I am in the process of building a new brick home and have had numerous water problems.  We think the water is coming through the mortar, and we probably will have to re-brick the home.  The problem I’m facing now is a mold issue.

I have a white fuzz-like substance growing on open facing wood as well as black spots forming on this same open wood.  I am very concerned about what’s happening in areas I can’t see.  We have had this problem for about two months so there has been lots of water behind the brick and also inside the house on all the floor levels.  I have three small children under three years of age and do not want to put them in an environment where there is a possible mold problem.  I would appreciate any advice on how to proceed. -Kent , Iowa 

            Brick veneer houses are highly prone to water intrusion problems like those that you describe.  This is particularly the case in houses built in the open ,those unsheltered by trees or adjoining houses.

            Many don’t realize that rain water can make its way through brick and mortar and reach the wall on the other side.  Both mortar and brick are somewhat porous to water with the mortar much more so.  In addition mortar may have tiny (and sometimes not so tiny) holes that start from the exterior of the brick into the wall cavity.

            Because of the porosity of mortar, and small penetrations (as well as the more limited porosity of brick) good building practice requires that there be a minimum of ¾ inch space between brick veneer and the wall, and that this cavity not be obstructed.  It should be served by weep holes at the base of the wall.

            Many brick masons in the Midwest do provide the minimum ¾ inches cavity (some, a half inch or less).  Most don’t remove the excess mortar which may pancake against the wall and provide a direct pathway for water to enter the wall.  Most masons don’t provide weep holes that are needed to allow moisture that penetrates brick veneer to flow out at the base, or if they do they may be obstructed by mortar that has fallen down to the interior base of the brick veneer wall.  Mortar on the inside of brick veneer may even form small “dams” that prevent water from draining down to weep holes.

            The water intrusion/penetration problem is particularly acute if the house is in the open and mortar is more porous than is normally the case.  During wind-driven rains the force of the rain causes liquid water to quickly move into the cavity between the brick and the wall.  In most present-day construction, a layer of Tyvek covers internal construction materials such as oriented strand-board, board insulation, wall studs, and wall cavity insulation.

            Tyvek is not water-tight.  Water passes through it in either vapor or liquid form or both and works its way into the wall where it can remain for days or more causing surfaces to become wet and subjecting materials to high relative humidities.  Such conditions are an excellent environment for mold growth.

            Water that has entered a brick veneer wall must find its way out..  This may be by vaporizing and moving out by diffusion and/or convection.  It may also occur by capillary movement to the exterior brick surface.  These can be seen as wet spots the day after or several days after a rain.

            Once a water intrusion problem has developed in brick veneer facade as you describe, the only effective remediation measure is to remove and replace it.  In general I do not recommend replacing it with brick veneer “that has been more correctly done”.  I’ve known of some such remediations that have resulted in subsequent water penetration and subsequent mold growth because it was not done correctly.  Alternatives include the use of vinyl, aluminum or fibrocement siding.  Vinyl is not recommended for houses in the open since it can be too easily damaged by wind gusts, and because of the effects of vinyl weathering, a match with new replacement material is not likely.  Fibrocement siding is, on the other hand, heavier and provides a range of façade surfaces.

June 23, 2003                                               

 Indoor Environmental Quality (2000), Thad Godish Ph.D., C.I.H

Direct E-mail 00tjgodish@bsu.edu