Thermoguard Fire Varnish Door Upgrade System
  • Thermoguard Fire Varnish Door Upgrade System

Thermoguard Fire Varnish Door Upgrade System


Thermoguard Fire Varnish Door Upgrade System is an intumescent varnish system to upgrade doors to 20 or 30min Fire Resistance:

  • Available as a convenient pack containing the required basecoat, topcoat and mastic to protect 3 doors in a clear or woodstain coloured Matt or Satin finish
  • Thermoguard UK will issue a Fire Certificate for Authority approved projects following completion
  • Current colour: Clear
Choose a colour
Close colour picker
  • Clear
  • White Low
  • White Medium
  • Light Oak
  • Teak
  • Pine
  • Ebony
  • Dark Oak
  • Walnut
  • Rosewood
  • Mahogany
  • Grey
VAT excluded

£319.20 Tax incl.


Fire Resistance to Doors using Thermoguard Fire Varnish Basecoat and Thermoguard Fire Varnish Overcoat (Exterior)

Please refer Thermoguards explanatory Technical Note (available to download HERE) to the appropriate Authority for approval before proceeding. Due to the hugely varying nature of doors and their construction, it is impractical and misleading to carry out NAMAS / UKAS Fire Test Laboratory fire door testing. Each door must be assessed for potential suitability.

The great majority of doors, including all hollow doors, are unsuitable for upgrading to 30 or even 20 minutes Fire Resistance.

There are, however, certain well constructed, solid and substantial doors capable of being upgraded with the Thermoguard Fire Varnish system as this is by far the most effective clear fire treatment or coating available.

Generally suitable doors are hardwood or solid with hardwood veneer.

Intumescent paint (white or coloured) is capable of significantly greater Fire Resistance. If you have softwood doors we suggest you refer to Thermoguard Timbercoat Door Upgrade System.

Please note: Remember, intumescent varnish is just one element of protection and DOES NOT create a ‘fire door’. Intumescent materials and hardware MUST be used to ensure your doors meet the required standards of your authority. 

Thermoguard Fire Varnish Class O Part 6 Fire Propagation Test and BS EN Class B result indicates the protected softwood did not burn significantly within the 10 mins (Part 6) and 20 mins (BS EN) test duration. Further in-house testing by Thermoguard indicated that when applied at three times the Class O / Class B spec. the Thermoguard Fire Varnish system added 15 minutes Fire Resistance.

Thermoguard assess projects requiring 30 minutes Fire Resistance on an individual basis, referring to the TRADA Char Rate Tables and calculated residual timber to ascertain whether they could issue a Fire Certificate for the project. In order to enable them to issue a 30 minutes Fire Certificate in the case of softwood the surface must be able to afford the loss of 10mm depth from all surfaces exposed to a fire. For oak or similar hardwoods the loss to take into account is 6mm.

In other words, the residual timber should be adequate, after such loss in the case of a door to avoid premature collapse, splitting or cracking ensuring neither flames or the substantial heat required to promote combustion can pass through the door.

Pine and Other Softwood

In general terms few modern softwood doors can be protected with confidence. Old and hence very well seasoned softwood doors can be protected but only if the frame can withstand 10mm loss. In these cases panels less than 16mm thick should be supplemented by inserting an additional panel to make the total panel thickness 16mm+, trapping the additional panel behind the door's beading. Substantial, solid doors unable to afford the loss of 10mm to the frame can achieve 20 minutes with the 30 min spec as below provided they can afford the loss of 4mm.

Oak and Other Resistant Hardwoods

(Including modern doors with solid compressed cores and 6mm oak veneer faces)

These doors with frames 35mm+ thick can be upgraded to 30 minutes. Any inset panel less than 12mm thick should be supplemented by an additional panel trapped by the door's beading to take overall panel thickness to 12mm+.

Door Surrounds & Seals

Thermoguard recommend the gap or joint between the architrave and wall is sealed with Intumescent mastic after application of Fire Varnish & FV Overcoat. They also recommend that intumescent strips are fitted in the door jambs and to the underside of the door.


30 Minutes Fire Resistance Specification (20 minutes in case of some softwood doors as referred to above)

  • 3 coats of Thermoguard Fire Varnish Basecoat @ 7m² per litre / per coat
  • 2 coats of Thermoguard Fire Varnish Overcoat (Exterior) – Matt or Satin @ 10m² per litre / per coat

Coverage 30 / 20 minutes (as above) - allows for the number of coats necessary

Each 3 door pack contains;

  • 2 x 20m² Thermoguard Fire Varnish Basecoat
  • 1 x 20m² Thermoguard Fire Varnish Overcoat (Exterior) – Matt or Satin finish
  • 2 x 310ml Thermoguard Intumescent Mastic White (you may need to purchase more tubes depending on the size of gaps to fill which can be done HERE)

This should be applied to 3 doors on BOTH sides (6 door sides in total) and it is assumed that this area will total no more than 14m². If your doors are unusual in size or total more than 14m² of area please contact the Technical Department.

IMPORTANT FIRE PRODUCTS NOTICE: The information displayed on this website should be used as a guide ONLY and our Technical Department should be contacted to obtain a tailored specification and any advice necessary before you place an order for fire protection products. Fire protection products are non-returnable except in accordance with Condition 8 of the Terms and ConditionsWe will not be held liable for any resulting damage to property, human life or monetary costs incurred due to the incorrect specification you have prepared or use of fire protection products caused by your negligence, including your failure to have contacted us to obtain the relevant advice/specification.

It is your responsibility to read the Product Data Sheets (available below) before you place an order and prior to application of the product. The content of this website is our best recommendation and is not advice. Coverage rates quoted are approximate, you agree that coverage depends on the condition of the substrate, surface absorption, texture and application method. We ALWAYS recommend a trial area is coated to ensure the product meets your requirements before use.

Product Details

Data sheet

Brush, Roller
3 Doors (6 doors sides) per pack

Customer agrees that before placing an Order, Customer has read and understood the most up to date Product Data Sheet for the Product. Where we have access to the Product Data Sheet from the manufacturer, we will either provide a copy on request, or include a link to the Product Data Sheet available on the manufacturer’s website. Customer further agrees that we have no liability for any errors or omissions contained within the Product Data Sheets. For more information, please see our Terms & Conditions of Sale.

questions James Henderson on 07/05/2019

Hi - can you paint over a clear varnish if you change your colour scheme in future?


Thermoguard Fire Varnish Door Upgrade System can be used to upgrade suitable doors that are either bare timber or previously varnished only. Once applied, the system cannot be overcoated with any other paint or varnish products. If you require an overpaintable door upgrading product we would recommend Envirograf Door Upgrade Paint System providing your doors are suitable.

questions Paul bamber joinery ltd  on 20/03/2018

I have just done a loft conversion can the existing doors be upgraded to 30 mins. ? They are 35mm hollow flush oak veneered doors?


Unfortunately hollow doors cannot be upgraded.

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