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Old 11-13-2020, 06:26 PM   #1
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Brand: Thor Motor Coach
Model: Majestic 23A
State: Missouri
Posts: 7
THOR #20977
Dust problems in the motorhome

Many of the places I want to travel to in the motorhome (former CA rental, Thor Majestic 23A), involves driving on gravel roads and of course they are dusty, and a lot of this dust makes it's way into the back of the coach. At first it looked that my side door was sprung a little bit at the bottom, but I think I've fixed that. But on a resent trip to the family farm to help with harvest, I found a lot of dust making it's way into the coach in the area of the cabinets that are over the rear tires. In looking under the coach in that area, there are gaps between the underside of the coach and sidewalls, so I believe that is where the dust is getting in. So I need to fill in this area, but the question is what should I use? Expanding foam, something like Flex Seal, or the tape used to seal the seam on the roof (don't remember it's name) ? But before I do this, is there a negative for using some type of sealant as it may trap moisture that leads to rot? Or does someone have a better idea? I should mention, I have an advanced degree in "Southern Engineering," and while most of the time my projects work out pretty well, every once in a while my "home brewed" fixes compound the problem, and that's what I want to avoid in this case. Any help or suggestions are appreciated. I guess what I'm asking is what should I use to seal the bottom edge of my coach?
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Old 11-13-2020, 07:10 PM   #2
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Brand: Still Looking
Model: Tiffin Wayfarer 24 BW
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THOR #8860
If it doesn't come off the road: you'll just track it in anyway...
Camping is an outdoor activity that still has the benefits of a T.V., a Fridge, and a nice bed...
We've learned to accept a little dust as part of the fun.
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Old 11-13-2020, 07:29 PM   #3
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The trick is to pressurize the inside more than the outside. How to is the difficult part.

Just opening a side window creates a venturi effect (?) and that causes a low pressure inside, sucking dust in the back, but if you add a deflector of some sort, you force air inside, thus pressurizing it and dust will not get in the cracks but 'blown' out.
I have read of some reversing the roof vent cover thus creating a "ram air' inlet, some have reversible roof vent fan motors (something I will try next summer) that appear to work. Good luck and let us know what works for you.
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Old 11-13-2020, 08:48 PM   #4
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THOR #8860
Eat lots of beans before the trip... The theory is sound.

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Old 11-13-2020, 10:31 PM   #5
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How big is the gap? If it is rather narrow, maybe a bead of painters caulk will fill the gap. Painters caulk does not last forever and it will fall out in a few years. If the gap is rather wide, take a measurement and buy some caulk backer the next size bigger. Stick it in the gap and see if that helps. I would stay away from expanding foam as it is messy. A 20 foot piece of caulk backer 5/8 inch in size is only 4 or 5 dollars at Home Depot.
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Old 11-14-2020, 05:54 PM   #6
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Brand: Thor Motor Coach
Model: Majestic 23A
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THOR #20977
Quote:
Originally Posted by Bob Denman View Post
If it doesn't come off the road: you'll just track it in anyway...
Camping is an outdoor activity that still has the benefits of a T.V., a Fridge, and a nice bed...
We've learned to accept a little dust as part of the fun.
Ah, no Mr. Bob, this is not a little dust. It's more like, "OMG,. Doesn't this guy ever clean out his RV?" in addition to all of the dust invading the coach are, I'm also loosing heat and a/c from these holes, too.

I was able to get a better look on the underside of the unit around the wheel wells and there's at least an inch gap at the top 1/3 of the wheel well. Its plenty big enough for the dust to migrate up along the side wall and into the lower cabinets. This is just on the right side, I haven't looked at the left rear tires yet. It's a little difficult for me to crawl under the thing as I'm not a small person.
I purchased some 4 inch wide Decor seal tape that I'll use. There were also gaps in the expanding foam around various drains and hoses in front of the right rear tires too. It looks like a poor job was done at the factory and not due to repairs from an accident.

I've got the rest of the coach pretty well sealed up, now it looks like I'll be spending some time crawling under the thing to seal things up too.
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Old 11-14-2020, 06:58 PM   #7
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Then that's a horse of a different color...

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Old 11-14-2020, 07:20 PM   #8
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Old 11-15-2020, 02:45 AM   #9
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THOR #20977
Quote:
Originally Posted by Bob Denman View Post
Then that's a horse of a different color...

https://www.thorforums.com/forums/at...1&d=1605380305
That horse must be so embarrassed.
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Old 11-18-2020, 07:56 PM   #10
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Model: Majestic 23A
State: Virginia
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I have the same RV as you and I haven't had that issue. Now I'll have to go outside and look up from the bottom of my rig to see if there are any gaps.

I would vote for expanding foam in those gaps. As for keeping it from falling out of the gap maybe some Eternabond on the bottom of the gap to hold it in? Keep in my that thee is a lot of vibration going down the road so this may not work. The next possible solution would be a wide board or plank wedged into the gap.
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Old 11-18-2020, 10:32 PM   #11
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We also had a big problem with dust in the back of our ACE 30.1. It was built with cheap materials and sloppy craftsmanship. That said my most recent attempts included stuffing fiberglass insulation into the large gaps and caulking in any other openings. Take the drawers out and start gooping it up. I put insulating tape on the cover that accesses the valves for winterizing and placed screws to anchor it down. We haven't driven it on dirt roads since my last attempt so I can't give you a report on how successful I was. Fingers crossed! I liked the ideas on creating positive pressure. Will try that next if this doesn't work.
I learned recently that if you use foam on the undercarriage to use the grey colored so the mice don't eat it.
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Old 11-19-2020, 03:38 AM   #12
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There is more that dust in that gap. Road dust and oils. You really need to clean and degrease for anything to stick and seal. If it is not sealed, water will penetrate. With most of the gap sealed, the water will stay and black mold may occur.
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Old 12-02-2020, 06:55 PM   #13
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Model: Palazzo 33.2
State: Georgia
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We had the same problem with our Palazzo - severe dust and even small debris in and around the rear cabinet., I removed the drawer on the bedside cabinet and found I was looking directly down through the floor to the ground - there was an incomplete bottom to this cabinet with a 9 inch gap in the floor. I fabricated a 1/4" plywood piece and glued it in place. That solved our dust problem.
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