With temperatures across the U.S. exceeding well beyond the 90° F during the day and relentless scorching sun I have been asked the same question a lot in the past few weeks. Can or should I use lime products above the suggested 85° mark?
Using Lime in extreme conditions can require extreme or excessive measure to ensure a job well done. There is saying that if the worker is happy then the work is happy. If you are in the shade and are well hydrated then this comfort is passed on to the work and potential problems can be reduced. The most common and critical issue would be that excessive drying out of the wall is occurring. Repointing, laying masonry units, and stucco work all require adequate suction control to achieve a good bond. Dampening porous masonry prior to application and occasionally dampening the work will help allow the lime mortar to cure at a slower rate preventing a “flash set” or no set from a occurring. A flash set occurs when water is pulled out of the mortar quickly and in the case of cement mixes the set happens too quickly which is prone to a compromising the intended results. When the water is pulled out of the mortar too quickly from a lime mortar usually the mortar turns to dust and is rendered useless. The work will have to be re-done in its entirety.
Even when a flash set does not occur controlling how the mortar cures is very important in hot weather. A good tip is to cover the recently completed wall sections with damp burlap. Damp burlap works well because it is relatively light, will provide shade, hold water to increase localized humidity and breathe. All these virtues help provide a good environment for mortar to cure the way it should, slow, steady, cool, and damp. Burlap is also used as an indicator tool. When it becomes dry then you know the wall is getting dry behind it or soon will be. Misting the burlap when dry keeps the wall from receiving a direct stream of water and over saturation.
Burlap can be found at agricultural supply centers and has a wide range of uses other than keeping masonry damp.