Hemp Shield vs Thompson’s WaterSeal: Which Deck Sealer Lasts Longer?

Quick Answer: In the Hemp Shield vs Thompson’s WaterSeal comparison, Hemp Shield lasts longer. Hemp Shield is a penetrating hemp oil stain and sealer that soaks into wood and protects for 2 to 3 years per coat. Thompson’s WaterSeal is a surface sealer that sits on top of the wood. Independent testing found its water protection fades in 6 to 12 months, and most users reapply it every year. Thompson’s costs less per gallon and is easier to find in stores. But Hemp Shield covers about three times more area per gallon and lasts two to three times longer, so it costs less per year of protection. Below is the full comparison with sources.

Full disclosure: This article is published by Hemp Shield. To keep the comparison fair, every claim about Thompson’s WaterSeal comes from Thompson’s own product labels or from independent third party testing, linked in the sources at the bottom.

Quick Comparison Table

What Each Product Is : Hemp Shield vs Thompson’s WaterSeal

Thompson’s WaterSeal is the most recognized name in deck sealing. The brand has been around since 1920 and sits on the shelf of almost every hardware store in America. The product line includes the original Clear Waterproofer, semi transparent stains, and solid stains, all at budget prices.

Hemp Shield is a hemp oil based 2-in-1 deck stain and sealer made in Eugene, Oregon. It was the first wood finish built on hemp seed oil. The oil’s small molecular size lets it penetrate deep into wood fibers instead of forming a layer on top. One coat stains and seals at the same time.

Both products clean up with water. The similarity ends there, and the reason is how each one protects wood.

The Big Difference: Surface Film vs Penetrating Oil

This one difference explains almost every result below.

Thompson’s WaterSeal works on the surface. It forms a water repellent layer on top of the wood. Independent reviewers describe it as sitting on the wood like thin paint rather than soaking in. Surface layers work at first, but sun, foot traffic, and rain break them down. When the layer breaks down, protection is gone, and stain versions can peel.

Hemp Shield works inside the wood. The hemp oil carries the pigment, UV inhibitors, and mildew inhibitors into the wood fibers. There is no surface film, so there is nothing to peel. When the finish ages, it fades slowly and evenly. You clean the deck and apply a fresh coat, with no stripping and no sanding.

Lifespan: The Test Results

This is the question in the title, so here is the data.

Thompson’s WaterSeal: DeckStainHelp, an independent review site run by a wood restoration contractor with over 30 years of experience, tested Thompson’s Clear Waterproofer on a real deck. Water repellency failed within 6 to 12 months. The stain versions were rated 2 out of 5 stars, with premature peeling and wear after about one year. Thompson’s own product line notes describe the original clear formula as 1 to 2 year protection. On Walmart’s review page, a long term user of the semi transparent stain writes that they restain every year.

Hemp Shield: The published spec is 2 to 3 years per coat on decks, based on the penetrating oil holding its water beading and color through that period. Like every penetrating stain, horizontal boards in full sun sit at the shorter end and shaded or vertical wood lasts longer.

A note on label claims: Thompson’s solid stain label advertises 5 years on decks. Independent testing of the product line has not matched numbers like that on real decks, which is why this comparison uses tested results, not marketing claims, for both brands.

Coverage and Real Cost Per Year

Price per gallon is where Thompson’s looks best, so let’s do the honest math.

• Thompson’s: about $40 per gallon. Independent testing measured real coverage at 150 to 200 sq ft per gallon. For a 300 sq ft deck, that is roughly $70 to $80 in product per application. Applied every year, that is $700 to $800 over ten years, plus a weekend of your labor every single year
• Hemp Shield: covers 450 to 650 sq ft per gallon in ASTM testing, roughly three times the tested coverage of Thompson’s. A 300 sq ft deck needs well under one gallon. Applied every 2 to 3 years, that is 4 or 5 applications in ten years instead of 10

Run the numbers with current prices and Hemp Shield costs less per year of protection even though the gallon costs more, because you buy fewer gallons and apply fewer times. The bigger saving is labor: 4 weekends over a decade instead of 10.

Mold and Mildew: The Clearest Difference

The most striking result from independent testing: after 2 years, the Thompson’s test deck was covered in black mold, and the reviewer noted the oils in the formula appeared to feed mold growth rather than stop it.

Hemp Shield takes the opposite approach. Its mildew, mold, and algae inhibitors are formaldehyde free and encapsulated, meaning they bond into the wood and release slowly over time instead of washing off in the first storms. For humid states like Florida, Georgia, and the Carolinas, and wet climates like the Pacific Northwest, this difference matters more than any other line in the table.

UV Protection

Independent testing found the clear Thompson’s Waterproofer provided no meaningful UV protection, with wood graying within months in full sun. The tinted Thompson’s stains carry some pigment but were noted for fading.

Hemp Shield builds UV protection two ways: pigment in the tinted versions physically blocks UV, and UV inhibitors in the formula neutralize radiation the way automotive coatings do. For high UV states like California, Arizona, Texas, and Colorado, pigmented penetrating protection is the difference between graying in one year and fading slowly over three.

