Why We Still Solder: The Case for Copper Over Plastic

In the modern construction world, speed is often the priority. You will see many new-build homes thrown together using plastic piping and push-fit connectors. It is fast, it is cheap, and it requires less skill to install.

At Ally Engineering, we take a different approach.

If you look under the floorboards of one of our renovations in Liverpool, you will see neat rows of soldered copper pipework. Yes, it takes longer. Yes, it requires a skilled tradesperson. But when that pipe is about to be buried under a screwed-down subfloor or behind a tiled wall, "fast" is not the goal. "Forever" is.

Here is why we stick to the gold standard of soldered copper, and why it matters for your home.

1. The "Torture Test": 60 PSI Pressure Testing

When we undertake a full system replacement or a complete house refurbishment, we don't just hope for the best. We cap off our new pipework and pump it up to 50–60 lbs (PSI) of pressure.

• Why we do it: This is significantly higher than the standard operating pressure of a heating system (which is usually around 15-20 PSI).

• The Result: If there is a weak joint, a hairline crack in a pipe, or a manufacturing defect, it will fail now, while the floor is open.

This testing ensures that the pipework isn't just "watertight"—it is structurally sound. You simply cannot stress-test push-fit plastic joints with the same confidence, as the pressure can sometimes force the fittings apart.

Important Note on Partial Repairs: We only apply this high-pressure test when we have replaced the entire plumbing system. If we are doing a partial repair or adding a single radiator to an existing system, we do not subject the old pipework to this pressure, as it could damage parts of the house we aren't renovating. Instead, we perform a rigorous physical inspection of the new joints under normal operating pressure to ensure they are leak-free and secure.

2. "Hidden" Should Mean "Forgotten"

The definition of a hidden pipe is that you should never have to see it again.

When you bury a pipe behind a luxury tiled bathroom wall or under expensive engineered wood flooring, the cost of fixing a leak isn't just the plumber's bill—it's the thousands of pounds in ripped-up decoration.

• Soldered Copper: A chemically bonded metal joint. Once cooled, it effectively becomes one continuous piece of metal. It doesn't degrade.

• The Peace of Mind: By using copper, we eliminate 99.9% of potential future maintenance issues.

3. The Problem with Plastic (Why We Avoid It for Hidden Work)

Plastic (PEX/Polybutylene) has its place, but it has distinct engineering downsides for hidden installations:

• The "O-Ring" Risk: Push-fit fittings rely on a small rubber O-ring to create the watertight seal. Over 20 or 30 years, rubber can dry out, perish, or deform. Copper solder has no shelf life.

• Rodent Damage: This is a horror story many homeowners don't consider. Rats and mice love to chew on plastic pipes, often causing catastrophic floods. They cannot chew through copper.

• Restricted Flow: Plastic fittings sit inside the pipe. This reduces the bore (diameter) of the pipe at every joint, which can reduce water pressure and flow rate to your shower. Copper fittings fit over the outside, keeping the full width of the pipe open for maximum flow.

4. Thermal Stability & Hygiene

Copper is a biostatic material, meaning bacteria cannot grow on its surface. It also withstands high temperatures (like those near your boiler) without sagging or warping, unlike plastic which softens with heat over time.

5. Are There Downsides to Copper?

Of course. There are reasons why many builders choose plastic over copper, and they usually come down to cost and speed.

• It Costs More: Copper is a global commodity, and the material cost is higher than plastic.

• It Takes Longer: Soldering a joint takes minutes; clicking a plastic fitting takes seconds.

• It Requires Heat: Installation involves blowtorches and open flames.

So why do we still do it? Because we aren't building for "fast" or "cheap." We are building for durability. We accept the higher material cost to give you a system that lasts 50+ years, and we take the extra time to ensure every joint is perfect.

Note: The only real enemy of copper is frost. Like any rigid metal, if water freezes inside it, it can split. That is exactly why insulation is so vital. By properly lagging the pipes, we nullify copper's only weakness.

Summary

We don't use soldered copper because we are stuck in the past. We use it because it is the only material we trust to stay watertight for the next 50 years.

When you hire Ally Engineering, you are paying for the peace of mind that what is behind your walls is built to the same high standard as what is on them.