To reseal a flat roof, first decide which job you have: sealing details (open seams, cut edges, flashings, pipe boots) or recoating the whole surface. Then follow the coating maker’s rules for your membrane: clean, dry, prove adhesion with a test patch, prime where the data sheet says so, reinforce seams with fabric, and apply the full gallons per 100 square feet. Most failed reseals skip one of those steps.
By The Roofing Brief Team. Last reviewed: October 2026.
This guide covers the when and how: which membrane takes which coating, what primer goes under it, how much material a roof needs, how often to recoat, and what the work costs. For choosing a specific sealant product, see our guide to flat roof sealant by membrane.
Key numbers at a glance
The figures below come from coating and membrane makers’ technical data sheets and two national cost guides. They are the numbers that decide whether a reseal lasts: field coverage, per-coat limits, primer rates, sealant yield, installed cost and inspection frequency. Treat each as the maker’s stated value for that product, not a universal rule for every brand.
| Item | Figure | Source |
|---|---|---|
| Silicone field coat (GacoFlex S20) | 1.5 gal per 100 sq ft on smooth surfaces, 2 gal on granulated or rough surfaces, for about 22 dry mils | Gaco S20 Product Data Sheet, rev. 08/2026 |
| Acrylic coat limit (GAF Quick Set Acrylic Top Coat) | No more than 1.5 gal per 100 sq ft per coat; air and surface at least 50°F and rising | GAF data sheet COMCO714 |
| Epoxy primer over asphalt (GacoFlex E5320) | 0.2 gal per 100 sq ft, 1 to 2 dry mils | Gaco coverage guide GW-5-1, rev. 08/2024 |
| EPDM lap sealant yield | About 22 ft per tube at a 5/16 in bead | Carlisle Sure-Seal EPDM Lap Sealant data sheet |
| Professional flat roof coating, installed | $0.75 to $5 per sq ft | Angi, updated Aug. 2026 |
| Inspection frequency | At least twice a year, spring and fall, plus after severe weather | NRCA |
Reseal, recoat or replace: which job does your flat roof need?
A flat roof needs a detail reseal when one seam, edge or penetration has opened on an otherwise sound membrane. It needs a recoat when an existing coating is worn but the roof underneath is dry and intact. It needs replacement planning when insulation is wet across a large area or the membrane itself is brittle. Coating makers restrict their recoat systems to roofs “in sound condition,” so the diagnosis comes before any product choice.
| What you find | Which job | Why | Source |
|---|---|---|---|
| One open lap, split cut edge, or cracked sealant at a pipe, curb or drain; rest of the roof sound | Detail reseal of that seam or penetration | A field coating does not glue an open seam shut; makers require open seams, tears and cuts repaired with like materials first | Gaco recoat spec RC-S20-38-20 |
| Existing coating chalky, thin or worn; membrane dry and attached | Recoat with a compatible coating | Recoat specs are written for a membrane “in sound condition” that needs surface renewal | Gaco recoat spec RC-S20-38-20 |
| Uncoated EPDM, TPO, PVC, mod-bit, smooth BUR or metal that is weathered but dry | First-time coating restoration | Listed as maintenance coating uses for silicone over weathered membranes | Gaco S20 PDS |
| Wet insulation found by an infrared or nuclear scan | Cut out and replace wet areas before any coating | Gaco requires the scan and removal of wet materials; Karnak says not to install its coating system if 20% or more of the roof is wet | Gaco RC-S20-38-20; Karnak spec 220.R-298 |
| TPO or PVC that has shrunk or turned brittle, or any single-ply with exposed scrim | Replacement planning, not coating | Gaco disqualifies these as coating substrates | Gaco spec ASP-S2000-22-10, sec. 3.1 |
| Water still standing 48 hours after rain | Fix drainage; if coating, pick a chemistry rated for it | NRCA defines that as ponding; GAF’s acrylic data sheet requires positive drainage | NRCA; GAF COMCO714 |
If the roof leaks now, find the entry point before you buy anything. Our guide to a flat roof leaking walks through tracing water back from the ceiling stain. When the scan or the age of the roof points toward replacement, compare the two paths in roof coating vs replacement.
