Mildew growth on a truck bed tonneau cover can be a frustrating issue for truck owners. The unsightly black or gray spots and stains not only look bad but can also damage the cover over time. Understanding what causes mildew to grow in the first place is the first step to preventing and removing it.
What are the Ideal Conditions for Mildew Growth?
Mildew is a type of mold that grows in damp, humid environments. For mildew spores to grow and spread on your tonneau cover, a few key conditions need to be present:
Does Moisture Exposure Cause Mildew on Tonneau Covers?
Yes, moisture is the number one requirement for mildew growth. Mildew needs a consistently damp or wet surface to be able to germinate and thrive. On a tonneau cover, moisture can come from:
- Rain, snow, and condensation directly on the surface of the cover
- High relative humidity in the air
- Spills, leaks, or standing water inside the truck bed under the cover
If the cover is frequently exposed to moisture from these sources, it creates an ideal environment for mildew.
Can Lack of Airflow and Ventilation Promote Mildew?
Absolutely. Mildew spores thrive in stagnant, still air with no ventilation. If air is not able to circulate under and around the tonneau cover, moisture gets trapped and cannot evaporate. This creates a prime condition for mildew to grow unchecked.
Tightly sealing the cover or having no vents prevents air circulation and moisture from escaping. Areas with poor ventilation under the cover are more prone to persistent dampness and mildew growth.
Does Improper Storage Cause Mildew on Tonneau Covers?
Storing your tonneau cover while it is still damp or wet can definitely lead to mildew growth. The moisture gets sealed in with no way to dry out.
Ideally, the cover should be completely clean and dry before storing it. Storing it wet allows any remaining mildew spores to flourish in the trapped moisture while the cover is packed away.
Can Inadequate Cleaning and Maintenance Cause Mildew?
Yes, lack of regular cleaning and maintenance creates optimal conditions for mildew. Dirt, debris, bird droppings, and other grime that is allowed to build up on the cover can retain moisture and humidity.
As this trapped moisture supports mildew growth, the dirt and grime also provide food for the mildew. Neglecting routine cleaning gives mildew the two main elements it needs to spread – moisture and organic matter.
What Areas of the Tonneau Cover Tend to Get Mildew?
While mildew can appear anywhere on a tonneau cover, there are a few areas that seem especially prone to recurring mildew issues:
Do the Seams and Stitching Get More Mildew?
Seams, stitching, and any other areas where two materials join together tend to collect moisture and dirt. These crevices provide the perfect niche for mildew to take hold and proliferate.
Mildew spores have an easier time germinating and growing undisturbed in the cracks versus exposed surfaces that get more air circulation. Pay special attention to treating and cleaning mildew in the seams.
Do Sections With Poor Ventilation Get More Mildew Growth?
As mentioned earlier, lack of airflow is a major factor in mildew growth. Areas of the tonneau cover that lack proper ventilation are more likely to have persistent moisture accumulation.
Corner areas, the front bulkhead, and wherever the cover contacts the side rails or truck bed are prone to condensation buildup and poor air circulation. Be diligent about allowing air to get to these sections to discourage mildew growth.
Why Does the Underside of the Cover Get More Mildew?
Gravity causes moisture to run downward and collect on horizontal surfaces. The underside of the tonneau cover is prone to this moisture accumulation, especially if drainage holes or channels are blocked.
The underside is also harder to inspect, clean, and treat regularly. The lack of light and air movement also promotes mildew on this hidden surface. Make an effort to regularly clean and treat the underside.
What are the Best Ways to Prevent Mildew Growth?
Stopping mildew before it starts is much easier than removing an existing infestation. Here are some tips for prevention:
Should I Clean and Dry the Cover Regularly?
Make a habit of periodically cleaning your tonneau cover, especially after rain or snow. Use a mild cleaner and rinse thoroughly with fresh water. Wipe or allow the cover to completely air dry before sealing it up again.
Regular cleaning prevents dirt buildup that holds moisture and gives mildew a foothold. Proper drying inhibits mildew spore germination and growth.
Will Improving Ventilation Under the Cover Help?
Yes, ensure there is adequate airflow under the cover when it is closed. Prop up one side slightly, crack open the tailgate, or open vents along the side rails or bulkhead.
If there are no built-in vents, you can add stick-on mesh ventilation patches. Allowing moisture to evaporate rather than being trapped will significantly reduce mildew risk.
Should I Store the Cover Somewhere Dry and Well-Ventilated?
Never pack up a damp tonneau cover for storage. Always store it clean and completely dry. Place desiccant moisture-absorbing packs under the cover while in storage.
Store in a dry, well-ventilated area out of direct sunlight and away from extreme temperatures. Avoid overly humid basements or garages. The storage space should allow air circulation around the cover.
Are There Any Mildew-Resistant Coatings or Treatments?
There are several mildew-resistant products made specifically for tonneau covers. Vinyl covers can be treated with bleach mixtures or mildew-resistant coatings.
Fabric covers are better cleaned with vinegar, mild soap solutions, or an anti-mildew camping gear spray. Always test any treatment on a small hidden area first before applying it to the whole cover.
Reapply these treatments periodically as directed to make the cover as mildew-resistant as possible. Mildew-resistant wax coatings for wood plank covers are also available.
What Causes Existing Mildew to Spread on Tonneau Covers?
If mildew has already taken hold on your tonneau cover, prompt action is needed to stop it from spreading further. Here’s how mildew growth can proliferate:
Does Moisture Exposure Make Mildew Spread Worse?
