Choosing Wood Deck Sealer

Choosing Wood Deck Sealer

what you need to know about wood deck sealers.

wood deck

People for years have been looking for the best wood sealer. This has become a challenge for us in a way because there are more sealers available than ever before. Years ago we tried every single sealer available, but with the widespread reformulating we saw in the last several years and all the new products popping up it has been hard to keep up with every change. The complications of reformulating any product are obvious, and some wood deck sealers changed formulation several times during this short period.

Wood deck sealers are made from a number of different bases with a variety of added chemicals. Some adders make the wood deck sealer perform better (application, bonding, flow, penetration, etc). Other ingredients simply add bulk to help hold the “cost per gallon” down. For example, what purpose does adding mineral spirits to an oil sealer have? Well, it thins the product to make it easier to spread and it helps carry the wood deck sealer into the wood. The fact that mineral spirits have a very low cost also enables a manufacturer to reduce the selling price of his product just by adding more mineral spirits! Of course the EPA has forced this practice to stop, so some manufacturers are actually dropping out of making wood deck sealer.

In any discussion of sealers, it should be understood from the beginning that there is no one perfect product. The most universal product we have ever used is Our Preferred Sealer, which is used regularly on everything from log cabins to docks successfully. We have other sealers available for those ‘different’ situations, but we use our preferred sealer for most of our jobs.

Oil – wood deck sealer

Oil sealers may contain any of several kinds of oil. Oil sealers may be coatings or penetrants or some blend of both characteristics. Pure coatings sit on top of the wood. Pure penetrants sit at and below the surface of the wood. A wood deck sealer that leaves any kind of surface coat on the wood is considered a coating, whether that is minor (i.e. 10% coating, 90% penetrant) or a full (100%) coating. Any product that contains linseed oil is a film-forming product (coating) to some degree. Ready Seal is made from 100% paraffinic oil (a crude oil derivative) and is therefore a full penetrant.

Generally speaking, coatings disguise flaws in the surface or flaws in the washing job. The closer they are to being solid color stains, the more they are able to hide flaws. They may be subject to visible wear in traffic areas as well. Coatings should be stripped before applying a new layer because they will not allow new layers to penetrate into the wood and bond to it. Most coatings require careful application, because flaws like drips and runs will show in the final job. In other words, you must have painting skills to apply any coating in a way that it will look good when it is new and as it ages on the wood. Coatings may flake and peel over time if humidity is trapped in the wood.

Generally speaking, penetrants won’t disguise flaws in the surface such as a poor wash job or stains. Penetrants do not show any traffic pattern wear. They normally do not have to be stripped to recoat down the road, either, because the new sealer penetrates through the old coat and bonds directly to the wood. Applications of full penetrants are fully forgiving, which means that drips or lap marks will not show. Fully penetrating products are not created to be tough like coatings, so they strip relatively easily when you need to remove them.

Water based wood deck sealers

Water-based finishes are becoming more popular as more and more homeowners attempt doing their own work. These products are sold by the big box stores with tag lines like “cleans up with soap and water” – which are very attractive words to the do-it-yourselfer. Latex and acrylic finishes make up the bulk of these alternative products. Water-based products are film-forming finishes. Water-based products and acrylics are very difficult to maintain and to work with.


PERMEABILITY: Sealers are supposed to be permeable, which means that they allow the wood to “breathe”. This means that ordinary humidity can enter and leave the wood during the normal cycle of the day, but droplets like rain cannot enter the wood. The more pigment the product contains, the less permeable the sealer is. A quality permeable sealer will allow sap to exit the wood without damaging the sealer as it passes through, for example.

Paints are non-permeable, which is why painted decks crack and peel drastically after a short time.

Ever notice what happens to latex paint on a window sill? The humidity present in the wood tries to escape when the sun hits the wood and raises the temperature. Since this moisture cannot pass through paint, the only natural result is that the humidity pushes the paint off of the surface of the wood to escape. That is why paint cracks and peels. This result happens most frequently on window sills (horizontal board) rather that on vertical window trim, because the top end of a vertical board is usually not painted (allowing the humidity to escape). This is why we NEVER paint a wood deck.

VOLATILE ORGANIC COMPOUNDS: For many years, manufacturers threw out terms like “percentage of solids” as a selling point for their products. In layman’s terms, this refers to the amount of product that remains in the wood after everything that evaporates is gone. What evaporates are called “volatiles” or “VOCs”. The EPA has been tightening regulations on VOCs for years because they harm the quality of the air and the ozone layer. Many sealers have had to reformulate once (or several times) to meet these changing regulations. Every time a manufacturer reformulates, the product characteristics change.

VOCs are often simple mineral spirits or turpentine.

NOTE: “High solids” does not mean that the product is thick. Our preferred sealer has the highest solids of any oil sealer we know of (87) and is also one of the thinnest oils you will ever work with. It simply doesn’t contain much volume of VOCs.

Sometimes sealers contain manufacturing by-products that manufacturers want to dispose of, such as benzene. A careful examination of the MSDS will reveal this.

PIGMENT: Pigment is a finely ground, inert, colored powder that is used to create color in your sealer. In most sealers these particles are iron oxides. In sealers it is the iron oxide pigment which gives it UV protection. The UV rays of the sun are reflected away from the wood by these minute iron particles of color before they can penetrate the wood and turn it gray. Over time, the rays of the sun use up the oxide particles, and the wood begins to gray once again.

Clear sealers, in spite of many label claims, do not effectively prevent graying because they contain no pigments.

LIFE: Most sealers are designed to last approximately two years on the horizontal surfaces and four years on the vertical surfaces. Some claim more, some make no claims at all. Customers will usually ask about the life of the product we are suggesting, and it is important that to know that the answer to that question is “Depends…” The life depends on the sealer, the location of the deck, the condition of the wood, the local weather conditions, the use of the deck, etc. Remember that sealers are never guaranteed to ‘look good’ for any amount of time. They are only guaranteed to repel water for a period of time. Manufacturers are notorious for not standing behind their products. They simply blame a poor application and leave you holding the bag.

Some manufacturers sell “lifetime” or “25-Year” finishes. These are almost always water-based silicone products. Silicone is an excellent water repellant, and lasts a long time. It cannot ever be fully removed from the wood later on, so selecting one of these products is a permanent decision. The drawback to these products is the UV protection, which often fails within a few years of the initial application. Once the wood starts to turn gray, the nightmare begins. If you can’t strip the product off, how do you get down to the wood to clean it and add more UV protection? There is no answer.


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