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Question DetailsAsked on 6/20/2016

I want to seal a new cedar deck. What do you recommend?

We live in Northern Minnesota. We do not want anything that will peal off of this beautiful new wood.

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If you look in the Home > Painting and Home > Decks and Porches links in the Browse Projects link at lower left, you can find a fair number of previous similar questions with responses.

Cedar is one of the hardest to care for deck materials, and unless old-growth clear cedar tends to be a maintenance issue - not my choice for deck materials for that reason plus it slivers badly and the slivers really hurt and fester up. And note - in caring for it, do NOT pressure wash - fuzzes up unless very expertly done (can even fuzz up with a regular jet hose nozzle) and then has to be sanded down to fix it.

The only truly effective solution I have found was done on one high-end California cliffside home I worked on - seal the wood with penetrating clear plastic (basically the same process used for the Bodies exhibitions) and then cover it with glass as the deck surface - not your normal solution, nor very economic, and probably not a great solution in extreme climate like yours.

To avoid the peeling sealer problem, which is especially common on Cedar, you do not want a heavy coat stain or sealer - you need a penetrating sealer with ultraviolet barrier additives, and to preserve the cedar color a clear one. Immediately that gets you into trouble - because clear sealers have short life because of their ultraviolet sensitivity, and also penetrate significantly differently in open grain and tight grain so you get a lot of intense variations in the tone of the cedar. However, without a preservative or sealer, it will yellow and eventually gray out over 5-10 years typically with aging.

Do NOT use polyurethane or varnish - both can look vdery nice when applied, but do not survive the exterior environment and cannot reasonably be over-coated in outdoor use so you will be stripping and refinishing every year or so.

In the good old days before the California eco-freaks made everything that works well illegal, I would have said the oil-based (NOT water-based or silicone based as they do not penetrate properly) Olympic Maximum deck stain and sealer line with extra mildewcide added - but they have now gone to water based and it does not last anything like it used to.

One thing you could try is a small sample of a linseed oil based clear sealer, though it will darken the wood a lot so try on a scrap first, and you DEFINITELY have to add mildewcide because linseed oil is a favored growth medium for moss and mildew and mold, so only works well in sunny locations not on shaded decks.

My personal recommnedation - do NOT use a silicone based product like Thomspons silicone waterseal - I have never seen one that worked worth beans, and they will typically very shortly start peeling and flaking due to outdoor exposure - commonly in the course of one season. Thompsons does have a timber oil product that supposedly gets away from the silicone problem, but the regular waterseal behavior drove me away from that brand so I have never used it and do not know of any decks that used it that I have seen.

There are pure oil peentrating products you could look into like Tung oil - but basically all those will significantly darken the wood, and most stain it too so you would probably lose the orangish cedar tone.

Penofin Marine Oil wood finish (a boat wood sealer) also gives a nice result, though I have never used it on cedar - I would contat the manufacturer on that, and also test a piece of wood before trying it on a whole deck.

Cabot Australian Timber Oil is another penetrating oil sealer which worked nicely on a couple of decks I have seen it age on - but again add mildewcide (as with any oil product), and be sure the mildewcide is non-coloring - some will tint clear products.

Here is a link to a review site for deck sealers/stains which might help - a lot of contractors are going to the TWP 100 series (1500 series in low VOC mandated states) now that Olympic has gotten away from high quality stain materials.

One thing - do NOT seal the underside of deck boards but to deal the ends to the extent possible (ideally before installation) - if you seal all around the board any moisture that gets in through small gaps in the sealer is locked in and cannot evaporate out effectively through the tiny access route, so causes rot - so leave the bottom bare for evaporation.

Also - check instructions - new cedar has a LOT of natural oils (which cause its normal long life) but they also block sealers for the first year or two - so commonly manufacturers recommend waiting a year or so, then cleaning with a good deck cleaner, thoroughly dry, and then seal.

Note that whatever you use, once you start the clean/stain/sealing process, it is something you have to do every couple to few years. About the only other alternative is to use a copper preservative compound to penetrate the wood and protect it from decay without sealing it, which can last 20-30 years on a treatment on treated wood, but that does not help you when you already have a new cedar deck in place - and while you can treat cedar that way, it is not clear - comes in bright green, a darkish brown, and the "wolmanized" orangish landscape timber colors only, so you would definitely lose your beautiful cedar look - though as that fades away you could consider the Cupreanol or similar copper preservative in the future to extend the life of the deck.

FYI - here is a link to a pretty clear, readable article on the deck finishing issue, with names of the most commonly used sealers, from this Old House -

Answered 4 years ago by LCD

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