ROOF COATINGS

SI-COAT 461 silicone roof coating on an industrial roof

SI-COAT 461 Silicone Roof Coating for Industrial and Commercial Buildings

SI-COAT 461 RC is a high solids silicone roof coating made by CSL Silicones and distributed in Southern Africa by Technical Solution Supplies. It waterproofs flat and low slope industrial, commercial and agricultural roofs with a seamless, flexible membrane that withstands permanent ponding water and strong UV.

It also reflects most of the sun’s energy. The white coating is rated by the Cool Roof Rating Council with an initial solar reflectance of 0.856 and an SRI of 107.9. In a CSL case study, the building ran 7 to 9°C cooler inside after coating. As a result, it lowers cooling costs across South Africa’s hot climate zones, and it far outlasts acrylic and polyurethane coatings that need recoating every few years.

Why a Conventional Roof Coating Fails on South African Industrial Roofs

Most flat industrial roofs in South Africa carry torch on bitumen, an acrylic coating or a polyurethane coating. All three have limits that make them poor long term choices for local conditions.

Torch on bitumen becomes brittle in sustained UV, cracks along laps and seams as the structure moves, and carries a fire risk during installation on occupied buildings. It also absorbs heat, so it adds to the building’s cooling load.

An acrylic roof coating is water based and works well on pitched roofs that shed water quickly. On flat decks where water ponds, however, acrylic slowly takes up water and softens, so it loses adhesion, blisters and lifts. It also breaks down in strong sun within a few years, which means repeated recoating.

A polyurethane roof coating resists UV better than acrylic at first, but it still yellows and loses flexibility over time. In addition, it usually needs several coats.

SI-COAT 461 deals with all three problems. Silicone does not take up water, it stands up to UV, and it stays flexible. For that reason, it is the right roof coating chemistry for flat industrial roofs in Southern Africa. For a full comparison, read acrylic vs polyurethane vs silicone roof coatings.

Key Performance Properties

Ponding water. This is the most important property on flat roofs. According to the TDS, SI-COAT 461 withstands permanent ponding water without affecting its cured properties, so water that sits after rain does not break it down. Read more on ponding water on flat roofs.

UV stability. The silicon oxygen backbone does not break down under UV the way organic polymers do. So CSL describes 461 as having excellent durability, colour stability and chalk resistance, which matters under some of the highest UV levels in the world.

Flexibility. The coating keeps its properties from −60°C to 200°C, with 282% elongation at 23°C and 330% at −18°C. In other words, it moves with the roof through every hot day and cold night without cracking.

Breathability. With a permeance of 4.44 perms, trapped moisture in the roof can escape as vapour through the coating. As a result, it reduces the risk of blistering on damp substrates.

Cool roof. The white coating reflects most of the sun’s energy instead of absorbing it as heat. For example, the CRRC lists an initial solar reflectance of 0.856, an emittance of 0.89 and an SRI of 107.9. Read more on heat reflective roof paint.

Service life. CSL reports 461 roofs in service in North America for more than 20 years. Because it lasts far longer than acrylic or polyurethane, the lifecycle cost is much lower once recoating, labour and downtime are counted. Later, a sound silicone roof can also be recoated with silicone, with no tear off.

Approvals and Certifications

SI-COAT 461 meets ASTM D6694, the standard for liquid applied silicone roof coatings over spray polyurethane foam. It also holds UL Certification R40482, and FM approval as a maintenance coating. In addition, the Cool Roof Rating Council lists it as Product ID 1368-0002. It is Title 24 compliant, Miami Dade County approved and listed under Florida Building Code FL41816-R2. Finally, the white carries NSF Protocol P151 for rainwater catchment.

Where SI-COAT 461 Is Used

Warehouses and logistics centres. Large flat concrete decks hold water after every storm, and a single leak can damage stock worth more than the whole roof. SI-COAT 461 handles that ponding water where acrylic fails. See our article on silicone roof coating for warehouses and shopping centres.

