Thor RV "Undercoating" and poor underneath waterproofing

[tmikea]

I've got a 2018 Thor Chateau 24FS (it's a 24' Class C with a Mercedes Benz Spriter 3500 Diesel chassis).

I'd like to request that we keep this thread focused just on the undercarriage and waterproofing of the undercarriage of Thor RV's.

I started looking under the auto-open stairs to figure out what needed lubricated (there is a lubricate every 30 days sticker on the stairs)...and in the process started looking around at the workmanship.

Here's my understanding of the walls on the RV portion of the unit: They are plywood with a fiberglass exterior finish and a wallpaper interior finish. The walls extend below the living area floor to hide the black water/gray water tanks and all the other stuff below the living area floor.

Well while looking at the slide out stairs, I found a lot of poor workmanship that include (1) visible interior wallpaper finish below the living area that was not undercoated, (2) many areas that should have been caulked that was not, and (3) unprotected plywood exposed to the elements.

To fix all of these problems, I believe I will have to spend untold hours of time (perhaps 100+), marine grade silicone caulk, and undercoating trying to seal up what was sloppily done at the factory.

After looking around underneath the RV , I'll be wincing when ever I drive the RV in the rain...until I have to time to properly undercoat, seal and also zip tie many dangling wires that are taped up....and the tape is coming undone.

Attached are some annotated pictures of what I saw in just two areas or the right side of the RV.

Do you have any recommendations as to what undercoating, caulking, etc, I.E. what materials I use to undercoat and waterproof my RV? Thanks for any help and advise.

[gmtech16450yz]

This is a perfect example of shoddy Thor assembly and workmanship that most owners would never see unless they really looked.


My '18 Vegas had pretty much the same issues underneath. One of the first things I noticed when my wife was driving was the huge amount of road noise coming from the door step area. It ended up being like in your pictures, lots of gaps in the sheet metal and framing. Sealing up all that greatly reduced the road noise in that area. So how many "happy" Thor owners are driving around with excessive, unnecessary road noise and don't know it?

Here's what I used underneath my Vegas.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I also completely backed the entire front fiberglass cap with this and also black spray on undercoating. The whole front end of the Vegas went from hollow sounding, rattly and loose to solid and quiet. So go for it! Insulate and waterproof away. It will absolutely make a difference in how solid and quiet your coach feels.

[JamieGeek]

Having used some on the RV in the past I would suggest Flex Seal. I know it sounds funny to use some of the "as seen on TV" stuff but it is very similar to the stuff sprayed in car wheelwells to seal and dampen noise.

You can even get it by the bucket! (Amazon).

In my case I used it to seal up the area behind the taillights.

[jabrabu]

I have similar issues with my Chateau. The wood behind the wing walls delaminated because it wasn't sealed. And everything underneath is very corroded/rusty. My RV was driven in December and got road salt on it, which made things even worse. I've had grounding issues causing errors in the leveling system, and I'm sure it's because of the excessive corrosion underneath.


I have also found gaps in some of the storage compartments and other floor penetrations that I could see light through, so I used expanding foam and flex seal to seal them up.

[Long & Winding road]

Same thing hear with my 2017 Axis. At first I was overwhemed by the amount of touching up and small fixes to be done (inside and outside). But let it soak in and just do one job at a time (for 52 weeks! LOL).

About two mo ago I purchsed one tube of black silicon and when all the way around and sealed up everything I could reach under the RV that looked like it needed to be sealed.

That only took about an hour so its not as bad as it looks time wise.

Then about a month later I purchaed some of that Flex seal and sprayed in the areas I could not reach before. I still have another can I will use on the notorious leaky tail lights and I might put a layer around the metal parts of the steps (Under coach) and the fenderwells to dampen more noise.

I am also on my 2nd pack of 100 count zip ties. The first round I took care of the real bad zip tie job under RV then the 2nd pack I used about 40 more to make it even better and I a few spares for furture projects and maintance.

Its not that bad of a job and it give you more confidence your RV will be Okay in rain storms.

[blw2]

Mine is exactly like that. While it's not even close to how I would specify it, or how I would do if building it myself.... but... I don't think all of that is really so much an issue.

I think that if these areas were so sensitive to moisture there would be some serious problems after just one drive in the rain. Mine is getting a few years on it now, and as of the last time I had a look around under there I had no obvious issues.

In fact, I'd be hesitant to completely caulk and seal all of those areas...some maybe, but not all. Virtually impossible to completely dry it in, and when water does get in it'll have no place to go so it'll just stay there and have all the time it needs to do it's thing.....and that's when you'll have problems (such as the rot I had behind my tail lights).

I'm not sure, but I believe that the plywood is probably some sort of exterior grade, so the glue is going to separate with simple water contact. I would have liked to see marine grade, or at least pressure treated plywood used here, but at least it seems to be exterior grade. Case in point, your last picture. In this exact same area, I had an issue on one side but not the other....but it was a leak from above that did it. Seriously shoddy work up on my roof membrane and the nose cone skin left me with a slow leak, that ran down the frame above into this little bulkhead wall on the passenger side. Because the water couldn't get out it stayed in there and rotted out significant areas till it finally worked it's way down to the bottom edge you show in that picture.

