Plans for finishing a new cedar deck

davidrmoJune 19, 2006

Hi, gang. I'm sorry to ask yet another permutation of a question that has been discussed a bazillion times. But, after spending 8 months planning and sweating to build my very first deck, I don't want to screw it up now. I've been trying to learn the best way to seal it so that it stays beautiful and solid for as long as possible.

The basic facts are,

- 1" cedar deck over PT

- we live in the midwest, so we see really cold and really hot, with a lot of wet mixed in from time to time

- ground level (deck is 12" from the ground)

- about 400 sq'

Over the course of the project, I have read all sorts of advice, lots of it contradictory. After taking it all in, the harebrained idea that's starting to form in my head looks something like this:

1. bring the cedar decking home from Menards

2. pretty soon after (same day), lightly sand it (80 grit, to remove any mill glaze)

3. pretty soon after (same day), dip each cedar board in a tub of semitransparent stain/sealer (brand tbd; my intention is to get good penetration, and to seal out moisture from any direction; plus, dipping seems easier than masking + spraying or brushing)

4. lay the boards out across the joists to dry for a couple days, with a little spacing between

5. cut and install the boards, reapplying sealer on any cut ends as I install them

6. install the boards with deck clips, or some similar hidden fastener system, to avoid divots created by counter-sunk screns on the top surface

Am I doing anything stupid? Do I need to wait between bringing the cedar home and sealing it? Are there good reasons not to seal new cedar on all sides?



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I've never built, or even stained a deck...

But in regards to #3, one thing I've seen discussed in my researching for staining my deck is to NOT stain the underside of deck flooring. If I remember right, the reasoning is that as the stain breaks down on the top surface, moisture gets into the wood, then the stained surface on the bottom traps the moisture inside the wood.

I know I've read that numerous times on this forum. I believe I've seen Ken respond to this question, but don't remember specific posts.

    Bookmark   June 19, 2006 at 4:12PM
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I hate to do this to do you because I am going to say I wouldn't do anything you are about to do. Here is how I build a cedar deck.

1) Purchase highest quality KD clear cedar from a reputable yard.
2) Build deck (the old fashioned way, not with clips)
3) Clean with Restore-A-Deck system to remove mill glaze, to remove any dirt particles or mold spores trapped in the wood, to clear off and stop extractive bleeding and to pH balance the wood to its slightly acidic natural condition.
4) Wait 3 days
5) Apply paraffinic oil based, trans oxide pigmented, semi transparent penetrating sealer..
6) Next year, light wash and another coat of sealer.

Why do it this way?
Sealing all sides of the wood is a bad idea. Sealer will wear off the top and cause drainage issue and cedar sucks with rot resistance (heartwood used to be more rot resistant.
 No sanding? If the wood was stored indoors and kiln dried it should be relatively smooth. Applying a paraffinic oil (Ready Seal is one) will actually soften the fibers and surface. You can sand if you have your heart set on it but I find most times it is not neccessary.
 Whats wrong with the clips? Nothing if you like cupped floor boards.

John, Steve, Al, jump in here. Maybe I am outta line?

    Bookmark   June 19, 2006 at 4:13PM
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my advice would be to get the cedar, (if you want that soft stuff... I'd prefer ipe, because cedar is like cheese. It dents)
Store it near the job site for at least a week to acclimate to the environment. If you don't do this and you gap it and screw it down, the wood will shrink and your gaps will be larger than you planned. Or, if you it comes from a dry storage area, and heated garage, it will swell once it reaches moist air. This goes for air or kiln wood because kiln is only good for indoors because it is dried and going in a dry area.(they hurry the process) Even with kiln, it should sit in the house for a week to adapt to the air in that location.
Also, air and kiln dried adapt to the environment they are in.. so both should acclimate.

