O quarto ficou por pintar, porque a tinta acabou.

Ficar por + infinitive is a common Portuguese structure meaning to remain left to do or to end up not being done.

So:

• O quarto ficou por pintar = The room was left unpainted / The room remained to be painted
• O quarto não foi pintado = The room was not painted

The difference is nuance:

• não foi pintado is more neutral and simply states the result.
• ficou por pintar suggests the action was intended or expected, but it did not happen.

In this sentence, that nuance fits well because the reason follows: because the paint ran out.

Here, ficou is the 3rd person singular of ficar in the pretérito perfeito (simple past).

Although ficar often means to stay or to become, in this structure it helps express the final state of something:

• ficou por pintar = ended up left unpainted
• literally, something like stayed remaining to paint

So ficou is not translating neatly as just one English word; it is part of the full expression ficar por + infinitive.

In this sentence, por pintar is a fixed and very common pattern.

• ficar por + infinitive = to remain left to do
• estar por + infinitive can also mean to still be to do

Examples:

• A carta ficou por escrever. = The letter was left unwritten.
• O trabalho está por fazer. = The work is still to be done.

If you said para pintar, that would usually express purpose or intended use:

• tinta para pintar o quarto = paint to paint the room
• um pincel para pintar = a brush for painting

So here por is required by the expression, not interchangeable with para.

Portuguese uses the definite article much more often than English.

So:

• a tinta acabou = literally the paint finished
• natural English: the paint ran out

In English, we often omit the article in this kind of statement, but Portuguese usually keeps it.

This is very common:

• O café acabou. = The coffee ran out / There’s no coffee left.
• A água está fria. = The water is cold.

Here, acabou means ran out or was used up, not just ended.

The verb is acabar, which can mean different things depending on context:

• O filme acabou. = The film ended.
• A tinta acabou. = The paint ran out.
• Acabei o trabalho. = I finished the work.

So in this sentence, a tinta acabou means there was no paint left.

In this sentence, porque means because, so it is the correct form.

These forms are often confusing:

• porque = because
• porquê = the reason / why as a noun
• por que = why / for which reason in certain question or relative structures
• por quê = usually why? at the end of a question

So:

• O quarto ficou por pintar, porque a tinta acabou. = correct

Compare:

• Porque faltaste? = Why were you absent?
• Não sei o porquê. = I don’t know the reason.

Because quarto is a masculine noun in Portuguese, so it takes the masculine article o:

• o quarto = the room

This has to be learned with the noun. There is not always a logical reason based on meaning.

For example:

• o quarto = the bedroom / room
• a sala = the living room / lounge
• a cozinha = the kitchen

The adjective or article must agree with the noun’s gender, but in this sentence there is no adjective modifying quarto.

Quarto usually means bedroom in everyday European Portuguese.

In some contexts, learners may see it translated more loosely as room, but that can be misleading. If you mean a room in general, Portuguese often uses:

• divisão = room/part of a house
• compartimento = compartment/room
• or the specific room name, like sala, cozinha, etc.

So without further context, o quarto is most naturally understood as the bedroom.

The comma separates the main statement from the explanation:

• O quarto ficou por pintar = main idea
• porque a tinta acabou = reason

In Portuguese, a comma before porque is often used when the second clause adds an explanatory reason after a complete first clause. It is natural here.

You may also see sentences without the comma in other contexts, especially in shorter or more tightly connected clauses. But in this sentence, the comma is fully normal and clear.

Yes. Ficou sem pintar is also natural, but the nuance is slightly different.

• ficou por pintar = it remained left to be painted; the task was not completed
• ficou sem pintar = it ended up unpainted / without being painted

Both work here.
However, ficou por pintar often sounds a bit more connected to an unfinished task, while ficou sem pintar emphasizes the resulting state.

Both main verbs are in the pretérito perfeito:

• ficou from ficar
• acabou from acabar

This tense is commonly used for completed past events.

So the sentence describes a finished situation in the past:

• the room ended up left unpainted
• the paint ran out

It is not describing an ongoing process; it presents the outcome.

Here pintar means to paint in the sense of applying paint, especially to a room or surface.

Portuguese uses pintar both for:

• artistic painting: pintar um quadro = to paint a picture
• house painting: pintar o quarto = to paint the room

The context makes the meaning clear. Since the sentence mentions a tinta and o quarto, it clearly refers to house painting, not making art.