Laco Flux is a reliable soldering flux used by plumbers, electricians and sheet metal workers across the UK. Available in 125g and 475g tubs, it cleans oxide from metal surfaces to ensure clean, solid solder joints every time.
Size
Price
QTY
125g
£5.95£7.14
475g
£9.95£11.94
Laco Flux is a paste soldering flux designed to prepare metal surfaces before soldering, removing the oxide layer that would otherwise prevent solder from flowing and bonding correctly. Whether you are sweating copper pipe joints, soldering electrical connections, or working with sheet metal, getting a clean joint starts with the right flux. This is it.
The paste consistency makes it straightforward to apply exactly where you need it, without the mess you get from liquid flux running where it shouldn’t. A small amount goes a long way, which is why the 475g tub is popular with tradespeople who go through it regularly on bigger jobs. The 125g size is handy for the van or smaller plumbing tasks where you don’t want a full tub rattling around.
Where Laco Flux Gets Used on Site
Plumbers reach for this most often when making copper-to-copper or copper-to-fitting solder joints on water and heating systems. It works across a wide range of metals including copper, brass and tinplate, making it equally useful for sheet metal fabrication and light electrical soldering work. On a busy plumbing job, the difference between a joint that takes first time and one you have to redo twice often comes down to flux application — too little and the solder balls up, too much and you are burning it off before the solder even flows.
Applying Laco Flux Correctly
Apply a thin, even coat to the cleaned surface before heating. You do not need to pack it on — it’s flux, not filler. The heat from your torch or iron activates it, drawing the solder into the joint. Clean off any residue once the joint has cooled, particularly on plumbing work, to avoid long-term corrosion around the fitting.
Available in 125g and 475g sizes, with honest bulk pricing from Discount Trade Supplies.
Pro Tip: Always wire brush or sand the pipe and fitting back to bright metal before applying Laco Flux — no amount of flux compensates for a dirty or corroded surface, and the joint will fail if the base metal isn't clean.
Laco Flux is used primarily in plumbing for soldering copper pipe and fittings on domestic and commercial heating, hot and cold water systems. It is also used by sheet metal workers, HVAC engineers and electricians wherever a reliable solder joint is needed on copper, brass or tinplate surfaces. On site or in the workshop, it suits any job where you need good solder flow and a clean, leak-free result.
Best For
Copper pipe and fitting joints
Plumbing and heating installations
Sheet metal soldering
Brass and tinplate work
Light electrical soldering
Compatible Surfaces
Copper
Brass
Tinplate
Lead-free solder applications
Key Features
Paste formula for controlled application
Removes oxide layer for clean solder flow
Available in 125g and 475g tubs
Suitable for plumbing and metalwork
Activates under heat for consistent results
Not suitable for: Not suitable for aluminium or stainless steel without a specialist flux formulated for those metals. Not recommended for high-temperature brazing applications.
Clean the surfaces to be joined thoroughly using wire wool or a pipe cleaning brush until the metal is bright. Apply a thin, even coat of Laco Flux to both mating surfaces. Assemble the joint and apply heat steadily until the flux begins to activate, then introduce your solder. Once the joint is complete and cooled, wipe away any flux residue with a damp cloth to prevent corrosion.
Clean pipe and fitting surfaces back to bright metal using wire wool or a pipe cleaning brush
Open the Laco Flux tub and apply a thin, even layer to both surfaces using a brush or small spatula
Assemble the joint immediately after fluxing to avoid re-oxidation
Apply heat evenly to the joint using a plumber's torch or soldering iron until the flux becomes active and starts to move
Feed solder into the joint, allowing it to be drawn in by capillary action
Remove heat and allow the joint to cool without disturbing it
Wipe away excess flux residue with a damp cloth once cool to prevent corrosion
Is Laco Flux suitable for lead-free solder?
Yes, Laco Flux is suitable for use with lead-free solders, which are now standard on plumbing work involving potable water systems in the UK. Always confirm compatibility with your specific solder if you are working on a specialist application.
Do I need to remove the flux residue after soldering?
Yes, particularly on plumbing joints. Flux residue left in place can cause corrosion around the fitting over time. Once the joint has cooled, wipe it down with a damp cloth to remove any remaining flux.
Which size should I buy, 125g or 475g?
The 125g tub is fine for occasional use or keeping in the van for small plumbing repairs. If you are working on larger installations or going through flux regularly, the 475g tub works out better value and means fewer trips to the merchant.
Laco Flux is a paste-form soldering flux formulated to chemically remove metal oxides from copper, brass and tinplate surfaces, allowing solder to wet and bond correctly. The paste is activated by heat during the soldering process, promoting solder flow and capillary action within the joint. Residue should be removed after cooling to maintain joint integrity and prevent corrosion.
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