My 5 Secrets to Prevent Wood Rot

By Scott Sidler • November 12, 2012

Rotted-Wood-SoffitLearning how to repair wood rot is a part of life when it comes to life in an old house. But what if you could prevent it? Working in a wet climate like Florida, I have assembled a very specific routine to prevent wood rot on anything I build that will be outdoors. The expense of PVC, fiber cement and other “rot-proof” products aren’t necessary if you build things the time tested right way. If you want to continue to build with real wood and have it last decades, follow these simple techniques.

 

And don’t miss the last secret because it is the most important!

1. Prime All 6 Sides (with oil-based primer)

It’s not enough just to prime exterior wood after it’s all been installed. You have to prime all 6 sides of the wood. That means front, back, both sides, and especially both ends. The end grain of wood is like a sponge. If you don’t prime it, you are asking for trouble. You have to prime everything before it is installed and after all the cuts have been made. If you have to trim a piece again, then you have to prime that piece again at the cut.

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On top of priming everything (I use 2 coats for extra protection), we use an oil-based primer. Oil-based primers penetrate the wood better than latex or water-based primers, and therefore provide better resistance to water. They are also less prone to being scraped off during installation.

2. Build Sloped Surfaces

Plugged Fasteners Cedar Porch Railing
This railing is sloped and the fasteners plugged. The white material is glazing putty to prevent water in the joint and maintain flexibility.

If you are building anything outside, it has to be able to shed water. Porches, window sills, hand rails, everything has to be sloped or designed to shed water. You have to think like water when planning your project. If water lands on your project, does it have a place to go or will it get stuck somewhere?

I see too many porch railings that are flat 2×4’s. Any horizontal surface will hold water and eventually rot. Whether you decide to round the tops on your railings like I do, or install them at a slight slope along their length is up to you, but intelligent design means less trouble in the future.

3. Plug Fasteners

Unplugged screws and nails are like highways for water. If you’re working outside, you should be using stainless steel or galvanized fasteners anyway. But when you nail or fasten wood (especially on horizontal surfaces), it is worth the extra effort to countersink and plug the fasteners. Doing this not only prevents fasteners from rusting, but also avoids any divots in the wood that will catch water.

How To Plug Fasteners

      1. Pre-drill a hole, the depth and width of your plug, slightly larger than the fastener head.
      2. Drive your fastener in the hole.
      3. Put a bit of wood glue in the hole.
      4. Place the wood plug in the hole. (You can find the wood plugs I use at my affiliate link here)
      5. Pound the plug into place gently with a hammer.
      6. Sand the surface level.
      7. Fill any remaining gaps with window glazing putty.

4. Use Rot Resistant Wood

There are lots of choices when it comes to rot resistant wood. Most of the tropical hardwoods like Ipe, Cumaru and Teak are all great choices for decking since they are so hard and resistant to rot and insect damage, but they can be more expensive. Western Red Cedar and Cypress are my go to choices for exterior items like siding, trim and screens. They are readily available and provide decent rot resistance at a fair price.

5. Allow for Airflow

Benjamin Obdyke Rain Slicker
This rain screen is the best product to install under new siding to keep it from rotting. Easy to install and much faster than furring strips.

Wood will get wet outside. But the best way to prevent wood rot is to provide a way for the wood to dry out. All the other tips I’ve given you merely serve to prolong wood’s life if it is getting wet, but the key to making wood last for centuries outdoors is letting it dry out.

Tips to Provide Good Airflow

      1. Make sure the wood isn’t in direct contact with the ground.
      2. Use a Rain Screen or furring strips behind siding to allow airflow behind the siding.
      3. If possible, design your project with gaps between horizontal and vertical surfaces.
      4. Use a nail or a carpenter’s pencil between deck boards to space them evenly.
      5. Avoid having wood in direct contact with cement or masonry.

Follow these secrets, and you’ll have a a project that will last longer than you and I will be around. Skip them and you may save some time and money for now, but in the long run it’s always cheaper to do it right the first time.
Do you feel it’s better to do it right the first time, or to just build quickly and replace when it wears out?

 

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34 thoughts on “My 5 Secrets to Prevent Wood Rot”

  1. Hi Scott,
    We have a wooden deck and stairs, When we bought the house it was already painted so I don’t know what kind of wood it is, if it has been primed etc. Some of the paint is chipping. What is the best way to prevent rot on this…should I be applying more paint for protection? Are there types of paint that you would recommend?

