cover would fit. When trying to remove the silicone that I had trimmed the silicone pealed right off the plastic Fantastic fan housing although it seemed to stick to the fiberglass roof OK. I resealed it with some Dicor lap sealant which I had never heard of until recently but gets great reviews by RVers so I will see how that works. While we are on the subject of maintenance have you ever checked your water heater anode. My Casita is only a year old ( I just bought it used) and I checked mine out of curiosity and was shocked to see that it is almost completely gone. I have ordered a new one.

        • Becky on December 2, 2014 at 4:50 pm

          Interesting Lee, the silicone stuck to my plastic vent covers on the black and grey tanks alright.

          And yes, according to the manufacturer the water heater anode should be checked and changed if needed every 3 months (twice a year for most who just use theirs in the summer). When I first picked up my Casita the anode was in bad shape and I changed it right away, I only had to change it once after that though – how fast they degrade depends on the water in the campgrounds you’re staying at.

  2. Pleinguy on November 14, 2014 at 8:42 pm

    Pretty good, but with one exception. Never, ever use silicone caulk on your RV. Why? First it does not weather well, and nothing will stick to it including more caulk. Plus, removing it does little good because the area it was in also will not hold new caulk.
    Pleinguy recently posted..BadlandsMy Profile

  3. paul on November 14, 2014 at 6:10 pm

    I found it neater to push the gun instead of pulling it it makes for a smoother bead. Really enjoy your blog!

    • Becky on November 15, 2014 at 6:35 pm

      Really Paul? Never thought to try it the other way. Thanks for reading!

  4. Becky on November 14, 2014 at 5:21 pm

    I’ve heard of that product, Casita owners use it to seal minute cracks in the fiberglass itself. Never thought of using it in addition to caulk for other seals, clever idea.

    My AC is front mounted so sealing around it is pretty easy, the fantastic fan vent on top is harder but the cover can be removed to get at the seal under it.

  5. ibrich on November 13, 2014 at 5:35 pm

    Another helpful product is called Captain Tolley’s Creeping Crack Cure (sorry to plug a brand but I don’t think there is anything like it out there). I have an 80s Toyota Escaper (love it!). I kept chasing leaks around a window seal and a pesky roof vent and kept thinking what I need is a low-viscous liquid that will become solid after drying to drip into the areas where I “think” the leak is coming from outside. This is exactly what this product does. And I didn’t have to re-do the whole window seal. Caulk can be difficult on the exterior window under the weather seal. I start from the outside. It can take several tries applying to areas where you think the leak is coming from. Last case try applying to the inside. I don’t suggest applying inside for a roof top leak – you never know where the leak is coming from and sealing an inside leak exit path will just force it to somewhere else, maybe worse.
    I’m still wondering how I will access the AC seal to caulk it – looks like I’ll have to remove the whole AC unit inside and out. Next summer’s job.

  6. Pam on November 13, 2014 at 4:11 pm

    I’ve also used the tip of a teaspoon to smooth caulking. Works like a charm and produces a very consistent bead.

    Love your blog!

    • Becky on November 14, 2014 at 5:17 pm

      Thanks for sharing that tip, I don’t even own a teaspoon but I imagine most folks do.

  7. Ramen on November 13, 2014 at 1:56 pm

    During which step do you utilize the pumpkin?

    • Becky on November 14, 2014 at 5:16 pm

      The pumpkin was supervising Ramen, a very important job. 😉

  8. Jodee Gravel on November 13, 2014 at 1:43 pm

    Just finished caulking around the tub in the S&B and thought “never have to do that again”. Oh well, guess I’m not off the hook after all……..Thanks for a great how-to post (even if I never want to do it again)
    Jodee Gravel recently posted..At the Risk of Jinxing It……My Profile

    • Becky on November 14, 2014 at 5:15 pm

      Aww, sorry to burst your bubble Jodee. Well, it shouldn’t be as often a least!

  9. Jack Nimble on November 13, 2014 at 10:23 am

    I just ordered some caulking after reading your instructions. I’ve tried it in the past but I wind up with more caulk on me than on the RV. Maybe the tool will help. Thanks for your helpful information.
    Jack Nimble recently posted..Hope Springs EternalMy Profile

    • Jack Nimble on November 13, 2014 at 10:29 am

      I found this while on Amazon. It seals an open tube of caulking. Hope it helps.
      Jack Nimble recently posted..Hope Springs EternalMy Profile

      • Becky on November 14, 2014 at 5:12 pm

        Glad you found this post helpful Jack, hope your next attempt goes better!