How to reseal a flat roof by membrane type
Each membrane has its own seam repair method and its own list of coatings and primers that bond to it. EPDM seams take primer and pressure-sensitive tape, TPO and PVC seams are welded, asphalt roofs need a bleed-blocking base coat under white coatings, and metal needs fasteners sealed and rust primed. The table pairs each membrane with what the maker documents actually call for.
| Membrane | Reseal seams and edges with | Whole-roof coating options | Primer or base coat | Maker cautions |
|---|---|---|---|---|
| EPDM (rubber) | Clean and prime the lap, then a pressure-sensitive cover strip; lap sealant on the cut edges of reinforced EPDM | Silicone (Gaco lists weathered EPDM); acrylic (GAF Quick Set lists EPDM) | Gaco’s wet adhesion results for EPDM are with E5320 primer; GAF Multi-Purpose Primer at 0.33 gal per 100 sq ft on smooth single-ply | Scan for wet insulation first; GAF says priming “is recommended and may be required” |
| TPO | Hot-air weld a TPO patch after cleaning the aged sheet; Carlisle’s Weathered Membrane Cleaner is sold to prepare aged TPO for seaming | Silicone (Gaco lists TPO/CPA); acrylic (GAF lists TPO) | Per adhesion test and the coating maker’s sheet | GAF: new TPO should weather at least 30 days before acrylic; Gaco: brittle or shrinking thermoplastics are disqualified |
| PVC | Hot-air weld a PVC patch | Silicone; acrylic (GAF lists PVC) | Gaco’s wet adhesion results for PVC are with E5320 primer | Same brittleness and exposed-scrim disqualifiers as TPO |
| Modified bitumen, SBS | Like materials; Gaco’s asphalt spec calls for torch-applied or heat-fused granule APP for repairs before its silicone; Karnak uses Karna-Flex mastic with polyester fabric, three-course | White silicone only (Gaco); acrylic over a bleed-block base coat (GAF); aluminum asphalt coating (Karnak 298) | Gaco: A4271 BleedTrap base coat required over SBS, and E5320 required under S2000 on asphalt | Gaco: do not pressure wash asphaltic substrates; Karnak: new cold-applied mod-bit should weather 90 to 180 days |
| Modified bitumen, APP, and smooth BUR | Same as SBS | Same as SBS | Gaco: BleedTrap strongly recommended | Gravel-surfaced BUR is excluded by Gaco’s asphalt spec and by GAF Quick Set |
| Low-slope metal | Encapsulate fasteners and seal seams with brush-grade flashing and fabric | Silicone (Gaco); acrylic (GAF HydroStop system) | Rust-inhibitive primer on rusty areas (GAF); E5320 on galvanized (Gaco test data) | Gaco: add 15% to 40% material for panel profile; GAF: repair severely rusted metal before coating |
EPDM: reseal the laps, then decide on a coating
Most EPDM leaks start at a lap seam or a cut edge, so an EPDM reseal usually means cleaning and priming the seam, then covering it with a pressure-sensitive cured cover strip, and running lap sealant along the exposed cut edges of reinforced sheet. Carlisle rates its Sure-Seal EPDM Lap Sealant at about 22 feet per tube with a 5/16 inch bead.
A full coating over EPDM is a second, separate decision. Gaco lists weathered EPDM among the substrates for its S20 silicone, and its published wet adhesion results for EPDM are with E5320 epoxy primer underneath. GAF lists EPDM as an approved substrate for Quick Set Acrylic Top Coat. For rubber-specific seam work, see our guide to rubber roof repair.
TPO and PVC: weld the seams, coat only a sound sheet
Thermoplastic seams are heat welded, so resealing an open TPO or PVC seam means cleaning the aged sheet and welding new material, not caulking over it. Carlisle markets its Weathered Membrane Cleaner to prepare aged TPO for seaming. A coating can then renew the surface, but only while the sheet is still flexible.
