Question: Can I dilute this product and use it through a spray gun.
Answer: Although this product does dilute with water it would make the product less efficient, so the answer is no.

Question: Can I use this on my metal gate
Answer: Yes, just wire brush off loose rust and flaking paint and away you go.

Question: Does it work on wood.
Answer: Yes although you have to make sure that the wood is good and solid, if it has been coated before make sure that the previous coating is not flaking, if it is then you will have to remove the loose coating.