W łazience wymieniamy stare kafelki, bo przy umywalce jeden już nie trzyma się dobrze.

Because w meaning in takes the locative case when it describes location.

• dictionary form: łazienka = bathroom
• locative after w: w łazience = in the bathroom

The ending changes from -ka to -ce here:

• łazienka
• w łazience

That k → c change is very common in Polish case forms.

Wymieniamy is the 1st person plural present tense of wymieniać.

So it means:

• we are replacing
• or more generally we replace

In this sentence, the natural sense is we are replacing.

Why this form? Because wymieniać is imperfective, so it is used for:

• ongoing actions
• repeated actions
• actions seen as a process

Compare:

• wymieniamy = we are replacing / we replace
• wymienimy = we will replace

It is the object, but for this noun the accusative plural looks the same as the nominative plural.

• nominative plural: stare kafelki
• accusative plural: stare kafelki

That happens because kafelki are non-masculine-personal plural nouns. In this pattern, the accusative plural often matches the nominative plural.

So after wymieniamy you get:

• wymieniamy stare kafelki = we are replacing old tiles

Both can mean tiles, and in many everyday situations they overlap.

Roughly:

• kafelki = tiles, especially bathroom/kitchen wall or floor tiles; very common in everyday speech
• płytki = also tiles, often a bit broader or more neutral

In home-renovation context, both are very natural. A Polish speaker might use either depending on region, habit, or style.

So stare kafelki is a very normal, idiomatic phrase.

Because bo introduces a subordinate clause, and in Polish that clause is normally separated by a comma.

So:

• W łazience wymieniamy stare kafelki, bo...

This is standard punctuation.

English sometimes feels looser with commas before because, but Polish is more regular here: with bo, you normally use a comma.

Because the preposition przy usually takes the locative case when it means by / near / next to.

• dictionary form: umywalka = sink / washbasin
• locative after przy: przy umywalce = by the sink / near the sink

Again, you see the common k → c change:

• umywalka
• przy umywalce

Jeden means one, and here it stands for one tile.

Polish often leaves out a noun if it is already obvious from context. So:

• stare kafelki = old tiles
• jeden już nie trzyma się dobrze = one already isn’t holding well / one is no longer firmly attached

The full idea is something like:

• jeden kafelek już nie trzyma się dobrze

But repeating kafelek is unnecessary.

Because it refers to kafelek, which is masculine singular.

• jeden kafelek = one tile

If the speaker had used płytka instead, that noun is feminine, so you would get:

• jedna płytka

So the form of one changes to match the gender of the noun it refers to.

Literally, it is something like does not hold itself well.

But naturally, in this context, it means:

• isn’t holding well
• isn’t attached firmly
• is coming loose
• isn’t sticking properly anymore

This is a very natural Polish way to talk about something attached to a wall or surface.

So the tile is not secure anymore.

Because trzymać się is the natural Polish verb phrase here.

Compare:

• trzymać = to hold something
• trzymać się = to hold on / stay attached / stick / remain in place

In this sentence, the tile is not actively holding something else. Instead, it itself remains attached, so Polish uses trzyma się.

This is one of those places where się is part of the standard verb expression and does not translate word-for-word into English.

Together, już nie often means no longer.

So:

• jeden już nie trzyma się dobrze

can be understood as:

• one is no longer holding well

Word-for-word, już is often already, but with negation it very often has the sense of not anymore / no longer.

So in context:

• już nie = no longer

Because Polish word order is flexible, and speakers often move information to the front for emphasis or to set the scene.

Starting with W łazience does this:

• it tells you the location immediately
• it frames the whole situation before the action is mentioned

A different order is also possible:

• Wymieniamy stare kafelki w łazience...

But W łazience wymieniamy... sounds very natural if the speaker wants to begin with the place.

Yes. You could also use:

• ponieważ = because
• gdyż = since / because

But the tone changes:

• bo = everyday, conversational, very common
• ponieważ = more neutral or slightly more formal
• gdyż = more formal, often written

In this sentence, bo sounds the most natural in ordinary speech.