Shed Floor Base Waterproofing: Tips and Fixes

If you own a shed, I would estimate that there is a better than 50% chance you have experience water on the floor. The water is resulting from just a few causes, and the good news is that all are fix-able.

Some require a bit more work than others, but needing to waterproof your shed’s floor, or the base of your shed, is not an uncommon problem.  Many, including me, have had to do it.  Here are some thoughts on the subject.

When do you Know you have a shed waterproofing problem?

I noticed that my current shed – which is about 20 years old and on a property I purchased – was having a waterproofing problem when I began to see water on the floor every spring. We are talking significant levels of water — to the point where I cut electricity to the shed for fear that someone would get hurt by the electrical currents and water.  It was caused by runoff of water on a nearby hill.

You might notice that the shed floor gets wet after any substantial rain — that is a sign of either poor drainage, or the need for waterproofing.

Another sign that can indicate a waterproofing issue is when you notice the growth of mold and mildew inside the shed. These fungi thrive in damp environments, and their presence indicated there was likely an issue with moisture seeping through the shed floor.

Additionally, I once observed that the wooden shed walls, as well as the items stored inside, were showing damage from moisture exposure. Wood started to show signs of warping and rotting, while my metal tools and equipment developed rust. This rapid deterioration was a clear sign that my shed was facing a major waterproofing problem. Not fixing it would mean that I was shortening the lifespan of the shed.

Figure out what kind of water issue you have

When I first notice water in my shed, it’s important for me to determine the source of the moisture. By doing so, I can effectively address the problem and properly waterproof my shed floor base.

One possible source of water is seeping up from the ground. To determine if this is the issue, I can check for dampness or wet spots on the floor, especially in areas closer to the ground. If the ground outside my shed is also damp in the same areas, there’s a good chance the water is coming up from the ground.  Water coming up through the concrete, dirt, or wood shed floor is usually not substantial. More of a minor nuisance.

Another potential source of moisture is a slope near the shed causing water to flow towards it. I can verify if this is the case by observing the gradient of my property during heavy rain, or during spring snow runoff; if water appears to be pooling or running towards the shed, I will need to adjust the landscaping to divert the flow of water away from the structure. Easier said than done!

Condensation can also be a culprit in introducing moisture into my shed. Increased humidity or a lack of proper ventilation may lead to condensation forming on the walls and ceiling. To determine if this is the issue, I can look for signs of moisture in the air and check if the walls or ceiling are wet to the touch. You can also lay plastic on the floor, and if the area under the plastic gets wet when other spots don’t, it is a condensation issue.

Finally, water may be entering my shed from other sources, such as gaps in the roof or walls. To identify these issues, I can perform a thorough inspection of my shed’s exterior during a heavy rain or use a water hose to spray the roof and walls to check for leaks.

In order to effectively waterproof my shed floor base, it is crucial that I pinpoint the exact cause of the water issue. Once I know where the water is coming from, I can quickly figure out how to fix it.

Applying Waterproofing Techniques

Liquid Membranes

Liquid membranes are a great waterproofing solution for your shed floor base, in many situations. This is the same as sealing your shed floor.  They are easy to apply using a brush, roller, or spray equipment. Apply the membrane in at least two coats to ensure full coverage, allowing each coat to dry before applying the next. This will create a seamless, flexible, and durable water barrier that will protect your shed floor from moisture infiltration.

Sheet Membranes

Another option to consider is the use of sheet membranes. These are pre-formed waterproofing sheets made from a variety of materials such as rubber, asphalt, or polyethylene. To apply sheet membranes, I first clean and prime the shed floor base before carefully cutting and placing the sheets according to the manufacturer’s guidelines. Ensure that the sheets overlap and are properly sealed, and use a blower or heat welder to secure the seams.  Granted, not everyone has the equipment to do this, so you may need to call-in a pro.

Cementitious Waterproofing

This works well when you are starting-out with a dirt floor in the shed.

Cementitious waterproofing is an effective technique for shed floor base waterproofing. I start by mixing the cementitious product according to the manufacturer’s directions. I then use a trowel or brush to apply the product evenly over the entire surface of the floor. Be sure to pay special attention to corners and edges where water may be more likely to enter.

You can add some elements to the cement mix while it is still wet. These include waterproofer (recommended in this case) and some grit to ensure it does not get super slippery.

Sealing the Joint Where the Wall Meets the Floor

Don’t forget to seal the joint where the wall meets the floor of the shed. I use a high-quality, flexible sealant to fill any gaps and create a watertight seal. This will prevent water from seeping into the shed at this critical junction and help maintain the overall effectiveness of the waterproofing system.

You can either use a caulking gun, if the area to be sealed is less than a quarter inch in width (think of the width of a common piece of cardboard).  Or you can use a paint sealer if the area to be sealed is not consistent and needs to be filled-in in spots.

Drain Tile Around the Shed

If your problem is from water runoff from a hill, or poor grading on a shed that cannot be undone, I recommend the installation of a drain tile system around the shed perimeter. This

involves digging a trench, laying perforated drainpipe wrapped in a filter fabric, and backfilling the trench with gravel. This system collects and redirects water away from the shed, reducing the risk of water infiltration and potential damage.

