The RV Roof Sealant Has Cracked and It Leaks Around the Vents
The sealant around the roof vents has dried and split, water is getting in, and the fix is a reseal on a schedule, with the sealant made for flat roof work
The short answer
Lap sealant is a wear item, not a lifetime fitting. Sun dries it, it cracks, and the cracks open at the fittings you cannot see from the ground: vents, skylights, the air conditioner base. The fix is a routine, not a rescue. Inspect the roof twice a year, clean the old sealant back where it has split, and reseal with Dicor 501LSW, the self-leveling form made for flat roof work. The owner record for this sealant at Opentip, a parts retailer, runs to 279 reviews with a five-star display, and owners in it describe resealing vents, air conditioners, and skylights with it, some for twenty years of repeat use. Two limits print here. Self-leveling sealant runs on a slope, so raised and vertical work takes the non-sag form instead. And this sealant ages out the same way the old one did, which is why the inspection row comes first on this page.
Why does this happen?
The sealant fails on a calendar, not by accident. It sits in full sun, flexes as the roof moves, and dries out over seasons. The surface crazes, then splits, and the split sits at the edge of a fitting where water pools. By the time a stain shows on the ceiling inside, the crack has been open for a while.
The wrong sealant makes it worse. Silicone does not bond to lap sealant or to most RV roof membranes, and nothing bonds well to silicone residue afterward. Owners who resealed over old sealant with hardware-store silicone inherit a joint that lets go and is hard to clean back. The roof takes lap sealant, and old lap sealant that has split gets cut back to sound material first.
The form matters as much as the brand. Self-leveling sealant flows out and finds the low spots around a fitting on a flat roof, which seals screw heads and flange edges with no tooling. On a vertical seam or a raised edge it runs off before it sets. Flat work takes the self-leveling tube; upright work takes the non-sag tube.
The fix, in order
In order, cheapest first. Stop at the step that solves it. The product step is the last resort, not the starting point.
Free step
Inspect the roof twice a year
The free step that prevents most of the damage: spring and autumn, walk the roof and look at every fitting, seam, and screw head. Cracked, lifting, or missing sealant goes on the list while it is still a tube job. The six-month rhythm is the step the rest of this page hangs on.
Habit step
Clean back to sound sealant
Cut away split and lifting sealant, wash the area, and let it dry fully. New sealant over dirt, moisture, or loose old sealant lets go early. Sound old sealant that is still bonded can stay and be sealed over.
The product step
Reseal flat fittings with the self-leveling form
Run Dicor 501LSW around vents, skylights, and the air conditioner base on the flat roof, covering flange edges and screw heads. It flows out flat and seals the hardware with no tooling. Raised and vertical joints take the non-sag form from the compare table instead.
The product for this step
Dicor 501LSW Self-Leveling Lap Sealant
Habit step
Log the date and recheck in six months
Write the reseal date in the RV's paperwork. This sealant ages in sun the same way the old one did, and the next inspection date is set by this one. Owners who reseal on the rhythm stop finding ceiling stains.
The evidence, in tiers
Tier 1 · The method
The method comes from RV technician guidance carried in the sources: inspect every six months, reseal on cracking, self-leveling sealant on flat roof work, non-sag on vertical work, and no silicone on a lap-sealed roof.
Tier 2 · This product
The large owner record for this sealant is carried by Opentip, a parts retailer: 279 reviews with a five-star display. Owners in that record name the jobs this page names, resealing vents, air conditioning units, and skylights, and repeat use across twenty years of RV ownership.
That record is a retailer's, printed here as a retailer's. It is owner evidence for the product, not the maker's test data, and this page treats it that way.
Tier 3 · What owners report
An independent weathered test of eleven roof sealants, run by All About RVs, found this sealant bonded best of the field on new roof material, and names its known wear pattern in the same report: it dries and cracks as it ages. That wear pattern is the reason the inspection row leads this page.
The alternatives, conceded where they win
| Option | What it is | The honest verdict |
|---|---|---|
| Dicor 501LSW self-leveling | Lap sealant for flat RV roof work, by the tube | The pick for vents, skylights, and flat fittings. Flows out, seals screw heads, and carries the owner record above. |
| Dicor non-sag lap sealant | The same sealant family in a form that stays where you put it | Wins on vertical seams, raised edges, and sidewall joints, where the self-leveling form runs. Most roofs need both tubes. |
| Roof seam tape | A wide sealing tape laid over seams and fittings | Wins on long straight seams and as a cover over sound old sealant. It is a bigger job to fit around vents and it costs more per roof. |
| Silicone caulk | The hardware-store tube most owners reach for first | Loses on this roof. It does not bond to lap sealant or roof membranes, and its residue stops later sealant bonding. Named here so it stays off the roof. |
The honest price comparison
The honest price comparison: two or three tubes and a morning on the roof, twice a year, against water damage that starts in the deck and walls and bills in the thousands. The inspection row is free and it is the row that decides which of those you pay.
Where it falls short
Below are the weaknesses from the product's own record: where buyers say it falls short, in their numbers.
- It ages out. The same drying and cracking that killed the old sealant will reach this one in seasons, not decades. The reseal is a rhythm, not a cure.
- It runs on a slope. Self-leveling sealant on a vertical joint or a steep fitting drains off before it sets. That work needs the non-sag form, and a roof usually needs both tubes.
- It seals the surface only. Water that has already softened the deck or stained the ceiling is a repair job first; sealant over damaged deck hides the damage, it does not fix it.
The product, in short
Dicor 501LSW Self-Leveling Lap Sealant
Questions people ask next
How often should RV roof sealant be checked?
Twice a year, spring and autumn. Look at every fitting and seam, and reseal any spot that has cracked, lifted, or pulled away. Most leaks start as a small crack found late.
Can I seal over the old sealant?
Over old sealant that is clean, dry, and still bonded, yes. Over split, lifting, or dirty sealant, no: cut it back to sound material first or the new seal lets go with the old.
Why not silicone caulk?
Silicone does not bond to lap sealant or to most RV roof membranes, and once it has been on a joint, other sealants struggle to bond there too. The roof takes lap sealant.
Which tube do I need for the side seams?
The non-sag form. Self-leveling sealant is made for flat roof work around vents and skylights; on upright joints it runs before it sets.
Opentip retailer review record for Dicor 501LSW, read November 2026 · All About RVs roof sealant weathered test, as reported by CamperFAQs, read November 2026
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