Dear Dave,
Would you have an idea of what may be causing the “soot” at the rear roof vent on our 5th wheel? There’s nothing below it except some cabinets. Thanks. —Tom, 2021 Montana 3813MS
Dear Tom,
That is a wastewater tank vent which could be either the black or gray water tank. It allows air to vent out from the tank to reduce a vacuum effect when dumping the tank.
I would question if this is actually “soot,” but maybe rather black mold? Taking a closer look at your roof material, it looks to be an embossed rubber membrane and has several different wear patterns with some spots even bubbling slightly. This leads me to believe it has not been cleaned and conditioned as often as recommended.
I also notice that the black pattern is just to the left of the vent. Since it is directly next to the roof air conditioner, and especially the vent slots for the condenser coil, exhaust air would be blowing out that side and basically clears moisture and dirt in the front and sides.
Mold and mildew on rubber roofs
Mold and mildew forms on dirt and moisture that gets caught in the crevices of a rubber membrane, whether it is EPDM or TPO. It is a parasite that doesn’t actually penetrate the material but can stain it. Periodically cleaning the material and conditioning usually keeps the mold and mildew from forming. However, sometimes a more drastic approach is needed, which includes using a fungicide. There are several products on the market starting with a bleach solution. Read more about cleaning mold and mildew in my recent article here.
So, I would recommend cleaning it with a soft bristle brush, water, and some type of fungicide. Make sure you rinse the side of the rig down before, during, and after to make sure you don’t get any stains or chalking on the sidewall material, windows, and decals.
I would also recommend washing and conditioning your roof material with the appropriate conditioner for the type you have. Dicor makes several different conditioning products, or you could use 303 Protectant. Another product is ProtectAll Rubber Roof Treatment, which you can get on Amazon here.
Could it be soot?
As I stated before, I doubt it is soot unless you have an issue with an appliance running on propane. That would be the only thing I know of that creates soot. If you have an absorption refrigerator running on propane, there would be a flame in the burner assembly and the hot air and any soot would rise up the flue tube. If there was a rich LP mixture, you would get more soot. However, there is a cap at the top of the flue tube that would block the soot and accumulate there.
The hot air coming out of the flue tube is designed to go up and out the refrigerator roof vent or side vent, if your refrigerator is in a slide room. If there was an issue with excess soot from the refrigerator, it would be showing up at the refrigerator vent, not at the waste tank vent.
One other scenario is dust and dirt from underneath the rig rising up along the wastewater vent if it is not sealed. I have witnessed some black stains in bedroom closets where the back cap has developed a leak or gap. Then dust and dirt from the road and even exhaust enter the back cap and are drawn up into the closets. If there is a gap somewhere around the waste tank and the actual vent pipe is not secured, dust could penetrate the area and be drawn up the vent pipe while traveling. It’s a stretch, but as I often say, never say never when it comes to RVs! Although my guess is that it is mold and mildew.
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What is the scheduled maintenance for RV roof sealant? How hard is it to replace?
Dear Dave,
My fifth wheel is about three years old, and I live in it full-time. While periodically checking my roof, I noticed that some of the sealant around the vents is starting to look aged, but not cracked. How often should I apply new sealant (Dicor) before having to remove the old material and replace it completely? And how hard is it to remove? —Peter, 2021 Grand Design Reflection 337RLS
Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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Hard to understand why this TWO year old roof looks the way it does. Even if it never got properly cleaned it must have rained a few times & got some of the crud off. Seeing all those bubbles in that small of an area is indicating a defective roof material! Wonder what the rest of the roof looks like. I would for sure take Dave’s advice on cleaning it ASAP. After cleaning taking another serious look to see what all the roof looks like! Good luck, hope it all clears up.
Snoopy
Thank you, Dave.
The vent on this roof looks like the “attic” vents on my Montana. At the front and rear there are vents like this one the ventilate the space between the ceiling and the roof. Don’t know why there is that black stain though if that’s what his are. Never see that on mine.