Step-by-step: How to Waterproof a Finished Basement

Water damage is a major concern for homeowners. It collects and wreaks havoc on anything in your basement. Waterproofing your basement is an excellent way to help prevent water damage. How to go about it can be confounding though. Don’t worry, follow these steps and it will all work out.

1. Inspect The Foundation Perimeter

The best way to waterproof a basement is to check the foundation. Circle your home and look for any potential hazards.

Hazards can include sprinklers spraying your house near any cracks in the foundation, hoses over-saturating an area, cracks in your foundation improperly sealed windows, and the age of your house.

Concrete allows gasses to pass through it. This includes water vapor. So while having the foundation be oversaturated by water isn’t necessarily a big deal, it will increase the amount of water passing through the concrete.

This is why you need to make sure your hoses and sprinklers aren’t operating around any crack and not oversaturating your ground.

The oversaturated ground is when the dirt stops absorbing water in an area. It gains a sort of, spongy look. It’s more like mud. Luckily this is pretty easy to prevent. If you have grasses, trees, or plants in general oversaturated grounds should take care of themselves pretty fast.

Even still, this will increase the amount of water vapor passing through your basement floor.

This is even less of a problem if your house was built after the ’70s. This is because vapor barriers were seldomly used when constructing a basement before then. A vapor barrier is a line of plastic that goes under your subfloor. It basically prevents water vapor from moving from past the concrete speedily.

It also prevents water vapor from leaving your basement if it’s already there. It’s pretty easy to dry a basement if there is a vapor barrier though. You can light a few candles, turn on a fireplace, or place some moisture absorbers around.

In the past, I’ve found that moisture absorbers work the best at limiting airborne water vapors. I need to change them about once a year, and there is no vapor barrier in my basement. Since they work so well without a vapor barrier, then they’ll work great if you do have one.

The last thing to check while you are outside are your windows.

2. Prep The Windows

Check the windows outside for proper sealing. If you see broken lines of caulk, rot, mold, or moss on any window outside then waterproofing it from the outside needs to be your top priority.

Clean up the outside and dry it well before you work on it. If there is only minor damage to wood then using a wood filler a great idea. Otherwise, you may want to consider replacing your frame.

If there is only a little caulk missing then putting a little down just to reseal should be fine. Make sure that if you do this you first remove all the oils off the old caulk before putting down new caulk.

Once the outside of your basement windows is waterproofed then move inside and start looking at the windows. You’re looking for the same signs: Rotted wood and broken caulk beads.

Any inside damage preventing waterproofing could be hidden by a window sill or window casing. You will have to remove these to know how well the windows are waterproofed.

After you’ve checked your windows for weak leaks in waterproofing and fixed any of them you can put your sill and case back on. Sills normally have only a few nails, making them pretty easy to just pull off.

In doing this though you might damage the wood underneath the sill. So pry carefully, slowly, and as straight up as possible. The same goes for the casing.

Once you’re done with windows it’s time to look at inside problems that need waterproofing.

3. Survey The Ceiling

The ceiling of your basement is a great indicator of any leaky pipes. What we are looking for here is any waterproofing that needs to be done between the floors. Mainly leaky pipes.

Water damage on a ceiling will have discoloration. Depending on the color of your ceiling, the discoloration will look different. On white ceilings, it will look like a brown outline.

There may also be molds growing around any discolorations. Especially if the discoloration is in a corner. Corner discoloration will be addressed in a little bit though.

The second big indicator is if the ceiling is sagging. This is a big problem. It means one of two things with both of them involving water damage.

The first one means one of your pipes is currently leaking and there is a lot of water being deposited there. So there is currently a whole lot of water being supported by the panels of your ceiling. The best way to fix this is to grab a lot of buckets, a Phillips screwdriver, and start poking holes.

Beware though. Doing this has the potential of causing the panels to fail and releasing all the water onto you. So make you have the area properly protected before you do this.

The second one means that there was once a leaky pipe and it has since been taken care of. That means there isn’t anything you can do except replace the panels for aesthetics.

Ceiling panels themselves really aren’t waterproof and they seldom are made to be.

4. Remove Flooring

For the rest of the waterproofing process, you will be dealing with flooring and insulation. Before you start continuing make sure that your house doesn’t have any vapor barriers and figure out if your basement has any supporting walls. This can be done by consulting a contractor and your building records.

Let’s talk about what a finished basement is. Basements weren’t ever finished until the mid-seventies. They weren’t intended to be lived in. A finished basement must have electricity, walls (other than exterior) that match the upstairs at least mostly, and heat. That means a basement finished by a contractor probably has a proper vapor barrier and shouldn’t be worried about.

If a contractor did not finish the basement then there’s a good chance it does not have a vapor barrier. This means you will need to install it by removing your flooring, plasterboard, and sub-flooring. It’s a big task. So if you don’t feel up to it then hire someone.