Shopping centres and retail. The seamless membrane removes the laps and seams where sheet membranes fail on complex roofs, so tenants see fewer leak repairs.

Factories and food plants. In food, pharmaceutical and electronics production, one roof leak can mean a hygiene shutdown. A sound silicone membrane therefore greatly reduces that risk.

Agricultural buildings. Grain stores, packing sheds and equipment sheds have uninsulated metal roofs that swing hard between hot and cold. SI-COAT 461 bonds to metal sheeting and moves with it.

Mining sites and data centres. Processing plants and conveyor galleries combine dust, heat, UV and airborne chemicals, and CSL rates 461 for excellent tolerance to airborne chemical exposure. Data centres, on the other hand, need every bit of heat kept off the roof. Read more on roof coating for mining and data centre roofs.

Substrates SI-COAT 461 Is Compatible With

Concrete and screed decks are the most common substrate. The surface must be clean, sound and free from laitance, dust, grease and loose material.

Metal roof sheeting, including IBR, Chromadek and corrugated steel, usually needs no primer. However, remove loose rust, loose coating and contamination first, and do an adhesion test patch, as CSL recommends for all metal roofs.

Spray polyurethane foam is a standard substrate for silicone, and ASTM D6694 covers exactly that system. The coating also protects the foam from UV.

Existing coated roofs and single ply membranes can often be overcoated, which saves a full strip and replace. Always do an adhesion test patch first, and use a CSL primer where the test calls for one.

Bitumen and torch on membranes always need a primer before coating, because applying directly risks adhesion failure and bitumen bleeding through. For these roofs, CSL makes CSL 468 epoxy primer.

The Complete Roof Coating System

CSL also makes the products around the coating, and their data sheets are in the documents below. First, CSL 471 concentrated roof cleaner is a biodegradable detergent, free of petroleum solvents, for washing the roof. For asphalt and single ply roofs, CSL 468 is a two part, water based epoxy primer that improves adhesion and stops bitumen bleeding through. Then CSL 463 roof sealant and CSL 465 flashing sealant seal seams, fasteners, flashings, drains and pipe penetrations. Finally, Si-COAT 462 RC walkpad forms a yellow, walkable path for light foot traffic, with CSL 469 recycled glass granules spread into it for grip.

Applying the Roof Coating

Preparation: first power wash with detergent and rinse, so the roof is clean and dry
Mixing: one part, so there are no components to combine. Still, stir with a power agitator for at least 5 minutes
Method: airless spray is recommended, but brush, roller or squeegee also work
Thickness: at least half a millimetre once dry (20 mil, 508 microns), roughly half a litre per square metre before losses. Apply it as a single coat. Where brush or roller cannot reach full thickness in one pass, then build it up wet on wet in the same session
Coverage: 2.1 m² per litre at 18 mil and 1.7 m² per litre at 22 mil, before losses
Temperature: 5°C to 60°C, and also at least 3°C above the dew point
Cure: skins over in about 68 minutes, then recoat in 4 to 6 hours, with full properties in 7 days
Safety: silicone coated roofs are extremely slippery, especially when wet. So use fall protection and take care walking on them

For step by step guidance, read our SI-COAT 461 RC application guide or the article on high solids roof coating for contractors.

SI-COAT 461 vs a Conventional Roof Coating

Acrylic is not designed to sit under ponding water, so on South African flat roofs it needs recoating far sooner than silicone.

Polyurethane yellows in the sun, needs several coats and is also moisture sensitive during application.

Torch on bitumen goes brittle in UV, cracks at laps and seams, carries a fire risk during application and absorbs heat.

SI-COAT 461, by contrast, withstands permanent ponding water, resists UV, stays flexible from −60°C to 200°C, reflects most of the sun’s heat and needs no topcoat. Read the complete guide to roof waterproofing in South Africa, or compare silicone vs liquid rubber on flat roofs.

Technical Solution Supplies distributes CSL Silicones products across Southern Africa, including the DRC and the Seychelles. For full technical data, download the data sheets below or contact us.

View the SI-COAT 461 RC FAQ