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750 ML WELD THRU RED + 2 MIXING CUPS £20.50 ex VAT In Stock
1.5 LTR WELD THRU RED + 4 MIXING CUPS £41.65 ex VAT In Stock
6 LTR WELD THRU RED + 4 MIXING CUPS £142.10 ex VAT In Stock

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Product Information


Rustbuster Weld-Thru Primer is a fast drying anti corrosion pre-fabrication primer. This two-pack modified zinc silicate shop primer is designed to be fully weldable and cuttable. When welding new steel to the steel coated with Weld-Thru Primer, the weld will have better penetration with the minimum amount of burn back.

  • Can be sprayed or brushed.
  • Fast drying – touch dry and ready to weld in approx. 6 minutes at 20c.
  • Will not give off harmful fumes during welding.
  • Suitable for MIG, TIG and MAG/G-FCAW welding.
  • Minimum burn back: 50% less burn back than our previous weld through primer.

Prime as you build with Rustbuster Weld-Thru Primer

On certain fabrications you will have to build from the inside, such as when an inner sill is fitted before the outer sill can be welded on. This scenario is perfect for our Weld-Thru Primer, as the weld can be cleaned and coated prior to the application of the outer sill panel. The primer will itself help to prevent corrosion, but we also recommend injecting the sill with cavity wax once the fabrication is complete.

As always, better surface preparation will ensure best results. We therefore recommend applying Rustbuster Weld-Thru Primer to steel that has been prepared to at least the St3 standard with hand or mechanical preparation tools such as wire brushes, abrasive wheels etc., or to a higher standard via blasting. (Read our guide to surface preparation standards for more information.) 

Rustbuster Weld-Thru Primer can be applied over steel treated with our Phos-Kleen B rust remover and phosphating solution. Rustbuster has also tested our Weld-Thru Primer with the ‘Enviro-Strip’ body stripping and phosphating process with excellent results.

Supplied as a two-component kit, with a mix ratio of 2:1 by volume: 2 parts component A (hardener) to 1 part component B (zinc paste). Please follow the instructions for best results.


Product description

Red two-pack modified zinc silicate pre-fabrication primer.

Pack description

750ml kit covers approx. 10.5m2. Includes 500ml component A and 250ml component B, plus two mixing cups.

1.5ltr kit covers approx. 21m2. Includes 1ltr component A and 500ml component B, plus four mixing cups.

6ltr kit covers approx. 84m2. Includes 4ltr component A and 2ltr component B, plus four mixing cups.

Mix ratio

Mix ratio: 2 parts component A (hardener) to 1 part component B (zinc paste).


Weld-Thru Primer is ready to use once mixed and thinner is not required.


Brush or spray.


Airless spraying use 15-23 tip.

Conventional spraying use 1-1.5mm nozzle.

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 Weld-Thru Primer, 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 allow to freeze.


Allow any waste mix to cure in your mixing cup and throw away as dry waste.


Clean up with standard thinner or gun wash. DO NOT thin Weld-Thru Primer 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.