# Staining underside of deck?



## Andyman

Do you stain the underside of decks (joists & bottom of floor decking or stairs) or just the top and sides? I have always done just the top, sides, beam, and posts but not the underside. Pros and Cons? Thanks.


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## PressurePros

Unless the boards are being sealed as they are being laid, it can cause more problems than benefits. If the decking is installed, you will have areas at the joist that will be unsealed and I would think that moisture may have an issue migrating. Even if my science is questionable, the only real benefit is aesthetics and customers are usually not willing to pay for the extra 140% of square footage under a deck (including joists)


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## cappaint

No. It traps the moisture and leads to failure.


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## Andyman

It has also been my theory that it will trap mositure unless you seal all 6 sides after drying.


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## Faron79

Gentlemen & Ladies,

Why do ya think natural wood siding needs to be primed on all sides?!

>>>> To keep most moisture OUT in the first place. <<<<

Same thing for decking....

Knowing what I know NOW...if I was rebuilding my Redwood deck, ALL sides would have a coat of Sikkens SRD.
* This is CRUCIAL for low decks...anything less than 3' above ground.
* For any SHEENED "film-forming" stains, like Sikkens DEK-Finish, ALL sides MUST be coated....to keep moisture OUT of the wood so it can't push off the surface films.
* All car surfaces are primed too don'cha know! Saaaammmme reasoning....

Do most people wanna PAY for that??? Obviously...NO.
Should they do it.....YES.

Faron


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## NACE

Faron79 said:


> Gentlemen & Ladies,
> 
> Why do ya think natural wood siding needs to be primed on all sides?!
> 
> >>>> To keep most moisture OUT in the first place. <<<<
> 
> Same thing for decking....
> 
> Knowing what I know NOW...if I was rebuilding my Redwood deck, ALL sides would have a coat of Sikkens SRD.
> * This is CRUCIAL for low decks...anything less than 3' above ground.
> * For any SHEENED "film-forming" stains, like Sikkens DEK-Finish, ALL sides MUST be coated....to keep moisture OUT of the wood so it can't push off the surface films.
> * All car surfaces are primed too don'cha know! Saaaammmme reasoning....
> 
> Do most people wanna PAY for that??? Obviously...NO.
> Should they do it.....YES.
> 
> Faron


If the boards have an acclimated moisture content of 8-12%, and they are coated prior to installation, you create dimensional stability that significantly reduces the expansion and contraction rates of the wood, in addition to delaying the cracking and checking, a flat grain wood delaminating and wanting to go back to the original roundness of the tree. Most effective in pressure treated. A plastic barrier under decks is effective too in addition to coating all six sides. There are very detailed studies of this from the US Forestry Service. Graining pattern and tightness of grain and flat grain orientation are also very critical in deck coating success. The tighter the grain, the longer the deck will last. Good luck finding tight grain pressure treated.


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## cappaint

I always thought that all wood is going to have moisture in it already no longer how long u let it dry out. Hence locking all sides would trap the moisture in and it would fight its way back out...hence failure.


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## NACE

cappaint said:


> I always thought that all wood is going to have moisture in it already no longer how long u let it dry out. Hence locking all sides would trap the moisture in and it would fight its way back out...hence failure.


All wood will have moisture. It will never be zero. Different species will acclimate to a constant level depending on the geography. Cedar and PT in the northeast will stabilize at 8-12%. If you coat it at it's lowest content, it will likely stay at that level. If you coat it and trap moistue in, it will fail. Moisture will not push a film off if it does not have enough force to do so as most coatings have the ability to breathe to some extent. If you put a piece of Swiss cheese on wood, the holes will allow moisture to pass. If you put two pieces on, you have less breathability. Put three on and all the wholes don't match. With wood, creating dimensional stability is key to longer term coating success. Dimensional stability is a measurable unit and the less force created by swelling, freeze thaw, uv etc is best and stresses the film or stain less. Check out us forestry online and there are tons of studies on this. We use to buy cedar from a small mill in northern Maine and specify that it must be cut from the north side of the Saco River. The tightest graining pattern you ever saw and therefore very stable. Tough to get that kind of wood these days. We back primed all clapboards, miter cuts with aluminum paint. All decking was coated with oil based wood stabilizer, and epoxy was put on end grain. Those days are over, but I could show you houses we did in the early 60's and 70's that still look like they were just built. My crappy pressure treated deck we built in 2004 still looks like furniture and it's 18 inches off the ground. I back primed everything with Sikkens Cetol DEK, and primed all the nail holes after I counter sunk them. Anal but haven't been on my hands and knees re-sanding or recoating since.


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## TJ Paint

NACE said:


> We use to buy cedar from a small mill in northern Maine and specify that it must be cut from the north side of the Saco River. The tightest graining pattern you ever saw and therefore very stable. Tough to get that kind of wood these days. We back primed all clapboards, miter cuts with aluminum paint. All decking was coated with oil based wood stabilizer, and epoxy was put on end grain. Those days are over,


Thanks for sharing about the old ways. Like to hear about it. :yes:


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## Deckquestion

NACE said:


> All wood will have moisture. It will never be zero. Different species will acclimate to a constant level depending on the geography. Cedar and PT in the northeast will stabilize at 8-12%. If you coat it at it's lowest content, it will likely stay at that level. If you coat it and trap moistue in, it will fail. Moisture will not push a film off if it does not have enough force to do so as most coatings have the ability to breathe to some extent. If you put a piece of Swiss cheese on wood, the holes will allow moisture to pass. If you put two pieces on, you have less breathability. Put three on and all the wholes don't match. With wood, creating dimensional stability is key to longer term coating success. Dimensional stability is a measurable unit and the less force created by swelling, freeze thaw, uv etc is best and stresses the film or stain less. Check out us forestry online and there are tons of studies on this. We use to buy cedar from a small mill in northern Maine and specify that it must be cut from the north side of the Saco River. The tightest graining pattern you ever saw and therefore very stable. Tough to get that kind of wood these days. We back primed all clapboards, miter cuts with aluminum paint. All decking was coated with oil based wood stabilizer, and epoxy was put on end grain. Those days are over, but I could show you houses we did in the early 60's and 70's that still look like they were just built. My crappy pressure treated deck we built in 2004 still looks like furniture and it's 18 inches off the ground. I back primed everything with Sikkens Cetol DEK, and primed all the nail holes after I counter sunk them. Anal but haven't been on my hands and knees re-sanding or recoating since.


Would this also be true about all the framing members under the deck boards, or is there a reason to not stain those. I'm talking about staining to protect against rot and insects, not aesthetics.


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## NACE

Deckquestion said:


> Would this also be true about all the framing members under the deck boards, or is there a reason to not stain those. I'm talking about staining to protect against rot and insects, not aesthetics.


Yes. But test the content prior to applying anything. Generally though, those boards are not exposed to the elements the same as front facing.


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## Forest Dan

Unlike what's available to us, if the structural lumber is of decent quality, it should last without the need of staining for the life of the deck. However, I've have seen many decks beside pools and most develop a tone of algae annually. As mentioned, pre-staining before installation is really the only sure way to protect the most vulnerable surfaces (the tops).


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