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Engr3454
Chimney Water Wicking

Our chimney is exposed two stories interior, one story on the south exterior, two stories on the north. Material is gneiss, struck joints, bluestone rain cap, constructed 2006.

When new it experienced water wicking during heavy rains, especially when wind-driven, sufficient to destroy ceiling and wall drywall, and threaten dry rot. Treatment of the exterior in 2009 with silicone masonry sealer (to refusal to accept additional solution) significantly mitigated the problem, but it has begun to recur.

The flashing is NOT the problem.

Any recommendations?

jackercracker
Re: Chimney Water Wicking

Water intrusion in your situation may be caused by a number of things e.g.
- cracks from weathering/movement
- gaps from poor workmanship, weathering (expansion/contraction)
- poor construction e.g. Incorrect surface slope
- permeability of mortar, masonry

Any of these problems can add up to problematic water intrusion

Let's deal with the permeability of your gneiss. Permeability is a measure of how much water can flow through the gneiss in a given time.
There are many different types of gneiss. Some are very impermeable and others are quite permeable.
If you have the latter, then you can mitigate the problem by adding engineering controls, like larger drip edges, wider chimney cap etc.
Also, you can apply a treatment to the gneiss to improve it's water resistance.
Prosoco makes a good sealant called Standoff slx100; they may have better sealants for your situation, give them a call for technical advice.

Engr3454
Re: Chimney Water Wicking

Symptoms and response to treatment are consistent with permeable stone and mortar. Thanks for the vendor name.

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