Limited Lifetime Warranty GacoDeck GacoDeck GacoRoof GacoShield

Application Instructions/Specifications

View the GacoDeck online video or the DVD application guide included in your GacoDeck Kit before beginning your project. All surfaces must be completely clean and dry - without wax, dust, oil, asphalt or contaminants. Do not apply GacoDeck if rain is expected. GacoDeck is not recommended over asphalt coatings or dimensional lumber.

Surface Preparation

The GacoDeck Kit includes everything you will need to get started.

Figure A

Figure A: Tape off termination points.

Figure B

Figure B: Apply GacoDeckFill to all joints and cracks. Smooth GacoDeckFill flush with deck surface.

Figure C

Figure C: Seal joints and cracks by applying GacoDeck Tape between two layers of GacoDeck TopCoat.

Figure D

Figure D: Seal corners by applying GacoDeck Tape between two layers of GacoDeck TopCoat.

Figure E

Figure E: Perimeter Detail

Figure F

Figure F: Change of Plane Detail

Figure G

Figure G: Joint Detail.

Figure H

Figure H: Plywood Drain Detail.

Figure J

Figure J: Apply a uniform first coat.

Figure K

Figure K: Allow surface to dry until it can be walked on and then apply a second uniform coat.

Figure L

Figure L: Add GacoGrip granules to the remaining GacoDeck coating and mix thoroughly.

Figure M

Figure M: Apply texture coats with parallel overlapping roller passes.

Figure N

Figure N:Allow surface to cure for 48 hours.

Special Circumstances

During weather above 90 °F (32 °C), apply coating in morning or evening. Do not apply during temperatures below 50 °F (10 °C) or if temperatures will fall below 50 °F within 6 hours. Wait two or more days before using deck or placing heavy objects on surface. In extremely cold climates 10-15 °F (-9 to -12 °C) over a three month period, GacoDeck Primer must be used in conjunction with GacoDeck. If GacoDeck Primer is not used with GacoDeck, your deck could experience surface cracks. There are two modifications to the instructions above for extreme cold weather climates. First, all taping and flashing details must utilize GacoDeck Primer instead of GacoDeck TopCoat. Second, apply one coat of GacoDeck Primer at rate of 1 gallon per 200 square feet over entire surface prior to the first base coat. After primer is dry, you can follow normal GacoDeck instructions starting with “Base Coats” section.


Previously Coated Surfaces: The use of GacoDeck Primer is required. If surface is previously painted and has a glossy finish, lightly sanding the surface is recommended before applying GacoDeck Primer.
Plywood: Prepare all major seams, cracks and joints before cleaning the substrate with GacoWash; do not wash a new plywood deck. Allow surface to dry for a minimum of 48 hours. Prepare all cracks and seams following “Flashing, Caulking and Taping” directions. No primer is required for new plywood applications. If it is a previously coated plywood deck please see “Previously Coated Surfaces” directions. Do not use unsuitable grades of plywood. GacoDeck is NOT recommended for teak, cedar or redwood due to tannin bleeding on light colors. GacoDeck is not recommended if joints and cracks exceed 1/8" wide. Refer to the “Deck Construction and Preliminary Preparation” for full details.
Concrete: Concrete surfaces to receive GacoDeck coating must be structural concrete that is properly ventilated. ‘On grade’ concrete slabs must be poured over minimum 4" pea gravel base or equivalent. Concrete must cure and dry four weeks before GacoDeck application. Concrete surface should be smooth and free from rock pockets or voids without being burnished. Etching of concrete is not normally required. If concrete surface shows evidence of dusting or chalk, etch surface prior to coating application as follows: Apply diluted muriatic acid (3 parts water/1 part muriatic acid) at a rate of 75 square feet per quart following label directions and precautions. Allow the solution to work for 2-3 minutes. Scrub with stiff brush and brush with clean water to rinse from surface. Allow surface to dry for a minimum of 48 hours.