Continued moisture exposure causes existing mildew patches to keep growing. The mildew produces countless microscopic spores that are dispersed around the cover.
These spores are so tiny they can spread through the air to surrounding areas. Anywhere the spores land that remains damp allows new mildew colonies to take root and expand.
Can Opening the Cover Expose New Areas to Mildew?
Opening an already infected tonneau cover can spread mildew growth in a couple ways. Air currents can disperse mildew spores as soon as the cover is opened.
Areas that were not previously exposed get contaminated with spores. Leaving the cover open also allows sunlight and fresh air circulation. This sudden change in conditions causes stressed mildew cells to burst and release more spores.
Any parts of the cover that remained damp are now exposed to these reproductive spores and can develop new mildew growth.
Do Touching or Moving the Cover Spread Mildew?
Touching mildewed areas then touching other parts of the cover will transfer spores on your hands. Dragging the cover over surfaces, rolling it up, or reinstalling it can all spread mildew.
The friction disturbs existing mildew and shakes loose fresh spores. These are then transferred wherever the cover makes contact as it is moved and manipulated.
Why Does Removing the Cover Not Fully Get Rid of Mildew?
Once mildew has taken hold under the tonneau cover, removing the cover does not solve the problem. The truck bed still contains mildew spores that can reinfect the cover later.
Mildew may continue to grow unchecked on the truck bed while the cover is off. When the cover goes back on, the mildew is still there waiting. Always treat the truck bed surface thoroughly when treating a mildewed cover.
Neglecting this step means mildew will return quickly after cleaning the cover.
How Can I Effectively Remove Existing Mildew from My Tonneau Cover?
If you already have mildew established on your cover, consistent treatment and thorough cleaning will be needed to get rid of it:
Should I Use Household Bleach or Vinegar to Kill Mildew?
For vinyl covers, a diluted bleach solution is effective at killing mildew and preventing regrowth. Make sure to rinse thoroughly.
For fabric covers, vinegar is a milder anti-mildew treatment. It kills mold and removes odors. Use white vinegar diluted with water and rinse thoroughly.
Will Scrubbing Help Remove Mildew Stains and Residue?
Vigorous scrubbing with a soft brush helps remove deeply set mildew stains, residue, and spores that cleaning alone will not eliminate.
Scrubbing also helps cleaning solutions penetrate and act more effectively. Pay extra attention to scrubbing crevices and seams.
Is It Effective to Use Mildew-Targeting Sprays or Wipes?
Yes, using a dedicated anti-mildew solution in conjunction with scrubbing gives the best results. Look for ones formulated for vinyl, fabric, or automotive use.
Wipes are convenient for spot application on visible mildew spots. Sprays are useful for large-scale treatment of the entire cover surface and hidden underside.
Why Should I Dry the Cover Thoroughly After Cleaning?
It is critical to completely dry the cover after any mildew removal process before putting it back on the truck. Remaining moisture will allow mildew to regenerate from any leftover spores.
Park the truck in the sun and allow the cover to dry out completely. Aim fans under the cover or use a wet-dry vac to remove pooled water after cleaning the underside.
Does Treating the Truck Bed Surface Help?
Yes, always thoroughly treat the truck bed with the same mildew-killing cleaning process as the cover. Remove any remaining organic debris.
If you neglect the truck bed, spores still present will immediately reinfest the clean cover. Treating only the cover provides temporary improvement at best.
How Can I Stop Mildew from Coming Back After Treatment?
Getting rid of mildew is only half the battle – you need to prevent it from quickly returning. Here are tips on keeping mildew at bay after treating an infestation:
Will Reapplying Mildew Treatments Help?
Yes, periodically retreat the cover with anti-mildew cleaners or coatings after the initial deep cleaning. This maintains residual mold and mildew resistance between deep cleanings.
Ongoing treatment is needed because you can’t remove 100% of spores. The small amount remaining will multiply into new growth if left untreated.
Should I Improve Ventilation Under the Cover?
Proper ventilation is key to stopping the moisture conditions mildew needs. Keep the cover partially open whenever possible or install mesh vents along the rails or rear bulkhead.
For hard covers, prop open the rear hatch window for airflow. Minimizing standing moisture will greatly reduce recurrence.
Is Parking the Truck in the Sun Effective?
Yes, sunlight has a fungicidal effect and can inhibit surviving mildew spores from taking hold again. Open the cover and park the truck in full sun whenever possible.
Ultraviolet light exposure helps deactivate mildew spores and dry out any lingering moisture that would allow the mildew to return quickly.
Will Keeping the Truck Bed Clean Help?
Be diligent about keeping the truck bed clean and dry at all times. Remove any items or debris that can retain moisture and provide “food” for mildew.
Keep the bed free of leaks and standing water. A clean, dry truck bed environment gives mildew little opportunity to return after removal.
Left unchecked, mildew can quickly spread to damage your whole tonneau cover. Understanding what environmental conditions promote mildew growth is the key to prevention. Moisture, poor ventilation, dirt, and improper storage or cleaning habits are the main culprits.
If mildew already exists, deep cleaning plus ongoing preventive care is needed to stop regrowth. Improve airflow under the cover, keep the truck bed dry and clean, and reapply anti-mildew treatments periodically.
With proper truck bed tonneau cover care and maintenance, mildew does not have to be an inevitable eyesore. A little proactivity goes a long way in keeping your cover free of ugly mildew stains for the long run. Implementing these mildew prevention and removal best practices will help maintain the appearance and longevity of your cover.