Dicor makes its lap sealant in two versions that share a formula family, the same six colors and the same 10.3 oz tube. The difference is how the bead behaves after it leaves the nozzle. Self-leveling (part numbers starting 501LS) flows out flat, so it is made for horizontal surfaces. Non-sag (part numbers starting 551LS) holds the shape you gun it in, so it is made for vertical surfaces and edges. Pick by the angle of the surface, not by the roof material. This guide uses Dicor's own product pages, FAQ and roof care handbook.
The short answer
- Flat on the roof (around vents, vent pipes, antenna bases, skylight frames and over screw heads): Dicor Self-Leveling Lap Sealant. Dicor lists it "for horizontal surfaces" and describes it as a seal "along the roof's edges, air vents, vent pipes and screw heads".
- On a vertical or sloped face (roof-edge trim, termination rails): Dicor Non-Sag Lap Sealant. Dicor lists it "for vertical surfaces" and names the roof's edges and termination rails.
- Most roof reseals need both: self-leveling across the top, non-sag where the roof meets the edge trim.
What the two have in common
According to Dicor, both versions are HAPS-free, compatible with EPDM, TPO and PVC membranes, and adhere to aluminum, mortar, wood, vinyl, galvanized metal, fiberglass and concrete. Both are UV stabilized, and Dicor says neither will stain or discolor the roofing they are applied to. Dicor's FAQ answers the TPO question directly: its 501 and 551 sealants are compatible with EPDM, TPO and PVC membranes.
Both are a secondary seal. The primary seal under a vent or skylight flange is butyl, either butyl seal tape or Dicor's gunnable butyl sealant, which Dicor describes as "a watertight primary seal between lapping substrates and joints". Lap sealant goes over the top of the flange edge and the screws.
Colors and part numbers
| Color | Self-leveling (horizontal) | Non-sag (vertical) |
|---|---|---|
| White | 501LSW | 551LSW |
| Dove (Bright White) | 501LSD | 551LSD |
| Tan | 501LST | 551LST |
| Grey | 501LSG | 551LSG |
| Ivory | 501LSV | 551LSV |
| Black | 501LSB | 551LSB |
All are 10.3 oz tubes for a standard caulking gun. If you go through a lot of white, the case of 25 white self-leveling tubes (501LSW-25) is the same sealant by the box. Match the color to your roof membrane; Dicor notes colors can look different on screen.
Cure times
Dicor publishes the same approximate cure times for both versions, for 50 to 70°F weather:
| Time after application | Stage |
|---|---|
| 5 minutes | Skins over |
| 4 hours | Waterproof |
| 48 hours | 80% cured |
| 30 days | 100% cured |
So plan the job for a dry day with at least four hours before rain. Dicor's FAQ adds two things owners often worry about. Some bubbling or rippling while 501 cures is normal and typically goes away within a week or two. And if the membrane lifts slightly where you applied 501, that is the solvent "biting" into the membrane as it cures; Dicor says the membrane lays back down, which can take up to two weeks. Both can take longer in cool weather.
How to apply it
- Clean the area of all dirt, loose paint, rust, oil and grease, then let it dry (Dicor's directions). On a rubber roof, use a cleaner made for it, such as Dicor Rubber Roof Cleaner; Dicor warns against cleaners with petroleum distillates, harsh abrasives or citrus ingredients on EPDM.
- Deal with the old sealant. Dicor's handbook says minor cracks may only need cleaning and a new bead; sealant that is cracked, brittle, loose or curling at the edges needs more of the old material removed first.
- In cold weather, warm the tube to room temperature before use, as Dicor directs.
- Run self-leveling over flat joints and screw heads and let it flow. Use non-sag on the edge trim and any vertical face, and tool it if you want a neat line.
- Keep it dry for at least four hours.
When lap sealant is not the right Dicor sealant
| Job | Dicor product | Why (Dicor's description) |
|---|---|---|
| Window, entry door and compartment door perimeters, and joints in bare or repainted materials | Cap Sealant (351CS, clear, white, black or tan) | Non-sag, for bare or repainted materials, fast drying and paintable |
| A primary seal between lapping parts, skylights, vents, termination rails | Gunnable Butyl Sealant (451BSG-1, grey) | Dries putty-like; about 11 ft per tube at a 3/8 in bead or 24 ft at 1/4 in |
| A roof coated with Dicor Signature silicone | Self-Leveling Ultra Sealant or Non-Leveling Ultra Sealant | Dicor names Ultra Sealant for upkeep on its silicone-coated roofs |
| Some TPO roofs (see below), PVC, metal, fiberglass | Ultra Sealant | Dicor's catalog calls it "a great alternative for PVC, TPO, EPDM, metal and fiberglass roofing" |
Ultra Sealant is a polyether sealant that Dicor says contains no solvents or isocyanates, is non-yellowing and can be painted. It has a catch: Dicor says polypropylene roof accessories and some membranes must be primed with Dicor Ultra Sealant Primer first, and the primer must not be used on polycarbonate, such as polycarbonate skylights. We sell the primer only inside the Dicor EPDM Plus roof installation kit, so ask us before you plan an Ultra Sealant job.
A note on newer TPO roofs
Dicor's current FAQ says 501 and 551 work on TPO. Its older roof care handbook (printed in 2012) adds a caution: some TPO membranes RV makers began using in 2011 were not chemically compatible with the lap sealants then on the market, causing cosmetic bloating. The handbook's rule was: if the TPO has a fleece backing, lap sealant is probably right; if it has no fleece backing, use Dicor's Ultra Sealant System. If your RV is a 2011 or later model with a TPO roof, check the edge of the membrane, and if in doubt, ask your RV maker. Our guide to resealing an RV roof by roof type shows how Dicor tells EPDM from TPO.
How many tubes?
Dicor doesn't publish a linear-foot figure per tube for its lap sealant (it does for the gunnable butyl), so we won't guess one. For scale, Dicor's full-roof roof installation kit carries six tubes of lap sealant. Our Dicor roof reseal and coating kits group sealant, cleaner and coating by roof type. Buy a spare tube; running out halfway along an edge is the usual mistake.
FAQ
Can I use self-leveling sealant on the roof edge?
On a vertical face it will run, because that is what self-leveling means. Dicor labels it for horizontal surfaces and the non-sag version for vertical ones.
Is Dicor lap sealant safe on a rubber roof?
Yes. Dicor formulated it for EPDM. Its FAQ explains that the petroleum distillate in the sealant is only there for curing and evaporates as it cures; the warning against petroleum distillates is about cleaners and conditioners that sit on the roof.
Can I paint lap sealant?
Dicor lists its cap sealant and Ultra Sealant as paintable. It doesn't say that about lap sealant, so don't plan on it.
Should I reseal before coating the roof?
Yes, and early. Dicor's FAQ says to do sealants about two weeks before coating so they can cure. See how much Dicor roof coating you need.
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