Planter Box Waterproofing

Planter Box Waterproofing

Waterproofing your planter boxes is an important step in making sure your boxes are intact for many growing seasons to come. Foundation sealant creates a waterproof membrane resistant to moisture and elements, in addiion to fertilizers and other chemicals found in soil. Sealant is safe for inedible plants.

Prep Your Planter Boxes

Get Your Supplies Ready

A successful project starts with preparation. Make sure you have all the supplies and products you need with our supply checklist.


Download Supply Checklist

Clean Your Space

All surfaces must be structurally sound, clean, dry and free from contaminants that would prevent proper adhesion. If not using kiln dried wood be sure that the new wood is sufficiently dried (less than 15% relative humidity. Chemically-treated wood and OSB should be thoroughly cleaned to remove treatments from the surface to which you will apply your Liquid Rubber Solution and allowed to dry. Sealants and existing coatings should be fully cured and well bonded. Loose/flaky material should be removed. Concrete: Etched, power washed and allowed to fully dry. Wood: Mildew and organic growth must be removed using Deck and Patio Cleaner. 

Clean Your Space

Secure raised nail heads, deck screws and loose boards. Pre-fill imperfections such as screw holes, knots and splits in the wood with a high quality wood filler. Use Liquid Rubber Caulking to fill gaps and cracks. Replace damaged and rotting boards and remove loose splinters. Wood should be scuffed to increase profile using a 60-80 grit sandpaper and cleaned. Steel: Should be scuffed with an emery cloth to increase profile, cleaned with an appropriate steel cleaner or power washed, and/or cleaned with a mild detergent. Existing coatings: Scuff to increase profile and clean with a mild detergent.

Contain The Mess

Set out a tarp or large piece of cardboard to keep all tools and containers on when you are not using them. Have a pail of soap and water, rags and mineral spirits ready in case there is a spill. If a spill happens, use rags to soak it up, cleaning immediately with soap and water. If it is dried, use a razor/scraper to remove. Use mineral spirits to weaken the material and remove with a wire brush or grinder.

*Note: Use mineral spirits sparingly.

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Step-By-Step Project Walkthrough

Tip From the Pros:

Avoid contact with solvents and solvent based cleaners, adhesives, and paints.

Prepare Your Space and Gather Your Materials

Make sure surfaces are properly scuffed, cleaned, and dried. Gather all materials needed for your project.

Detail Work

Corners, joints, drains, around protrusions: Use Seam Tape or Geo-Textile applied via the 3-course-method to reinforce these area’s prone to movement and leakage. 3-Course Method: Apply a thick 6’’ wide coat and embed 4’’ wide Geo-Textile reinforcement fabric followed by a second coat (known as the 3 Course Method). For all gaps/cracks greater than 3mm (1/8’’) fill with a high quality wood filler, concrete patch material or Liquid Rubber Sealant & Adhesive prior to 3 Course Method. Ensure the surface is smooth and flush.

Tip From The Pros:


Tape-off, block-off, or otherwise mask area’s that are not to receive your selected sealant.


As an option, use Liquid Rubber Multi-Purpose Primer to increase bond.

Apply Coating

Apply your selected sealant when temperature is 10°C/50°F and rising. Begin with your detail area's (i.e. joints, corners, etc.) as per the Detail Work specification above. Once the details have dried, use a brush, roller or appropriate sprayer to apply at a final thickness of (40-60 mils, 1-1.5 mm). Generally you can apply 2 heavy coats per day. Applications generally take 3-4 coats. Apply next coat when dry to the touch and nothing is wet underneath and is uniform in color. Tacky is OK. Avoid applying in high humidity (over 80%) or in direct, intense sunlight. Apply all recommended material.

Inspect and Protect

Inspect for pinholes, blisters, voids, thin spots or other defects after each coat. Repair as necessary. Allow 48-72 hours to dry, depending on product and environmental conditions.

Clean Up

Remove tape and close container to secure leftover product. If spillage occurs, soak up as much material as possible with rags. Clean immediately with soap and water. If spill is dried, scrape off as much as possible with a razor or scraper. Use mineral spirits to weaken product and an appropriate tool such as a wire brush or grinder to mechanically remove. If splashed on the skin immediately wash thoroughly with fresh water. If the product has dried on the skin massage the area with medical grade mineral oil, baby oil or edible oil, then wash with soap and water. If irritation persists seek medical attention.

Need Some Help?

Tips & Tricks

How to Waterproof a Planter Box

View video instructions of how to waterproof a planter box.

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