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  • Jay G.

Can You Waterproof A Foundation from the Inside?

Updated: Jun 21, 2020

You have water in your basement and you know you have some cracks in your foundation wall that are the cause. The next step is to waterproof your foundation wall. But there's a problem: you can't waterproof it from the outside because the neighbors are too close. Is it possible to waterproof your foundation from the inside?


To waterproof inside a basement, remove the basement framing and insulation to expose your foundation walls. Use a jackhammer to dig a trench around the perimeter of your interior walls. Lay perforated PVC drainpipe and cover interior walls with delta membrane so it covers walls and pipe. Fill the rest of the trench with gravel and cover with concrete.


Interior waterproofing can be messy and requires you to remove all the interior framing and finishing, if there is any, from the foundation walls. However, once removed, the process of digging, installing pipe, membrane, gravel and concrete can be done in a few days if you have some help.


In this article we'll briefly take a look at the process to waterproof your foundation and why you would need to waterproof your foundation from the inside.


Why Waterproof Your Basement from the Inside


If you have water in your basement, then you've got two choices: waterproof from the inside or from the outside. While you could try other methods or products that promise to cure your basement water problems with an injection into concrete or a roll-on sealer, it won't fix your issue for the long term.

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Can't Waterproof the Exterior - Interior Works Too

Both interior and exterior waterproofing can be a long term solution, done properly.


However, only exterior waterproofing can truly keep your foundation safe and structurally sound.


There are reasons, though, that waterproofing from the outside won't work, such as:

  • Your house is too close to the neighbors to excavate

  • You don't want to dig up your asphalt or lock block driveway

  • There is a deck, concrete stoop, or other structure in the way

It is possible to move your deck, which isn't as hard as you'd think, but some decks are simply too big or awkward to move. In that case, you are looking at interior waterproofing.


An asphalt driveway also presents problems. Digging it up is possible with a small excavator, but you'll have the cost of repairing it later on which is not easy. Lock block is easier to repair yourself, and you can remove only the amount of blocks you need to in order to excavate.


Another issue is the proximity to your neighbor's house, which is a very common reason to waterproof from the inside.


To do exterior waterproofing properly, or quickly, you'll need a small excavator. If you can't safely fit one between your property and the neighbors, you'll need to waterproof from the inside.

You can dig out your exterior foundation the old fashioned way - shovels - this is possible if your foundation is only a few feet below grade.


But if your house is like mine and is 6' below grade, then you cannon dig that out on your own unless you want to spend months doing it - avoid.

What is Done to Waterproof a Basement on the Inside

Let's have a look at the process for waterproofing your basement from the inside. Remember, if you have a finished basement, then you are going to have to take some or all of your interior walls down that are against your foundation walls.


1. Remove Basement Framing, Insulation, and Drywall Along Perimeter

Some basements won't require interior waterproofing around the entire interior perimeter of the basement. If you only have issues with a south-facing wall, it is possible to only waterproof one section of wall.


Wherever you decide to waterproof your basement interior, just know that any framing, insulation, and wallboard of any type will have to come down. You can save the framing and insulation, but any drywall you had will have to be removed.


If you have vapor barrier, you can carefully remove it to re-use. When reapplying the vapor barrier, use sheathing tape to cover up any small holes that were created during the teardown process.


After removing your insulation and wallboard, you can work on removing the framing.


If you are careful, you can remove your wall sections in 8-foot sections. If they are bolted to the floor - not likely - simply remove the bolts. If framing is nailed to the floor, then you can use a framing hammer or pry bar to remove.


There will also be nails or screws attaching the top plate to the joists overhead - remove these in the same manner.


Once the fasteners are removed, the framing should come right down. If you have space, simply drag it and place it against an adjacent wall.


2. Jackhammer Concrete 16" from Interior Foundation Wall


This is the hardest part of the whole job, and the dirtiest. There are several ways to go about removing concrete from your basement floor in terms of what tools to use:

  • jackhammer

  • concrete saw and sledgehammer

  • sledgehammer and pickaxe

I recommend the jackhammer for several reasons. First, the concrete saw creates an absurd amount of dust. You can rent one that hooks up to a hose to minimize the dust, but then you've got water all over your basement. Last, you use the saw, you still need a sledgehammer to break up the pieces.


You can rent a jackhammer from any Home Depot or tool rental store for cheap. When renting, get something over 40 pounds. The 60 pound Bosch or 40 pound Makita will work just fine.


Now, where to jackhammer? Your concrete slab is actually poured on top of your foundation wall footings. Typically slabs are somewhere around 4" thick. Below the slab, your block or poured concrete walls sit on a footing that likely protrudes about 8" under your slab from the walls.


Your drainpipe is going to sit between the footing and the slab you've broken apart. Therefore you have to hammer at least 16" from your interior walls. This will give you room to dig out the earth next to the footing, with a few inches to spare.


