How to Water­proof a Base­ment from the Interior

Aug 5, 2012 • By Matthew Stock.

Ask the aver­age home­own­er how base­ment water­proof­ing is done and the first words out of his or her mouth are like­ly to be ​“I guess they have to dig up my foundation.”

This isn’t nec­es­sar­i­ly wrong. In many cas­es, the best way to per­ma­nent­ly water­proof a base­ment will begin with exca­va­tion to install an exte­ri­or water­proof­ing mem­brane and/​or exte­ri­or drain tile. These are very effec­tive meth­ods that are rec­om­mend­ed under cer­tain con­di­tions such as when water seeps over the top of a foun­da­tion wall or when seri­ous degra­da­tion has occurred in the mor­tar joints of a mason­ry foun­da­tion wall.

What may sur­prise a lot of home­own­ers is that many base­ment water­proof­ing tech­niques, includ­ing the one used most fre­quent­ly, are imple­ment­ed from inside the basement.

Even when the base­ment is fin­ished cer­tain inte­ri­or water­proof­ing tech­niques are still the rec­om­mend­ed approach because the minor impact on the fin­ished space is out­weighed by the ben­e­fits of the water­proof­ing system.

So, how is base­ment water­proof­ing done from the inside?

Water­proof­ing a Base­ment from the Interior

There are two main meth­ods of water­proof­ing a base­ment from the inte­ri­or, crack injec­tion and inte­ri­or drain tile.

The most com­mon type of foun­da­tion in Amer­i­can homes is one con­struct­ed of poured con­crete and the most fre­quent­ly found source of seep­age in such a foun­da­tion is a non-struc­tur­al crack in the base­ment wall. A non-struc­tur­al crack is one that does not indi­cate a prob­lem that threat­ens the sta­bil­i­ty of the foun­da­tion and is gen­er­al­ly nar­row­er than 1÷8”.

The best way to repair a seep­ing wall crack is to inject it with expand­ing polyurethane. An installer begins by clean­ing the crack of loose con­crete and debris and plac­ing plas­tic injec­tion ports at inter­vals along the length of the crack. An epoxy seal­er coat is then applied to cov­er the crack and secure the ports.

After the epoxy has cured, the installer injects each port, begin­ning at the top, with the polyurethane mate­r­i­al that fills the crack all the way to the out­side soil and seals it against water. The polyurethane remains flex­i­ble after cur­ing to pro­hib­it re-open­ing of the crack due to minor foun­da­tion movement.

Regard­less of the con­struc­tion of the foun­da­tion, two com­mon sources of seep­age are cracks in the con­crete base­ment floor or the joint between the floor and the foun­da­tion walls, called the cove joint. Seep­age from either of these sources is caused by hydro­sta­t­ic pres­sure under the foun­da­tion that forces water in through even the small­est opening.

Hydro­sta­t­ic pres­sure is relieved and seep­age stopped by installing inte­ri­or drain tile, a sub­soil drainage sys­tem con­nect­ed to a sump pump.

Installing inte­ri­or drain tile starts with remov­ing a sec­tion of the base­ment floor about a foot wide around the entire perime­ter or along only the affect­ed wall. A trench is then dug in the soil below to cre­ate an open­ing next to the foun­da­tion foot­ings. The bot­tom of the trench is filled with washed gravel.

Flex­i­ble, per­fo­rat­ed pipe, wrapped in a ​“sock” of fil­tra­tion fab­ric is laid on top of the grav­el and con­nect­ed at one or both ends to the sump basin. The trench is then filled with more washed stone and the con­crete floor is replaced.

The inte­ri­or drain tile will alle­vi­ate the hydro­sta­t­ic pres­sure by col­lect­ing ground­wa­ter and stop seep­age by car­ry­ing it to the sump pump for dis­pos­al. When prop­er­ly installed, inte­ri­or drain will remain maintenance-free.

When inte­ri­or base­ment water­proof­ing is required, the home­own­er will need the advice and ser­vices of a pro­fes­sion­al base­ment water­proof­ing con­trac­tor to ensure that the job is done right with a min­i­mum of incon­ve­nience and at a rea­son­able cost. At U.S. Water­proof­ing we’ve been keep­ing base­ments dry from the inte­ri­or (and the exte­ri­or as well) since 1957 and have more than 300,000 sat­is­fied cus­tomers to our cred­it. Why not ask for our free advice?

Tags: basement waterproofing facts, interior drain tile, interior foundation crack repair

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