Chair

[north idol]

the image explains the problem.
im making a chair but the floor under doesnt show anything

[calm cairn]

Welcome to the help forum!

Please make sure to read #1029373817119838218 as it may answer your question!

Once your question has been resolved, please mark the post as closed by using the </close:1163944441741049897> command.

[mossy mango]

i think model bigger then 1 block

[cerulean minnow]

!faq java-culling

[calm cairn]

FAQ

Java: Culling

Minecraft hides (culls) the faces between solid blocks to improve performance. To avoid this, remodel a non-solid block. For example: Glass, Pressure Plates, Flowers.
Alternatively, display the model by putting it into the head slot of an invisible Armor Stand or inside an invisible Item Frame, or by using the new Item Display entity.

[cerulean minnow]

to be more precise, it culls the side of a block if the hitbox of a neighboring block completely covers that side

So in your case it doesn't matter if it's a spurce plank, a spruce stair or a red carpet, they would all cull (at least) the floor below them.
Hence the need to either use a item_display entity or some block whose hitbox doesn't cover the full floor.

[north idol]

can you tell me a block that i could use ?

[cerulean minnow]

k, slight correction to what I said:
If the hitbox of a opaque block covers a side.
For something transparent like glass for example that rule doesn't apply (except for other glass blocks perhaps).

As the bot mentioned, some block that can be used are pressure plates, glass, flowers, but also stuff like fences or any other block that is either not opaque or that doesn't cover the whole bottom side.