It is a lot of work, but it is very effective in situations where you have runoff to the shed each year, or after every big rain.

Regrading the Ground Near the Shed

People forget about properly grading the ground around the shed. Ensure that the ground slopes away from the shed in all directions, directing surface water runoff away from the structure. This will minimize the amount of water reaching the shed floor base, reducing the risk of moisture problems and extending the life of your shed.

This is easier to do on a shed that is already built. Harder when you inherited a shed on a property that you purchased.

Maintenance Tips for Waterproofed Floors

I recommend performing regular maintenance to keep your waterproofed shed floor in top condition, regardless what type of shed you have. Maintaining a shed floor’s waterproofing will keep the floor in better shape for longer, and will reduce the chances of having a musty shed.

Here are some helpful tips to ensure the longevity and effectiveness of your floor’s waterproofing system.

It’s important to keep the floor clean and dry. Use a soft broom or vacuum cleaner to remove dirt and debris that could potentially damage the waterproofing layer. Avoid using harsh chemicals or abrasive cleaners, as they can potentially degrade the waterproofing material. Instead, opt for mild soap and water or a cleaner specifically designed for waterproofed floors.

In addition to cleaning, it’s essential to inspect the floor regularly to spot any signs of damage. This could include cracks, peeling, or bubbles in the waterproofing layer. If you notice any issues, address them promptly by repairing or resealing the affected areas. Prompt action will prevent further damage and maintain the integrity of your floor’s waterproofing system.

Also, pay attention to the quality and condition of any floor mats or rugs used in the shed, as they can play a role in preserving your waterproofed floor. Non-abrasive, high-quality mats help to protect the floor surface and prevent water from pooling on the waterproofing layer. Make sure to clean the mats and rugs regularly to prevent mold and mildew growth.

Remember that heavy or sharp objects can cause damage to the waterproofing layer. To avoid this, use caution when moving furniture or equipment and place protective padding under any objects that could potentially puncture or scratch the floor.

By following these simple maintenance tips, you can keep your shed’s waterproofed floor base in excellent condition and prolong its lifespan. Regular care and attention will help ensure that the floor remains watertight and continues to protect your shed from potential water damage.

Final Thoughts

When it comes to shed floor base waterproofing, the best solution is of course building it right. But for many of use, we either inherit a shed on a property we buy, or we build the shed and discover the water issues down the road.

In addition to selecting the right base material, I’ve found that using a waterproofing membrane or a water-resistant floor coating adds an extra layer of protection to prevent moisture from seeping in. It’s crucial to properly install and maintain these products for optimal results.

Proper shed ventilation is vital in avoiding moisture buildup inside the shed. Adequate ventilation not only helps regulate temperature and humidity, but it also reduces the chances of mold and mildew growth, which can cause damage to both the shed and its contents.

Lastly, I’ve learned that regular maintenance checks are crucial in ensuring that the shed floor base remains waterproof. By inspecting for any damage, wear, or gaps in the waterproofing materials, I can address these issues promptly and extend the shed’s lifespan.  Be sure to check the shed in all seasons, even if it is one that you only use a few times a year.

Frequently Asked Questions

How can I prevent water damage to my shed floor?

As mentioned above, to prevent water damage to my shed floor, I ensure proper drainage around the shed, and I keep it elevated from the ground using foundation elements. Additionally, I install a waterproof membrane between the base and the floor, and I ensure regular maintenance to check for signs of water damage or rot.

What materials are best for waterproofing a shed base?

For waterproofing my shed base, I prefer using materials like a damp proof membrane, pressure-treated wood, and closed-cell foam, or a paint-style sealant. These materials effectively prevent moisture from penetrating the floor and causing water damage or rot.

Is there a type of shed floor that is better in wet conditions?

Yes, I find that plastic or treated composite shed floors perform better in wet conditions. These materials are naturally water-resistant and durable, ensuring that my shed floor stays protected from moisture and the elements.  A dry floor means that it will last a lot longer.

Are there any effective sealants to protect the bottom of my shed?

To protect the bottom of my shed, I apply a wood preservative or a waterproof paint made specifically for exterior wood surfaces. I make sure to apply multiple coats, allowing each to dry properly before applying the next, to create a durable and effective barrier against moisture.  You just have to have the presence of mind to apply this when you are building the shed.  Doing it afterward works, too, but is not as effective.

What techniques can be used to avoid shed floor rot?

To avoid shed floor rot, I use pressure-treated wood for the floor and foundation, and I apply a waterproof sealant to the wood. I also ensure proper ventilation in the shed by installing vents or louvers to allow air circulation, which helps to control moisture levels.

Also, ensure the shed is being built in an area that has natural drainage away from it. That is a huge factor in keeping your shed floor dry.

How can I waterproof a shed base from the inside?

To waterproof my shed base from the inside, I lay a damp proof membrane or a closed-cell foam insulation on the floor before installing the flooring materials. These membranes act as barriers to prevent moisture from seeping through the base and into the shed floor.

If the shed is already built, start by pressure-washing the floor so it is perfectly clean. Then, apply a sealant.