2.I would definitely seal all 4 sides of the wood. Water is in the air in vapor form.. It will aborb into the wood and create an uneven moisture absorption which leads to cupping. It's a pain to seal all 4 sides but it's protecting the board from moisture absorption. Finishing one side is like wearing only a hat in the winter hoping the cold will go through the hat and out your feet. You need 4 side protection. (now, with woods like ipe, cedar, this stuff lasts for decades... Contractors don't typical stain all 4 sides because it draws the process out, it doubles the finishing area and would take a long time to see the mistake manifest) source for the staining of 4 sides, forest products lab. They actually do time-tests)
3. The wood should weather slightly, at least get 2-3 rains to wash the excess tannins out then use a cleaner to kill mold, algae, etc and oxalic acid -available at any paint store. I got cabots cleaner/brighter from Lowes and it worked fine in dilution.
Most of this stuff is a form of chlorine,oxygen cleaner or other chemical sanitizer. (if you can avoid chlorine, it's better because chlorine isn't the best for wood..

4. Stain should be applied at least 2-3 warm days after this cleaning in dry weather. if you apply it in direct sun, it can flash dry before it absorbs. So a cloudy, later in the day, application will work best.
Wipe it off 15 minutes later so it dries in a matte finish and not have stick, shiny spots. Get right on the deck and polish it and walk backwards, polishing the floor and your footprints out.
Everyone has their own ways, it's wood and will take alot for you to screw it up. You will be doing this process yearly or every 2 years. So, don't drive yourself crazy with some of the details I said above. If you can come close to them, you'll be like 99% of other deck owners. lol

    Bookmark   June 19, 2006 at 6:00PM
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I still say sealing four sides is a good idea that turns bad. I wouldn't use an oil on the bottom surface of a deck that is 1' off the ground (unless you like mold infestation)

Also, I find holes in the theory of evaporating moisture promoting cupping. Rapid wet/dry cycles cause the wood to warp. That would lead one to believe that a wood is better off with a slightly higher moisture content. Say from evaporating moisture? What happens when that top surface of sleaer wears off and water starts penetrating the top? It is going to be trapped. Cedar and water don't mix.

The jury is out on this one. I say don't do it. I think it is a complete waste of time.

    Bookmark   June 19, 2006 at 8:41PM
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It is a waste of time.. that's why people don't do
But forest lab did studies on this and staining 1 side just puts a little skin on the board. The entire board is prone to moisture in the air. The bottom especially because it's shady and moisture will hang around there and the wood will breath it in from underneath entirely unprotected without any moisture blocker.
This is how cupping starts.
The edges is another area that drinks in moisture that's why everyone seals them. The tested way to protect a board is to moisture block the entire 6 sides.
You should at least doing this with constructing a deck. As far as maintenance it, you can simply do the top because it will be eaten up by the sun and direct weather assault. Protecting all 6 sides of a board will add years of durability to the wood condition.
I have no idea how staining the 'top only'caught on. It's definitely easier but as far as the reasoning of it.. I'm just puzzled. Can anyone post a link to where it says only stain the top because it makes a board more protected from
moisture? It's a very popular theory here and I'd like to read more about it.

    Bookmark   June 20, 2006 at 12:00AM
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P.S. I mistakenly said '4 sides' in the first post, I meant 6- 2 faces, 2 sides, 2 edges.
Also, I think staining both sides of a deck became such a lengthy task that it was shortened to staining 1 side. It would cost twice as much time, twice as much stain, and twice as much labor in flipping boards, cleaning, staining, waiting for dry weather..etc. Decking material such as pressure-treated, cedar, ipe go many years with or without bottom-staining so it's almost a 'you don't have to'... which turned into a science theory of 'you shouldn't'.
Sealing all sides of exposed wood is always a good idea and will definitely protect a board better from my readings. If you plan on building an outdoor bench or arbor with a more delicate wood you wouldn't want to seal just certain sides of it, it would be the whole thing.
hardly anyone does it with a deck. I did it with mine but I wouldn't do it for anyone else. lol I also sealed the joist edges and tops, beams, 6x6 posts..etc. It's really a pain sealing a deck, then flipping and doing the other side.
I never had a deck board cup and projects were more predictable with acclimating lumber, sealing it entirely, and applying stain on cloudy or late day times.
I think if we put the wood in a test area with tons of steam it will curl right up from the bottom with the bare wood, in time. Face-screwing definitely will help slow this process.
I don't mean to contradict your opinion pressure-pro's. Your method is what most people do and have no problem for years. I just became a believer in full-seal from the link above at the forest lab, furniture makers and boat makers who specialize in moisture issues. Is this conversation too anal-retentive for a deck? Definitely. lol

    Bookmark   June 20, 2006 at 1:01AM
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No problem, I love a good debate and by no means do I claim to have the perfect answers for everything. Stain manufacturers have been trying for 80 years to get it right and still nothing lats more than a year or two.