Surface Preperation

Remove large areas of dirt, mildew, grease and other debris with a broom. For general cleaning, apply GacoWash Concentrated Cleaner according to label instructions; do not wash a new plywood deck. Allow surface to dry for a minimum of 48 hours. Note: Drying time depends on weather conditions such as temperature, humidity and air movement. If more than 12 hours elapses between washing and application, wipe surface with a clean cloth to remove dust.

Flashing, Caulking & Taping

Flashing: All flashing must be flush with surface. If installing flashing, nail or screw every six inches. Care should be taken not to buckle the flashing during installation. Metal surfaces must be primed. Lightly sand surface and prime with exterior metal primer, according to label instructions. All flashing must be taped following the directions below.
Caulking & Taping: Apply GacoDeckFill according to application instructions to all joints, fastener indentations, cracks and transitions. GacoDeckFill is the only approved joint filler for the GacoDeck system.
Cut GacoDeckFill nozzle at an angle to the desired bead size. Start small, and cut further down if you need a larger bead. Load GacoDeckFill cartridge into standard caulking gun. Apply GacoDeckFill to all joints, fastener indentations, cracks and transitions from the flashings to the plywood. Apply when temperatures are between 50-90 °F (10-32 °C). Joint and crack size should not exceed 3/8" wide. If width is greater than 3/8", use backer rod. Smooth flush with deck surface using a putty knife. Allow GacoDeckFill to dry for 6 hours before using DeckTape. After taping, let dry for a minimum of 6 hours before coating with GacoDeck TopCoat and allow the surface to sufficiently dry prior to any sanding. If GacoDeckFill has shrunk or settled, reapply as needed following the listed instructions. Note: Longer dry times may be required for cold temperatures, high humidity or when filler is heavily applied.

GacoDeckFill that is allowed to dry more than 24 hours should be wiped with a damp cloth prior to top coat application. Once the GacoDeckFill is fully cured, tape all seams, joints, cracks, flashings and changes of plane with DeckTape. Working in small sections, apply a 5-6" wide stripe of GacoDeck TopCoat. Cut the DeckTape to desired length, making all cuts with scissors. While coating is still wet, center the strip of DeckTape over the seams, joints, cracks and flashing. Embed smoothly into the coating. Immediately brush another layer of coating over the DeckTape, smoothing out any wrinkles with a brush. Verify the DeckTape is completely covered with TopCoat. If more than one piece of tape is used, overlap any adjoining pieces by a minimum of 1/2". Allow the surface to dry. Inspect tape when coating is dry or nearly dry, to ensure the tape is bonded to substrate and completely smooth. Press down any fish mouths or wrinkles, cutting and re-bonding if necessary. Once dry, inspect DeckTape for fish mouth cavities, wrinkles, bare spots and other defects, and repair as needed. For a seamless finish, lightly sand the edges of the coated tape with medium grit sandpaper using a palm sander or sanding block before applying the first top coat. To prevent dirt pick-up, do not leave DeckTape exposed; coat with GacoDeck TopCoat as soon as it is applied.

If the GacoDeck TopCoat will terminate where there is no natural break, use painter’s tape to create a clean, sharp edge.

Coating Application

Confirm the substrate is completely dry by laying a 4 square foot piece of plastic sheeting on the deck, taped at all four corners. After a minimum of 4 hours, pull back the plastic and verify there is no amount of moisture on the deck or plastic. If moisture persists, continue drying until moisture no longer exists.

Four coats are required; recommended final film build is 28 dry mils. GacoDeck must be applied at the proper rate of 100 sq. ft. per kit to ensure proper coating thickness. Failure to do so voids the warranty and may result in the product’s failure to provide a waterproof membrane. Mix before application to ensure uniform color and consistency.

Base Coats: Two base coats are required; apply at a rate of 0.75 gallons per 100 square feet by roller as received. Apply a heavy coat over the entire surface, including taped or flashed areas, in order to create the waterproof elastomeric membrane. Allow the first base coat to dry for a minimum of 2-4 hours. Apply second base coat as soon as the first coat can be safely walked on. Wrap roller cover in aluminum foil or plastic in between coats.
Top Coats:
Add all of the GacoGrip Texture Granules to the remaining coating. Stir thoroughly for uniform consistency. Apply two separate coats at a rate of 0.75 gallons per 100 square feet by roller as received. Apply first coat in a North-South direction and allow to dry for a minimum of 2-4 hours. Apply final coat in an East-West direction as soon as the first coat can be safely walked on. If more than 72 hours elapses between coats, clean with GacoWash according to label directions. Final coat should be allowed to cure for 72 hours (depending on temperature and humidity) before suitable for heavy objects or foot traffic.

