£5.50£128.65 +vat @ 20%

Free Delivery

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

Delivery Details

Free Shipping UK mainland (Most Destinations)

Free Standard Shipping (not next day) on orders worth £90 +vat or more, which also weigh 20kg or less to non-remote, UK mainland locations.
Free shipping is shown at checkout on valid orders

Rustbuster intend to ship all orders within 24 hour via economy carriage shipping, this can be next day but could be up to 2 days.

Next day delivery DOES NOT include Saturday or Sunday. Any next day orders placed on a Friday will be received on Monday, as Saturday is not included as a working day.

Rustbuster Standard Economy shipping is £8.50+vat for up to 20kg.

Remote areas/Scottish Highlands and non-UK Mainland areas may be subject to additional charges and a longer delivery time. This is determined by our couriers not Rustbuster.

Northern Ireland and Ireland
Up to 20kg of Hazardous goods can be sent, this currently costs £25.00+vat, we do however have a Stockist in Ireland and this may workout a more cost effective way to purchase.

International shipping
International shipping prices vary, please contact Rustbuster if your country is not listed at Checkout.

Need Assistance?

For more product information or have general question, please contact us.

Customer Feedback

We’d really appreciate it if you could answer three survey questions to help us improve our customers’ online buying experience and marketing.

Your Name *
Fill out this field
Email Address *
Fill out this field
Recent Order Number or Product Purchased
Fill out this field
Did you find our website easy to use? *
Fill out this field
Can you suggest any improvements, or products we could add ? *
Fill out this field
Where did you hear about Rustbuster and our products? *
Fill out this field
Any other comments, even constructive criticism, are most welcome *
Fill out this field
27 - 4 = ?
Enter the equation result to proceed

Share This Product

Product Details



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 & 500 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.)
Thinning 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 top coating once the first coat has fully cured (after approx. 7 days), lightly abrade first with P320 paper.

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

Spraying Minimum 1.8mm nozzle or an 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, 150 bar – 2176psi

Pot life Pot life is the time from mixing the two components to the point at which the mixed paint is no longer useable. For Custom 421, you have 2.5 hours of 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

Disposal Allow any excess mixed paint to cure in your mixing cup and be thrown away as dry waste.
Cleaning Clean up with standard thinner or gun wash. Do not thin the paint with standard thinner as this will affect the paint cure.
Safety 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.

Rusty's Top Tips from Rustbuster

Hello Corrosioneers!

RUSTY here, for handy tips and guides on how to get the best from our Rust busting products, check out my helpful guides at Rusty’s Tops Tips

Related Products