El acabado mate necesita una capa de imprimación.

Because acabado is a masculine singular noun in Spanish, so it takes el.

• el acabado = the finish
• los acabados = the finishes

Even though -o often signals masculine nouns, it is still something you have to learn with each noun. In this case, acabado is masculine.

Mate is an invariable adjective here, meaning its form does not change for masculine/feminine or singular/plural in this use.

So you can say:

• acabado mate
• pintura mate
• acabados mate

This is common with some colour and finish adjectives in Spanish. So mate stays mate.

Acabado means finish in the sense of the final surface or texture of something.
Mate means matt / matte, meaning not shiny.

So el acabado mate is the matte finish.

This is very common in painting, decorating, furniture, cosmetics, and product descriptions.

Because the subject is el acabado mate, which is singular.

• el acabado mate necesita = the matte finish needs
• los acabados mate necesitan = the matte finishes need

The verb necesitar must agree with the subject:

• yo necesito
• tú necesitas
• él/ella necesita

Here, el acabado mate works like it, so Spanish uses the él/ella/usted form: necesita.

Because capa means coat or layer, and the sentence is specifying one coat of primer.

• una capa de imprimación = a coat/layer of primer

If you said just imprimación, that would mean primer in a more general sense, but una capa de imprimación is more precise in practical contexts like painting or decorating.

Imprimación means primer: the preparatory coating applied before paint or another finish.

It is a fairly standard word in DIY, decorating, construction, and painting contexts in Spain.

You may also hear related wording such as:

• aplicar una imprimación = to apply a primer
• capa de imprimación = coat of primer

So yes, it is common in the right context, though it is more technical than everyday household vocabulary.

Spanish often uses de to link two nouns, where English might use of or sometimes just put the nouns together.

• capa de imprimación = coat of primer
• botella de agua = bottle of water
• mesa de madera = wooden table / table of wood

So de shows what kind of coat it is: a coat of primer.

Because they are doing different jobs:

• el acabado mate refers to a specific matte finish being discussed
• una capa de imprimación means one coat of primer, introducing it as something needed

So:

• el = the
• una = a / one

This is very natural in Spanish: a known item needs a certain thing.

Yes. In other contexts, mate can refer to the South American drink maté / mate, but in this sentence it clearly means matt / matte because it describes acabado.

Context makes the meaning clear:

• beber mate = to drink mate
• acabado mate = matte finish

So here it is definitely the adjective meaning non-glossy.

Yes, it is very natural. In product, decorating, or design language in Spain, acabado mate is a standard expression.

You might also see similar phrases such as:

• pintura mate = matte paint
• barniz mate = matte varnish
• efecto mate = matte effect

So the sentence sounds normal and idiomatic.

Yes. Requiere means requires, and it sounds slightly more formal or technical than necesita.

Compare:

• necesita = needs
• requiere = requires

Both are correct.
Necesita is a bit more everyday; requiere is a bit more formal or instructional.

It is pronounced approximately im-pree-ma-see-ON in Spain.

The written accent on -ción shows that the stress falls on the last syllable:

• im-pri-ma-CIÓN

A few pronunciation notes for Spain:

• c before i is usually pronounced like th in thin in much of Spain, so -ción sounds roughly like thyON
• in many parts of Latin America, it sounds more like syON

Both are valid depending on accent.

Here it is literal: the matte finish needs a primer coat.

But necesitar is a very general verb and can be used for all kinds of needs:

• Necesito ayuda. = I need help.
• La pared necesita pintura. = The wall needs paint.
• El acabado mate necesita una capa de imprimación. = The matte finish needs a coat of primer.

So learning necesitar is very useful beyond this sentence.