Welcome to Family Roofing

CALL FAMILY ROOFING FOR ALL OF YOUR ROOFING, GUTTER AND CHIMNEY/BRICK REPAIR NEEDS IN WASHINGTON, DC AT (202) 276-5004 OR EMAIL US AT FAMILY.ROOFING@YAHOO.COM!!

 

 

 

 

 

 

Best Way to Waterproof a Chimney

Asking what’s the best way to waterproof a chimney or what are the best waterproofing products are both understandable enough questions, but they’re also too broad for a simple answer. Best way to waterproof what kind of chimney? Are we waterproofing a vertical wall or the breast of the brickwork?

Sealing Brick Chimney

One of the central issues concerning waterproofing is the porosity of the material being waterproofed.  This makes sense: you don’t have to waterproof steel or vinyl because water doesn’t penetrate them in the first place.  While bricks are generally less porous than many other materials, different types of bricks vary in porosity themselves.

This explanation is to set the stage for understanding that sometimes you have to waterproof a chimney more than once. Ask your Pro to go over it twice just for good measure (even if it costs a bit more).  If you have spalling brick, i.e. the faces of the brick are popping off, don’t bother to waterproof the chimney.

Now for some specific information, still with bricks:

How is chimney waterproofing applied?

Waterproofing is applied with a sprayer. On the vertical walls, i.e. most of the chimney, waterproofing should be applied from bottom to top because as the waterproofing material comes out of the sprayer it runs down the chimney and gets absorbed into the chimney below the area being working on.  It almost amounts to doing it twice.  Obviously, the top needs extra attention.  After you finish about 10 minutes’ worth, do it again just to make sure the whole structure gets a good soaking.  Special considerations should be given to breast walls, re-application, the crown, the flashing area and the mortar joints.  The breast wall is where a chimney doesn’t go straight down to the ground, rather goes around something (almost always a fireplace.) These areas should get different treatment.

Sealing the Chimney Breast

Because the chimney breast has a more severe exposure to rain and particularly snow, it needs more coats of waterproofing.  Most waterproofing used these days is water-based material.  This is for a couple reasons: one is that water-based materials cost considerably less than solvent based materials. They are safer to ship, store and use and they are perfectly adequate to the task. The exception to the advantages is on non-vertical surfaces.

One way to deal with a non-vertical surface is to waterproof it over and over and over. Another is to use a solvent-based material, still with polysiloxanes, because it soaks deeper into the substrate. For a chimney with a breast below, opt for the more expensive solvent-based waterproofing. A special note about re-applications. If one needs to re-apply waterproofing after the water-based material has already dried, solvent-based waterproofing should be used.  Whether re-applying the next day or ten years later, use solvent-based waterproofing.

Sealing a Chimney Crown

The chimney crown is an almost flat surface and it’s made of concrete or mortar.  It shouldn’t be made of mortar, but there’s a good chance that it is anyway.  Based on what you’ve just read about waterproofing the chimney breast, you’d reasonably think that you’d just use a solvent based waterproofing material there. But that is not so: a crown requires more than ordinary waterproofing.

The crown is rather porous.  If you’re lucky the crown will be made of concrete and will have been worked in a way that makes the top quite smooth and non-porous. But on average, crowns are fairly porous and have more exposure to rain and snow than all of the rest of the chimney, and accordingly more problems (e.g. leaks) that the rest of the chimney as well.
There are coatings made specifically for crowns (the two major brands are Weather Tight and Saver Systems and both are generally available to the trade only.)  Regardless of the brand being used, crown preparation is key.  All the moss and dirt must be wire-brushed away.  The crown should be wetted down before the material is applied.  Crown coatings applied to dry surfaces don’t develop the necessary bond you’re looking for.  Large cracks should be caulked with high resin filler before the crown coat is applied.

There are terrific flashing products which, in my opinion, are sadly underused. Flash Seal and Flash Tight (once again, Saver Systems and WaterTight products) are high-resin coatings specifically for this purpose. To waterproof the flashing really well, ask for one of these products.

Now for the big one: the mortar.  Since most leaking occurs at the joints, you want to be extra sure you soak them real well with the waterproofing.  You should know that as a rule mortar joints are often not as well bonded as you might think they are, and there are actually small cracks in the mortar (usually not visible though.)  The joints themselves have different properties on different chimneys depending upon whether mortar cement or Portland cement was used, not to mention the particle size of the sand used and the pH of the water that was mixed to make the mortar.

How long does chimney waterproofing last? 

Before moving on, let me answer another FAQ. The question is how long does chimney waterproofing last? Answer is, as a general statement, probably about 20 years for most people. If you have the wind blowing sand at your chimney a lot, perhaps in the desert or by the sea, the brick surface can wear away, but most people don’t have that. 

What is the difference between beading and repelling water?

A related subject: there’s a difference between “beading” and repelling water. Right after anything is waterproofed, there is a very satisfying effect called beading.  This is where you see beads of water just sitting on the surface, kind of like seeing water sitting on oil.  As neat as it is to see, the effect is temporary.  I don’t know why, but the fact remains that waterproofing remains effective for many, many years beyond the beading effect is gone.