Question
I have recently installed a stone walkway through our garden. The stones are set in concrete, and are gray in color, but not flagstone.  Two questions: When I fill in the joints with mortar, can I add some color to make the stones stand out more?  If I use gray mortar, the walkway almost looks like it is just all concrete.  Could I correct this by using a sealer which would enhance the color of the stones?  What might be the best alternative, and does the walkway need to be sealed regardless of which method I go with?

Answer
John:
First, if there stones are set on sand and not set in concrete then any mortar you put down between the joints will just crack and come up when the first frost heaves the soil beneath and moves the stones. However, if you have a slab and the stones are mortared in place then grouting the joints can look nice. Yes you can use colored mortar to contrast with the stones. Their are many colors to choose. Check your local masonry supplier or hardware store for color charts.
Yes, you may also seal your stone and it will certainly make the colors show up stronger. Beware though, if you use a heavy gloss sealant and it sets up on top of the stone they can be extremely slick when wet. To avoid this be sure you get a penetrating type sealant that is thin and soaks in. Also if you use a heavy gloss sealant, they will be much hotter as the small pores in the surface will be filled. Bare feet will be unbearable on hot summer days.
Sealing is always good to preserve masonry joints and keep water out. What happens to patios is that there are typically tiny or small gaps under the grout between the stones and the slab. When it rains water seeps into the small cracks, joints, and pores of the masonry and collects there until it evaporates or drains into the slab or soil below. However, if this happens on a cold day and it happens to freeze before the water migrates out of these gaps, it pops the stones and mortar loose from the slab. A good sealant can help keep this from happening by closing off the routes that water usually takes to get to these gaps.

I like a sealant called Rez-Seal. Google it and try and find a local vendor.

Best of luck.
Sean J Murphy, LA, ISA, LEED AP
www.seanjmurphy.com