Liquid Roofing Installation Guides


Classic Liquid is a new liquid flat roofing system which combines the pragmatism and ease of 'straight out of the tin liquid' with fibrous incline, detailer and fabric additional options to give slope and upstand installation without slump - even up to vertical.

Giving the user the flexibility of liquid with the strength of fibre.

Quick Guide to liquid roofing Installation (for full guide to all Classic Liquid products and installation see pdf above)

ClassicLiquid Waterproof Coating is a single component rapid curing polyurethane liquid membrane that is easy to apply over existing roofing systems, creating a durable and seamless waterproof layer. Its formulation allows a fast curing, bubble free, single coat application roofing system to be created. Due to its excellent tensile strength, there is usually no need to incorporate a reinforcing fabric, unless it is applied over a bituminous substrate, making application a breeze

General Surface Preparation & Priming

Clean the surface to be treated with a high pressure washer or a stiff broom and soapy water to remove all oil,grease, wax contaminants, cement laitance and loose particles.

ClassicLiquid Primer must be applied to all surfaces prior to the application of the waterproofing membrane.


Make good all cracks and blisters and fill surface irregularities with a suitable product.

Allow to fully dry. Apply Primer at a sufficient coverage rate to seal the surface.

Primer coverage rates will vary dependant on surface porosity.

Allow primer coat to fully dry.

Any gaps in the substrate over 2mm wide or movement joints must first be filled with Joint Mastic prior to the application of the ClassicLiquid Detail Coating.

If the membrane is to be installed over timber decks, OSB3 T&G 18mm must be used. The T&G joints must first be “glued” together by applying Joint Mastic into the rebate. Boards are then pushed together and surplus Joint Mastic tooled smooth. The joints must then be reinforced by applying the Self Adhesive Tape equally across the joint. It is recommended to create a fillet or cant strip using Joint Mastic at the base of all upstands.

Application of Joint Sealer if required

Clean the joint thoroughly and ensure that no oil, grease, silicone or wax contaminants are present. For most

applications primer is not required unless onto a very porous or friable surface. If primer is required, use

ClassicLiquid Primer.


Bond area surfaces thoroughly to avoid the possibility of air bubbles being blown into the

uncured product should the substrate temperature rise. On applications where the depth of the expansion joint

exceeds the width, then it is necessary to use an open cell polyurethane backing rod (of suitable size) to ensure a

firm backing to the Joint Mastic against which it can be tooled off.

Slide the 600cc foil cartridge into the application gun, cut off the very end of the sealant packaging and fit the gun

with the nozzle that has been cut to deliver the right bead size for the given application.

Extrude the Joint Mastic into the joint ensuring that no air is trapped in the joint. Wide joints may well require more

than one pass of the application gun to ensure full contact of the Joint Mastic with the sides and bottom of the joint.

Tooling of the Joint Mastic is recommended immediately after application of the sealant to ensure that all air bubbles are excluded and a smooth finish provided, if other products are being applied over.

classicliquid_joint_mastic (1).jpg

Application of Primer

It is essential that the intended substrate is thoroughly cleaned with a high pressure washer; on smaller areas a stiff

broom and soapy water and rinse will suffice. Remove all oil, grease and wax contaminants, cement laitance and loose particles. Make good all cracks and blisters and fill surface irregularities with a suitable product. Allow to fully dry.

Apply Primer at a sufficient coverage rate to seal the surface. Primer coverage rates will vary dependant on the surface porosity. Allow the primer coat to fully dry (approximately 2 hours but this is dependent on ambient air temperature and humidity).

Coverage Rates

Approximately 0.1-0.3 ltrs/m2 dependant on the porosity of the substrate. For semi-porous substrates the coverage rate is typically 0.2ltrs/m2.


Clean tools and equipment initially with paper towels and then with a suitable solvent. Rollers and paint brushes will not be re-useable.


Product will discolour if used as an exposed sealer. This is purely visual and does not affect the performance of the membrane. If the primed surface has been rained on then the area must be dried and further primer applied.

ClassicLiquid waterproofing coating

Application of Membrane

Use a low speed (300rpm) mixer. Mix thoroughly taking care not to introduce air into the liquid, creating bubbles.

It is recommended that all detail and perimeter works are carried out before the main field areas.


On vertical surfaces, internal/external corner details and outlets/pipe collars, Detail Coating should be used at

approximately 1kg per m2 as this product is thixotropic so will not sag.


Waterproof Coating must be applied over this detail at approximately 1kg per m2. Apply the material with a roller,

brush or squeegee in one or two coats, ensuring that you achieve a bubble free and even application. Do not exceed

48 hours between coats as this will affect inter-coat adhesion.


Surfaces that have exceeded 48 hours between coats will need to be primed with Primer to ensure a proper bond to the previous coat.


Coverage Rates

Suggestion: If the area to be treated is substantial, it is good practice to grid out the roof to ensure that the recommended

coverage rates per m2 are achieved.


Clean tools and equipment initially with paper towels and then a suitable solvent.

Roller heads will not be re-useable.

classic liquid coverage chart


All substrates must be sound, clean and any bubbles and blisters must be made good before work commences. Waterproof Coating cannot be used in areas where the system may come into contact with chemically treated water such as swimming pools. It is not safe for fish ponds.