Drylok on Drywall: Stop! The Hidden Dangers You Must Know
You have a damp basement or a humid bathroom with drywall, and water is the enemy. A persistent question arises: can a heavy-duty masonry waterproofer like Drylok be the quick fix? It’s a tempting thought, applying a thick, waterproof coating to solve your moisture woes once and for all.
However, this seemingly simple solution hides critical complexities. Using a product designed for porous concrete on a paper-faced gypsum board is not a straightforward task. The wrong approach can lead to peeling paint, trapped moisture, and an even bigger headache than you started with.
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What is Drylok and Why is it Used?
Drylok is a brand name for a line of specialty paints known as masonry waterproofers. Its primary function is to stop water from penetrating surfaces like concrete blocks, cinder blocks, stucco, and brick. It works by seeping into the pores of the masonry and expanding as it dries, creating a robust, watertight barrier.
This product is a go-to solution for unfinished basement walls where groundwater pressure can force moisture through the porous concrete. The key takeaway is its design: Drylok is formulated to bond with and seal masonry. This fundamental purpose is where the conflict with applying it to drywall begins.
The Core Problem: Drywall is Not Masonry
Drywall, or gypsum board, is fundamentally different from concrete. It consists of a hardened gypsum plaster core pressed between two thick sheets of paper. This paper facing is the critical point of failure when it comes to moisture.
While Drylok can technically be applied to drywall, it’s not designed for it. The manufacturer itself states the product is for masonry surfaces. Applying this thick, non-breathable barrier over a paper surface can create more problems than it solves if not done with extreme care and proper preparation.
The Critical Question: Can You Put Drylok on Drywall?
The short answer is yes, but the long answer is that you must proceed with caution and understand the significant risks. Applying Drylok directly to bare or improperly prepared drywall is a recipe for failure. It is not a substitute for addressing the root cause of the water issue.
Think of it as a last-ditch effort, not a primary solution. If you have persistent water issues, Drylok on drywall is merely a temporary patch that covers up a deeper problem which could lead to structural damage and mold. Addressing the source of the water is always the first and most important step.
The Dangers of Using Drylok Incorrectly on Drywall
When used improperly, Drylok can trap moisture instead of blocking it. Drywall’s paper facing can absorb moisture from the air or from behind the wall. If you coat the front with a non-breathable barrier like Drylok, any moisture that gets trapped has nowhere to go.
This trapped moisture can lead to the paper and gypsum core deteriorating, causing the drywall to become soft and crumble. Furthermore, this creates a perfect breeding ground for mold and mildew. Often, homeowners may not even see the mold, as it thrives in the dark, damp space behind the wall, which can pose health risks. For a deeper understanding of this specific risk, learning more about Drylok and its relationship with mold is essential.
When Is It Acceptable to Use Drylok on Drywall?
Despite the warnings, there are very specific, limited scenarios where applying Drylok to drywall might be considered. This is typically in a below-grade basement where concrete walls were already covered with drywall before proper exterior waterproofing was done.
If you have minor, ambient dampness seeping through and removing the drywall is not feasible, a correctly executed application could offer a degree of protection. However, this assumes you have already taken every possible step to mitigate the moisture from the outside, such as fixing gutters, grading the landscape away from the foundation, and sealing foundation cracks.
The Step-by-Step Guide to Applying Drylok on Drywall (The Right Way)
If you have exhausted all other options and determined this is your only path, preparation is everything. Do not skip a single step. Cutting corners here will almost certainly lead to failure.
Step 1: Find and Fix the Source of Moisture
Before a drop of Drylok touches your wall, you must become a detective. This is the most critical step. Look for the source of the water and fix it. Common culprits include clogged gutters, downspouts emptying too close to the foundation, improper yard grading, and cracks in the foundation.
Simply painting over a water problem is like putting a bandage on a wound that needs stitches. It won’t hold, and the underlying issue will worsen. True waterproofing starts on the exterior of the home.
Step 2: Prepare the Drywall Surface
The drywall must be immaculately clean, completely dry, and structurally sound. Use a wire brush to remove any loose dust or peeling paint. If the drywall has been previously painted, you’ll need to sand the surface to remove any gloss so the primer can adhere.
Repair any holes, dents, or cracks with joint compound and sand them smooth. Clean the entire surface with a mild detergent solution and allow it to dry completely. A dehumidifier can help speed up this process and ensure no residual moisture remains.
Step 3: Prime with the Correct Product
Do not apply Drylok directly to bare drywall or over a standard latex primer. This is the secret step that prevents most failures. The paper facing of the drywall needs to be sealed from the heavy water-based Drylok coating.
You must use a high-quality, oil-based, stain-blocking primer. An oil-based primer creates an impermeable barrier between the drywall’s paper and the Drylok, preventing the water in the Drylok from soaking into and weakening the gypsum board. This primer also helps the thick Drylok adhere better to the slick surface.
Step 4: Apply the First Coat of Drylok
Once the oil-based primer is fully cured, you can apply Drylok. Stir the product thoroughly before and during application. Use a high-quality, stiff-bristle brush or a 3/4″ nap roller designed for textured surfaces.
