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What to do with an old deck?

The deck, essential of a relaxed summer life. Although there’s no obvious architectural era for this elevation of outdoor enjoyment, the current North American passion for decks is likely related to the ‘backyard culture’ that developed with the rise of the suburban housing developments after the second world war.1 In Canada, there may also be a tie to ‘cottage culture’ – the cabin in the woods where families retreat from the summer’s heat and everyday life. 

Century homes were not built with backyard decks, but many have been added. Five of the six homes I’ve owned had them. The sixth house had a spectacular front porch. Front porches survive a long time because of the protective roof. 

The average life of the uncovered deck varies by climate, but averages 20 years. They’re high maintenance, especially in multi-season areas. Rotting floor and rails are easiest to manage. Deck floors are fastened flat into the joists below, so replacing a few is an easy task. My current quandary is about repainting/staining2, to make the deck last as long as possible.

When I moved in, the remnants of paint (or something) was peeling from the deck floor. The railings were in better shape but unevenly stained, with dribbles. A friend pointed out bright, moss-green patches particularly on the ends of boards that showed more after a rain. This is some kind of micro-organism, likely algae. 

There began confusion about how to refinish an existing deck. After some reading, questions remained:

1. How to prep the old wood. Power washing? Chemical cleaner? Sanding? All of these?

2. How long to wait before the wood has been wet (either by prepping it or rain) before applying stain?

3. What’s the best product to put on old wood? Oil-based stain or paint? Water-based stain or paint? Clear, semi-solid or solid finish? Which brand? Which other properties (UV resistant, mildew resistant, penetrating)?

4. How many coats? What weather conditions?

5. How often does it need to be done?

These questions were hard to answer because:

#1, For a change, the internet had all kinds of conflicting information. Deck staining isn’t a regulated trade, like plumbing or electrical work. Many sites with ‘how to’ information come from companies that sell deck finishing materials, or are sponsored by manufacturers of deck finishing products. 

#2 My experience: over the past three years, the deck looks as awful after each winter as before I cleaned, sanded and stained the previous year. Am I’m doing the wrong things, or if it’s just the best that can be achieved in a Canadian multi-seasoned climate with partially tree-covered deck?

Round 4: The semi-transparent stain I applied previous year peeled up. Stain is supposed to sink into the wood. Unless the wood was saturated with stain, it shouldn’t. ‘Poor surface preparation’ could cause stain to peel. This site3 suggests that wood should be throughly sanded, but NOT pressure-washed because it could damage the wood. It also states that stain should only be applied after the wood has dried for a few days after being wet, and mid summer, rather than the cold, damp spring or fall. The recommended product is an oil-based transparent one, which they sell.

Another site4 agrees that the problem with frequent peeling is poor surface prep, but suggests good prep consists of using a chemical deck cleaner, but NOT household bleach. Sanding is also not recommended, except to remove old, peeling paint. The refinishing product recommended is a penetrating one, with a strong recommendation to ‘do research’ on the products to find ones that actually do what they say they do.

This site5 suggests peeling can result from not rinsing off the cleaner before applying stain, or applying stain in the direct sunlight or to damp wood. 

Some sites recommend a full chemical peal of the deck. Didn’t like the sound of that. There’s chipmunks, bees and the occasional raccoon family under my deck, along with loads of birds who come by to use the feeder and water bath. None of them need to be exposed to paint stripper. 

In a variety of YouTube videos, I’ve seen many suggestions to pressure wash the deck to prepare the surface and suggestions for household cleaning alternatives (vinegar, baking soda and bleach) to prepare the wood but the recipes are inconsistent. 

All in all, I’m finding this exercise very annoying. And want to conclude that the real answer is either:

  • no one knows, ie. there isn’t enough publicly available, objective research to show what is damaging to outdoor wood decks and how best to preserve them,
  • each individual situation is so different collecting advice doesn’t make any sense,
  • [conspiracy theory] no one will say it but the building materials available over the past few decades for decks were of low durability and all current efforts at maintenance are temporary – it needs to be torn down and rebuilt (a dreadful trend, all too common ‘these days’).

Still, the deck needed attention. Enough reading and time for action. 

What I actually did:

1. Identify weak areas in wood or construction. 

2. Remove as much dirt, green-glow and old stain as possible.

3. Re-stain, with focus on water proofing.

4.Direct water away from deck as much as possible.

To elaborate:

1. A careful inspection of the structural integrity of the deck. I can see some patches (that look weird – over time, my instincts get better at what’s likely to be a problem) which turn out to be rot on the underside of the deck (beam and joists)6 and a few floor boards on the lower level flex when walked on. 

To fix wood with rot7, repairing-rotted-wood-101 requires finding out why the wood has rotted. Much goofing around under, over and within the deck doesn’t answer the question. Wood left outside long enough will deteriorate as the smallest crevice or focal point for water accumulation will lead to rot and ruin. 

Pulling up a number of boards only reinforces my conclusion that the rot is random, rather than due to a specific source of water. To fix, I:

  • scrape each clean of debris, 
  • use ’30 second’ bleach-based cleaner to kill any micro-organisms feasting on the rot, 
  • allow to dry as much as possible during afternoon thunderstorm season, 
  • soak weak areas in liquid epoxy8 and fill with putty when needed,
  • when that’s cured wash entire area with Mr. Clean, 
  • and then coat with a penetrating, water repelling stain. 