Maintenance or Recoat

GacoDeck TopCoat will maintain your GacoDeck waterproofing system by renewing color and increasing durability. Every 5-7 years apply two maintenance coats of GacoDeck TopCoat mixed with GacoGrip Texture Granules (12 oz./gallon) at a rate of 133 sq. ft. per gallon. No primer is required.
TopCoat will also renew decks coated with acrylic, urethane or Hypalon® waterproofing systems. Apply one coat of GacoDeck Primer before applying two coats of GacoDeck TopCoat.

Deck Construction and Preliminary Preperation

Grades: Plywood should carry the trademark of the American Plywood Association. Grades “Exterior/APA A/C Group I” and “Exterior/APA B/C Group I” are suitable, as well as “Marine” grade plywood. Unsuitable grades are interior grade plywood with or without exterior glue, underlayment grade plywood, such as “C/C Exterior,” OSB, Waferboard and Exposure I markings, and Hardwood-Faced and pressure treated plywood. Do not use unsuitable grades. GacoDeck is NOT recommended for pressure treated, Teak, Cedar or Redwood. 

Installation: All panel edges, including tongue and groove plywood, should be supported on blocking or primary framing. Plywood should be continuous across supports with all edges in moderate contact. Ideally, plywood joints and cracks should be 1/8" – 1/4" wide.
Thickness of plywood and spans should meet the following minimums:
  - 1/2" for plank or other solid substrates only
  - 5/8" for supports 16" OC
  - 3/4" for supports 24" OC
  - 1-1/8" for supports 48" OC
Stagger joints when installing plywood over sheeted or dimensional (planked) decks.  

Repairs to Plywood: Plastic wood patch materials may be used to repair damaged plywood. Sanding before taping, especially at the joints, will improve the final appearance of the deck.
The deck should be sloped so as to freely drain, preferably to a drain or gutter. 1/4" slope per foot is recommended. Slope is a function of structural design, and the GacoDeck Kit cannot be used to provide such a slope where it does not already exist. A deck that lacks adequate slope may experience leaks at low thresholds, standing puddles or surface stains from ponded water and debris. Avoid soiling the fascia by incorporating a gutter or drain into your design. Insert drain flush with plywood. Install a positive drip so that drainage is outside the fascia.

Ventilation: Allow a minimum of 1" air space between the bottom of the deck and any thermal insulation. 

Nailing: Use corrosive-resistant screws and nails or hot-dipped galanized box nails only. The nails should be 6D for 3/4" or less plywood, 8D for 7/8" or more and 10D for 1-1/8" plywood. Space fasteners 6" on center, along panel edges and 12" on center in all directions in the field. Drive nails flush without indenting plywood.


Warning: A darker GacoDeck coating will reflect less sunlight, creating a potential increase in the temperature of your GacoDeck.

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  • When installing new plywood, make sure edges are butted together with minimal gaps.
  • Use of Bondo and Fix All type materials NOT recommended.
  • For plywood imperfections, use a solvent-based wood filler.
  • Use GacoDeckFill sparingly, and follow with a putty knife to ensure a smooth surface.
  • For a seamless finish, lightly sand the edges of the coated tape before applying the first coat.
  • Apply between 50° - 90 °F
  • GacoDeck Kit is a coating, which needs to be applied at a rate heavier than paint.
  • Before recoating, check that previous coat is dry to the touch, and doesn’t stick to shoes.
  • Allow at least 48 hours after finishing deck before replacing furniture or subjecting to heavy traffic.
  •  A darker GacoDeck coating will reflect less sunlight, creating a potential increase in the temperature of your GacoDeck.