  2. Howdy ya all i have been in construction most of my life i was a metal lather/framer for over 25 years and did lawn and tree on evenings and weekends… i have built many things and learned alot along the way….this was my first arrow project and i have to say it sucked im used to building my own stuff and following directions like theirs was a pain along with the joke fasteners… i bought my own for the roof that made that go much faster….My problem is the system they have on the floor i built my floor very well with pt wood rated for ground contact … we had rain and saw where a lil water came under the floor… so i had some heaver tar paper and ripped it down unscrewed the shed had a buddy lift it and made a sill plate re screwed it down etc….well he had heavy rain and no leaks but i could see moister along the inside edge of paper where i trimmed it neatly along the bottom frame …. in my experience any moister is bad even on pt… It is very humid in Florida and if you do not vent things the will rot…. even pt….So my question is i could use silicon along inside and never see a drop….but it seems this thing has channels and im not sure if the water is under or on top of both… i dont want my floor to rot from it staying damp to long…and was thinking pull paper back out the caulk the inside and the pt the pt would dry faster with the small amount of moister between just the metal and wood…. zi am worried i created a worse issue with the tar paper….sorry to be long winded i try to be specific the people at arrow seem to be retarded and not even know what a make shift sill plate was….I only used it as cost wise i would have paid 3 time the price to build another one….its fine except this moister…and i try to look ahead….thanks.

  3. To make this quick. We had cement put in for a metal shed; then we put a wood floor on the cement; then put up our metal shed. Since I had put bricks, I didn’t need, on one side it has caused the wood to start rotting. I was told to use “liquid nails heavy duty construction adhesive” to stop it from getting worse. Also was told that “bondo” is better as it will seal it hard and will not have to worry about it. Please let me know which I should use. I want it to last and not have to try to fix that again. Taking down the shed is not an option. Also, the sealer will probably touch the cement and also the shed as I am now a widow and not too good about doing jobs like this, although I am trying to learn. Thank you Scott for any advice you can give me.

  4. Hello Scott,

    Do you have any suggestions for sealing wood that is years old? My husband and I bought a house and the wooden posts holding up the deck are cracking in some places. They are not on the ground by rest on cement blocks. Any suggestions would help as I am reading a lot of different approaches! It all gets a bit confusing! Thank you!

  5. How do I prevent wood rot on lumber . I have a patio cover made up of 2×8 running horizontal and 2×3 running vertical where they on top of each other I get wood rot. I am replacing some 2×8 and 2×3 How do I stop the rot on the new boards. I was thinking of putting silcone on the horiontal 2×8. Should I use oil base primer and oil based paint. Do I put silcone on board before I paint or on top just before putting up.

  6. Hi Scott,
    I am replacing 6 column bases on a outside porch 1930’s House with a cement flooring. I have had a column company custom make the base/plinths – 2 pieces( circular donut base & Square) which donut sets on top Square to the exact measurements of the orginal bases that have rottened. The bases are made of solid mahogany. Both bases donut & square have good center cut out airspace. I bought aluminum flashing to cut out to measurement to put under the wood base/plinth so it will not contact cement floor of the porch. Question…. should the aluminum be the exact size of the square base & do your caulk around the base of the wood and cement. should it be water base: latex or oil primer paint? This is my first time for repairs on column bases and I hope I can make it all work. I need your advise.
    Thank you

    1. Hi Susan! First it should always be oil-based primer for exterior wood. You can finish with either oil or latex too coats depending on what you prefer. Mahogany is a great choice for exterior wood too! Rather than the aluminum and caulk I would actually use small spacers (1/4″ or so) under the bases so that water that gets in can get out. That also keeps them from contacting the concrete floor and allow airflow for better drying.

      1. Describe the 1/4″ spacer that is placed under the column base. Is it just an add 1/4″ solid wood cut to the measurement of the new column base?
        I’m handy home owner not a contractor that’s familiar with terminology. I will hire a contractor.
        I just want to be on point discussing the work w the contractor that my son has hired. I will be over seeing the work since he will not be present to watch.
        Please advise… your previous reply has been very helpful.
        Thank you!!!!

      2. We are looking at a 1923 Colonial in need of restoration. It’s located on the Gulf Coast of MS. After Katrina, the entire bottom floor was gutted to the studs and has new wiring and plumbing already installed. You can see the siding from the inside including some gaps. I read where you suggested to someone to remove the siding to apply a vapor barrier. Aside from completely removing the siding, do you have another suggestion for a vapor barrier and priming the inside of the siding?

