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Troubleshooting guide

RV delamination: What causes it, and what the makers actually document

A bubble in an RV sidewall is the outer skin coming away from whatever is glued behind it. The usual explanation is water, and water is one cause. It is not the only one, and that matters, because the assumption shapes both the diagnosis and the repair. What follows is what the people who make the materials and the walls say, including the parts they disagree about.

Last reviewed: Sep 27, 2026, against the sources listed below.

The short version: delamination is a failure of one specific glue line, the one between the exterior fibreglass and the substrate behind it. The substrate supplier calls it the Gold Bond and says it is the single bond that decides whether a wall delaminates. Water is one documented cause of several, and the others include glue coverage at the factory and temperature cycling. Check for moisture before assuming a leak, because the repair differs.

What it actually is

Azdel make the composite substrate that some RV walls use instead of plywood, and their definition is as direct as you will find: "Google defines Delamination as 'a structural failure where a material fractures, splits, or peels into separate layers. It is commonly caused by weak adhesion, mechanical stress, or environmental exposure'. We concur." They then say what it looks like in practice, in a sentence that names both layers: "Each image below shows a clear example of delamination. The exterior FRP layer has separated from the wood (lauan) layer behind it."

So the bubble is not a paint fault or a gelcoat fault. It is the outer skin no longer attached to the panel behind it.

Azdel go further and name which bond matters: "The most critical adhesive bond in laminated walls is the outermost glue line between the exterior fiberglass and its substrate. Also known as the 'Gold Bond', the strength and longevity of this all-important bond is largely what will determine whether or not you experience delamination." That single sentence is the whole subject. Everything else on this page is about what breaks that bond.

Water is not the only cause, and the substrate maker says so

This is the part that upends the usual story, and it comes from a manufacturer rather than a forum: "Some believe that water intrusion is required for delamination to take place. While this is indeed one cause, delamination can occur due to a number of reasons: poor glue coverage or workmanship; subpar quality in adhesive or substrate; frequent and/or extreme temperature fluctuations; and harsh weather conditions. Any one or a combination of these can initiate and accelerate delamination."

The temperature mechanism is documented separately, and it is a materials problem rather than a water problem: "As the temperature increased, FRP expanded but lauan contracted. As the temperature decreased, FRP contracted and lauan expanded... The result: no matter which direction the temperature fluctuates, lauan is continuously fighting with the FRP to move in the opposite direction, initiating and speeding up the delamination process."

That is a substrate supplier describing plywood as the wrong material for the job, which is a fair reading of their commercial interest, but it is also a specific physical claim you can check against your own situation. A bubble on a wall that has never been wet, on an RV kept in a hot climate, fits this explanation better than it fits a leak.

Where water is involved, Azdel describe the sequence on a plywood-backed wall: "Wood warping... Breakdown or rotting of the wood fibers... Breakdown and reduction in the adhesive bond between the wood layers themselves and the bond between the wood and the exterior FRP." The wood fails first, and the glue line follows it.

How the wall is built, from the makers who build them

Jayco describe their own laminated sidewall in five layers, and the order matters: "a layer of interior decorative plywood board is laminated... The exterior layer of the sidewall is formed utilizing a one-piece, glossy composite fiberglass panel... The final layer of the sidewall is a lauan plywood panel that is bonded between the fiberglass and the aluminum and foam wall assembly." On that build, the fibreglass is bonded to plywood, and the plywood is what the bubble separates from.

Jayco also make a claim about process that is worth quoting because it is the variable Azdel named first: "Jayco pinch rolling technique and the use of hot melt urethane allows Jayco to consistently provide 100% glue coverage."

Not every wall uses plywood, and a current maker's own repair document says so plainly. Brinkley, in a sidewall replacement procedure: "The fiberglass is backed with an azdel material which may separate from the fiberglass and stick to the structure." And Keystone, in a sidewall crack repair bulletin, note the layered version: "Please note the skin is backed with double layer of luan."

Grand Design's structural warranty treats the assembly itself as structural, which is the clearest statement of how serious this is: their defined "'Structural Components' consist of materials and/or workmanship directly attributable to Warrantor, namely, the laminated fiberglass sidewall assembly."

Checking it, and the mistake the instrument makers warn about

Before concluding water, measure. Protimeter, who make the meters, publish the thresholds and the method: "pin-type meter measurements should be used to confirm the readings found by a pinless meter and are the most accurate." Scan first to find the area, then confirm with pins.

Their scale, for a wood-based material, is dry at 6 to 16.9 percent, at risk at 17 to 19.9, and wet at 20 percent and above. They also explain the unit: WME stands for wood moisture equivalent, "a representative measurement of moisture content in a material as if it were wood", which is the right frame for a slide or sidewall floor because the material behind the skin is wood-based.

