We are building a new house and want to waterproof the drywall walls in our garage so I can wash cars without damaging the walls. Due to expense, I don't want to use the more expensive waterproofed drywall used in shower backings. Any suggestions on how to apply some type of water proofing to regular drywall?

I have done this for one of my garages in the past.

Three things must be in you favor to have any degree of success on what you know is less than perfect settings.

1. You must have a floor that slopes and drains water easily away from all your walls. Note: a drain in the floor itself may be a code issue check it out.

2. You will need to install a baseboard and be sure to prime, seal, and caulk under and place bead of caulk next to the floor/baseboard seams and the baseboard/drywall seams to shed water asap. Make sure the drywall is up off the floor 1/2"+ to help.

3. You will need to prime and paint the drywall with a gloss or semi-gloss paint to keep water from penatrating the rock/paper surface. I assume you will have taped and filled all holes before doing this.

This still is a short cut and is not the kind of material to have near water, period. I did it as a get by item and planned on replacing the drywall before I moved out. It lasted 5 years with not a wet spot.

If you notice that the drywall looks damp and "you will know it" remove it immediately and replace because it is like a sponge and will aid in rotting the wood behind it. I had cement walls with furring strips.

You would be better off from the beginning using some of the sheet goods available for bathroom remodeling.

Or as I now have done in a recent home used stainless steel sheets and have enjoyed the reflected light and the ability to wipe grease, paint overspray off with a cleaner etc.

Has anyone ever considered vinyl siding for the walls?