The short answer is that you can’t use blackjack on a rubber roof. The long answer is that there are a few factors to consider.
One issue is that rubber roofs are not meant for heavy play. They are designed to deflect rain and snow, not absorb impact from cards or players.
Plus, the rubber roofing material itself can be quite slippery when wet, making it difficult to keep your hands and cards stable. .
Another issue is that blackjack is a very high-risk game. Even if you hit on every hand, you could still lose big if the dealer has a good hand.
On a rubber roof, even a small mistake could lead to disaster.
Finally, there is the question of legality. Many jurisdictions do not allow gambling of any kind on property covered by a rubber roof, regardless of the type of game being played.