Gaco disqualifies aged thermoplastic membranes “that shrink or have become brittle due to plasticizer loss,” and any reinforced single-ply worn down to exposed scrim. GAF asks that new TPO weather for at least 30 days before its acrylic goes on. For welded patch steps, our TPO roof maintenance guide covers seam care.
Modified bitumen and built-up roofs: block the bleed first
Asphalt roofs release oils that stain and soften white coatings, so mod-bit and smooth BUR recoats start with a bleed-blocking base coat. Gaco requires its A4271 BleedTrap over SBS and strongly recommends it over APP, smooth BUR and mineral cap sheets, at about 1 gallon per 100 square feet for a continuous 6 dry mils. Gaco permits only white silicone over asphalt.
The traditional alternative is an asphalt system. Karnak’s silver reflective specification lays fibered asphalt emulsion at 3 gallons per 100 square feet, embeds polyester mat, adds a second 3-gallon coat, cures it 7 to 10 days, then tops it with 298 Alumin-R aluminum coating at 2 gallons per 100 square feet. Gaco and GAF both exclude gravel-surfaced BUR from these coating systems.
Metal: seal fasteners and treat rust before the field coat
A metal roof reseal focuses on fasteners, end laps and side seams, because those move with temperature every day. GAF’s metal restoration sheet calls for securing or replacing loose fasteners, priming rusty areas with GAF Metal Roof Primer, encapsulating every fastener with brush-grade flashing, and three-coursing ridges and rakes with 12 inch fabric at 30 linear feet per gallon.
Corrugated and ribbed panels have more surface than their footprint, so Gaco tells estimators to add a 15% to 40% surface factor for metal profiles. GAF recommends repairing severely rusted metal before coating rather than coating over it.
Coating compatibility: what can go over what
A recoat must bond to whatever coating is already on the roof, and silicone is the main constraint. Gaco says existing silicone should be recoated with silicone and should not be primed, and its GacoRoof data sheet warns against recoating with acrylic or urethane. Acrylic and other elastomeric coatings can usually take a new coat after cleaning, an adhesion test and, where needed, a primer.
| Existing top surface | New silicone coat | New acrylic coat | Source |
|---|---|---|---|
| Existing silicone coating | Yes; clean it, do not prime | No; Gaco says recoat silicone only with more silicone | Gaco S20 PDS; GacoRoof Compliant PDS |
| Existing acrylic coating | Yes after an adhesion test; Gaco lists a wet adhesion pass over acrylic, and its recoat spec allows primer where testing calls for it | Usually yes after cleaning and a test patch; GAF Multi-Purpose Primer is rated for existing coatings | Gaco S20 PDS and RC-S20-38-20; GAF COMCO735 |
| Previously coated asphalt (aluminum or asphalt coating) | Only after the maker reviews it; Gaco asks applicators to contact Technical Services | Test patch and maker review | Gaco RC-S20-38-20, sec. 3.2 |
| Bare weathered single-ply (EPDM, TPO, PVC) | Yes with the primer the maker specifies | Yes; GAF says priming is recommended and may be required | Gaco S20 PDS; GAF COMCO714 |
| Bare asphalt (mod-bit, smooth BUR) | White only, over bleed blocker and E5320 (Gaco) | Over a bleed-block base coat (GAF) | Gaco GW-5-1; GAF COMCO603 |
If you do not know what is on the roof, treat it as unknown and run an adhesion test on each surface type. For how silicone and acrylic compare on ponding, reflectivity and cost, see our roof coating comparison.
How to recoat a flat roof step by step
A flat roof recoat follows the same order on every membrane: qualify the roof, repair it, clean it, let it dry, prove adhesion, prime, reinforce the details, then apply the field coat at the specified rate. GAF’s restoration sheets and Gaco’s recoat specification both put the moisture check and the adhesion test ahead of any coating, because those two steps decide whether the job bonds.
- Check for trapped moisture. Gaco’s recoat specification requires an infrared or nuclear scan and removal of any wet roofing materials. Karnak says not to install its coating system if 20% or more of the roof is wet.
- Repair seams, tears and blisters with like materials. Gaco tells applicators to fix open seams, tears and cuts before cleaning so wash water does not get into the roof.
