You need to ensure that any table top you use is a reasonable size for the number of blocks you're using. The blocks have a relatively large surface area, so as long as there isn't too much overhang a glass top should be stable!
For table arrangements with horizontal blocks:
We would recommend using a top no bigger than 120cm in diameter for two spaced blocks, or 100cm for two blocks pushed together. For a single block with a rectangular top we would recommend using a top no wider than 50cm, and no longer than 90cm.
For table arrangements with upright blocks:
We would only suggest using a round top for upright blocks with a minimum of three blocks for stablility. For rectangular tables, we would recommend using a top no wider than 50cm and no longer than 90cm with a minimum of two blocks for stablility.
We provide four clear rubber circles per block with every order to protect your top from the concrete, and four felt circles per block to protect your floor.
We can take no responsibility for the success of any table tops you choose to use in conjunction with the blocks, however.