Chimney ? leak

[Dana]

Masonry sealers do not create problems with chimneys, but it may not completely fix your moisture absorption issue. If the exhaust condensate has attacked the mortar enough to open up hairline cracks between the mortar & brick or make the mortar crown/dome on the top of the chimney extra-porous, a masonry sealer won't fix it- it would need new mortar. You should be able to figure this out when you clean the acidic exhaust-grunge off the brick.

I'm not sure if the Thompson product is really ideal for chimneys but it might be. There are some specifically designed for use with clay brick or chimneys. (LastiSeal, etc.) None are cheap- expect to pay $50/gallon or more for anything that will go the distance.

 

[Barry J]

Now my stainless steel liner is in, they waterproofed the exposed brick. Now what should I use to clean the inside brck (living room), and now I will seal up around chimney in attic. I was thinking about stuffing Roxul in to the box around chimney and then metal flashing around the top and seal with fire coating sealant. Then another layer of roxul over that. Would that stop any cold air/warm air condensation problems from the winter??
Thanks

 

[Sponsor]

 

[Dana]

Use metal flashing with fire rated caulk or mastic as an air barrier & fire-block anywhere the masonry chimney passes through a wall, ceiling or roof.

It's a code violation to stuff insulation between the masonry and any flammable materials. Chimneys are required to have a 1" air gap between the masonry & combustible, that must not be filled, so don't stuff it full of rock wool.

Non-flammable fire blocking is required at every floor/ceiling transition within a chimney chase. An air-tight metal barrier at every floor limits both fire spread & humid air convection.

The full IRC specs regarding what you can / can't /must do regarding masonry chimneys are found in Chapter 10.

In the attic it's OK to wrap the masonry with rock wool, as long as you don't use anything combustible to secure the insulation. (Chicken wire fencing is good enough.)

 

[Smunderdog]

I had a similar issue - evidence of water leaking through the ceiling around my chimney in the living room. We replaced the flashing and it helped but still had a bit of seepage during heavy rains. Ended up sealing the cap and brick/mortar joints up on the roof and that ended up solving it completely. There were no large visible cracks in the cap or any poor mortar joints, but it must have become porous enough to allow water through somewhere before we sealed it. Can't recall what we used - my contractor buddy had some leftover industrial grade sealant we sprayed it down with....