O rodapé da sala ficou com tinta branca, porque o pincel estava demasiado cheio.

Yes, rodapé can mean a footer in writing or on a page, but in this sentence it means the baseboard / skirting board along the bottom of the wall.

In everyday Portuguese, the correct meaning depends on context:

• rodapé in a text = footer
• rodapé in a room = skirting board / baseboard

Because the sentence mentions da sala and tinta branca, the physical meaning is the one being used here.

Because da is a contraction of de + a.

So:

• de + a = da
• de + o = do
• em + a = na
• em + o = no

Here, o rodapé da sala literally means the baseboard of the room.

This kind of contraction is extremely common in Portuguese and is something you will see all the time.

Here, ficou com means something like ended up with, got, or was left with.

So:

• O rodapé da sala ficou com tinta branca
  = The baseboard ended up with white paint on it

The verb ficar is very flexible in Portuguese. It can mean things like:

• to stay
• to become
• to end up
• to be left

In this sentence, it is not really stayed. It is more the idea that the baseboard got paint on it as a result of what happened.

In Portuguese, adjectives usually come after the noun.

So:

• tinta branca = white paint
• casa grande = big house
• livro interessante = interesting book

Putting the adjective before the noun is sometimes possible, but it often changes the tone, emphasis, or style. For a basic descriptive phrase like this, tinta branca is the normal order.

Because tinta is a feminine noun.

In Portuguese, adjectives must agree with the noun they describe in gender and number:

• tinta branca — feminine singular
• carro branco — masculine singular
• paredes brancas — feminine plural
• carros brancos — masculine plural

So branca agrees with tinta.

Because estava is the imperfect form of estar, and it describes an ongoing background condition.

• o pincel estava demasiado cheio
  = the brush was too full

This suggests that the brush’s being too full was the state that caused the accident.

Very often in Portuguese:

• imperfect = background, ongoing state, description
• perfect/simple past = completed event

So the structure here is very natural:

• result/event: ficou com tinta branca
• background cause/state: porque o pincel estava demasiado cheio

If you used esteve, it would sound more like a finished event, and it would be much less natural in this context.

Here, demasiado means too or overly, not just very.

So:

• demasiado cheio = too full
• muito cheio = very full

That is an important difference.

In this sentence, the idea is that the brush had more paint than it should have had, which caused the paint to get on the baseboard. So demasiado is the right choice.

A few similar examples:

• Está demasiado quente. = It’s too hot.
• Está muito quente. = It’s very hot.

Because cheio describes o pincel, and pincel is masculine.

So the agreement is:

• o pincel estava demasiado cheio
• not cheia

Compare:

• O balde estava cheio. = The bucket was full.
• A garrafa estava cheia. = The bottle was full.

The adjective must match the noun it refers to.

Yes, cheio de tinta would be a fuller, more explicit version:

• o pincel estava demasiado cheio de tinta

That means the brush was too full of paint or more naturally the brush had too much paint on it.

In the original sentence, de tinta is left out because it is easy to understand from context. Since the sentence already mentions tinta branca, the listener naturally understands that the brush was too full of paint.

So both are possible:

• o pincel estava demasiado cheio — natural, context makes it clear
• o pincel estava demasiado cheio de tinta — more explicit

Usually, yes, in sentences like this.

• porque = because

But Portuguese has several similar-looking forms, and learners often mix them up:

• porque = because
• porquê = the reason / why (usually as a noun, often with article: o porquê)
• por que = why / for which reason
• porquê? can also appear in some question contexts, depending on punctuation and structure, but for beginners the most important contrast is:
  • Porque faltaste? = Why were you absent?
  • Faltei porque estava doente. = I was absent because I was ill.

In your sentence, porque is simply the conjunction because.

Yes, it is natural and understandable in European Portuguese.

A European Portuguese speaker might also say things like:

• O rodapé da sala ficou com tinta branca porque o pincel estava demasiado cheio.
• O rodapé da sala ficou manchado de tinta branca porque o pincel estava demasiado cheio.
• O rodapé da sala sujou-se com tinta branca porque o pincel estava demasiado carregado.

But the original sentence is perfectly fine.

One small note: in painting contexts, people may also say a brush is carregado with paint, meaning loaded with paint. Still, demasiado cheio is easy to understand and works well.