In a perfect world where everyone did maintenance when they should, used the products they should, and were positively anal about controlling mold growth and were willing to pull up all their floor boards every year to clean and then maybe reseal, sealing on all sides would be a great idea.

Just be prepared to seal the top every six months or so and you would be fine. In that same perfect world with no limitations on time or budget, everyone should use 2" x's for deck flooring with a full sanding every three or four years and never use any type of abrasive stripping chemical.

Gorilla is right about one thing, many people do get caught up in details that don't really make a measurable difference in the long run.

    Bookmark   June 20, 2006 at 6:26AM
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Wow, thanks for sharing your experience, guys. It sounds like you've both had good experiences doing things in pretty different ways.

Thanks for the detailed suggestions, pressurepros. I've gone to your site and read up on the RAD system. It sounds impressive, and I'm thinkin about using it. The cedar is already bought and paid for, so I may be stuck with the non-kiln-dried variety from the big-box store. I've made some calls, though, and may be able to trade for KD stuff if it will make a difference. It sounds like gorillabuilder doesn't think it will. What's the advantage you see in it?

Thanks for the pointer to the forestry guide, gorrillabuilder. Actually, I love hearing about the science behind what I'm doing. Today I read most of chapter 15 on finishes. You pros probably know most of this stuff already, but it was educational for me. If any other novices are reading this with similar questions, you can find the guide online at

Some of the stuff I took away from the guide was,

  1. You want a finish that is going to repel water, but also allow vapor to pass in and out because, (a) water vapor is going to get in, it's just a question of how quickly, and (b) when water does get in (either as vapor or liquid), you want it to leave; you don't want your coating to hold it in the wood.

  2. A finish that puts a thick film on your deck (eg. paint) will keep out vapor the best. If you cover all surfaces. And only until it cracks. Then, it's going to cause the most water to be retained in the wood.

These sort of supported what I think pressurepros has been saying here for awhile - you don't want to finish the wood in a way that's going to trap water inside. However, the guide also said

"The paint film inhibits drying, as shown. This retardation of drying can have a drastic effect on the durability of painted wood fully exposed to the weather. The moisture content of the wood can approach the range where decay fungi can become active. This type of wood paint failure usually occurs on painted fences and porch railings that are fully exposed to the weather (Fig. 1510). Applying a water-repellent preservative or priming the end grain of wood used in these applications inhibits the absorption of water at the end grain and thus works in concert with the coating to keep the wood dry.

For a coating to be effective in minimizing moisture content changes in the wood, it must be applied to all surfaces, particularly the end grain. The end grain of wood absorbs moisture much faster than does the face grain, and finishes generally fail in the end grain first (Fig. 1511). Coatings with good moisture-excluding effectiveness that are applied to only one side of the wood will cause unequal sorption of moisture, increasing the likelihood that the wood will cup (warp). When finishing siding, it is important to allow the back side of the wood to dry, particularly if it is finished with paint with high moisture-excluding effectiveness. Applying a water-repellent preservative or primer to the end grain and back of siding (see section on back-priming) prior to installing the siding improves resistance to water yet allows the siding to dry. Cupping can be minimized by using vertical-grain lumber and by minimizing the aspect ratio."

What I take away from this chapter is that applying a vapor barrier (eg. paint) to all 6 sides will do exactly what pressurepro is warning against. However, since a water-repellent preservative is not a vapor barrier, applying it to all 6 sides shouldn't have that affect, but should in fact be beneficial. At worst, it sounds like a waste of preservative. If we're all still around in a few years, I'll report back and let everyone know how it worked out.

Gorillabuilder, how do you apply the sealer to your deck? Did you brush and flip, or dip the boards?

