Can mortar set in the rain?

Can mortar set in the rain? Can mortar dry in rain?


Can mortar set in the rain?

Yes, it does. Mortar will keep on setting, as it is undergoing a chemical reaction. It is the chemical reaction that causes the mortar to set, not the drying out process. The chemical process occurs when sand is mixed with cement. This leads to the formation of calcium silicate compounds, that cause the mortar to harden.

In fact, it is usually recommended by masons to keep the mortar moist for at least 36 hours, so that the chemical process occurs completely. When the chemical process is occurring, it generates heat which can cause the mortar to get dehydrated, which makes it crumbly and causes it to disintegrate. So wetting the mortar is an important part of masonry. Especially if bricklaying, mortar needs to be kept wet for 36 hours minimum.

So, a little rain will not stop your mortar from setting, hardening, or drying out. But bear in mind a lot of rain can actually cause the mortar to lose lime {Ca(OH2)} which can result in reducing the strength of the mortar. The more lime you lose, the less amount of calcium is available to make calcium silicate compounds and the less hardened the mortar will be after it sets.

So, to answer the original question “Can mortar set in the rain?”. Yes, it does. This means that you do not need to start covering freshly laid mortar with plastic wraps and tarps. You can just wait out the rain. Your mortar will keep on setting.

If you get exposed to a heavy downfall immediately following freshly laid mortar and you are thinking that the mortar will lose lime and get weakened then there is a simple solution to this. You can just mix cement with water in a ratio of one part cement and eight parts water and make a slurry. You can then pour this slurry on top of the already laid mortar. This will then provide the lime to make the mortar harden.

Can mortar set in the rain?

Does rain affect new mortar?

If it’s just a light drizzle, it won’t affect the mortar at all even if it is fresh. But if it is a monsoon rain that continues for more than six hours then it could wash away the lime from the mortar and can lead to mortar that is not as strong as was initially intended for it to be.

Can bricklaying be done in the rain?

Bricklaying can be done in the rain. A light drizzle will not affect the mortar and will definitely not dilute it. But heavy rain can wash away the lime as I mentioned earlier. This becomes especially important if you are placing bricks that will eventually have a roof on top of them. If the mortar doesn’t hold the bricks together firmly when it hardens then it can lead to a lot of problems when you start putting a concrete roof on top of them. Hence it is generally advised to stop bricklaying if there is a forecast of heavy rain. But if you want to continue building you can consider using a tarp to prevent rain on top of freshly laid bricks.

How do you protect mortar from rain?

You can protect mortar from rain by just placing a plastic drape or a tarp over the mortar. Bear in mind that in the mortar a slow chemical reaction is taking place which will eventually harden it. So leaving the mortar for long periods of time will cause it to harden and that can lead to a lot of problems in trying to remove it later on.

Can Pointing be done in the rain?

Pointing is the art of applying mortar to the joints in between bricks or blocks to make a tight seal. When it rains, pointing can be done. But pointing is not an urgent matter, and the main purpose of pointing is to waterproof it is better if do the pointing after the bricks or blocks have dried after rain in the sunshine. So in short, it can wait and I would advise you to wait out the rain before you start pointing.

How long until the mortar dries when it is exposed to rain?

Mortar in a wet environment will take a longer time to harden. If an extra 100ml of water got added by the rain mortar will take an extra hour to dry. If 200ml of water got mixed with it then it will take two hours and so long and so forth. If the mortar gets too runny most builders will usually add more cement and sand in the appropriate ratio to make it thick again, instead of waiting the extra time for it to dry.

What happens if it rains on mortar?

If it rains on old mortar, nothing will happen. Water does not react with calcium silicate compounds found in hardened mortar. If it was a fresh mortar mix, that is recently applied, heavy rain can damage the mortar by diluting it which increases the hardening time and reduces the strength. But if it is just a light drizzle, mortar strength is not affected even if it is fresh.


So in short mortar is usually not affected by rain. Light and moderate rain will not affect mortar, but heavy rain can affect the chemical reaction taking place in mortar. What light rain mostly affects, is the bricklayer or mason who does not want to get wet. So he is going to give you the best excuse to stop working. 🙂


H.W. Reinhardt, C.U. Grosse,
Continuous monitoring of setting and hardening of mortar and concrete,
Construction and Building Materials,
Volume 18, Issue 3,
Pages 145-154,
ISSN 0950-0618,

If you are making a pavement or a pathway it’s best to make concrete and use that instead of plain mortar as it is stronger than regular mortar. You can view this article for a dedicated concrete mixing guide.

If you are looking to make plaster instead, see this dedicated article.

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