Archive for Monday, July 1, 2013


Fix-It Chick: How to make lime mortar

July 1, 2013


Lime-based mortars are flexible and pervious, allowing for shifts in older foundations and structures and facilitating the movement of moisture in and out walls. This malleability is paramount to maintaining the integrity of older structures. When repairing masonry in homes built prior to 1910, cement products should be avoided. Making and applying traditional lime-sand mortars is an art form often learned through trial and error.

Step 1: A lot of expertise and research can go into identifying and matching the specific aggregate and lime-to-sand ratios of historic mortars. More often than not, standard mixtures consisted of three parts sand to one part lime. Make traditional mortar by filling three buckets with sand. Fill a fourth bucket with hydrated lime.

Step 2: Pour the three buckets of sand onto a large sheet of plywood or into a wheelbarrow or mortar pan. Hollow out the center of the sand, like a volcano, and pour the powered lime into the center of the sand pile. Do not inhale the lime dust.

Step 3: Lime mortar can be slaked (cooked) overnight or for up to two years to increase its strength. To slake the mortar mix, slowly pour a third of a bucket of water over the lime. Use a shovel and cover the lime-water mixture with the sand from the outer edges of the sand pile. Heat generated from the lime will dry the sand, forming cracks along the surface area.

Step 4: Once the slaked mixture has cooled, thoroughly mix the lime and sand together to form a putty-like mortar. Smooth the mixture by pounding it with a large wooden mallet or stick.

Step 5: If slaking is not desired, thoroughly mix the dry lime and sand together until a uniform color is achieved.

Step 6: Slowly add water to the dry mix, turning and stirring the mortar until a uniform, stiff putty texture is achieved. The mixing process should take a minimum of 15 minutes. Use as little water as possible, less than half a bucket, to ensure the strength of the mortar mix.

Step 7: Mortar mixes can be stored covered with a damp tarp or in a sealed bucket for several weeks.

Step 8: Once applied, facilitate the curing process by keeping the walls and mortar moist for several days or weeks. Do not allow uncured mortar to freeze.


Mari Aubuchon 2 years ago

Thank you so much, Linda. This is just the info I need for my upcoming project. Duly cut and pasted. :)

P1rky 2 years ago

Disappointed to read such an ill informed piece. Hydrated lime is never as succeful as lime putty because of the lack of free water. Hydrated lime starts to carbonate the moment it is made. Therefore after 6 months you will have a bag of both hydrate and chalk or limestone. ( check the lime cycle somewhere.

Hydrated lime is already slaked quicklime. So your ideas of "cooking" has nothing to do with slaking and every thing to do with re-hydrating. Or addi g the free water found in lime putty.

It is obvious to me that you have never actually performed your method because hydrated lime will not creat an exothermic reaction (create heat).

If you have actually mistaken hydrated lime with Quicklime then your proportions are all wrong.

If this is so, what you are describing is a hot mix. Where, because quicklime will expand by three when slaked. You actually need 1:9 ratio of quicklime to agrigate.

Linda Cottin 2 years ago

Yes, you are correct, by adding water to hydrated lime you are re-hydrating it. It would have been better if I used the word "re-hydrating" rather than "cooking." I selected the word "cooking" thinking it would add less authority to the article, as there are so many other factors I could not possibly have covered in 400 words or less. With hydrated lime there is not a true exothermic reaction, but the absorption of water does create the illusion of one. Using quicklime rather than hydrated lime would be dangerous and could cause an explosion.

P1rky 2 years ago

You cannot make hydrated lime without quicklime. You get quicklime, add just 27% water by volume. The exothermic reaction creates heat it does not explode. The reaction takes up the water into the hydrate and because just enough water is added we end with a dry hydrate. So you have added h2o to Cao and you get ca(ho2) commonly known as Cacuim Hudroxide.

When you heat or burn limestone, chalk, shell, marble, all different forms of calcium. you drive off the calcium dioxide oxygen hydrogen etc, and create Quicklime. Because energy cannot be destroyed the heat put in whilst burning off carbon dioxide it is stored in the quicklime. When you return water (ever heard of slaking your thirst) the quicklime releases it's stored energy , heat, an exothermic reaction.

Whilst making lime putty we actually add 300% water not 27% is means that the 27% is still taken up but we end up with a paste because we have added too much water to make a powder. Lime putty is what we add to sands to make a mortar.

So far we have replaced the oxygen and hydrogen back to the caluim. When we expose the mortar to atmousphere the lime takes in the missing carbon dioxide. Originally burned off. When that is done it becomes chalk limestone again,

So we have taken a lump of chalk to bits, added sand, with carbonisation we now have a lump of chalk combined with sand which is stronger than the the individual parts. Which were chalk, limestone etc and sand.

One last point, people are so pre-occupied by the danders of lime. Consider this. I for one would much rather handle lime lime putty and quicklime . Than your average househ

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