Fiddlin' on the Roof: Motorhome Rubber Roof Replacement
May 26, 2009
Filed under Tech Tips
There may come a time when the rubber roof on your motorhome needs to be replaced. Whether
it’s because of old age due to sun and general weathering, damage from tree limbs or even
poor original installation, it’s the kind of job that can be done successfully and
effectively to make your roof as good as new.
While it is possible for an experienced
do-it-yourselfer to install a new roof, it’s a lot of work, and after reading the following
story you may conclude that the job is best left to the professionals. If you do decide to
go with a professional you’ll also enjoy the benefits of the work being warranteed by the
We recently spent some time at the George M. Sutton RV service center in Eugene,
Oregon, to observe a complete rubber roof removal and replacement project. Sutton service
technicians Mark Swanson and Pat Tallderday did the work and explained the step-by-step
details an owner would need to know to complete such a job. The material prices quoted here
are courtesy of the Sutton parts department per the manufacturers’ suggested retail
pricing, so your local prices might vary. The materials are available at most RV parts
Our project vehicle was an older Yellowstone Class C motorhome. Some minor roof damage, long ago
repaired, had allowed some leakage in the curbside front corner, and minor leakage had been
detected inside near the holding tank vent tubes. The original rubber roof had aged
ungracefully, so the owner decided it was time for a change. This project not only called
for a full roof replacement, a bit of deck underlayment repair was also in order.
Sutton’s techs started by removing all trim strips and
other fasteners, plus rooftop appliances, such as the air vents, sewage pipe caps, air
conditioners and so on. At this stage, it’s helpful to note which vent or fan goes in which
rooftop opening, and which trim strip fits where, for correct reassembly later.
old rubber roof loose is the most physically demanding part of this project. Properly
installed, the adhesive hangs tight, and ensures it’s necessary to peel the rubber back
using pure muscle. Doing so in a warm environment may help soften the adhesive. One trick
is to use a sharp utility knife to cut the rubber into strips between 6 and 12 inches wide,
and pull up a narrow strip one at a time. This Class C‘s roof was stuck tight and the newly re-exposed adhesive still
had a tacky feel to it. As the rubber comes up, it sometimes pulls some of the wood decking
with it, like pieces of the first layer of the lauan plywood, and that’s normal.
Small portions of the lauan underlayment had rotted near some
water leaks, so replacing those bad sections was the next step. The Yellowstone’s roof had
a polystyrene core assembled with a lauan plywood deck, and fortunately the damage was
isolated to the upper wood deck material.
Swanson used a framing square to mark the damaged
section perimeter, and then cut the piece out using a sharp utility knife. Most of the
rotted wood came loose without damaging the polystyrene underlayment, and gaps or holes
were patched with the wood filler used in the next step.
EPDM is thin and flexible so it
will reveal any defects in the surface over which it’s applied. Fix-it-All wood filler is
the product of choice for the Sutton technicians when prepping the surface for the rubber
installation. Loose chunks or splinters of wood must first be removed, and adhesive-backed
fiberglass joint tape, designed for plaster drywall work, is used to help reinforce the
joints before adding filler. The filler is troweled into any cracks, gaps or irregular
spots in the wood deck and, after drying, is sanded smooth. The smooth surface also makes
for improved adhesion by the rubber roof glue. The wood filler is allowed to dry overnight
before applying the roof adhesive and installing the rubber.
The new EPDM rubber and some
of the adhesives and sealants are from Dicor Corporation. Several standard-size EPDM rolls
are available to fit different RV widths and lengths, or you can place a custom order to
fit your vehicle. For this Class C, the techs used #13-1215, a 9-foot 6-inch by 30-foot roll,
which retailed for $564.
Sutton’s technicians used an air hose to clean the sanding dust
from the roof deck, but a vacuum, broom or shop rags will also work.
There are a couple of ways to engineer the rubber roof installation.
The first method, generally used for longer RVs, starts with unrolling the fabric the
length of the roof and positioning it to ensure it has roughly the same overhang side to
side and that it reaches all the way from end to end. This also verifies that the new
rubber is large enough to cover the vehicle. The techs then reroll the fabric about halfway
and finish the gluing-down procedure from there to one end, then they reroll the opposite
still-loose half and complete gluing it down. By starting in the middle, they know the
rubber is properly aligned for the opposite half of the roof, and, most importantly, the
part being glued down will likewise be suitably positioned.
