Historic Brick Mortar Requires an Extended Curing Time Before Painting

Lime mortar requires an extended curing time before it can be painted.  In other words, after tuckpointing,  a wall needs a long cure time before it can be painted.  Paint requires a dry substrate.    The simple fact is that lime mortar retains moisture for a much longer period of time than other types of mortars such as the common Portland mortars.

In the adjacent picture you can see an example where Paint was applied to an improperly prepared masonry substrate. The paint has failed and delaminated from the surface of the brick masonry.

painting-over-brick-mortar (5)

Even in brick wall types there can be a wide variety of types of lime mortar used in historic restoration, generally though mortars used in historic brick will cure in approximately 3 to 6 months after tuckpointing. The variation or range of a range of expected dry times for final curing is based on several factors. An abbreviated and truncated list of factors affecting dry times follows below.

  1. The directional facing of the wall or facade can make a big difference. Exposure to the sun can increase dry times. North facing walls by comparison rarely get direct sunlight.  In fact, sometimes a south facing wall can dry too quickly even to the detriment of the mortar itself.

 

  1. Guttering or rain diversion is generally outside of the scope of tuck pointing but the building owner should also consider adjacent building systems such as rain diversion when pointing and analyzing masonry cure times. Leaking gutters or downspouts, for example, can significantly increase the expected curing time for historic brick mortars.

 

  1. Rear ells and building bays have restricted natural airflow.   Restricted air flows will also increase cure times.

4.  Rising damp can deter or extend mortar cure times. Rising damp is a condition that wicks groundwater upwards through capillary action of the masonry. Repair of rising damp or installation of damp proof courses can ameliorate this type of situation but it’s generally outside of the scope of brick tuck pointing.

painting-over-brick-mortar (7)In the adjacent picture at the base of the interior wall, you can see the effect that rising damp has had on the paint.  Over time,  The paint has begun to delaminate and bubble away from the brick substrate. Essentially behind the paint where it is impossible to see without removal of the paint there’s efflorescence and build-up which is causing the separation and delamination of the paint.

Paint requires a dry substrate, as mentioned above;  However to really understand the concept it helps to know a little bit more about how paint bonds and adheres to the substrate. Paint adheres or has cohesion to the substrate on a molecular level.  Paint is made up of two principal component classes: pigment and binder.   In a simplified explanation, It’s useful to understand that the pigment basically provides the paint’s color. The binder, on the other hand, creates both an enamel and both in a narrow and enhances the adhesion to the substrate.

Some of the principal factors of paint and substrate bond analysis also include adsorption and mechanical interlocking.  For proper adsorption, a dry substrate is required.  Many lime mortars set and cure through a process called carbonation.  A slow process of chemical reaction with the air allows the mortar to cure but this natural reaction takes time.

In the adjacent photos you can see another example where paint has been applied but significantly failed to maintain proper cohesion to a brick substrate.

This list of conditions, factors, and considerations are some of the many reasons we say that even if a client is not working with a company such as ourselves, we recommend they choose a company similar to ours who is willing to consider a wide range of building facade system issues, building concerns and interrelated systems.   It’s smart to have a strong relationship with a good local contractor.  Be aware of these conditions as they affect your property and ask your contractor for advice on these specific issues.

In this article we talked about the following terminology and  concepts, click the links below for more related information from the IDS website:

  • Lime mortar
  • Curing times
  • Tuckpointing
  • Portland mortars
  • Directional Facade Facing
  • Guttering
  • Rain Diversion
  • Rear Ell
  • Facade Bay
  • Substrate adhesion 
  • Delamination
  • bonds and adheres to the substrate
  • Molecular level
  • Paint Pigment
  • Paint Binder
  • Paint Enamel
  • Adsorption
  • Mechanical interlocking
  • Lime Mortar Carbonation.

These concepts are part of the fundamentals of modern and historic masonry building construction, coating applications and upkeep, maintenance, repair and restoration.

The links in the list above will take you to other articles with more information on defects, failures, preservation and repair of historic masonry.  You can learn a lot more on our blog.  Feel free to check it out.  If you have questions about the historic masonry of your building in Washington DC, fill out the webform below and drop us a line.  We will be in touch if we can help.