Freeze-Thaw in Central Anatolia: Preparing Outdoor Stone for Winter

In Central Anatolia, winter is the harshest time of the year for outdoor stone. In cities such as Ankara, Kayseri, Sivas, Konya and Eskişehir, night temperatures stay below zero for weeks on end and rise again with the sun during the day. This back-and-forth causes the water inside the stone to freeze every night and thaw every day. For a dry stone, this cycle matters little; but for a water-saturated step, garden path or façade cladding, every cycle means a small amount of damage. In this article we look at how freezing and thawing damage stone, why the water absorption rate is decisive, what to do in autumn, how to choose a de-icer, and what to check in spring.

In short: When water freezes, its volume increases by about nine percent; when water that has filled the pores of the stone freezes, it pushes outward from within, and repeated cycles crack and flake the stone. The basic steps for protecting stone are to choose stone with low water absorption, prevent water from standing on the stone, check the joints and slope in autumn, use de-icer sparingly, and catch damage early in spring.

How Do Freezing and Thawing Damage Stone?

Water is one of the few substances whose volume increases, by about nine percent, as it freezes. This is why a jar of water cracks when you put it in the freezer. The pores and capillary cracks of stone behave like small jars: when the water that has filled them freezes, it wants to expand and pushes against the pore walls.

A single freeze usually does not break sound stone. The problem is that this event is repeated dozens of times throughout the winter. With each cycle the pores and micro-cracks widen a little more, the water that melts the next day penetrates deeper into these enlarged voids, and the following night it creates even greater pressure. Over time thin flakes lift from the surface, stair nosings break, and slabs crack from end to end.

The continental climate of Central Anatolia strengthens this cycle in particular. The temperature difference between night and day is large; on a snowy day, when the sun comes out, the snow on the surface melts, the water seeps into the stone and freezes again at night. South-facing steps may thaw and freeze many times in a day, while stones in the shade on the north side may stay frozen for weeks. What determines the number of cycles is not just the cold, but how often the temperature swings back and forth around zero.

Why Is the Water Absorption Rate So Important?

The basic condition for frost damage is the presence of water inside the stone. A stone that absorbs little water is far less affected by freezing cycles, while a porous stone that absorbs a lot of water wears down more every winter. For this reason, the first value to look at when choosing outdoor stone is its water absorption rate.

The water absorption and frost resistance values of natural stone are measured with standard test methods. Water absorption shows, as a percentage by weight, how much water the stone takes in under specified conditions. For frost resistance, in the EN 12371 standard used in Europe, stone specimens are frozen in air and thawed in water through repeated cycles; the result is evaluated as the change in the stone's strength after the cycles, or the number of cycles at which cracking begins. We explained in detail how to read these values in our article on the technical values of natural stone in detail.

In practice, this means: when buying stone for outdoor use, you should ask the manufacturer or supplier for the stone's water absorption and frost resistance test results. Two stones sold under the same name can show very different values if they come from different quarries or different layers. A stone that looks beautiful but has high water absorption may stay trouble-free for years indoors, yet begin to flake within a few winters in a Central Anatolian garden.

Which Stone Is More Frost-Resistant?

As a general tendency, dense-textured, low-porosity stones are more frost-resistant. Granite, basalt and dense-structured andesites usually fall into this group; thanks to their low water absorption, they last a long time outdoors. Some dense marbles can also perform well outdoors, but because polished marble becomes very slippery on an icy, wet surface, walking surfaces need a textured finish.

Porous limestones, some types of travertine and soft tuffs, on the other hand, can be more sensitive to freeze cycles. This does not mean these stones can never be used outdoors; but it indicates that test results should be checked when selecting them, water should be prevented from standing on the stone, and regular protection should be carried out. The fact that local stones used in the region's traditional buildings have stood for centuries also often depends on their being used in the right place and in the right way, and on water being drained quickly away from the structure.

Surface finish and thickness matter as much as the type of stone. Thin slabs yield to frost pressure more easily than thick ones; adequate thickness should be chosen for steps and areas where vehicles pass. A stone with a flamed or brushed surface provides safer footing in icy weather and also makes small flakes, which would go unnoticed on a polished surface, less noticeable. When cleaning textured surfaces, a plastic brush should be used instead of a hard wire brush.

What to Do in Autumn

The best time to prepare outdoor stone for winter is the dry autumn days before the first frosts. During this period the stone can still dry out, joint repairs can cure, and protective products can work properly. Repairs made after winter arrives are both difficult and often not lasting.