And the warning that will save you a false diagnosis: "Metal is a moisture meter's worst enemy. Conductive... contact with metal makes for moisture meter false readings. Areas that are actually dry will seem incredibly moist." RV walls contain aluminium framing and, on a slide-out, steel gear racks. Reading wet beside a metal member may be the meter reading the metal.

On a fibreglass or composite laminate specifically, the marine-style meters use a comparative index rather than a percentage. Tramex describe theirs as taking readings on "the comparative scale (0 to 100)", penetrating up to about 30 mm, and they are explicit about the limits: "Persistently high moisture readings may indicate an osmotic condition, but any diagnosis must include a thorough visual examination", and the instrument "will not detect or measure moisture through any electrically conductive materials or coatings."

What no RV maker publishes is a moisture threshold for their own sidewalls. The figures above are from instrument makers, and they are the best available rather than an RV standard.

The seals that lead to it, and the interval the makers specify

Where water is the cause, the entry points are documented and they are specific. On a slide-out they are documented separately, in the slide-out leaking guide, where the maker names the window seal rather than the roof. Winnebago publish a sealant callout sheet naming the locations by part: "Side marker light Sealant A... Roof to Sidewall transition on Roofcap Sealant A... Roof to Rear Trim Joint Sealant B... TV Antenna... Radio Antenna Sealant B and C... Edge Molding Sealant A." Airstream name their own list: "external seams and joints, such as end-shell segments and around window frames, light bezels, beltline and rub rail molding."

The maintenance interval is where the makers are stricter than most owners expect. Grand Design's structural warranty requires it as a condition of any claim: "Maintain all exterior seals and sealant, which must be inspected every 3 months to assure there are no gaps or voids and maintained annually." They add that if you seek a repair related to seals or sealant, "you must provide documentation acceptable to Warrantor that confirms completion of sealant inspections and maintenance for coverage consideration." Keystone give the same cadence for the roof: "any attachments, seams, or joints in the roof material require maintenance every 90 days."

Crane Composites, who make the exterior skin, state the stakes from their side: "A water tight seal is necessary to maintain the integrity of the composite wall system. Follow the RV manufacturer's guidelines. Damage caused by moisture in the RV wall will void any warranty."

Ninety days is short. It is also the interval the makers put in writing, and two of them tie warranty coverage to whether you did it.

What the makers document about repair

What is documented is re-skinning, not injection. Brinkley's sidewall replacement procedure and Keystone's sidewall crack repair bulletin both describe removing and replacing the skin, and Keystone's bulletin includes the structural check that should come first, because a wall can crack for reasons that have nothing to do with water: "Inspect frame welds at sidewall securement plate(s). Take photos. Repair if necessary", and repair cracked joints with aluminium gussets.

That is worth holding onto. A crack or a bubble can be the visible symptom of a broken weld or a structural overload behind the skin, and Grand Design have run a customer satisfaction campaign for exactly that on a limited number of fifth wheels: "concerns of excessive frame flex or wall securement in the front upper deck area... due to a combination of manufacturing variations, an overload condition, or hitch modifications."

What is not documented by any RV maker found for this page is a low-viscosity epoxy injection procedure for a delaminated wall. Injection is a well-known technique and the materials exist, but the makers document replacement, not injection. Nor is there a maker-published answer to the question every owner actually asks, which is when a delaminated wall is worth repairing and when it is not. Those figures circulate widely and none of them come from a manufacturer, so this page does not repeat them.

Opening a wet wall safely

If you are cutting into a wall that has been wet, this is the part to read twice. OSHA, on porous materials: "As a general rule, if a porous material has been wet for over 48 hours it is best to remove and replace." That is a strong instruction and it applies directly to a water-damaged RV wall.

On protection, OSHA require for "areas greater than 100 ft.2, areas where mold is heavy... or areas where substantial dust is generated" an approved respirator, at minimum a half or full-face N, R or P-100, along with non-vented goggles, long gloves and protective clothing. The EPA set the same 100 square feet as the point where full containment is recommended.

The EPA also give the clock, and it is shorter than most people assume: dry wetted materials or remove them within 24 to 48 hours.

What this costs

The honest answer is that this page cannot give you a number, because no manufacturer publishes one and the widely quoted figures come from service providers rather than makers. What the makers do state is the shape of the decision: the bonded sidewall is a structural component in Grand Design's warranty language, Crane say moisture damage voids their warranty, and the documented repair is replacement of the skin rather than a patch.

That sets the order to work in. Seal maintenance costs a tube of sealant and an afternoon every ninety days, and two makers make it a condition of coverage. A moisture meter costs little and tells you whether the wall is actually wet. Only then is there a repair decision, and it is a large one. The step that is cheap, repeatable and documented is the one worth doing first, and the interval is not annual.

Sources