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Intumescent Varnish

Intumescent Varnish

Fire retardant (Intumescent) varnishes for wood and timber substrates, are clear protective coatings which are designed to fire protect and enhance the natural beauty of the timber substrate. These types of coatings have been used for many decades across the country to help fire-protect buildings with internal or external timber cladding as well as exposed timber beams.

Intumescent clear coatings are generally referred to as fire retardant varnishes, fire varnishes, or fireproof varnishes, these types of coating can offer a variety of fire protection depending upon the substrate you have. Euroclass B and C and British class 0 and 1 are the most common types of fire ratings used in construction, followed by an integrity rating of 30 to 60 minutes.

Fire retardant varnishes are ideal for fire protecting any size or area of exposed wooden beams, timber cladding made up from both solid timber or composite timber such as, OSB, Particle board, MDF, Plywood and veneered board.

When do I require a 30 to 60-minute fire rating on timber?

Firstly, you should always speak to your building control officer, architect or fire officer to confirm if a fire integrity rating of 30 to 60 minutes is required. Please be aware that on fire compartment walls and ceiling an EI30 or EI60 rating may be required. Below is an explanation of the E and I ratings:

E Stands for Integrity, this is the ability of the substrate to hold back the flames from one side of the fire compartment wall to the other.

I Stands for Insulation, this is the ability of the substrate to maintain the insulation without the spreading of heat from once side of the fire compartment wall to the other. The side of the compartment without the fire should not reach temperatures of more than +140ºC up to 180ºC

EI stands for Integrity and Insulation, No Smoke, No Flames and High temperature insulation. For example, an EI30 wall has an integrity and insulation rating of 30 minutes, with no smoke or flames penetrating through the wall in this timeframe.

It is really important that you check the exact requirement of the fire wall before purchasing an intumescent or fire-retardant paint/varnish.

When do I require a Euroclass B or British Class 0 fire rating?

The British class 0 Surface spread of flame and the Euroclass B reaction to fire are classifications that refer to the spread of fire, smoke and flaming particle production. These classifications are used to minimise the spread of fire over timber walls and ceilings internally and timber walls externally.

Can I use fire retardant varnishes externally?

The simple answer is yes, however we do not recommend the use of any intumescent or fire retardant varnishes to be used externally on timber. The reason for this is because these types of coating are not microporous and can cause moisture to be trapped behind the coating causing premature failure of the coating.

The general specification for external use of intumescent varnishes if this is your preferred method is as follows:

1 coat of Adhesion Primer (This is used to seal the timber and prevent moisture from entering the fire retardant from the back).

2 coats of Intumescent Varnish (This is the fire protection layer)

2 coats of External grade solvent based top coat (This is used to seal in the intumescent and protect it from moisture)

For External timber we would recommend the use of the clear impregnation treatment Flametect C-WD. This product can be applied in 1 to 2 coats depending upon the density of the softwood or hardwood, to gain up to a Euroclass B s2 d0 fire rating. For this rating, the substrate must be at least 16mm thick at its thinnest. For a Class 0 rating, it must be at least 12mm at its thinnest. Flametect C-WD has been tested for external use and is suitable for most untreated timber. For more information on this product please email sales@firproofpaint.co.uk.

Can I use fire retardant varnish over existing paint/varnish?

Yes, you can over coat various varnishes over existing coatings, however we would first recommend you speak to our technical team on 01752 690997 or email sales@fireproofpaint.co.uk to check you have the correct products.

Before starting on a project of over coating existing varnishes or paints we would recommend an adhesion test first. We can perform an adhesion test for you FREE OF CHARGE. All we require is a sample of the timber with the existing coating on, at least 150mm x 150mm in size. Please contact us before sending this in to our main office address with all of your contact details inside.

Adhesion tests can be performed directly on site with the help of our technical team, please contact us on 01752 690997.

Once the adhesion test has been successfully performed you will need to apply the following coatings over suitably prepared surface:

1 coat of adhesion primer (This may not be required please check first)

2 coats of Intumescent Varnish

1 or 2 coats of top coats depending upon the level of moisture in the environment.

Do I need a top coat over the intumescent varnish?

Yes, most intumescent clear coats and varnishes are moisture sensitive and require a protective top coat to help protect them from moisture as well as wear and tear. Without the top coat you will notice that the coating will start to change colour quite quickly, ruining the look of the timber. We recommend 1 coat of top coat in internal low wear environments and two top coats in medium moisture and higher wear environments.

How do I get a fire certificate?

To gain a fire certificate we would always recommend you speak to our technical team first before buying any of these products to ensure you receive the correct amount and type of product.

To receive a certificate, we will need the following information:

Invoice number
Address of the building where the work was undertaken
Name and address of the company or person who applied the product.

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