You'll find the jackhammer to be surprisingly adept at handling the job of breaking up your basement slab. Your arms will be tired at the end, and you'll need steel toe boots unless you don't care about losing a toe or two.


Remove all the old concrete chunks.


Tip: If you don't have a place to rent a jackhammer, or you want to use it for more than a day or two, then consider buying one. While expensive, you can re-sell it for close to what you paid. On the other side, consider buying one used, too. DIYers like you are often unloading heavy equipment used only for one job - you might find a deal.


3. Jackhammer and Dig Out a Sump Pit

If you don't already have a sump pit and sump pump, then you are going to need one. The perforated drain pipe will drain into the sump pit. A sump pit is a large bucket that sits flush with your slab floor.


A sump pit is deep - usually about 30", so the water collecting in the pipes you are about to lay will drain into the pit via gravity. A sump pump at the bottom of the pit will take your water to wherever you want it to an outlet.


Many municipalities mandate that sump pumps outlet not to the city sewer or storm drains but simply to someplace on the exterior of your property, in order to avoid clogging city waste plumbing during heavy storms.


If you live in the bush and are on a septic system, you'll be able to outlet your sump pump to a spot away sloping away from your house.


In colder areas, some people will drill an outlet through their foundation walls and then dig a trench to a trench far beyond the house. The trench and earth above it insulate the pipe in winter.


Regardless of where you outlet it, the sump pipe and 1 1/2" drain pipe will outlet either up through your basement wall or the joist header.


Speaking of outlets, you'll want to situate your sump pit at the end of your run of drain pipe. This is often a corner. IF you've run the drain pipe all around the entire perimeter of your basement, then both end will connect to the sump pit.


Your typical sump pit is either 18" or 24" in diameter. You'll need to jackhammer a space slightly larger so that you can dig comfortably - remember, you'll be digging out at least 2 feet of earth, so you'll want room to maneuver.


Once you put your sump pit in, you can pour concrete around it to make the surrounding area flush with the pit for a cleaner look. A large sump pit is better than a small one, especially if you live up north with lots of snow and frozen earth. Spring runoff will fill up a sump pit in minutes if you've had an amount of snow hang around in the winter.


Another thing to consider would be installing a sump pump with a battery backup. Basically this is a sump pump that includes a large battery that will take over and operate the pump in the event the power goes out.


Many sump pumps can be bought as a package with a battery backup. Since power often goes out during extreme weather events, there's a good chance you'll need your sump pump removing water from the pit during that time. A battery backup can really save you.


Some sump pits are perforated. While this might seem counter intuitive, it's actually a good idea. Your pit has a pump constantly removing water. That allows water to drain from underneath your slab into the pit, if there is any.


Any water not caught by the perforated pipe will then drain into the pit anyway. Just make sure you fill in the area around your pit with crushed stone before spreading a new layer of concrete around the top of the sump pit.


4. Dig a Trench Next to Your Footing

Now you'll want to dig down at least 4" right next to your footing that you've just exposed. This may be clay, gravel, sand or a combination. Use a shovel to dig. If the pipe doesn't site perfectly flush against the footing, don't worry. Water will still flow down toward the pipe.

You are going to be moving away chunks of concrete, so it won't be easy digging. You'll be laying your perforated 4" drainpipe in that trench, so it needs to be straight.


Using the vertical edge of the footing is a good guide. This also ensures water will flow right off your walls, down the footing, and into the pipe instead of under your concrete slab.


5. Install 4" Rigid Perforated Drainpipe

Don't confuse this stuff with the black, flexible landscape drainpipe that goes in exterior weeping tile applications. You want the white, perforated drain pipe that is rigid. You can get this at any big box home reno store.


Place your pipe in the trench. Do not place the pipe in a position so that a row of holes is at the bottom, where the pipe meets the earth. You want the holes on either side, so water can enter and drain smoothly into the sump pit.


If the holes are on the bottom, then water will eventually sink under the pipe and potentially create problems down the road.


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Your install should look something like this...

Connect your drain pipe to your sump pit. If you've done your entire basement then both ends will connect to the sump pit.


If you've only done one or two walls you will only have one connection to your sump pit. Your pit will already have a connection to accept a 4" pipe, so it is just a matter of attaching it.


6. Drill holes in the Your Block Foundation

This is a step often neglected by installers. Drill a row of holes along the bottom course of concrete blocks on your foundation walls. Concrete blocks are hollow on the inside, with two cavities per block - usually.


Drill 1/2" holes using a masonry bit and a corded drill in each block, near the bottom where the block meets the footing. You'll drill two holes per block, one on each side. This will allow any water standing in the block cavities to escape, creating a thoroughfare through your wall into your drainpipe.


No one wants water in their walls, and installing an interior waterproofing system doesn't prevent water from entering your house.


