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Thermoguard Fire Varnish Door Upgrade System


Thermoguard Fire Varnish Door Upgrade System is an intumescent varnish system to upgrade solid 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
  • This product is available in up-to 4,000 colours, here

Please Note : Woodstains are only available on the following shipping options:

  • Express: 1-3 Working Days Delivery (Thermoguard DS)
  • Economy: 7-10 Working Days Nationwide Delivery

See further below for representations of available translucent wood stains - these are shown in the colour picker as solid colours

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£245.70 Save 10%
£294.84 Incl. VAT
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Thermoguard Fire Varnish Door Upgrade System

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

Transparent Wood Stains

Representations shown below; represented as solid colours in the colour picker further above.

Please refer Thermoguard's 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: Intumescent varnish is just one element of protection and DOES NOT create a ‘fire door’. Doors should only be considered for upgrade when the historic integrity of the door must be maintained, evaluation of ironmongery and gaps around the door should be undertaken and then all works should be carried out by a specialist to meet the requirements of your authority.

Thermoguard's Fire Varnish tested for Fire Resistance at a UKAS Fire Test laboratory for 30 mins - Results indicated Thermoguard Fire Varnish added 15 mins Fire Resistance.

Thermoguard Fire Varnish Class 0 Part 6 Fire Propagation Test and BS EN Class B result indicates the protected softwood did not burn significantly within the 10mins (Part 6) and 20mins (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 (included in this pack) after application of Fire Varnish & Fire Varnish 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 (Interior) – 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 (Interior) – 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 13m². If your doors are unusual in size or total more than 13m² of area please contact the Technical Department.

Important Application Notes

The Thermoguard Fire Varnish System should only be applied to dry wood, with dry conditions during application and drying of basecoat and overcoat.

Thermoguard Fire Varnish Basecoat is a water-based 2 pack coating.

Thermoguard Fire Varnish Overcoat (Interior or Exterior grade) should not be applied unless the basecoat is dry. Drying time of the basecoat in good conditions is overnight. Once the basecoat has dried in good conditions the basecoat remains ideal to overcoat for a further 4 days. Thereafter, the basecoat becomes gradually harder, until it reaches a point where the overcoat may not obtain a good bond.

Thermoguard therefore recommend overcoating when basecoat is dry, within the following 4 days in good conditions.

Delamination of overcoat caused by application to near-full cured basecoat has NEVER occurred when the overcoat was applied within 7 days. The longer the delay beyond '4 days after basecoat has dried' (so typically 5 days after application), the greater the risk of overcoat delaminating.

If overcoating is delayed notably beyond 7 days after the basecoat was dry, it is advised;

  • Basecoat is abraded to obtain a key with 120 grit abrasive
  • Apply a light coat of basecoat to replaced material removed during abrasion
  • Apply overcoat within the ideal window or as near to it as possible

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 Conditions and should be applied only by an individual with the necessary expertise and experience. We 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.

Product Details

Data sheet

Brush, Roller
3 Doors (6 doors sides) per pack
Fastest Delivery
Next Working Day

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 Ian on 2022-06-15 08:24:57

I am considering a loft conversion and understand I need doors connecting to the landing below to be 30 minute fire resistant. The doors are 3 inch solid oak and 100 years old. I would rather do without the loft conversion than swap out these doors. Will this product upgrade these solid oak doors to 30 mins fire resistance?


To assist with this enquiry we will need the questions below answering and sending to [email protected] along with pictures of the doors.

- Level of Fire Protection required? (i.e. 30min, 60min, etc.)
- Style of door? (i.e. panelled, ledge & brace, etc.)
- Solid or hollow core? - (please note we cannot provide anything to upgrade hollow doors)
- Door size? (height and width)
- Door thickness? (include thickness at thinnest point (i.e. panel))
- Number of doors to do?
- Clear or coloured finish required?
- Bare or previously painted?

questions Kelvin Elliott on 2021-03-15 09:19:26

Hello, I need to upgrade 4 doors to FD30, I see you do a product that be used on previously varnished doors which is a kit for 3 doors. Do you do a 4 kit package or a single door package that can be bought with the 3 door package kind regards Kelvin


No, we list a 3 door pack but we can provide a specification specific to the projects requirements, we have contacted you directly.

questions James Henderson on 2019-05-07 11:22:25

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 a coloured paint finish then we would instead recommend Thermoguard Timbercoat Door Upgrade System. Once the full system has been applied, if desired Thermoguard Flame Retardant Additive could be added to a conventional, single pack decorative, oil based gloss or eggshell paint in the colour of your choice to allow you to overpaint the system.

questions Paul bamber joinery ltd  on 2018-03-20 17:48:57

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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