Can you paint roof felt & how?

Why would you paint over roof felt?

Flat roof systems can be good to have for your property, it’s cost-effective, low maintenance, and simple to install. However, over time the weatherproofing and quality of flat felt roofs will begin to deteriorate, but there is a solution for this.

Bitumen paint is another cost-effective and reliable solution to rejuvenate not only shed felt but metal, concrete and most other types of roofing material too.

View our guide on installing a felt roof. 

What is bitumen?

Bitumen is a term used to define a classification of natural minerals that mainly consist of carbon and hydrogen molecules (hence the name hydrocarbon) but also consist of nitrogen, sulfur, and oxygen. In a physical sense, Bitumen is a black, sticky, and thick substance, the viscosity of bitumen is similar to molasses at room temperature. 

Bitumen is hydrophobic, which means it repels and doesn’t mix easily with water, this characteristic makes bitumen-based paints and coatings ideal for waterproofing a variety of structures and materials. 

Bitumen can also come in the form of bitumen-coated roofing felt which is also known as waterproofing membranes, this is used to protect flat and pitched roofs from water ingress and serves as the base material for roof shingles. 

So what’s bitumen paint?

Bituminous paints are a bitumen-based coating product that is designed to be applied in a liquid or semi-liquid form. The paint consists of hydrocarbon materials that are dissolved in another solvent- such as naphtha or mineral spirits. 

Since bitumen is insoluble in water due to its hydrophobic nature, coats that are deprived of it serve as an effective sealant or repellant against water ingress; so this combined with its natural adhesive properties means that it can prevent moisture and air from coming into contact with anything that it coats. On top of waterproofing, it also provides excellent protection against UV degradation. 

Preparation and apply Bituminous Paints

Before applying bitumen paint, it’s important to carry out the necessary surface preparation in order to positively influence the paint’s adhesion and performance. 

The first step is to make sure all the surfaces are clean and free from debris such as dirt, moss, and fallen leaves that might be present on the felt roof. This can be done using a pressure washer, a chlorine wash, or sodium hydroxide. 

It’s also important to make sure the felt roof is in good condition, if not then carry out repairs before applying the paint as it will lead to problems down the line. 

Applying your paint is relatively simple, ensure the bituminous paint is applied evenly across the flat roof and in as many coats as you desire, two coats is the recommended minimum. To paint the felt roof with maximum effectiveness, it’s important to choose the right tool for the job. 

The tools for the job

Depending on your environment, the coating requirements and coating formulation for the paint, bituminous paints can be applied with brushes, rollers, trowels or a sprayer. 

It’s always important to check what environment you’ll be working in, the coating requirements such as if it’s cold or hot-applied, and the coating formulation of the paint of choice. All of this information can typically be found on the paint itself or online.

Using your tools 

Brushing is conventionally used on areas you can't reach with a sprayer and/or on jobs where setting up spray equipment isn't practical. When brushing, the coating thicknesses range from one to 65 mils.

Spraying is the most popular method for applying cold coatings. When you spray, coating thickness ranges from one to 250 mils; coating consistency is the key to obtaining your desired thickness. You can use conventional paint-spraying equipment for coatings up to six mils thick, but for a heavier coating, it will require mastic spray guns fed from pressure pots or heavy-duty pumps. 

Troweling is typically usually used in inaccessible areas or where it’s necessary to produce a very heavy coating in one application. Trowel coats are usually applied in thicknesses above 250 mils.

There are two types of coating applications from a heating requirement, hot and cold applied. 

1. Hot-Applied Coatings are either 100% bitumen or bitumen-blended with selected fillers which is typically 10% or 20%. Hot-applied coatings are heated to the desired application viscosity.
2. Cold-Applied Coatings employ both solvents and water to attain the desired application viscosity. A wide range of solvents are used for bitumen paint, and the choice mainly depends on the drying characteristics desired and the solvent power needed to dissolve the particular bitumen being used.