Dampness penetration from balconies

Dampness penetration from a balcony

By: Eng. Ron Arad

Dampness is one of the most common and troubling problems in Israel. Trace its sources and you will quickly find that one of the most frequent causes of dampness entering an apartment is a failure in the balcony's waterproofing system, letting water seep through.

This article breaks down the components of a balcony waterproofing system and looks at the common failure points in each one.

A. Components of the waterproofing system in balconies

A balcony's waterproofing is actually four systems working together.

The first is the flooring system: the tiles themselves and the grout between the joints. It is the first line of defense against dampness, draining water quickly and efficiently into the drainage system.

The second is the bituminous layer applied over the concrete floor. Done properly, it stops water from reaching the concrete and drains whatever water still gets through the flooring system above it.

The third is the balcony drain itself.
The fourth is the separation sill between the balcony and the living room, meant to block dampness from reaching the apartment even if the other three systems fail.

B. Possible failures in each system

The flooring system (the first system):

Poor slopes: too shallow a slope, or none at all, lets water pool and seep beneath the tiles, which in severe cases can cause flooding. The Israeli standard requires a minimum slope of 1%.
Joint filling: epoxy grout is the recommended fill between tiles, though ordinary, unsealed grout is often used instead to save money. Either way, the grout needs to be intact, with no cracks or gaps. Common failures in the joint fill:

A water-to-powder mix that doesn't match the manufacturer's instructions.
Joints narrower than 3 mm, where grout can't penetrate deep enough or build up enough volume, so it wears away and disappears over time.
Grout not rated for outdoor sun and rain.

The bituminous system (the second system):

Balconies need to be waterproofed with bituminous sheets or polymer-modified bituminous materials, applied evenly and without flaws. The waterproofing needs protection until the sand bed goes down on top of it; even so, it sometimes gets damaged while still exposed, from workers stepping on it and similar wear.

The waterproofing has to continue up the balcony walls that border the apartment, and the transition from floor to wall needs a cant strip, a concrete triangle that keeps the waterproofing from cracking there. Skip or botch the cant strip, and the waterproofing fails.

The drainage system (the third system):

A balcony's drainage runs through an upper drain, a lower drain and a drainpipe, with the upper and lower drains typically sharing a single fitting. The lower drain, sitting beneath the tiles, carries away water that gets under the flooring. A common failure is skipping the gravel-and-geotextile filter that should surround it, and in many cases the lower drain is either poorly built or missing altogether.

The waterproofing belt (the fourth system):

Another frequent failure point is the transition between the balcony and the apartment itself, which SI 1752 Part 1 governs: the standard calls for a concrete belt separating the balcony from the apartment's interior, with the waterproofing applied on top of it. Typical failures in building that belt:

a. The belt is often left off the plans entirely and forgotten during construction.
b. The formwork panels don't sit flush against the wall on both sides, letting thin concrete mix leak out through the gap, which causes segregation in the concrete and sometimes even a step; the waterproofing over that damaged section ends up discontinuous and gets cut by exposed aggregate.

c. No chamfer is cut into the belt as the standard requires, so the waterproofing fails at the resulting right angle in the concrete.
d. No cant strip, as required, so a 90-degree bend in the waterproofing ends up damaging it.

e. Pipe penetrations through the concrete belt aren't properly sealed.
f. The waterproofing doesn't reach the edge of the belt, as the standard requires.

Summary

To keep dampness from getting into the apartment through the balcony, we recommend a quality-control process that checks, among other things:

1. A double drain wrapped in gravel on the balcony.
2. Flooring sloped at least 1% toward the drains.
3. Joints of at least 3 mm in the flooring, filled with grout per the manufacturer's instructions.
4. A complete, chamfered separation belt.
5. Waterproofing that follows SI (Israeli Standard) 1752 and its details.
6. Proper sealing of any sleeves running through the walls or the belt between the apartment and the balcony.