البلاط والسيراميك جديدين.

Because Egyptian Arabic usually leaves out is/are in the present tense.

So:

• البلاط والسيراميك جديدين
• literally: the tile/the tiling and the ceramic new
• natural meaning: The tiles and the ceramic are new

This is very normal in Arabic. The linking verb is just understood in the present.

Because both nouns are definite: the tiles / the tiling and the ceramic.

In Arabic, if two connected nouns are both definite, each one usually takes its own الـ:

• البلاط والسيراميك
• not just one الـ for both

That is similar to saying the tiles and the ceramic, not the tiles and ceramic.

Because here جديدين is a predicate adjective, not an adjective directly attached to a noun.

Compare:

• البلاط والسيراميك جديدين = The tiles and the ceramic are new
• البلاط الجديد = the new tiles / the new tiling

So when the adjective is part of the statement are new, it does not take الـ.

Because the sentence is talking about two things:

• البلاط
• السيراميك

In Egyptian Arabic, when exactly two things are being described together, speakers often use the dual form of the adjective. That is why you get:

• جديدين = new for two masculine things

So the ending -ين here is basically showing both of them are new.

Because البلاط and السيراميك are treated as masculine nouns.

So the adjective agrees with them in gender:

• masculine dual: جديدين
• feminine dual: جديدتين

For example, if you had two feminine nouns, you would expect -تين instead.

It often behaves like a mass/collective noun in everyday Egyptian Arabic.

So البلاط can refer to:

• tile as a material
• tiling
• floor tiles in general

Even if English uses a plural like tiles, Arabic may still use البلاط as a single collective word.

That is very common with materials and categories of things.

Because جديدين describes the whole subject البلاط والسيراميك together.

The structure is:

• subject: البلاط والسيراميك
• predicate adjective: جديدين

So the adjective comes after the full subject, just like saying:

• The tiles and the ceramic → are new

If you put the adjective right after one noun, it would usually sound like it describes only that noun.

A natural pronunciation is:

il-balāṭ wis-sirāmīk gedīdēn

A few useful notes:

• ج in Egyptian Arabic is usually a hard g sound, so جديدين sounds like gedīdēn
• ال before س is pronounced with assimilation, so السيراميك sounds like is-sirāmīk
• و is often pronounced wi- before a consonant, so والسيراميك sounds like wis-sirāmīk

Sometimes yes. In real spoken Egyptian, agreement after two joined nouns can vary, and you may hear a plural adjective in some contexts.

But جديدين is a very natural choice here because it clearly matches exactly two things.

So for a learner, البلاط والسيراميك جديدين is a very good model to remember.