The flex of board comes from two things: 

  • Some of the boards aren’t screwed to the joists. I can’t see any reason other than someone forgot. Handy screw gun and structural deck screws turn a bunch of squishy into solid.
  • Looking at the framing, there’s three feet between joists. Or possibly the support members qualify as beams, since each is constructed as a pair of 2×6’s flanking a 4×4 post with a footing. Whatever, as this portion of the deck is two feet above ground (i.e. no one will plummet to their death due to structural failure). It could be less springy with a different construction, but as an existing structure, it will do.

2. Prepping the boards. 

I did a trial.

Boards treated with household bleach, vinegar and vinegar after baking soda (left to right)9. I scrubbed each solution into the board, doing the trial in three boards next to each other. For good measure (or want scientists would call the control), I also scrubbed a board with plain water (right). 

And the answer is – all boards looks the same, including the one treated with only water. Far cleaner than unscrubbed boards, but still with faint traces of green, suggesting the algae is still there.

Or is it? If it disappears completely after a dry spell, is it gone or just waiting for a sip of water to burst into it green glow? It makes sense that if the boards are completely sealed from absorbing water, and the algae needs water to thrive, then the algae is more of a warning signal that boards can be penetrated by water. 

While this line of though suggests that as long as the boards are dry (this has to do with their ability to absorb the stain properly), the boards are ready to re-stain. I bought some deck cleaner anyway – which from my previous experience was the best at getting rid of the greenness in parts of the deck that were green. Questions that still linger in my mind about this – is the algae (if that’s what it is) a hazard? Is it a symptom rather than a cause, or in other words, if the deck has green stuff, has the integrity of the wood been compromised? rather than there being a risk to wood decay if algae sets in. Either way, getting rid of the green glow is at best good and at worst harmless.

There remained some areas on boards that had previous years stain, so I took my orbital sander to these with 60 grit paper.

Even after scrubbing with Mr. Clean, treating with deck cleaner and sanding (the process I followed), there were some boards with various dark areas. I assume these are areas where pigments (from paint products or the environment) are absorbed deep into the wood, and staying there. 

Interlude: Could it stop raining long enough for me to prep (need two days after the last washing to stain) and then stain should be applied when no rain forecast for 24 hrs.? Even when I go by the forecast, it’s tricky. Applied stain at 6 pm one night when no rain forecast for 36 hours only to wake 12 hours later to a warning heavy rainfall was on its way.

3. Re-staining.

The product I choose for the floor boards was one that came out high in independent comparisons, was available in my area and was the best for waterproofing. For the rails, I repurchased the product I put on them previously as I wanted a colour match and it had held up reasonably well.

4. Added some caps and flashing to areas where water shouldn’t flow or pool. Also caulked between boards on flat surfaces that were close enough to let water sit between them, rather that flow through (this is why deck boards have gaps, to let water drain). 

Did learn a few things that made some of the conflicting info clearer: 

1. It depends on the product. I had two different stains (one for the railing and another for the platform). One said ‘more than one coat is unnecessary’. The other ‘two coats is recommended.” Lesson – some of the discrepancies are between products.

2. Going through the cleaning, sanding, re-staining process does produce boards that look like completely different that before. This is the same cycle I’ve been through for the past four years. Maybe this is the reality.



There’s a whole other post about paint vs stain as treatment for the outside wood of a deck. I’m using the terms interchangeably here. A bit of a summary on the options (but not sure what’s available in my area):

  • water-based vs oil-based (interestingly, this video says water-based resist mildew better, even though they don’t penetrate into the wood as well, but Defy extreme and Restore a deck* (ok in Canada & this particular product can be applied on wet wood) products are water based and penetrate well; wood penetration is related to how long lasting the product is
  • there’s something called deck resurfacing products, which are essentially part filler for cracks etc, but not recommended because they don’t last
  • then there’s solid colour (prone to peel and doesn’t refinish easily), semi-solid (relatively rare but oil based ones work ok), semi-transparent (good penetration but oil-based are preferred) and transparent (need to be redone annually)




6These are only small areas, a few inches long by half an inch deep or wide at most, or board replacement would be a better option. Also, if board replacement was trivial it would be the preferred option, but these are boards that would require significant demolition to replace.

7Weak areas here are those that can be stabbed with a tapered tool (screw driver, chisel, paint scrapers, or my favourite – fingernail) and the tool sinks in. If a probing stab, i.e. not murderous but also not a gentle tap, bounces off, the wood is good.

8My favourite YouTube construction folks use Bondo to fix gaps/gouges/missing bits in existing wood structure. I am a fan an epoxy system that combines liquid and solid approaches. Pouring/brushing liquid epoxy on pithy wood hardens it, then filling the gaps with epoxy putty that fills out the surface as a solid is a great solution for small areas of rot where replacement would involve major restructuring. The difference from Bondo is turning the deteriorated wood into a solid substrate for repair rather than having to cut out all the deteriorated wood. It just has to be dry for the epoxy to sink in and solidify.

9Found a number of recipes for these ‘natural’ cleaners. They varied widely. I settled for a tablespoon in a cup of both bleach and vinegar (not together, don’t mx them), and sprinkling baking soda on the board.

Thanks for reading.

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