All types of lime mortar require protection from adverse weather conditions both during application and afterwards while curing.
The longer you can damp “cure” lime mortar the more resilient your joints will be. Humidity and frequent misting deposit CO2 into the masonry that lime requires to get hard. If at all possible protect your pointed walls with dampened burlap raised 1-2 inches away from the wall for a period of at least 3-5 days.
It needs to be kept moist (not wet) for at least 10 days. This aids the process of carbonation. Keeping the work moist can be achieved by the use of a garden pump sprayer. During and after application, protection should be in place for as long as necessary for the mortar to cure properly and dry sufficiently.
Standard practice for protecting lime renders is with Hessian sheeting draped over the subject area in relatively close proximity to the render. This should be left in place for at least two weeks and while this is a standard requirement for any kind of rendering it's one that is regrettably seldom practiced.
Lime plaster, render or even mortar should not be sealed. Lime plasters are a breathable building material, they help control moisture within your building, and sealing them would disrupt this. Sealing lime plasters can lead to extensive damage to the plaster and substrate that they have been applied to.
Silguard reduces water penetration and surface dusting, making it the ideal alternative to acrylic sealers for a wide range of lime plasters, renders, floors and related materials.
For pure lime putty mortars the hardening process through carbonation takes up to a month for each mm of thickness. Therefore it may take 20 months before a lime putty mortar has carbonated to a depth of 20 mm.
Lime mortar has better waterproofing
This caused the mortar to expand and contract as it heated and cooled. Also the water in the mortar would be susceptible to freezing. All this would mean your mortar, over time, would crumble. Lime mortar reduces this water intake and reduces the chances of crumbling.
Allowing mortars to be saturated by rain should be avoided for the following reasons: – Over saturated mortars can result in lime leaching which, in severe cases, will affect the binder ratio with negative effects on the durability of the mortar. A typical example is if the mortar is too sandy when rubbed.
It's not just the building envelope that benefits from this multi-faceted natural material. Because lime mortars and plasters are porous and open-textured, moisture will be absorbed and released thus stabilising the humidity within the building whilst reducing surface condensation and mould growth.
New lime mortars will age and weather and therefore change appearance over time. Lime mortars will also appear different when dry and when wet.
One of the main reasons lime mortar crumbles is due to it drying out too quickly after application. Lime mortars gain strength via carbonation. Carbonation is slow and can only take place if the mortar remains damp. Allow fresh mortars to cure slowly over 2-4 weeks to allow for proper carbonation.
If you notice your lime work is turning white very quickly, then it is drying out too quickly! The optimum curing conditions for hydraulic limes are 15-20°C and a Relative Humidity (RH) of 55-85%. If you have these conditions in place then your mortars will be fully cured at 90 days.
Non hydraulic lime hardens by a slow process of carbonation, reacting with atmospheric carbon dioxide over a period of weeks. Hydraulic limes and cements set rapidly by reacting with water in a matter of hours.
Although the setting process can be slow, the drying time of a lime mortar must be regulated at a slow rate to ensure a good final set. A rapidly dried lime mortar will result in a low-strength, poor-quality final mortar often displaying shrinkage cracks.
In carbonation of lime can only take place in the presence of water. It can years for a new plaster/render to reach its full strength. If plaster/render dries before sufficient carbonation has taken place then cracking can occur.
As mortar hardens and develops strength more slowly in cold weather, new masonry, or areas under construction, should be covered and protected from the elements. This is likely to require two layers - thermal protection such as hessian or some form of quilting and a waterproof sheet to stop the under layer getting wet.
Always check the weather forecast before planning your lawn care projects. If heavy rain is on the way, delay applying lime or fertilizer until after the showers are over. In fact, wait for your property to drain thoroughly. Never add lime and fertilizer to soggy soil, and certainly not if the lawn has puddles.
Disadvantages. Non-hydraulic lime plaster sets slowly and is quite caustic while wet, with a pH of 12. Plasterers must take care to protect themselves or use mild acids as vinegar or lemon juice to neutralize chemical burn. When the plaster is dry, the pH falls to about 8.6.
On any surface one should be looking to apply a uniform thickness of lime render of about 9-12 mm (plasters being the top coat are applied much thinner, 4-7 mm). For the best results it is recommended to actually 'throw, cast or harl.
Generally, hydraulic lime mortars and plasters should remain reasonably workable for 24 hours. It's best to use bagged hydraulic lime powder six months after purchase when stored well; the official use-by date is 6-12 months.
No mortar will last forever, and any form of mortar requires maintenance to keep it in the best condition. However, in most settings pointing tends to need to be replaced every century. As pointing ages, the mortar in the joints tends to weather and erode, causing it to crack and slowly crumble.
Portland cement based mortar is more durable. Lime mortar is softer, which is good in some ways but it wears away over time, especially with acid rain.
over Cement
Lime-based buildings expand, contract and flex with changes in temperature and moisture. The use of lime also allows damp to be absorbed to a limited degree and then evaporate harmlessly away.