As Shapeways indicates in their material portfolio, sandstone is brittle and should be kept away from moisture. I have found the final printed sandstone models to be quite strong and solid. However, I wanted to find a way to seal and protect the material.
I made a mistake with the colors of one of my sandstone prints. So I thought I would experiment on that. Here you can see the before photos:
I followed the instructions on the can and sprayed a couple of light layers a few minutes apart.
Here are photos of the same model several hours later:
The instructions on the can said the model will take about 24 hours to dry completely. I am very impressed with the result; not only is the sandstone sealed now, but the model has a nice glossy look.