Bathroom Vent Fan Caulk Replacement Turned Full Restoration

What started as a simple task of replacing the aging caulk around my RV's bathroom vent fan quickly turned into a much bigger project. I initially planned to remove the old caulk, reseal the edges, and call it a day. However, upon closer inspection, I discovered that the fan casing had rusted significantly. Rather than replacing the entire fan, I decided to restore and improve it by removing the rust and applying a durable powder-coated finish.

• If you choose to replace the bathroom fan, it is available on Amazon: VENTLINE/DEX VP543 6" 12V Powered Round Vent
• Butyl Tape for sealing fan into roof: Dicor BT-1834-1 Butyl Seal Tape - 1/8" x 3/4" x 30' 
• Polyurethane Sealant: Sika Sikaflex-221 White or Sikaflex 521 White (more UV resistant)

Removing the Fan Assembly

The first step was to remove the fan cap, which was secured by two screws. With the cap off, I had access to the fan case, which was fixed to the roof with eight self-tapping screws. Once I removed these screws, I was able to lift out the fan assembly.

The fan was originally sealed to the roof using butyl sealant, with a bead of caulk around the casing and roof. I carefully scraped away the old caulk and butyl, making sure not to damage the roof surface. It was clear that the factory paint on the fan case had deteriorated, allowing rust to take hold over time.

The picture shows rust debris from the fan casing embedded in the butyl seal. The fan power wires use barrel-type connectors and can be easily disconnected.

Severely rusted bathroom vent fan casing.

Restoring the Fan Case

Instead of replacing the entire vent fan, I opted to restore and improve it. The original factory finish was simply painted metal, which had not held up well against years of exposure to moisture and the elements. To give it better long-term durability, I decided to:

• Remove the Rust – I used a combination of sanding and rust remover to clean off the corroded areas.
• Apply Three Layers of White Powder Coat – Unlike standard paint, powder coating offers superior resistance to moisture, corrosion, and UV exposure. I applied three generous layers to ensure maximum protection.

The fan motor mounts were removed before powder coating and re-riveted afterward.

Reinstalling the Fan

Before reinstallation, I thoroughly cleaned the roof opening for the fan. With the fan casing fully refinished, I reinstalled it on the roof by first connecting the power wires and applying fresh butyl tape to ensure a watertight seal. I secured it with #10 ¾" stainless steel screws and applied a new bead of high-quality exterior caulk around the edges. Finally, I reattached the fan cap, completing the restoration.

After cleaning the roof vent opening and removing the old butyl sealant.

New butyl tape is applied around the opening, with extra layers on the lower portions to even out the final surface, ensuring the fan sits flush and creates a complete seal.

The fan is secured with eight stainless steel screws. Tighten them evenly to ensure it sits level and creates a complete seal with the roof. The screw heads are covered with sealant (not shown).

I then use painter's tape and electrical tape to outline a circle around the fan, helping shape the caulking for a cleaner, more professional finish.

Fully sealed. Use a soapy water spray to help smooth the sealant. Avoid using alcohol on Sikaflex sealant, as it can prevent proper curing.

With the vent cap secured, don't mind the small solar panel mounted on top; it powers a DIY vent fan for the holding tank roof vent.

Final Thoughts

What started as a routine caulk replacement turned into a much larger restoration project, but I’m glad I took the extra steps to refinish the fan case. The powder-coated finish should provide far better weather resistance than the original factory paint, extending the life of the vent fan significantly.

This unexpected project serves as a good reminder that sometimes, when tackling minor repairs, you uncover hidden issues that require extra work—but in the end, it’s worth the effort to do the job right!