Por si fuera poco, la tarlatana sigue húmeda.

As if that weren't enough, the mull cloth is still wet.

Breakdown of Por si fuera poco, la tarlatana sigue húmeda.

• seguir: to remain
• húmedo: wet
• la tarlatana: the mull cloth (bookbinding)
• por si fuera poco: as if that weren't enough; to make matters worse

Questions & Answers about Por si fuera poco, la tarlatana sigue húmeda.

What does por si fuera poco mean in this sentence?

It’s a set expression meaning something like:

• as if that weren’t enough
• to make matters worse
• on top of that

It introduces an extra problem or annoyance after other problems have already been mentioned.

So Por si fuera poco, la tarlatana sigue húmeda means that the cloth still being damp is one more bad thing added to the situation.

Why is it fuera and not es, era, or fue?

Because por si fuera poco uses the imperfect subjunctive of ser: fuera.

This expression is not stating a plain fact like it was little or it is little. Instead, it has a more hypothetical or idiomatic sense, like:

• as if that were not enough

That kind of idea often triggers the subjunctive in Spanish.

So here:

• fuera = imperfect subjunctive of ser
• the phrase is idiomatic, and native speakers learn it as a chunk: por si fuera poco

Is por si fuera poco a fixed expression, or can I change it?

It is very commonly used as a fixed expression, and learners are best off memorising it as one piece.

You may also see close variants, such as:

• por si eso fuera poco
• como si fuera poco

These mean roughly the same thing.

But por si fuera poco is the standard, very natural version. Even though you can analyse its grammar, in practice it often works like an idiom.