După avarie apar scurgerea, umezeala și mucegaiul.

Because the subject is actually a list of three things:

• scurgerea
• umezeala
• mucegaiul

Each noun is singular by itself, but together they form a compound subject, so Romanian uses the plural verb: apar = appear.

If there were only one item, you would use apare:

• După avarie apare mucegaiul. = After the damage/breakdown, the mold appears.

They are singular because each word names one phenomenon/category:

• scurgerea = the leak / the leakage
• umezeala = the dampness
• mucegaiul = the mold

Romanian often lists singular nouns like this when talking about types of damage or effects in a general way.

In English, you might sometimes prefer a plural in similar situations, but Romanian does not have to match that pattern exactly.

Those are the definite articles, which in Romanian are attached to the end of the noun.

So:

• scurgere = leak / leakage

• scurgerea = the leak / the leakage

• umezeală = dampness

• umezeala = the dampness

• mucegai = mold
• mucegaiul = the mold

Romanian puts the at the end of the noun, not before it as English does.

După avarie is a more general expression meaning something like after a breakdown / after damage / after a fault.

Romanian often leaves nouns indefinite in this kind of time or circumstance expression.

Compare:

• după avarie = after damage / after a breakdown, in general
• după o avarie = after a breakdown
• după avaria de ieri = after yesterday’s breakdown
• după avaria conductei = after the pipe failure

So avarie here is not wrong at all; it just sounds less specifically tied to one fully identified event.

Avarie usually means a breakdown, fault, damage, or failure, especially in a technical context.

Depending on context, it could refer to:

• a plumbing failure
• a pipe burst
• a mechanical breakdown
• damage to an installation or system

In this sentence, because the later problems are leakage, dampness, and mold, avarie most likely refers to some kind of water-related fault or damage.

Yes, it is normal.

Romanian often puts the verb before the subject when introducing something that appears, happens, or exists. This structure can sound natural in informative or descriptive statements.

So:

• După avarie apar scurgerea, umezeala și mucegaiul.

is natural, and so is:

• Scurgerea, umezeala și mucegaiul apar după avarie.

The first version feels a bit more like After the damage, these problems appear.

Here după means after.

So:

• după avarie = after the breakdown / after the damage

Be aware that după can also mean other things in other contexts, such as according to:

• După mine... = In my opinion / According to me...

But in this sentence, it clearly means after.

It can be, but it depends on context.

Scurgere can mean:

• leakage
• a leak
• draining / flow / runoff

In a water-damage context, scurgerea is understandable as the leakage or the leak.

However, in everyday building or repair language, you may also see other words depending on the exact problem, such as:

• infiltrație = infiltration
• scurgeri = leaks / leakages

So scurgerea works, but the most natural choice can vary by situation.

They are related, but not the same.

• umezeală = dampness, moisture in a practical/everyday sense
• umiditate = humidity, moisture level, often more technical or measurable

In a sentence about building damage, walls, and mold, umezeala is usually the more natural word because it suggests damp conditions in the home or structure.

Usually mold is the safest translation.

Mucegai is the general word for mold/fungal growth on walls, food, surfaces, etc. In some contexts, English might use mildew, but mold is usually the better general equivalent.

So:

• mucegaiul = the mold

It is understandable and grammatically possible, but many native speakers might choose a slightly different wording depending on context.

For example, a more general or natural version might be:

• După o avarie apar scurgeri, umezeală și mucegai.

This version sounds a bit more like a general statement about typical consequences.

The original sentence, with all three nouns definite:

• scurgerea, umezeala și mucegaiul

can sound more specific, almost as if these are the identifiable effects being discussed in a report or explanation. So it is not wrong, but it may sound a little more formal or context-dependent.