VOCs and Eco Profile

• Hemp Shield: 9 g/L VOC, plant based hemp seed oil from a renewable crop, formaldehyde free preservatives, biodegradable base ingredient
• Thompson’s: formulated to meet the 250 g/L VOC compliance limit

At 9 g/L, Hemp Shield is legal everywhere in the country, including California’s strictest air districts, and it is the obvious pick for decks above gardens, lawns, and anywhere runoff matters.

When Thompson’s WaterSeal Makes Sense

An honest comparison names the cases where the budget product is the right call:

• You need a sealer today, from a store shelf ten minutes away
• You are sealing a low value surface for one season, like a temporary structure or a fence panel you plan to replace
• Upfront cost is the only number that matters and yearly reapplication does not bother you
• You want a very forgiving first time application; reviewers note the clear waterproofer leaves no lap marks

When Hemp Shield Is the Better Choice

• You want to seal the deck once and not think about it again for 2 to 3 years
• Your climate is humid or wet and mildew is a real threat
• Your deck gets serious sun and needs real UV protection
• You care about what washes off the deck into your yard, or you live in a strict VOC state like California
• You want the lowest cost per year of protection, not the lowest price per gallon

The Verdict

For a deck you plan to keep, Hemp Shield is the better buy. It lasts 2 to 3 times longer per coat, covers about 3 times the area per gallon, resists the mold that independent testing found growing on Thompson’s, and does it at 9 g/L VOC instead of 250. Thompson’s WaterSeal wins on shelf availability and upfront gallon price, which makes it a reasonable short term fix and a poor long term plan. If you are searching for a Thompson’s WaterSeal alternative because your deck grayed, grew mold, or lost its water beading within a year, a penetrating hemp oil stain fixes the exact failure you experienced.

Frequently Asked Questions (FAQs)

Q.1: Which lasts longer, Hemp Shield or Thompson’s WaterSeal?

Hemp Shield, by a clear margin. Hemp Shield protects for 2 to 3 years per coat. Independent testing found Thompson’s clear waterproofer loses water repellency in 6 to 12 months, and its stain versions wear or peel in about a year.

Q.2: Is Thompson’s WaterSeal a penetrating sealer?

No. Independent reviewers describe it as a surface product that forms a layer on top of the wood rather than soaking in. That surface layer is why it wears off quickly and why the stain versions can peel. Hemp Shield is a penetrating oil that absorbs into the wood fibers.

Q.3: Why did my deck grow black mold after using Thompson’s WaterSeal?

You are not alone. In a 2 year independent field test, the entire Thompson’s test deck developed black mold, and the reviewer concluded the formula’s oils appeared to feed mold rather than prevent it. A sealer with built in, slow release mildew inhibitors, like Hemp Shield, is designed to prevent exactly this.

Q.4: Is Hemp Shield more expensive than Thompson’s WaterSeal?

Per gallon, yes. Per year of protection, no. Hemp Shield covers about three times the area per gallon (450 to 650 sq ft vs 150 to 200 sq ft in testing) and lasts two to three times longer, so over ten years you buy fewer gallons and spend fewer weekends applying.

Q.5: What is the best Thompson’s WaterSeal alternative?

A penetrating oil based stain and sealer. If your Thompson’s finish grayed, peeled, or stopped beading water within a year, those are surface sealer failures. A penetrating product like Hemp Shield’s hemp oil 2-in-1 formula addresses all three: pigment and UV inhibitors against graying, no film to peel, and oils that keep protecting inside the wood.

Q.6: Can I apply Hemp Shield over old Thompson’s WaterSeal?

Not directly. Any old surface sealer blocks a penetrating oil from reaching the wood. Clean the deck first, and if any old finish remains or is peeling, strip it with a finish remover, then brighten, dry, and apply Hemp Shield to bare wood.

Q.7: Does Thompson’s WaterSeal protect against UV and graying?

The clear version showed no meaningful UV protection in independent testing, with graying within months. Tinted versions have some pigment but tested poorly for fading. Hemp Shield combines pigment with UV inhibitors for measurably longer color hold.

Q.8: How many coats does each product need?

Both are one coat products. The difference is coverage and repeat frequency: one gallon of Hemp Shield covers 450 to 650 sq ft and lasts 2 to 3 years, while Thompson’s covers 150 to 200 sq ft in testing and is typically reapplied every year.

Q.9: Which is safer for plants and gardens around my deck?

Hemp Shield. It is plant based, formaldehyde free, and just 9 g/L VOC, compared to formulas built to the 250 g/L compliance limit. For decks over landscaping, lower VOC and biodegradable ingredients mean less harmful runoff.

Q.10: Where can I buy Hemp Shield?

At hempshields.com with free shipping on orders over $100, and on Amazon and Walmart.com. It ships to all 48 continental states. Thompson’s is available at most hardware and big box stores.