- Clean the way your coating maker specifies. Gaco’s recoat spec uses GacoWash with a 10 to 15 minute dwell and a power washer over 3,000 psi, plus 1 part household bleach to 3 parts water on algae or mildew. Gaco also says not to pressure wash asphaltic substrates, while Karnak’s asphalt system power washes at a minimum of 2,000 psi with its own cleaner. Follow the sheet for the product you are using.
- Let the roof dry completely. Gaco warns that residual water causes blistering and that its drying assumptions are based on 70°F days with no rain.
- Run an adhesion test patch. GAF says to conduct test patches before starting work. Henry’s instruction for its 885 silicone sealant is to apply, let it cure fully, then pull one end. Gaco recommends wet and dry adhesion tests before bidding a recoat.
- Prime where the data sheet calls for it. GAF Multi-Purpose Primer goes on at 0.33 gal per 100 sq ft on smooth EPDM or PVC and must be topcoated within 48 hours. Gaco E5320 goes at 0.2 gal per 100 sq ft over asphalt. Do not prime existing silicone.
- Reinforce seams, penetrations and drains. Gaco’s asphalt spec embeds 4 inch polyester mesh in a 6 inch wide band of silicone at 1.5 gal per 100 sq ft, then encapsulates it. GAF three-courses loose seams with 6 inch fabric at 30 linear feet per gallon.
- Apply the field coat at the full rate and check wet mils. Gaco S20 goes on at 1.5 gal per 100 sq ft on smooth surfaces and 2 gal on rough ones. GAF limits acrylic to 1.5 gal per 100 sq ft per coat and applies the next coat perpendicular to the last.
- Keep traffic off until cured. Gaco S20 needs 24 to 48 hours before light foot traffic. Wet silicone is slippery, so plan a walk path.
When can you apply roof coating? Weather limits by product
Silicone tolerates cooler and damper weather than acrylic. Gaco S20 can be applied as long as rain is not expected within one hour, while GAF’s acrylic needs 50°F and rising with no rain, dew or fog in the 8-hour forecast. Asphalt-based systems sit in between but need long cure times before a topcoat.
| Product | Temperature | Rain and moisture window | Cure or recoat timing | Source |
|---|---|---|---|---|
| GacoFlex S20 silicone | Contact Gaco below freezing or above 120°F | Not if rain is expected within 1 hour | Dry at least 4 hours at 55°F; recoat within 4 to 48 hours; light foot traffic after 24 to 48 hours | Gaco S20 PDS, rev. 08/2026 |
| GacoRoof Compliant silicone (retail) | Not below freezing or above 120°F | Not if rain is expected within 2 hours | First coat dries 3 to 12 hours; minimum two coats | GacoRoof Compliant PDS, June 2015 |
| GAF Quick Set Acrylic Top Coat | Air at least 50°F; surface 50°F and rising | No rain, dew, fog or freezing in the 8-hour forecast | Skins over in 30 to 60 minutes; dry 5 hours at 75°F and 50% RH | GAF COMCO714 |
| Karnak 220 fibered emulsion base | 40°F to 100°F, humidity 85% or less | Not stated in the spec | Cure 7 to 10 days before the next coat | Karnak spec 220.R-298 |
| Karnak 298 Alumin-R aluminum | 50°F to 100°F, humidity 85% or less | Cure 24 to 48 hours before any moisture | Single coat | Karnak spec 220.R-298 |
| Henry 885 silicone seam sealant | 35°F and rising | Not if rain is expected within 1 hour | Tack-free 1 to 2 hours; cured in about 48 hours | Henry 885 TDS |
How much coating do you need to reseal a flat roof?
