The black streaks running down every stored RV’s sidewalls are runoff trails — rainwater carrying oxidised roof residue over the edge and down the fibreglass. Cleaning them is routine RV washing; stopping them means dealing with the roof they come from.
Where the streaks come from
RV roofs — especially rubber membrane roofs — oxidise and chalk in UV. Rain lifts that residue, mixes in dirt and pollen, and drains over the sides in the same paths every time, concentrated at awning rails, corner mouldings and around fixtures. The streaks are simply the roof’s condition, published down the walls.
That is why washing walls alone never lasts: the source recharges the streaks with the next rain.
Getting them off
Dedicated black-streak removers dissolve the oxidised residue without attacking fibreglass gelcoat or decals — applied, briefly dwelled, and rinsed at low pressure. Set-in streaks on chalky, weathered sidewalls take more work and sometimes leave ghosting where the gelcoat itself has oxidised.
High pressure is the wrong tool on an RV generally: it finds every seal, seam and decal edge, and water intrusion is the one problem worse than streaks.
Stopping the cycle at the roof
A properly cleaned roof sheds dramatically less residue, and a UV protectant on the membrane slows the chalking that feeds the streaks. Roof care is also leak prevention — inspecting seams and sealant while cleaning catches the failures that end in interior damage.
Wash the roof first, then the walls, always. And a covered or treated roof turns streak season from monthly to occasional.
Walls, roof, awning and glass in one visit, wherever it is parked. Send a photo and the length and we will quote it. Read more about RV washing →