Sealing underside of deck

JR Wood

New Member
I am coming up against a guy that is telling everyone that you should seal the underside of the deck,so far three people in the last few days have mentioned this.I don't think this has been discussed anywhere on the boards,I was always under the impression that you are protecting the top part of the deck from rain and sun.I can't see sealing the underneath.water doesn't sit there and it doesn't get sun,I suppose it could absorb moisture but if you seal the bottom and some water somehow gets inside won't it be trapped?SOMEBODY GIVE ME A CONVINCING ARGUMENT AGAINST IT WILL YA!!!
 

Express clean

New Member
I just looked at a deck that is only 2 yrs old and is cedar that the customer sealed underneath and al the decking boards are rotted.I think it was caused by just what you said.The cedar could not breathe.I would not recommend sealing underneath. Besides it is a pain in the neck
 

Richard

New Member
Hey JR;
now this is only my opinion, we've only done a few decks, but I did refinish antiques for years and when ever I refinished a table be it cherry, rosewood, mahogany or whatever I never sealed the underside, woods need to breath and if they don't they'll warp and rot.
just my 2 sense
Richard
 

Clean County

New Member
I Have sealed and stained the bottom of second floor decks before if the home owner really wanted it done. Its pretty much an appearance thing as far as the deck looking uniformed. The wood really doesn't need it for protection. But as far as hurting the wood that is debatable. When it rains for example the water runs between the boards and probably soaks in on the under side a little bit and without protection this can't be good for the wood. And also dont most people stain both sides of a fence? And you know that definately isn't bad for the wood. So in a nut shell does a deck need to be stain on top and bottom of a deck the answer is no. But would it hurt the wood I Don't think so. Just my two cents worth.
 

Jim Bilyeu

New Member
The best way to seal a deck is to dip the boards before installing them. This will give you 100% protection. This is very rarely done by the contractors. The only decks we clean and seal on the bottom side are what we call walk unders. We do it at the owners request and we charge accordingly. The sealer that you use must be breathable. There are several reasons why cedar will rot out. The two main reasons are #1. The deck is built to close to the ground without a moisture barrior and #2 is that someone painted it. The other reasons are mostly due to construction . Cedar and redwood must be able to breath. When these two types of wood rot from the center out, it is a sure sign that something has been put on them that will not allow the wood to breath. Moisture raises, moisture comes up from the ground, collects on the bottom side and penatrates into the wood. The top side being warm, wants to draw the moisture in deeper and expell it out the top. If your sealer won't let the wood breath, then the moisture will sit in the middle of the board and eventually rot it out. The same thing holds true with other species of wood but cedar and redwood are the most prone because they are a softer wood. Hope this gives you a little insight.

Jim Bilyeu
Exterior Woodcare
 

Clean County

New Member
I remember Jim Bilyeu well. Its seems like only yesterday he was giving us "Youngsters" then great advice. I think about him once in awhile.
 

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