Bricks are very hard and dense, so the moisture is probably not coming through the bricks themselves. The mortar between them is likely the source. The actual leaks can be through either tiny cracks in the mortar or the surface where the mortar touches the brick.
Most likely, if you inspect the wall carefully, you will see tiny cracks in the vertical mortar joints. These are often called head joints. The cause of these tiny cracks is usually poor workmanship or improper proportions of lime and cement in the mortar.
First, we will try to fix your current leaks. If your inspection turns up significant flaws in the mortar, chip it out and repair those spots. Next, apply a sealer to block the moisture’s path through the very tiny cracks that you cannot easily see.
Read the sealer can label thoroughly. Many of the stearate- and silicone-based sealers essentially form a film over the wall instead of penetrating it. This film can seal in moisture and it can get cloudy over time.
The best brick wall sealers to use contain silanes and siloxanes or a combination of the two. These actually penetrate the brick and mortar to partially fill the tiny cracks. You do not want to totally seal them or moisture can get trapped in the wall. This is a real problem in freezing weather.
Many of the sealers should not be applied below a certain outdoor temperature for them to be effective. ProSoCo and SaverSystems both make good-quality sealers.
Now that you have your existing leaks repaired, here are some brick veneer wall design and construction tips that you can discuss with the contractors handling your new room addition.
The use of flashing, and its proper installation, is key to building a leak-proof brick veneer wall. Flashing should be used at the door sill, window sills, and anywhere that there is a horizontal break in the wall. W.R. Grace & Co. makes an excellent brick flashing called Perma-Barrier.
Water-resistant membranes are also a must. Standard old tar paper is still an effective choice. The seams should overlap generously. A better choice might be one of the newer synthetic air/water barrier films. It is important that flashing is placed behind the film.
An adequate number of weep holes is your next line of defense against future water leakage. These should be placed at the base of the walls and above all doors and windows. Although most building codes allow a four-foot spacing, a two-foot spacing is probably better.
Make sure that the proper number of wall ties are used. These are nailed to the framed wall and extend out into the mortar. These actually hold the brick wall up against the framed wall.
Talk to your contractor about using a mortar with a higher lime content. This will not be as strong as the premixed high-strength mortars, but extremely high strength is not needed on a brick veneer wall. A low-strength mortar mixture will not form as many tiny cracks as it sets and from slight movements over years.
