clog up

block something so nothing can pass through

B2

What does "clog sth up" mean?

Clog up describes a process where material gradually accumulates inside something and prevents flow or movement. A drain clogs up when grease, hair, or debris builds up over time; an artery clogs up when fatty deposits narrow the passage. The key idea is gradual accumulation — something that should allow flow becomes increasingly blocked. The phrasal verb works for physical systems like pipes, filters, and gutters, but also for abstract systems where the idea of "flow" is metaphorical, such as a court system clogged up with cases or an inbox clogged up with spam. Adding "up" gives a sense of completeness — the blockage has really taken hold — which makes it slightly stronger than using "clog" alone.

Examples

How to use it

something clog up

Used without an object when the focus is on what becomes blocked, not what is causing the blockage.

The gutter clogs up every autumn when the leaves start falling.

clog up + object

Used when naming what is being blocked, especially with longer noun phrases where the object naturally follows the particle.

Years of grease had clogged up the entire drainage system.

clog + object + up

Used with short noun objects when separating the verb and particle sounds natural and emphasises the object.

Dead leaves have clogged the filter up again — it needs clearing out.

clog + pronoun + up

Pronouns must always go between the verb and particle — placing them after 'up' is ungrammatical.

Hair keeps clogging it up, so I clean the shower drain every week.

get/be clogged up with + substance

The passive construction, especially with 'get', is very common and often followed by 'with' to name the blocking material.

The nozzle got clogged up with dried paint and stopped working properly.

Common Collocations

drainpipefiltersinkarteriestraffic

Common Mistakes

Pronoun placement

Pronoun objects must go between 'clog' and 'up', never after 'up'. Saying 'clog up it' is ungrammatical in English.

✗ Grease clogged up it completely.
✓ Grease clogged it up completely.
Confusing 'clog up' with 'block up'

'Clog up' implies gradual accumulation of material causing a blockage. 'Block up' can describe deliberately sealing something, like a window or hole, which is a different action that 'clog up' cannot express.

✗ They clogged up the gap in the wall with cement.
✓ They blocked up the gap in the wall with cement.
Separating with a very long noun phrase

Separation works well with short objects and pronouns, but placing a long noun phrase between 'clog' and 'up' sounds unnatural. With long objects, keep the phrasal verb together.

✗ Debris clogged the main drainage system of the entire building up.
✓ Debris clogged up the main drainage system of the entire building.

Usage

This phrasal verb is neutral in register and works in both spoken and written English. It is often followed by 'with' to say what is causing the blockage (e.g. 'clogged up with grease'), and the 'get' passive ('it got clogged up') is very common in informal speech.

Frequently Asked Questions

Can 'clog up' be used in the passive?

Yes — the passive is very natural with this phrasal verb. You can use 'be clogged up' or the informal 'get clogged up', which is especially common in spoken English. For example: 'The pipe was clogged up with grease' or 'The sink keeps getting clogged up.'

What's the difference between 'clog up' and just 'clog'?

Both are correct, but 'clog up' adds a sense of completeness — it suggests the blockage is more total or developed. In practice, 'clog up' is more common in everyday spoken English, while 'clog' alone appears more in formal or technical writing.

Can I use 'clog up' for things other than pipes and drains?

Absolutely. 'Clog up' works for any system where something should flow or move freely but becomes blocked through accumulation. You can use it for traffic ('the roads clog up at rush hour'), digital systems ('spam is clogging up my inbox'), or even abstract processes ('the courts are clogged up with minor cases').

How do I say what substance is causing the blockage?

Use 'with' after 'clogged up' to name the material responsible: 'clogged up with grease', 'clogged up with leaves', 'clogged up with debris'. This pattern is very common and sounds natural in both speech and writing.

Is 'clog up' used in both British and American English?

Yes, it's used in both varieties without any strong regional preference. You'll encounter it in everyday conversation, DIY contexts, health advice, and traffic reports on both sides of the Atlantic.

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