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Here's How: Improve Appearance of Limestone Patio With New Grout

James Dulley on

Dear James: The mortar in my new limestone patio is deteriorated and looks bad. Can I remove and replace the bad mortar without having to disturb the limestone pieces? -- Ellen P.

Dear Ellen: The large, irregular limestone piece is what makes these patios look so attractive and natural. Limestone is typically much more durable and weather-resistant than mortar to the stones pieces are likely still sound. You will know quickly when you begin to remove the old mortar if the stones are okay.

Mortar will not last forever, but it should not start deteriorating in many spots unless the base was laid improperly initially. The base should be a sand layer for this type of patio, and it generally provides good support for the large stones. Another cause could be soil shrinking and expanding with weather changes. This is particularly true of expansive clay soil.

You really won't know what the quality of the base that is under the stones until you remove the cracked mortar between them. A local builder or civil engineer should be able to tell you what type of soil is typical in your area. If it happens to be a type of soil that expands and contracts a great extent, once it is repaired, you will have to keep your patio watered to stabilize the moisture content in the base.

Since the mortar is already cracked and crumbling, you should not have too much trouble breaking it out with a chisel and a hammer. Be very careful not to break any of the pieces of limestone. You might also consider using and electric hammer to break up the mortar. This reduces the possibility of hitting a stone and it certainly is easier on the shoulder muscles.

Save the old mortar that you chiseled out. The volume of it will give you an idea of the amount of new mortar you will have to mix to refill the joints. Also, you can use some of the small pieces of mortar along with sand under the low pieces of limestone to level up the patio.

The new mortar should be made from coarse sand and Portland cement. Try to determine how much cement and sand you need and get 10% more. The color of sand and cement impacts the color of the mortar joints. If you run out of materials and have to buy more, the mortar joints may not match.


Clean out as much of the old mortar and dust as possible from the joints. It is important for the mortar to adhere to the sides of the stone pieces. If the sides are dusty, it will not adhere well. Before you mix and apply the new mortar, mist the sides of the stones with plain water. This both cleans off any dust and allows the mortar to form a better bond with the stones.

Mix about one part of Portland cement to two parts of sand to make the mortar. Add just enough water so the mortar has a stiff feel and it can be mounded up on the trowel one to two inches without collapsing. Only mix as much as you can lay in an hour.


Send your questions to Here's How, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com. To find out more about James Dulley and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

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