Before you start pulling things up you need to look around the flooring and walls trying to find any water damage. If there is any, mark the area. We will come back to this after everything is removed.

If you are removing carpet there isn’t much to it. Remove the baseboards. This can be done by simply prying them off. Pull the carpet off of its tack strips. Be careful so you don’t damage the carpet (unless you are going to be getting new carpet). Pulling the pad off can be a pain though.

Carpet pads often rip. They are really fragile. So either, be careful when pulling it up. Very very slow and careful. Or plan on buying a new pad. Then pull the staple out of the floor. You must remove all the staples. If you do not, then reinstalling the carpet will be much more difficult. Not to mention that they stab through the carpet and poke bare feet.

If you are removing hard flooring then you will need to essentially do the same thing.

Keep removing things until you get down to OSB or plywood. That’s the subflooring and we’ll address that next.

5. Remove The Sub-Flooring

Before you start tearing this out (if there is any) look around for water damage. Mark the area and we’ll come back to it.

If your basement was finished by someone who didn’t know much about this, there might not be any subfloor. Subflooring is OSB or plywood. Newer subfloors can have vapor barriers on the bottom of them.

Removing this is pretty straightforward. It will just be removing anchors and pulling the boards up. Be careful as you remove anchors. Chances are that they are anchored straight into the concrete. That means that any damage done to the concrete will need to be repaired for the anchors to be effective again.

6. Remove Walls

To properly waterproof you might need to remove your walls to expose the foundation of your house.

Before you start removing any of the walls, you need to turn the breakers off to stop the flow of electricity in your basement.

If you have plasterboard in your basement you can’t reuse it after it’s been taken off the wall. So make sure that you need to waterproof before you do this. Plasterboard isn’t expensive, but it’s not exactly cheap either. Removing plasterboard is pretty simple though. Very messy though.

The first thing you need to do is cut a seam that runs along the top of your wall. In the corner where your walls meet your ceiling, there will be some that you need to cut. If you don’t, then chunks of your ceiling texture and paint will come off with the plasterboard.

The easiest way to remove the plasterboard is to take a saw and cut your boards into pieces before removal. The problem with doing this though is that you might cut through wires if you’re not careful. If you do this you’ll need to call a professional to repair the damaged wire. Then pull off the pieces. Make sure you remove any fasteners holding the plasterboard up.

The harder method (though more fun and less likely to cut anything) is to take a hammer and start swinging. Then remove the pieces and fasteners.

Before you can start waterproofing you’ll need to clean up the mess of plasterboard. This stuff literally gets everywhere, and leaving enough of it around will make properly waterproofing your basement very difficult. So just make sure that if you remove your plasterboard that you clean it up after.

You might just have a type of paneling though. This requires that you:

  1. Pry the panels away some
  2. Push the panels back to expose nails
  3. Pull nails out
  4. Remove paneling

Much less clean up needed.

7. Install A Vapor Barrier

Alright, so now we get the actual waterproofing part.

Remember all those damaged areas you marked? Now’s the time to fix them all. First, you need to repair any damaged material. That means sealing any cracks, replacing any boards, and putting a stop to any leaks. After that, you’ll be adding a vapor barrier.

A vapor barrier (as said near the beginning) is basically a type of plastic that prevents water passage and encourages dryness. There are a couple of different types, but all basically do the same thing.

The easier to install is an OSB panel that comes with a pre-installed barrier. This is more expensive, but faster to install and fix.

The cheaper is to install a couple of sheets of plastic. A drainboard and the barrier itself. Drainboard is a type of corrugated plastic the runs up against the wall. The vapor barrier goes over this to encourage drainage.

Here are two videos of the two different types. The first is of the drainboard and barrier.

The second video would not embed, so here is the link instead. It is very informative and worth the watch.

8. Reinstall The Flooring and Walls

Now that you’ve installed your new waterproofing you need to put it all back together. Now’s a good time to consider any new looks you’ve been considering.

A fresh coat of paint, a new type of carpet, and new windows. The basement is torn apart anyway. Remake it the way you want. Just make sure you don’t mess with any walls without first consulting a contractor.

Aside from your walls, knock yourself out. Don’t forget to consider adding a new type of insulation to your basement walls. This would especially come in handy if you live in a cold area. But now that your basement is waterproof, anything goes.

After going through all these steps you might be asking if you can do this. Honestly, big waterproofing jobs should be left to the professionals. So the best thing to consider is hiring a contractor. If you choose to do it yourself though, you’ll be okay as long as you follow these instructions and take the necessary measure to be successful.

Ricky Kesler

With all of the projects I've done over the years, you'd think that I work on my house full-time. But I actually enjoy other things like spending time outdoors and time with my family.

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