  7. Hi Scott
    I saved some 50 year old 2×8 and 2×10 untreated main floor joists made from spruce or pine after tearing down a house. They are dry and straight. I am building a covered porch. The joists for the floor of the porch will sit about 1.5 feet off the ground. Can I expect a decent rot free life span on this 50 year old wood if I treat it or use oil based primer or what about a tar based undercoating. Or am I smarter to not use this wood and buy new pressure treated lumber. Located in Ontario I am in a Canadian climate.

    1. Steve, in Canada you are probably safe as long as it is not in contact with the ground. Though I would consider using a borate treatment first if you really want to use them. In the end using PT wood would not add much to the cost and give you longer life though.

      1. Thanks Scott. Your right I checked the cost of building it with Pressure Treated Lumber and the cost is not that much.

    2. What should the ground under. A deck 3-4 feet to underside have on it as a moisture barrier if any at all? Thank you for you’re response.

      1. I used black plastic covered with 3/4 stone with great results. You have to make sure the ground has good pitch away from the house for water drainage.

  8. I have treated wood for a roof support. It rests on a concrete slab, but is exposed on 2 sides. I am considering putting cement on these exposed surfaces for protection as it is located at a chain down spot. Good Idea/No?

  9. Hi,

    Today, I had an interview with a carpenter with more than 30 years of experience. He has had no experience with rain screens. He said to me that rain screens are the same thing as Tyvek.

    Are they the same thing?

    Thanks,
    Wondering

    1. They are not the same thing. Tyvek, is a vapor retarder and does help to stop bulk water from entering the building. If you place siding directly on top of Tyvek then there is no airspace for water that gets trapped behind the siding to flow out of the building envelope. A rain screen helps prevent this and extends the life of the siding.

      1. Thank you for the reply. So I’m guessing this means a rain screen is NOT some type of moisture barrier either. Is that correct?

  10. Hello! Reading your articles gave me some hope. I recently bought a 1920’s colonial French home in October. After 3 weeks of my move, came hurricane Patricia. I’m still fighting with leaks from the roof and dormers. Can you recommend a good source that
    Sells cypress wood? My roofer destroyed the wooden dormers and a few boards on the side of the house. I so much want to restore my home.
    Do you also offer classes on restoring old windows?

    1. Kathy, It depends what part of the country your in to find cypress. Many lumber yards in the Southeast have it but outside of that region you may be better off with things like red cedar or redwood. As for classes on restoring windows I have a book that may help you called Old Windows Made Easy. I also teach at a variety of workshops occasionally. The next one is in Tampa, FL Feb 19-21 2016. Let me know if you’re interested!

  11. Hey, ty for info. Wish I read this earlier. Already bought the wood (Pine planed kiln dried) for my balcony louvres. So even more keen now to give it a fighting chance to survive with the best finish possible.

    If I use a good decking screw, put sealent on the head, then apply 2 coats of shellac based primer over all the wood/fixings would that work? Not sure i have the skill for your plug recommendation.

    Also not sure how to seal where the M6 150mm bolts go through. The 30mm thick steel angle support and 100mm piece of wood. The side that has the steel angle support creates a gap that I cant really get too. Some kind of valve rubber type washer would be cool. Not even sure that exists though.

    Any ideas? Ty any help is appreciated

    1. Stephen, if it’s exterior application don’t use Shellac primer. It’s not intended for exterior use. I’d stick with a oil based primer. You can also treat the wood with a borate treatment like BoraCare to help prevent termites and rot.

      1. Ty for advice.
        I think you may have just helped me avert a disaster a year down the line. It was Zinsser B-I-N primer which on a closer look says interior and ‘spot’ exterior. I think by ‘spot’ exterior it is leaning more towards stopping a nasty stain coming through rather than a full exterior prime. I will drop by and exchange it for an oil based one like you suggested. Rot treatment is definitely a good idea as well.

        Oh and the bolt gap on the top where I was worried about water getting in. I think I’m going to use a rubber washer, under a steel washer & bolted tight on top. Then hang it from my steel bracket. The bracket is hollow which I didn’t realise before which can hide away the extra bolt.

        Can’t wait to get started ^^

        cheers

  12. Thanks for tips and insight!! We are a Home Repair / Remodel company and like providing our customers and prospects with helpful tips definitely be posting your advice!!

  13. My church is building playground equipment for Haiti. We don’t think we can transport oil based paint. Is there a water based paint that works well for pressure treated wood?

    1. If you’re using pressure treated wood the first thing is to make sure you give it a few weeks to dry out before painting. If they won’t let you transport oil-based paint (which would surprise me) then any exterior latex wood primer should be fine. Kilz makes a good one and so does Binz. Then top with 2 coats of 100% acrylic paint.

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