Because this coach was a fairly
short vehicle, the Sutton techs used an alternate technique that involved starting at one
end with the fabric completely rolled up. They positioned the fabric and “squared it by
eye” to aim it at the opposite end of the rig, then began the gluing-down process, working
their way along the coach. These techs have done so many roof replacements they can eyeball
the rubber alignment and have the correct placement by the time it’s rolled to the far end
of the rig.
Dicor’s 901BA adhesive (msrp $59/gallon) is specifically designed for gluing
EPDM rubber to a porous substrate. The Sutton techs applied it with short-nap paint
rollers, applying about 24 inches across the roof at a time and working from the bare-wood
side of the roof. After laying down a healthy coat of the adhesive (but not enough to leave
puddles), they reached over and unrolled the rubber over the glue, pulling it snug as they
went. They used their hands to do the initial smoothing and pressing the rubber into the
glue. The 901BA is not a contact adhesive and is fairly slow drying, so it allows time to
reposition and work with the rubber as it’s laid down. Hand-held plastic squeegees, usually
sold as Bondo spreaders, serve well to work any remaining air bubbles from beneath the
rubber and ensure the rubber is bonded well to the wood deck.
Some rooftop obstructions,
such as holding-tank vent pipes, are very difficult to remove before installing the new
roof. It’s necessary to cut the roof rubber to fit over those pipes. This calls for some
guesswork, as the rubber is laid up to the obstruction, then an “X” is cut in the fabric
and it’s stretched up and pulled down over the pipe.
As each section of the new rubber is
applied, the technicians move back, lay down more adhesive and continue. When they reach
the end, they move to the new rubber side of the project, lay the last segment and work the
air bubbles out.
Although the hand-application and plastic squeegees eliminate most of the
air bubbles, it’s possible a few may remain. A household push broom is highly effective for
working any remaining bubbles out from under the new roof. As a rule, the technicians
prefer to stay off the roof when the adhesive is wet, but it is necessary to be on the roof
to work out some air bubbles and ensure proper rubber adhesion.
It’s recommended that the
new roof adhesive be allowed to cure overnight so it’s stable when it’s time to climb back
up and start reinstalling the roof vents and accessories.
Buttoning It Up
All of the original putty and sealers must be removed from the trim, vents, skylights and
other rooftop accessories. A putty knife works to remove those stubborn bits of dried gray
putty tape. There’s a plastic tool sold at auto body shop suppliers called a “puttybone”
that also does a good job if you’re working on a delicate surface, such as a plastic shower
stall skylight dome, and you don’t want to scratch the surface with a metal tool. You can’t
get a good seal unless you start with a clean surface.
After applying a new line of gray
putty tape to the underside of each sealed surface, the roof edge trim and end cap trim, as
applicable, are installed in their original locations. The technicians normally use new
fasteners because at this point it just isn’t worth it to reuse rusty screws. Before
installing each screw, the excess roof fabric is pulled snug under the trim strip to avoid
wrinkles. This can be tricky for one person to do alone, so a helper makes the job a lot
Once the trim is screwed tight, a sharp utility knife works well for trimming the
excess rubber hanging past the trim. By not cutting too hard or deep the wall material
isn’t damaged by the knife.
Back up top, the techs locate each vent opening and make an “X”
cut, almost corner to corner, with a sharp utility knife. The resulting flaps are pulled
down snug and can be left hanging loose or stapled to the wood frame lining each opening.
No adhesive is used for this step.
Any pertinent wiring related to rain sensors, fans or
lights is reattached with the vent or other device in its approximate location. Putty tape
is applied to the flange and the part is set loosely in position. Swanson goes inside the
motorhome to visually check each component if possible and make sure the vents, for
example, are centered in the opening before screwing them down.
A Dicor product called 501
LSW Lap Sealant (msrp $8) is the Dicor-recommended material, designed for use with EPDM
rubber roof fabric, for sealing screwheads, flanges and the like when the seal is on a
fairly flat surface. The 501 LSW type is fairly thin and after application in a “blob” it
flows down a bit and smooths itself before curing. For parts on vertical or steep surfaces,
such as the trim that holds the rubber to the RV side wall, Dicor 551 LSW (msrp $8) is
recommended because it’s a bit thicker and holds its shape until it dries. As is true for
the roof adhesive, allow the sealant to cure overnight before exposing it to the weather.
When the seal is between two hard surfaces, such as the edge trim and fiberglass wall or
end cap with no roof rubber in contact, Sutton’s techs recommend and use Sikaflex 221 (msrp
After much ado, that’s all there is to it. The new roof is
as good as when the motorhome rolled off the factory line – possibly even better – and its
owner should enjoy leak-resistant travel and camping for years to come.