I have other damp walls on my historic brick or stone building. What could be causing this?

Moisture that is seen in the masonry walls at first and second floor level when it has been determined that no plumbing is leaking within the wall, or improper pointing, flashing or cracks are apparent on the outside, may be due to various causes.

  1. “Rising damp” originating from earth sloped toward the building instead graded to lead water away may sometimes absorb into the mortar or stucco. To correct this the grade should be sloped away from the building. Heat from the baseboard units pull the air containing water toward itself too. This is apparent when plaster crumbles near the baseboard of the first floor or above the baseboard heating unit. A full damproof course of low absorptive masonry such as terra cotta tile can be installed to arrest this condition. Below grade it has been a traditional building technique to parge coats of external plaster on the foundation and coat the parging with tallow, (animal fat). Dig down along that side of the house and after a parge coat of 1 part NHL 5 and 1 part sand apply a bituminous foundation coat to seal out moisture. Consider use of a sheet drain which leads to a french drain tile. Finally remember to grade away from the building and remove loose-fill that causes drainage against the building instead use a less percolating soil that allows water to be shed-off.
  2. There are unused flues built directly into the thickness of solid brick or stone walls that need to be filled with vermiculite or if used, properly lined. Sometimes you will see an accelerated decay of the brick faces and joints where the hidden chimney within the wall is located. If a high efficiency heater is installed without a liner in these hidden chimneys you may see old creosote being carried through the brick or stone wall by the catalyst of condensed water from the efficient heater to the outside face of the wall. This often leaves a brownish streak coming down the wall. The correction is to properly line the chimney with insulative liner.
  3. The moisture content in the room or an adjoining room/basement is great and requires proper ventilation. Often rooms in older houses are tightened up with thermal windows and further power-cooled. They should be equally power-ventilated and not rely on ridge, soffit, or unbalanced venting methods. Natural venting ports in basements are sometimes closed-off. This modification sometimes changes the dynamics of the original design for proper ventilation.
  4. When north-east driving rains push against a wall which was recently repointed or re-stuccoed in Portland cement based material the result is often a water infiltration into the building’s bedding mortar. You may see a “water-logged” look to the exterior masonry. The moisture gets caught up in the punky, loose and absorptive bedding mortar in the deep mass-masonry wall and can’t get out. The answer is not to replace the bedding mortar. The answer is to re-repoint or remove and re-stucco the exterior with the correct lime/sand mortar and stucco so as to return to the appropriate breathability of the historic system.

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