YourRubberRoofIsSupposedtoChalk.Here'sWhatIsn'tNormal.

A rubber RV roof does several things that look alarming and are completely normal, and a couple of things that look minor and are not. Owners routinely get those two lists backwards. They scrub hard at chalk that was never a problem, and they use a cleaner that quietly causes the problem that actually is one.

Most of what follows comes straight from Dicor, one of the major suppliers of RV roofing. It is worth reading as a manufacturer's view of its own product, because it is more candid than most of what circulates on forums.

Normal: the white chalk

EPDM is designed to oxidize at the surface. Dicor's FAQ says it plainly: their EPDM roof is supposed to oxidize, and over a dozen years it may lose around ten percent of its thickness that way, which they describe as normal. The powdery white residue on your hands and the white haze on the roof are that process.

The catch is where the chalk goes. Rain carries it down over the sidewalls, where it mixes with dirt and leaves streaks. So chalk is not a roof problem, it is a cleaning schedule. The FAQ recommends cleaning the roof at least four times a year with a medium-bristle brush, which removes the loose chalk before the weather moves it somewhere you can see it.

Normal: air bubbles in the membrane

This one causes the most worry. You walk past the rig on a warm afternoon and there is a soft bubble in the middle of the roof that was not there in the morning. The manufacturer's answer is that bubbles come and go with temperature and humidity, that they can form over decking seams from the twisting a rig does in transit, and that they do not affect the roof's performance. Their advice is explicit: do not puncture them.

Their reasoning is worth knowing. A membrane installed without being stretched has room to expand and contract. A bubble that comes and goes is that slack doing its job. Cutting it to make it lie flat creates a hole in a waterproof layer to fix something that was not wrong.

Normal: ripples around new sealant

After a roof is resealed, owners sometimes see the membrane rippling or lifting slightly right beside the new beads. The explanation in the FAQ is that the lap sealant carries a small amount of solvent that evaporates during curing and bites into the membrane to form the bond. The membrane lies back down as the sealant cures, which can take up to two weeks, longer in cool weather.

So rippling in the first couple of weeks after a reseal is expected. Rippling that is still there a month later is worth asking about.

Chalk, bubbles that come and go, and ripples beside fresh sealant all look like trouble. None of them are.

Not normal: swelling and loose areas

This is the important one. The FAQ names two signs that a previous owner used petroleum-based products on the roof: swelling, which shows up as uneven thickness in the material, and loose areas where the membrane has let go of the deck. Petroleum distillates make EPDM swell and balloon, and that damage does not reverse.

The difference from a normal bubble is behavior. A normal bubble moves with the weather and the membrane around it looks uniform. Petroleum damage looks thick and puffy in patches, feels different underfoot or under your palm, and stays.

The common sources are products people reach for without thinking about the roof: general-purpose cleaners and degreasers, tire shine and protectants with petroleum carriers, bug and tar removers, and any conditioner not made for rubber roofs. Citrus-based cleaners and harsh abrasives are on the same do-not-use list. A cleaner that works beautifully on the sidewalls and then gets rinsed down from the roof edge is how a lot of this starts.

Not normal: tears, punctures, and pulled edges

Branches, hail, a dropped tool, or a ladder hook dragged across the edge can all cut a membrane. Small tears are very repairable. According to the FAQ, a properly applied patch should last as long as the membrane itself, which is a strong statement from the people who make the membrane. The key word is properly: the area has to be cleaned and prepared for the patch to bond, and a patch stuck over dirt and chalk will not hold.

Look along the edges too. The membrane should run cleanly under the edge molding on both sides. If it has pulled back, curled, or lifted at a corner, water has a path under it, and that needs addressing before it spreads.

Not normal: stains that will not come out

The same FAQ warns that fruit, tree sap, and heavy environmental fallout left on the roof for a long time can cause stains that cannot be removed, and that roofs parked in those conditions may need more frequent cleaning to avoid premature deterioration. In the Valley that usually means a rig parked under an oak, a pine, or a fruiting tree in a backyard. The stain itself may be cosmetic. The deterioration around it is not.

A small detail that matters more than it sounds

The company also recommends staying away from roof products that smell fruity or flowery, because the scent attracts birds, bees, squirrels, raccoons and other animals. Anyone who has found a nest in a roof vent or chewed sealant around an antenna base will appreciate why that is in a roofing manufacturer's FAQ.

What a good care routine looks like

• Clean the roof at least four times a year with a mild, non-abrasive cleaner made for rubber roofs and a medium-bristle brush. Rinse the sidewalls as you go so nothing dries on them.
• Use nothing with petroleum distillates, citrus, or abrasives on the membrane, and be careful what runs down onto the roof edge from products used elsewhere.
• Leave the bubbles alone.
• Inspect the sealant every time you clean. You are already up there.
• Move the rig out from under fruiting and sap-dropping trees if you have any choice in where it sits.

If you bought your rig used and you are not sure what the previous owner put on the roof, it is worth having someone look for swelling and loose areas before you invest in sealant or a coating. Both of those go on top of the membrane, and neither one fixes what is wrong with it.