I would check out an elastomeric coating as they are designed to bridge cracks and are waterproofers as well. If you have large cracks there are fillers that go along with the coating for these areas. Go to your local paint store and they will be able to help you out.

There is a new product distributed through Dunn Edwards in California called Envirocoatings. It has water proofing plus 170% elongation to prevent cracking on surfaces like stucco. Here is the site info:

www.envirocoatings.com

We are the future of ENVIROsmart performance coating systems. ETI manufacturers and distributes the proprietary ceramic insulcoat R:E paint and coatings systems throughout Canada, the USA and overseas. This family of products is formulated with, a proprietary formula of precision blended high performance ingredients, and have over thirty features and benefits and provide thermal barrier, long lasting, long life, lower cost and extremely high quality as well as many more features.

Long Lasting/ Weatherproof / High Breathability/ Ceramic Thermal Barrier / Energy Saving / Environmental / Highly Flexible with Full Memory/ Goes Further-Costs Less/ Easy to Apply and Clean Up and more ...

I did not know this was a site for people doing advertising of their products.