The sequence that can be followed in autumn preparation can be summarized as follows:

1. Joint inspection: Cracked, hollow or separated joints are identified and repaired; an open joint sends water directly under the stone all winter and causes the slabs to lift.
2. Slope and ponding: Puddle-forming hollows and sunken slabs after rain are marked; the places where the freeze cycle is most severe are the spots where these puddles occur.
3. Drains and gutters: Terrace drains, garden channels and downpipe outlets are cleared of leaves and soil; a blocked drain turns into a frozen pond in winter.
4. Repair of breaks and cracks: Breaks on stair nosings and small cracks are repaired with materials suitable for outdoor use and resistant to frost; a small crack grows throughout the winter.
5. Water repellent check: By dripping water onto the surface, you observe how quickly the stone absorbs it; if the drop is absorbed quickly, a breathable water repellent is renewed while the stone is clean and dry.
6. Planters and furniture: Planters on the stone are raised or removed so that water does not collect beneath them; the underside of a planter that stays damp all winter is one of the places where freezing does the most damage.

It is very important that the water repellent allows the stone to breathe. A coating that completely closes the pores prevents water that has somehow entered the stone from getting out and can increase frost damage. We compared suitable product types in our article on water repellent application in detail.

Choosing and Using a De-Icer

Products used against icing are the second major load stone faces during winter. The most widely used de-icer is sodium chloride, that is, road salt. Calcium chloride and magnesium chloride, which are effective at lower temperatures, and acetate-based products are also available on the market. Studies on the effects of these products on stone and concrete do not always give the same result; some products may be more harmful to concrete while behaving differently on stone.

Regardless of the type of product, the main risk for stone is the same: melting salt water enters the pores of the stone, and when the water evaporates the salt crystallizes and presses on the pores. When the salt water freezes again, freezing and salt crystallization work together and accelerate the damage. So how the de-icer is used matters as much as which one it is.

Things to watch out for when using a de-icer:

• Mechanical cleaning first: Snow and ice are removed first with a shovel and broom; de-icer is used only for the remaining thin layer of ice and only in the amount needed.
• Measured spreading: Salt spread in excess is useless; it mixes with the meltwater into the stone and the surrounding soil.
• Removing meltwater: The salt water formed after the ice melts is, if possible, swept away or removed with a squeegee before it can stand on the stone.
• Testing the product: A new de-icer is first tested on an inconspicuous step; the warnings given for stone and concrete surfaces in the product documentation are read.
• Role of sand: Sand or fine aggregate can be used for slip prevention, but it is carried indoors on shoes and scratches interior floors; a good chain of doormats is needed at the entrance.

Metal shovel blades can also break the nosings of stone steps and the edges of joints. Using shovels with plastic or rubber edges noticeably reduces this kind of damage. We also covered preventing salt and mud from being carried onto the interior floor at building entrances in our article on building entrances in winter separately.

Spring Inspection and Repair

When winter is over and the frosts have ended, the condition of outdoor stone should be carefully reviewed. This inspection allows damage that occurred during winter to be caught early and repaired before the next winter. A small flake or a single crack can turn into much greater damage the following winter if it is not repaired.

In the spring inspection, you first look for thin flakes lifting from the surface and areas that have turned powdery; these are the first signs of frost and salt damage. Check whether there are breaks and cracks on stair nosings. Slabs that move when stepped on or sound hollow are identified; these may indicate that ice has formed beneath them and the bed has deteriorated. Surfaces showing white salt marks are washed several times with clean water to draw the salt out of the stone.

The table below summarizes a maintenance calendar that can be applied to outdoor stone throughout the year:

To understand the cause of loose or lifting slabs, you can take a look at our article on why stone flooring bulges Damage of this kind often points to a problem not only on the surface but also in the bed beneath the stone and in the drainage.

Recommendations for New Outdoor Areas

If a new garden, terrace, entrance staircase or plaza is being built in Central Anatolia, the most effective measures against freeze-thaw are taken at the design stage. The stone's water absorption and frost resistance values should be requested, textured finishes should be preferred on walking surfaces, and slabs should be chosen with a thickness suited to the load they will carry.

During installation, a slope should be provided so that water drains quickly away from the surface, the joints should be filled fully with a compatible material, and the bed beneath the stone should be prepared so that it does not hold water. Making sure the nosing detail on steps directs water outward rather than under the step, and that downpipes discharge into a channel rather than onto the stone surface, prevents major repairs in the long run.

If you want to prepare your outdoor stone for winter or assess damage after winter, you can send photos of the areas and the type of stone used through the service request form ; after an inspection, we will propose a maintenance plan suited to the season.