Coating quantity follows from the maker’s gallons per 100 square feet, and one gallon spread over 100 square feet is about 16 wet mils. A 1,000 square foot smooth roof takes about 15 gallons of GacoFlex S20 for 22 dry mils, or 20 gallons on a granulated cap sheet. Buy to the rate on the data sheet, then add waste for wind, texture and the bottom of each pail.
| System and surface | Maker rate | 500 sq ft roof | 1,000 sq ft roof | Source of rate |
|---|---|---|---|---|
| GacoFlex S20 silicone, smooth single-ply, metal or smooth mod-bit | 1.5 gal per 100 sq ft, one coat | 7.5 gal (two 5-gal pails) | 15 gal (three 5-gal pails) | Gaco S20 PDS; GW-5-1 |
| GacoFlex S20 silicone, granulated mod-bit | 2 gal per 100 sq ft | 10 gal (two pails) | 20 gal (four pails) | Gaco GW-5-1 |
| GacoRoof Compliant silicone, smooth roof | 1 gal per 100 sq ft per coat, two coats minimum | 10 gal | 20 gal | GacoRoof Compliant PDS |
| Gaco E5320 primer over asphalt | 0.2 gal per 100 sq ft | 1 gal | 2 gal | Gaco GW-5-1 |
| Gaco A4271 BleedTrap over SBS | 1 gal per 100 sq ft | 5 gal | 10 gal | Gaco GW-5-1 |
| GAF Multi-Purpose Primer, smooth EPDM or PVC | 0.33 gal per 100 sq ft | 1.7 gal | 3.3 gal | GAF COMCO735 |
| Karnak 298 Alumin-R over asphalt | 2 gal per 100 sq ft | 10 gal | 20 gal | Karnak spec 220.R-298 |
The film math explains why acrylic usually takes two coats. A US gallon is 231 cubic inches, and spread over 100 square feet (14,400 square inches) it makes a film 0.016 inch, or 16.04 mils, thick. GAF lists Quick Set Acrylic Top Coat at 55% volume solids, so its 1.5-gallon per-coat maximum dries to about 13.2 mils (16.04 x 1.5 x 0.55, a Roofing Brief calculation). Reaching 20 dry mils takes about 2.27 gallons per 100 square feet in total, which has to be split across two coats.
The same arithmetic checks Gaco’s silicone figure: 1.5 gallons x 16.04 x 0.95 volume solids is about 22.9 dry mils, in line with Gaco’s stated 22. Our roof coating mil thickness chart runs this conversion for other solids levels and warranty targets.
How much does it cost to reseal a flat roof?
A professional coating on a flat roof runs about $0.75 to $5 per square foot installed, per Angi’s August 2026 cost guide, or roughly $750 to $5,000 for 1,000 square feet. Acrylic sits at the low end and polyurethane at the high end. A spot reseal of seams and penetrations costs far less, and Fixr puts typical flat roof repairs at $300 to $1,100.
| Job | Cost | 1,000 sq ft at that rate | Source |
|---|---|---|---|
| Acrylic coating, installed | $0.65 to $1.75 per sq ft | $650 to $1,750 | Angi, Aug. 2026 |
| Silicone coating, installed | $1.50 to $2.50 per sq ft | $1,500 to $2,500 | Angi, Aug. 2026 |
| Bitumen (asphalt-based) coating, installed | $1.25 to $2.50 per sq ft | $1,250 to $2,500 | Angi, Aug. 2026 |
| Polyurethane coating, installed | $2 to $5 per sq ft | $2,000 to $5,000 | Angi, Aug. 2026 |
| Roof cleaning before coating | $300 to $625 per job | n/a | Angi, Aug. 2026 |
| Roof inspection | $125 to $350 | n/a | Angi, Aug. 2026 |
| Contractor minimum service fee | $150 to $300 | n/a | HomeAdvisor, June 2026 |
| Flat roof repair (spot work) | $300 to $1,100, average $700 | n/a | Fixr |
The 1,000 square foot column multiplies each guide’s per-square-foot range by 1,000. HomeAdvisor describes silicone as a coating that “doesn’t require a primer,” but Gaco’s own data sheet calls for E5320 primer on several substrates and BleedTrap over SBS. Ask any bidder which primer and base coat their price includes.
