CUSTOM 421 GREY  - Rustbuster

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CUSTOM 421 GREY £32.99 ex VAT In Stock

1.25 ltr Custom Epoxy 421 Kit £32.99 ex VAT In Stock
2.5 ltr Custom Epoxy 421 Kit £60.99 ex VAT In Stock
6 ltr Custom Epoxy 421 Kit £117.50 ex VAT In Stock
200ml Custom 421 Hardener £12.20 ex VAT In Stock
1ltr Custom 421 Hardener £32.50 ex VAT In Stock
Epoxy Thinner 250ml £5.50 ex VAT In Stock
Epoxy Thinner 500ml £9.50 ex VAT In Stock

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On orders over £90.00+VAT, up to 20Kg.

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Product Information





Rustbuster Custom 421 is the perfect base for priming steel, aluminium and GRP bodywork. It will not absorb moisture so rust will not form within the primer if left exposed for long periods, unlike soft and porous easy-sand primers. Custom 421 is therefore ideal for the home auto restorer and garages that do not have the benefit of a controlled body shop environment.

Custom 421 can be over painted with single pack cellulose or two pack finishes after a light sanding with a P320 abrasive.


Product description

2 pack modified epoxy rust proofing primer.

Pack description

1.25ltr kit covers approx. 10m2. Includes 800ml component A, 200ml component B & 250ml thinner.

2.5ltr kit covers approx. 20m2. Includes 1.6ltr component A, 400ml component B & 500ml thinner.

6ltr kit covers approx. 50m2. Includes 4ltr component A, 1ltr component B & 1ltr thinner.

Application temperature

Can be applied to steel as low as 5c. The steel must be at least 3 degrees above the current dew point. (See our dew point calculator.)


Use only the epoxy thinner supplied, from 5 to 20% max.

Application & recoating

Brush or spray.

A second coat or topcoat can be applied any time after approx. 8 hours* with no need to abrade between coats. If recoating or topcoating once the first coat has fully cured (after approx. 7 days), lightly abrade first with P320 paper.

* At 20 degrees centigrade. Longer interval may be required in colder conditions.


Minimum 1.8mm nozzle or a HB (high build) primer set up. Test atomisation on a test panel first. Viscosity will vary, i.e. thicker in colder temperatures. Data correct at 20c.

Conventional Spray (Air) 3-4bar - 44-58psi

Airless Spray 18thou tip, 150bar - 2176psi

Pot life

Pot life is the time from mixing the two components together to the point at which the mixed paint is no longer useable. For Custom 421, you have 2.5 hours pot life once mixed at 20c – longer at colder temperatures.

Shelf life

We recommend storing upside down in a dry place at around 20c. In these conditions the product has a shelf life of 12 months.

Do not store below 20c as this can affect performance.


Allow any excess mixed paint to cure in your mixing cup and throw away as dry waste.


Clean up with standard thinner or gun wash. Do not thin the paint with standard thinner as this will affect the paint cure.


Use in a well-ventilated atmosphere. Use a respirator face mask when spraying or brushing in an enclosed space. Please see the MSDS (material safety data sheet) in our data sheet area.

Wear suitable protective clothing, gloves and eye protection.

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Contact Rust

Rustbuster Ltd
Welland House
Cradge Bank
South Lincolnshire
PE11 3AN

01775 761 222

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Rustbuster is a registered trade mark of Rustbuster Ltd, registered in the UK Trademark number 2211446 Class 02 & 37.
Any unlawful use of the Rustbuster name or logo or passing off will result in legal proceedings. Rustbuster Ltd UK registerered 3639350.