With all that said
for areas that you feel need to be sealed, I'd guess that a traditional undercoating would probably work for some...or maybe something like flex seal. Some larger openings could probably use some spray foam, or caulk...depending

but definitely not silicone. IMO that stuff is horrible. It's like those split lock washers that you see almost everywhere, but that really serve no purpose.... except it's even worse. The lock washer at least does no harm in most cases.

Silicone on the other hand will prevent anything from ever sticking or sealing that area again, without significant effort. It's a horrible adhesive, and because it doesn't stick well, it's a horrible sealant....then it leaves a nasty residue.

I've thought a lot about silicone, and the only examples I've been able to come up with where silicone seems to work well is for glass fish tank corners (where it's factory applied in what I guess to be a very carefully controlled way... and the other is the RTV sealant used in places like engine gasket surfaces...where it's not depending so much on it's adhesive qualities as it is just forming a simple rubber gasket.

[oleflier]

I just went through drying out tail lights when i notice paper below window (inside) bubbling. I heard on other blog that this is common. I would like to find out if windows are leaking or are aluminum frames sweating. I was hoping to find out because they look tough to handle,and I would want to have my fix ready before I try. These blogs are great.

[JamieGeek]

Originally Posted by oleflier

I just went through drying out tail lights when i notice paper below window (inside) bubbling. I heard on other blog that this is common. I would like to find out if windows are leaking or are aluminum frames sweating. I was hoping to find out because they look tough to handle,and I would want to have my fix ready before I try. These blogs are great.

If you are talking about the wallpaper below the front driver and passenger windows: Yes that is common in Axis/Vegas units (I had my passenger side wall rebuilt by Thor).

Take some of the screws out on the bottom of the window trim ring you should be able to see where the leak is coming from if its coming from the windows (others have seen the leak come from the awning mount on the outside).

[Lt Keefer]

I agree with doing it a little at a time. I spend a couple of hours every other day looking for and fixing minor faux paus from Thor's total lack of quality. I even follow this routine while on the road. Luckily, I have not found any show stoppers, but the list of minor annoyances is not getting any shorter either. I really like my Hurricane, but I will never buy or recommend anything from Thor ever again.

[Stolbert1]

I Recently purchased thor 2019 miramar 37.1
2x4 inch gaping hole on floor. Between break foot peddle and firewall.

Also right next to it, OSB Exposed on undercarriage

Anybody else have this issue? what is it suppose to look like under there?
What is proper way to remedy?

[Judge]

I have a Class C E-450 and there is not much in the way of undercoating. I thought of professional undercoating but there is a rat nest of wiring running all under the coach. I don't want undercoating all over it in case I need to repair something electrical later.

The Flex Seal idea is a good one.

Cleaning up the wiring mess under the coach is on my (long) list but I think I'll add using some Flex Seal to protect as much as I can on my own makes more sense.

[MichFigs]

Originally Posted by gmtech16450yz

This is a perfect example of shoddy Thor assembly and workmanship that most owners would never see unless they really looked.


My '18 Vegas had pretty much the same issues underneath. One of the first things I noticed when my wife was driving was the huge amount of road noise coming from the door step area. It ended up being like in your pictures, lots of gaps in the sheet metal and framing. Sealing up all that greatly reduced the road noise in that area. So how many "happy" Thor owners are driving around with excessive, unnecessary road noise and don't know it?

Here's what I used underneath my Vegas.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I also completely backed the entire front fiberglass cap with this and also black spray on undercoating. The whole front end of the Vegas went from hollow sounding, rattly and loose to solid and quiet. So go for it! Insulate and waterproof away. It will absolutely make a difference in how solid and quiet your coach feels.

Have to agree with GMTech on the "shoddy Thor assembly" comment After taking delivery of our Vegas in late 2017, one of the first things I did was get underneath and fill jn protrusions, wire ways and just gaps with expanding foam. Then tied up wires and harnesses with lotsa zip ties!

Next on advice of one of my mechanic friends, purchased a wax based undercoating that sprays on with an aluminum gun and an air compressor. Very nice stuff to work with (about $200 for everything including two gallons of product) and easy to control on when applied. Entire job took less than two hours to do chassis/underbody. Have gone back annually in the spring re-coated and still have a gallon of product left over.

Will look up the product name when we get back from Warren Dunes and post the name.

Happy Father's Day to all you Dads.

[Bob Denman]

another Sprinter Chassis here...
Time to do some creeping under the RV, and figure out how many spary bottles of Flex-Seal I might need.

[txc2936@yahoo.com]

Since Winter is coming, and this was a nice day in Nov. I got under the RV and inspected every inch along the bottom edges. No corrosion found. I spray a light layer of clear flex seal along the seam between the lower cap and side walls, This seems to be the first place corrosion will start. All the screws are 1/2 driven, just enough to hold the lower cap on, but there is a gap that can collect water.

Never had this RV on salted roads, and picked it up in Nov a few yrs back, 2 weeks prior to the first snow in Ohio. I also check the plywood closeouts around the step well, that would be the first spot for wood rot. That gets a coat also.