BUT, drilling weeper holes into the blocks to speed up water passage is the next best bet. By not allowing water to sit in your basement walls, you allow them to dry out faster and maintain their structural integrity for longer.

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Watermarks Descending in Stair-step Pattern = Water Problems

Water in block foundations will start at the top and drain to the bottom - you can see it on the walls with watermarks in stair-step patterns.


It often stops at the bottom row, gradually seeping out through the gap between the blocks and footing. Weeping holes will prevent that.


7. Install the Delta Membrane

Your delta membrane will go on over the interior walls of your basement or crawlspace and overlap the drainpipe so that it is completely covered. But before you install the membrane, use 3/4 clear gravel to fill in the gaps around the perforated drain pipe. This will facilitate water moving into the pipe.


Once complete, it is time to install the Delta MS membrane. When installing the membrane you'll need the fasteners and adhesive that goes along with the membrane. They should be sold right next to the Delta MS membrane.


Installation is relatively straightforward, but you need to do some measurements first. It is a good idea to make sure that the Delta reaches up to where the ground level is outside.


For the most thorough instructions, see the delta membrane installation instructions. Understand that you'll need a Hilti nail gun or equivalent to nail in the concrete nails. Delta membrane uses special fastening brackets, and they need to be anchored to the block or poured concrete walls.


You'll also need the special Delta adhesive to connect the membrane to the top of the walls. Delta specifies a molding strip to go over the top of the membrane, but that is for exterior installation. It is not necessary in interior installation.


When rolling out the membrane, you'll need two people. One person rolls while the other person nails. Make sure the membrane goes over the PVC drain you've just installed.


Last, pay special attention in the instructions with how to deal with "service penetrations". A service penetration, or protrusion, is any wire or pipe coming through your wall. Failure to adequately membrane around these will negate your entire work.


You'll use adhesive and end one layer where the protrusion starts. You'll start a new layer and it will go over the old one. That way each protrusion has two layers of membrane adhering to it.


Note: Using tools such as concrete nail guns requires you to either rent or borrow. But consider buying one, and here's why: you'll probably use it more than once. After you do, the resale of these tools while net you nearly what you paid in the first place. Resale of high end, heavy-duty tools is almost always a seller's market.


8. Pour the Concrete

Now that you've installed your membrane over your PVC perforated drainpipe, you can finish the job by pouring the concrete over the section you've jackhammered out.

What type of concrete should you use? Don't make it complicated - go with a Sakrete product that is formulated for heavy-duty applications. Eventually, the floor will be covered up by a subfloor and framing, so looks don't really matter. You'll be able to use a trowel to level it as well.


The next question is how much concrete will you need? If you've filled up your trench with gravel, then it won't take as much as you think. Use a concrete calculator to help you determine how many bags of concrete you'll need.


Last, you are going to need a concrete mixer or simply a wheelbarrow with a mixing paddle. Some people use a shovelhead or old canoe paddle to do this. An electric concrete mixer is much easier, but you still have to get it into your basement. After hauling bags of concrete into your basement, you might as well opt for the mixer too!


When pouring the concrete it is critical that the membrane covers the pipe. Failure to do so could result in concrete getting into the pipe.


The concrete will stay wet for awhile, so you'll have time to pour your concrete and then trowel it smooth after. In most cases, you won't even need to trowel. If you want a nice, finished look, then you'll need special tools and additional products, which we won't cover in this article.


Wrap-Up

Done! You've successfully installed an interior waterproofing system that will keep your basement dry forever, and likely saved thousands of dollars in the process. While inferior to exterior waterproofing, we understand that sometimes interior waterproofing is the only option.


Once installed, you can put walls and insulation over the membrane and new concrete just as you would have before without the interior waterproofing system.


Be sure to check your sump pit and pump on a regular basis, particularly during hard rains or heavy spring melt off. Ensure water is exiting the pit and that the sump pump is ejecting the water adequately.


Lastly, remember that you still will have water coming through your basement walls. Structural damage and degradation can still occur. If you notice your exterior foundation walls sagging, the floors in your house out of level, or cracks in your drywall then you might need more foundation help than just interior waterproofing outlined in this article.


Conclusion

Interior waterproofing is a big job for an average homeowner but is not complicated. The hardest part is digging with the jackhammer - consider hiring the local teenager to do this or do like my friend did and talk to the bartender of the nearest pub at lunch hour - he might know someone willing to make a quick buck!


Regardless of who does the heavy digging, do this job with a friend. Heavy equipment and digging safety starts by making sure you have another person around to help if you need a hand.


Thanks for taking the time to read this article. I hope you found it helpful and inspired you to consider doing a basement waterproofing job on your own. Please leave a comment below or send us a shout about how we can help you achieve your DIY basement waterproofing goals.





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