Work the product into the surface, ensuring you fill any small pinholes or voids. Apply a generous, even coat. The goal is to create a continuous, unbroken film.
Step 5: Apply the Second Coat
Drylok requires at least two coats for effective waterproofing. Follow the manufacturer’s instructions for drying time between coats, which is typically a few hours. Apply the second coat perpendicular to the first (e.g., if the first coat was applied vertically, apply the second horizontally).
This cross-hatch application helps ensure complete coverage and fills any pinholes you might have missed in the first pass. Two solid coats are essential to achieve the hydrostatic pressure resistance the product promises.
Step 6: Curing and Topcoating
Allow the final coat of Drylok to cure completely as per the product’s directions. The surface will have a distinct, slightly rough texture. While Drylok can be left as the final finish, it can also be painted over with a quality latex paint if you desire a different color or a smoother finish.
Drylok on Drywall: Choosing the Right Product
Not all Drylok products are the same. Understanding the differences is crucial for any application, especially an unconventional one like on drywall. The table below compares some of the common options.
| Product Name | Base Type | Primary Use | Drywall Suitability | Notes |
|---|---|---|---|---|
| DRYLOK® Original Masonry Waterproofer | Latex | Interior/Exterior bare masonry walls | Not Recommended | Has a sandy texture to help fill pores in concrete. This texture is generally undesirable on drywall. |
| DRYLOK® Extreme Masonry Waterproofer | Latex | Interior/Exterior bare masonry, above or below grade | Acceptable (with proper priming) | This is the best choice if you must use Drylok on drywall. It has a smoother finish than the Original formula. |
| DRYLOK® Floor & Wall | Latex | Masonry floors and walls | Not Recommended | Formulated for abrasion resistance on floors and offers a gloss finish, which may not be suitable for walls. |
| DRYLOK® Pro | Oil-Based | Interior/Exterior masonry, for professionals | Not Recommended | Has a strong odor and is more difficult to work with. Overkill for this application. |
Alternatives to Using Drylok on Drywall
In most cases, there is a better tool for the job than forcing a masonry product to work on drywall. Choosing the right material from the start can save you from future failures and costly repairs.
For High-Moisture Areas (Bathrooms & Kitchens)
The industry standard for wet areas like bathrooms is to use moisture-resistant drywall (often called “green board” or “purple board”). For areas with direct water contact, like shower surrounds, a topical waterproofing membrane should be applied directly to the drywall or cement board. Products like RedGard or AquaDefense on drywall are specifically designed for this purpose, creating a waterproof barrier beneath the tile.
For Basements
The best and most effective way to waterproof a basement is always from the exterior. However, if that is not possible, the next best interior solution is to waterproof the concrete foundation walls *before* you install insulation and drywall. Seal the bare concrete walls with a proper masonry waterproofer first.
Then, build your stud wall an inch or two away from the concrete wall to create an air gap. This allows any moisture that does penetrate the concrete to dry without ever touching the framing or drywall. Using closed-cell spray foam insulation against the concrete can also act as both insulation and a vapor barrier.
Improving Ventilation
Never underestimate the power of air circulation. In any area prone to dampness, improving ventilation is crucial. Installing an exhaust fan in a bathroom or running a dehumidifier in a basement can often solve moisture problems without needing any coatings at all. Proper airflow prevents condensation and allows damp surfaces to dry out quickly.
Frequently Asked Questions (FAQs)
Can you apply Drylok over painted drywall?
Yes, but the surface preparation is critical. The existing paint must be in good condition, with no peeling or flaking. You must thoroughly clean the surface and then sand it to remove any sheen. After sanding, applying an oil-based primer before the Drylok is still the safest course of action.
Will Drylok stop mold on drywall?
No. Drylok is a waterproofer, not a mold remediation product. While some formulas are mildew-resistant, they only resist new growth on the paint film itself. If you have existing mold, you must kill and remove it completely before painting. Painting over mold, especially with a non-breathable coating, will likely trap moisture and make the problem worse.
What is the best primer for Drylok on drywall?
An oil-based, stain-blocking primer is the best choice. It creates a necessary barrier to protect the drywall’s paper facing from the moisture in the Drylok and ensures strong adhesion between the two different types of coatings.
Final Verdict: Should You Use Drylok on Drywall?
Using Drylok on drywall should be viewed as a non-standard, last-resort measure, not a first-line defense. It is not the intended use for the product and carries significant risks if not executed perfectly. The potential for trapping moisture, causing drywall to degrade, and promoting hidden mold growth is high.
In almost every situation, a more appropriate solution exists, whether it’s using moisture-resistant building materials, applying a topical waterproofing membrane designed for bathrooms, or addressing moisture issues at their source. Always prioritize fixing the root cause of water intrusion over simply covering the symptoms. Before you reach for that can of masonry waterproofer, ensure you have considered all the alternatives for a safer, more reliable, and longer-lasting solution.
