Le plombier a enfin colmaté la petite fuite, si bien que le mur peut sécher.

A colmaté is in the passé composé, a very common French past tense.

It is formed with:

• a = the present tense of avoir
• colmaté = the past participle of colmater

So:

• il a colmaté
• le plombier a colmaté

It is used here because the action is seen as a completed event: the plumber finished sealing the leak.

Because colmater takes avoir as its auxiliary verb in the passé composé.

In French, most verbs use avoir:

• a réparé
• a fermé
• a colmaté

Only certain verbs use être, especially verbs of movement or some reflexive verbs:

• il est arrivé
• elle est partie
• il s’est levé

So a colmaté is just the normal pattern for this verb.

Not exactly.

Colmater means something like:

• to seal up
• to plug
• to stop up
• to patch so that something no longer leaks

It is more specific than réparer, which simply means to repair.

So with une fuite, colmater is a very natural choice because the idea is that the plumber stopped the leak by sealing it.

In French, short adverbs such as enfin, déjà, bien, mal, souvent often go between the auxiliary and the past participle in compound tenses.

So:

• a enfin colmaté
• a déjà fini
• a bien travaillé

This placement is very natural in French.

English speakers sometimes expect the adverb to go elsewhere, but in French this middle position is extremely common.

Because petit is one of the common adjectives that often goes before the noun in French.

A useful rule is that many short, very common adjectives—especially ones about:

• beauty
• age
• goodness
• size

often come before the noun.

So:

• une petite fuite
• un grand problème
• un jeune homme
• un bon livre

That said, adjective position can sometimes change nuance, but here la petite fuite is just the normal, natural order.

Because fuite is a feminine noun in French, so it takes:

• la
• and a feminine form of the adjective: petite

That gives:

• la petite fuite

Like many nouns in French, grammatical gender has to be learned with the word itself. There is not always a logical reason from the English point of view.

Because in the passé composé with avoir, the past participle usually does not agree with the direct object when the object comes after the verb.

Here the structure is:

• Le plombier a colmaté la petite fuite

The direct object la petite fuite comes after colmaté, so the participle stays unchanged:

• colmaté

If the direct object came before the verb, agreement could happen:

• La fuite qu’il a colmatée

There, fuite is feminine singular and comes before the participle, so colmatée gets an extra e.

Si bien que is a conjunction that introduces a result.

It means something like:

• so that
• with the result that
• to such an extent that
• as a result

In this sentence:

• Le plombier a enfin colmaté la petite fuite, si bien que le mur peut sécher.

the second part is the consequence of the first:

• the leak has been sealed
• therefore the wall can dry

It is a more connected and slightly more elegant way of expressing result than just using donc.

Because the result is true now.

The plumber finished the action in the past:

• a colmaté

And now, as a consequence:

• le mur peut sécher

So the sentence moves from a completed past action to a present possibility or present result.

This is very natural:

• past cause → present consequence

Because pouvoir is a modal verb, and modal verbs are followed by an infinitive.

So:

• peut sécher
• peut venir
• peut partir
• peut fonctionner

You do not say:

• peut sèche
• peut sèchet

After peut, the next verb stays in the infinitive: here, sécher.

Because here sécher is being used intransitively, meaning to dry.

So:

• Le mur sèche = the wall is drying / the wall dries
• Le mur peut sécher = the wall can dry

By contrast, sécher quelque chose can mean to dry something:

• sécher ses vêtements

And se sécher means to dry oneself:

• se sécher les cheveux
• se sécher avec une serviette

A wall does not dry itself in that reflexive sense, so sécher is the correct form here.

Le mur refers to a specific wall, the one affected by the leak.

French often uses the definite article when the thing is:

• already known from the situation
• understood from context
• the obvious item involved

So here, once the leak has been mentioned, the wall is a specific wall in the place where the leak happened.

If you said un mur, it would sound more like a wall, introducing it less specifically.

Here it takes the indicative, which is why we get:

• le mur peut sécher

That is because si bien que introduces a real result, not something doubtful, desired, or hypothetical.

So the sentence presents a factual consequence:

• the leak was sealed
• the wall can now dry

That is why you do not use a subjunctive form here.

Yes, that would be grammatically correct, but it is not exactly the same in nuance.

• réparer la fuite = repair the leak / fix the problem
• colmater la fuite = seal the leak specifically

Colmater sounds more precise for a leak, crack, hole, or opening that is being blocked or sealed.

So the original sentence is a good choice if the emphasis is on stopping the leak itself.