I'm taking to heart the suggestions you guys made to weather the wood a little onsite before installing it. I'm a little nervous, though, because I've had one unfinished board sitting at the site for a few weeks (I had used it as a sample to get a feel for spacing), and it is now *really* warped. If I lay the new boards flat across the joists, though, and don't leave them out in the elements for weeks, maybe they'll hold up better.

No one seemed keen on the deck clips, so it looks like I'm stuck with deck screws through the surface. That may have saved me a couple hundred bucks, but it'll expose my imperfectly-aligned and spaced joists.

So, my revised plan would be,

1. Bring the wood to the site, lay it across the joists
2. clean it right away w/the RAD system or Cabots cleaner/brightener (no sanding!)
3. Let it weather for 3 days
4. Stain all 6 sides with a "paraffinic oil based, trans oxide pigmented, semi transparent penetrating sealer"
5. Let the stained wood dry for 2 days (again, across the joists)
6. Install it (the old fashioned way, not with clips)

Thanks for sharing your time and experience, guys.


    Bookmark   June 20, 2006 at 7:44PM
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The thing I like bout kiln dried lumber is the controlled way the moisture is released from the wood. It is the expansion and contraction of wood through moisture release that causes warping.

If you are going to seal the bottom side, which I still say is not only unneccesary but detrimental over the long haul. Be prepared to have an excessive amount of mold undertake your boards from underneath. I would rather see you start with straight lumber, screw it down and keep the top and grain sides sealed to prevent cupping then go on the path of sealing all sides. Your call on that one.

    Bookmark   June 20, 2006 at 9:41PM
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"Excessive amount of mold undertake your boards from underneath."

You're saying this because you're thinking stain is food for mildew.. hence it will grow there. But mildew can also grow on wood and the wood itself is the food.
The common denominator is moisture.
At least with stained wood, it resists moisture, has a mildew inhibitor and stops water vapors from entering the naked wood from underneath, holding moisture, and pushing the top stain off causing repetitive staining on top and a moist damp area for mold underneath.
-Both settings, stained and unstained are susceptible to mildew.. that can be hashed around. Definitely have adequate ventillation.
But we also got to talk about the other detriments to not encapsulating a board. Wood deterioration based on absorption of water vapors from the unfinished side. Stained or painted wood always last longer than bare wood.
The finish also suffers and wears off faster because the vapors come right underneath and work through the wood... and begin to push the stain off from above. This is how peeling, finish buckling and finish vanishing comes about.
So, based on the mildew discussion.. which could not be right're giving up 2 other protectionary pitfalls.
David.. seriously.. my way or pressure pro's way will give you a deck for a long time. I just slap a coat on underneath, he doesn't. Both last long.. The differences would only appear more drastically if we were talking of sealing a wood like plywood or other 'non-decking' wood. Such as with boats... Boat-builders at times use material that is not as durable or as ventilated as home decking material.. why? Because it's too heavy for some applications and some of this stuff is put in areas not ventilated and that can get tons of humidity.
They encapsulate wood for all-side protection from vapors. Water is in the air. Now if we reduce this to a home-deck.. the same principals apply only it's outside, ventilated.. and it would take a long time to see the boat example manifest in a home-deck.
I washed and brightened the wood, let it dry stained it. 15 minutes later, wiped and polished it so no shiny spots were there. Let it dry, then flipped. I cleaned, brightened and stained that side. Wiped it down 15 minutes later.
I also had the boards spread so I could get the edges.
You can do it pressure pro's way too if you want. Like he said it's up to you. It's not like we're dealing with a car engine where a wrong technique will leave you stranded within 15 minutes. lol
I presented my side, he presented his side.. it's your call. Now let's worry about bigger things like solving diseases. We covered the deck stuff. lol

    Bookmark   June 21, 2006 at 3:48PM
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Moisture is a part of the equation but mold lives and thrives off of an oil based sealer. My only sugestion is to make sure you get a decent brand of sealer with potent mildewcide..nothing from Home Depot or Lowes

    Bookmark   June 22, 2006 at 9:32AM
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