DIY materials for a 1,000 sq ft roof (Roofing Brief estimate)
Doing the work yourself on a 1,000 square foot smooth roof with a contractor-grade silicone costs about $887 to $990 in field coating at October 2026 retail listings, before primer, fabric and sealant. The table builds that figure from Gaco’s coverage rate and dated Google Shopping listings, so it changes when prices or the substrate change.
| Line item | Quantity | Listed price (Oct. 13, 2026) | Line total |
|---|---|---|---|
| GacoFlex S20 silicone, 5 gal, smooth roof at 1.5 gal per 100 sq ft | 3 pails (15 gal) | $295.50 (Arbor, S2000 white) to $329.92 (Lowe’s, S2022 gray) | $887 to $990 |
| Same coating on a granulated cap sheet at 2 gal per 100 sq ft | 4 pails (20 gal) | Same | $1,182 to $1,320 |
| GacoFlex E5320 primer, 2-gal kit (asphalt roofs need 2 gal at 0.2 gal per 100 sq ft) | 1 kit | $219.99 (City Mill) to $303.59 (Paint Supply) | $220 to $304 |
| Carlisle Sure-Seal EPDM Lap Sealant, about 22 ft per tube | 5 tubes for 100 ft of cut edge | $11.95 to $14.08 per tube | $60 to $70 |
| Carlisle pressure-sensitive cured cover strip, 6 in x 100 ft | 1 roll | $385 (CRS Supply) | $385 |
| Henry 183 reinforcing fabric, 4 in x 150 ft | 1 roll | $17.75 (Arbor) | $18 |
For comparison, a retail acrylic such as Henry Solar-Flex or Kool Seal listed at about $95 to $135 per 4.75 to 5 gallon pail, and fibered aluminum coatings at about $89 to $182 per 4.75 gallons on the same date. Use each product’s own coverage rate, not the silicone rate, to count pails. For a full repair budget by scope, see our flat roof repair cost breakdown.
How often does a flat roof need to be recoated?
A flat roof needs recoating when inspection shows the coating has worn thin, chalked or lost adhesion, and the maker’s warranty term is the best planning number. Gaco ties a 10-year term to 1.5 gallons per 100 square feet of S20 on smooth substrates. GAF’s acrylic specs run 10 or 15 years over asphalt and up to 20 over metal. Inspect at least twice a year either way.
| Roof or system | Planning interval | Source |
|---|---|---|
| Any flat roof | Inspect at least twice a year, spring and fall, and after hail, hurricanes or other severe weather | NRCA |
| GacoFlex S20 silicone at 1.5 gal per 100 sq ft (2 gal on granulated mod-bit) | 10-year term at that rate; heavier builds for longer terms | Gaco GW-5-1, rev. 08/2024 |
| GAF acrylic over asphalt | 10 or 15 year limited warranty, depending on the spec followed | GAF COMCO603 |
| GAF Premium Acrylic HydroStop over metal | 10, 15 or 20 year limited warranty, depending on spec | GAF COMCO607 |
| Acrylic coatings in general | Reapplication every 10 years or sooner | Angi; HomeAdvisor |
| Sealant at penetrations, laps and edges | Reseal when an inspection finds cracking, gaps or lost adhesion | NRCA inspection schedule |
Some contractor sites recommend resealing every 5 years. That figure does not appear in the maker documents reviewed here, which tie service life to dry film thickness, substrate and maintenance. A roof that ponds will wear coating faster in the low spots, so fixing drainage often stretches the interval more than a thicker coat. Our guide to ponding water on a flat roof covers the drainage fixes.
Do you need a permit to recoat a flat roof?
It depends on your jurisdiction. The 2021 International Residential Code, Section R908.3, lets a new protective roof coating go over an existing coating, BUR, modified bitumen, single-ply, metal or spray foam roof without tear-off. Section R908.3.1.1 does not permit a recover where the existing roof is water-soaked or too deteriorated to serve as a base.
Local adoption and amendments vary, so check with your building department before work starts. Angi lists roofing permits at about $100 to $500. A coating over a wet roof fails both the code test and the maker’s qualification step, which is another reason to scan before coating.
Frequently asked questions
What is the best way to seal a flat roof?