        Interesting, thanks for sharing that. 🙂

  10. Jim@HiTek on November 13, 2014 at 6:03 am

    Nice article.

    A suggestion or two. When you’re running a bead, and need to stop for a moment, just use the release on the caulking gun to remove pressure from the piston. This helps to slow the flow of silicon down quite a bit so you don’t end up with a silicone snake all over the place.

    I did some tube caulking a couple times on my roof and didn’t care for the work it took. So I checked around and found that Eternabond is highly favored by many RV’ers. It comes in 50 foot by 4″ width rolls. It does a terrific job but once it’s down, it stays down so you have to be careful. Because it’s 4″ wide, I can just clean up old caulking, remove big chunks and the like. Then span the old caulking with the tape so I don’t have to remove it. Makes the job much simpler.
    Jim@HiTek recently posted..More from Rome…My Profile

    • Becky on November 14, 2014 at 6:17 am

      I’ve heard good things about Eternabond, it scares me because it’s so permanent but I can definitely see the benefits for larger projects and if you’re confident doing repairs.

      Thanks for the plunger suggestion, I’ve done that before but totally forgot to mention it!

  11. Dawn on November 13, 2014 at 4:53 am

    What a helpful post–thank you so much! Jerry, I appreciate your comment too–although we have a cover on our trailer right now, I noticed a couple of drops of water in the bathroom–we (I mean Hubby) should check the vent cover up there.

    Your work schedule sounds like quite a challenge. I had the opportunity many years ago to find out I was NOT a night shift person. Never had an accident on the way home but I did see a lot of spiders that weren’t there.

    Take good care!

    • Becky on November 14, 2014 at 6:12 am

      Yikes Dawn, I guess not! Glad you never had any close calls. Now me on the other hand, I don’t think I could wake up at 4:30am to go in for the day shift. Glad you liked the post.

  12. Kristin on November 12, 2014 at 8:07 pm

    This is very helpful information! Thank you so much Becky. I am going to print this post and put it in our Casita binder for when the time comes to do some calking of our own. 🙂
    Kristin recently posted..First Attempt at Camping with our Casita Travel TrailerMy Profile

    • Becky on November 14, 2014 at 6:09 am

      Glad you found it helpful Kristen! Hopefully it’ll be a long time before you need to use it. 😉

  13. Old Fat Man on November 12, 2014 at 7:16 pm

    I found that a sharp wood chisel did a wonderful job of removing old caulk. Just put the flat side against the fiberglas and push gently.

    • Becky on November 14, 2014 at 6:08 am

      Interesting! Thanks for sharing.

  14. Dan on November 12, 2014 at 6:55 pm

    I liked the artical about caulking. I use masking tape, like you described, but I have found that if you put the masking tape on, caulk, and then remove it as soon as you can before the caulk “skins” over. This leaves a nice professional caulking job.
    I enjoy reading your blog, keep it up.

  15. Jerry Minchey on November 12, 2014 at 6:07 pm

    Thanks for a very good article, Becky. Anyone who has an RV, will have to do some caulking from time to time.

    Here’s a tip that might come in handy. Check your caulking gun. Almost all of them have a hole back near the handle that you squeez. Insert the tip of the caulking tube into the hole and pull the trigger to cut the end off. It’s a lot easier than using scissors. If you’re up on top of your rig and need to use another tube of caulking, it really comes in handy.

    I had a small leak in my bathroom. Every time it rained, I would get about a tablespoon of water on the floor right below the vent. I caulked around the vent three times and it still leaked. This went on about all summer.

    Then last week I noticed a small hairline crack in the plastic dome. I put some caulking on the crack and no more leaks. The domes are not expensive, so I may replace that sometime. I had just assumed that it was leaking around where the vent was fastened to the roof.

    Thanks for the tip about using soapy water on your finger to smooth out the caulking. I had been using just water and it kind of worked, but I can see that soapy water would work a lot better.

    • Becky on November 14, 2014 at 6:02 am

      Jerry; that happened to me too. First summer I had Cas I kept getting water in the closet where the grey vent came in. Turns out the plastic was cracked, I got 2 new ones at Camping World and replaced them, wasn’t too hard.

      I’ll have to check and see if my gun has one of those nifty cutters.