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Do I need to spot test Universal Cleaner first?Updated 3 days ago

TL;DR: Yes. Always spot test Universal Cleaner in an inconspicuous area before using it on any new or unfamiliar surface. Particularly important on natural stone, sealed timber, soft metals, and soft furnishings. Three quick steps, a few minutes, peace of mind.


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Koh Universal Cleaner 20+ uses around the home
Koh Universal Cleaner safe for homes and surfaces

Why do I need to spot test Universal Cleaner?

Koh Universal Cleaner is alkaline at pH 12.5. Most hard surfaces handle it without issue, but porous and reactive materials can respond differently to alkaline cleaners than they do to neutral or acidic ones. Natural stone (marble, granite, travertine, limestone), sealed timber, soft furnishings (carpet, upholstery, leather), and any vintage, hand-finished, or unusual surface should always be spot tested first. Soft metals (zinc, copper, brass), raw aluminium, and aftermarket window tints are known to react with alkaline cleaners and should be avoided entirely. A five-minute test catches any issue before you apply Universal Cleaner to a full surface.

✓ Always spot test

Universal Cleaner is alkaline (pH 12.5). Most hard surfaces handle it fine, but natural stone (marble, granite, travertine, limestone), sealed timber, soft furnishings (carpet, upholstery, leather), and any vintage or unusual finish can react. A five-minute test catches any issue before you apply it to the full surface.

Natural stone Sealed timber Upholstery Leather

⚠ Known incompatible

Soft metals (zinc, copper, brass) will discolour. Raw aluminium will oxidise. Aftermarket window tints can peel. Glass with factory-applied or aftermarket easy-clean coatings (such as ShowerGuard, Diamon-Fusion, ClearShield, EnduroShield, or similar hydrophobic glass treatments) can break down. Skip the spot test and avoid these surfaces entirely.

No soft metals No raw aluminium No aftermarket tints No easy-clean coatings

How do I spot test Universal Cleaner?

Spot testing Koh Universal Cleaner takes three steps and about five minutes. First, pick a hidden spot such as the back of a cabinet, the underside of a chair, the hem of upholstery, the back of a wardrobe, or any corner that won't show if something goes wrong. Second, spray a small amount of Universal Cleaner onto the hidden area, wait a few minutes for the alkali to have full contact time, then wipe clean with a Koh cloth. Third, check for colour loss, discolouration, sheen change (matte patches on glossy surfaces or vice versa), etching, softening, or texture change. If the area looks unchanged, you're clear to clean the full surface. If anything looks off, stop and use a more surface-specific cleaner.

✓ Three-step spot test

1

Pick a hidden spot. Back of a cabinet, underside of a chair, hem of upholstery, back of a wardrobe, or any corner that won’t show if something goes wrong.

2

Spray a small amount of Universal Cleaner onto the hidden area, wait a few minutes for the alkali to have full contact time, then wipe clean with a Koh cloth.

3

Check for changes. Look for colour loss, discolouration, sheen change (matte patches on glossy surfaces), etching, softening, or texture change. If clear, proceed to the full surface.

What should I look for during a spot test?

During a spot test on a hidden area, watch for subtle changes that signal the surface is reacting to the alkaline formula. Colour loss or darkening is the most common sign. Sheen change shows up as matte patches on glossy surfaces or shiny patches on matte. Etching or pitting is more common on stone. Softening, stickiness, or tackiness suggests the sealant or finish is breaking down. Fabric texture change indicates damage to fibres or backing. Any discolouration on metal hardware near the test patch is also a warning. If any of these appear, stop and reach for a cleaner specifically formulated for that surface type. If the area looks unchanged after a few minutes, proceed with cleaning the full surface.

⚠ Warning signs to watch for

Changes can be subtle. Colour loss or darkening. Sheen change (matte patches on gloss, shiny patches on matte). Etching or pitting on stone. Softening, stickiness, or tackiness on sealed surfaces. Fabric texture change. Any discolouration on metals. If any of these show up, stop and reach for a more surface-specific cleaner.

Colour change Sheen change Etching Softening
Koh Universal Cleaner 2L

Universal Cleaner

2L bag-in-box refill. The same two-ingredient formula in our most popular size. Approximately 3 months of cleaning for the average UK home.

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Last reviewed: August 2026 · Koh UK

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