The best way to seal a flat roof is to match the method to the membrane: prime and tape EPDM seams, weld TPO and PVC seams, block asphalt bleed on mod-bit and BUR, and seal metal fasteners. Then coat the whole surface with a chemistry the maker approves for that substrate, at the full gallons per 100 square feet on the data sheet, after an adhesion test.
How much does it cost to reseal a roof?
Professional flat roof coating costs about $0.75 to $5 per square foot installed, per Angi’s August 2026 guide, so roughly $750 to $5,000 for 1,000 square feet. Acrylic runs $0.65 to $1.75 and silicone $1.50 to $2.50 per square foot. Doing it yourself with a contractor-grade silicone costs about $887 to $990 in field coating for 1,000 square feet at October 2026 retail prices.
How often does a flat roof need to be recoated?
Plan around the coating’s warranty term and your inspections rather than a fixed calendar. Gaco ties a 10-year term to 1.5 gallons of S20 silicone per 100 square feet on smooth roofs, and GAF’s acrylic specs run 10 to 20 years by substrate. NRCA recommends inspecting at least twice a year, so recoat when the film is thin, chalked or losing adhesion.
Why does my flat roof leak in heavy rain?
Heavy rain raises the water level on a low-slope roof, so water can reach a lap seam, a low flashing or a cracked sealant joint that stays dry in light rain. Clogged drains and scuppers make it worse. NRCA treats water still standing 48 hours after rain as ponding. Trace the leak from the interior stain to the nearest seam or penetration before resealing.
Can you put silicone coating on an EPDM rubber roof?
Yes, with the maker’s primer. Gaco lists weathered EPDM as a substrate for its S20 silicone, and its published wet adhesion results on EPDM are with E5320 epoxy primer underneath. Clean the rubber, confirm the insulation is dry, run an adhesion test patch, prime as the data sheet directs, then apply the full rate. Seams should be repaired with EPDM materials first.
Can you put acrylic over a silicone-coated roof?
No, not according to the silicone maker. Gaco’s GacoRoof data sheet says not to recoat it with acrylic, urethane or Hypalon coatings and to recoat cleaned GacoRoof only with more GacoRoof. Gaco’s S20 data sheet also says existing silicone should not be primed. Once a roof is silicone, plan on silicone for every future recoat.
Should you pressure wash a flat roof before recoating?
It depends on the substrate and the coating maker. Gaco’s recoat spec uses a power washer over 3,000 psi on previously coated roofs, but its coverage guide says not to pressure wash asphaltic substrates. Karnak’s asphalt system power washes at 2,000 psi minimum with its own cleaner. Follow the cleaning step in the data sheet for the exact product you are applying.
Sources
- Gaco, GacoFlex S20 Series Product Data Sheet, revised 08/2026.
- Gaco, GW-5-1 Silicone Roof Coatings and Accessories Coverage Rates, revised 08/2024.
- Gaco, RC-S20-38-20 specification for recoating elastomeric roof coating systems, revised 06/2021.
- Gaco, ASP-S2000-22-10 specification for modified bitumen and smooth BUR, revised 05/2020.
- Gaco, GacoRoof Compliant Product Data Sheet, June 2015.
- GAF, Quick Set Acrylic Top Coat data sheet (COMCO714), Multi-Purpose Primer data sheet (COMCO735), Acrylic over Asphaltic 5-Step Roof Restoration (COMCO603) and Premium Acrylic HydroStop over Metal 5-Step Roof Restoration (COMCO607), GAF document library.
- Karnak, Silver Reflective Coating System application guidelines, 220.R-298(KF).
- Carlisle SynTec, Sure-Seal EPDM Lap Sealant and Weathered Membrane Cleaner product data sheets.
- Henry Company, Tropi-Cool 885 100% Silicone Seam and Repair Roof Sealant technical data sheet.
- NRCA, roof system inspection guidance published in Professional Roofing magazine.
- Angi, How Much Does Roof Coating Cost per Square Foot, updated August 2026; HomeAdvisor, Cost to Seal a Roof, June 2026; Fixr, Flat Roof Repair Cost.
- International Code Council, 2021 International Residential Code, Section R908 Reroofing.