Here are the two biggest myths about sanding exterior porches and decks.
Exterior porch refurbishment is a great summer project, but misconceptions about the process abound.
Let’s debunk some of them.
Myth #1: Porches are easy and quick to sand.
My porch is only about 300sqft and just has some paint on it. I’ll be able to sand that clean in a couple hours, right?
It takes more work to sand a porch than you might think:
- Porch paint is difficult to remove because it is dense and thick. Because it was intended to resist the wear of foot traffic, it contains a higher percentage of solids than ordinary exterior paint. Paradoxically, even when porch paint looks worn and scratched, it is still a beast to sand off.
- Every customer who comes to us with a porch with any paint on it, even when they swear up and down that their paint isn’t very thick, eventually resigns themselves to using the coarsest grits available, starting with 16- or possibly even 12-grit. That means you’ll take several passes, just to get the paint off, then more passes to get out the scratch from removing the paint.
- Old porch paint is more likely than clear finishes to contain lead. And while it is perfectly legal for a homeowner to sand off this lead-paint bearing finish, the lead dust that you release will poison you and your neighbors. Do a Lead Check test and if it’s positive, hire an RRP accredited flooring firm. It will be worth every penny.
- Porches in Minnesota are primarily installed the short way, meaning the boards run parallel to the short depth of the porch (see photo above). That depth is typically only 7-8 feet, which makes it more awkward to use the drum sander.
- Porches have railings. You have to sand under the railings. We rent a special Radiator & Stair Edger for that, but you still have to do it.
- Because of their direct exposure to water, the individual boards of most porches are likely to be cupped and you’ll have to sand that curvature level before you can sand the boards clean. Luckily, most exterior porches are made with fir which is relatively soft and easy to flatten.
Myth #2: Outdoor finishes should last at least a decade without maintenance.
Floors in porches are exposed to more sunlight and more water than any other area of the home.
Water and sunlight are deadly – and let me say that again more emphatically – deadly – to wood.
We have tried everything in our search to sell something that protects exterior wood for long periods of time without maintenance. Even reputable boat maintenance products, when you read the fine print, require sanding and coating every year, or at best, every other year.
So why do ship’s decks last forever? Historically, ships had abused, shanghaied sailors who scrubbed those decks with bricks and sand every week. Those pretty wood decks on current day ships are coated with 4-5 coats of spar varnish and then re-coated annually or every other year.
If you could scrub your porch with sand every week, or topcoat it every year, it too would look fabulous!
But most people, even the good citizens at Pete’s, expect that once you put a coat or two of something or a porch or deck you should be able to ignore it for years at a time. But we’ve learned that those expectations are unrealistic for the amount of environmental abuse that exterior wood must withstand. Especially horizontal surfaces.
Clear finishes will degrade very quickly on a porch because, unlike paint, they let the sun right into the wood where it can break down the lignins, which are essentially the connective glue that makes wood hold together.
Once those lignins are broken down, the varnish has nothing left to cling to, and so it peels or powders away.
Paints are better at protecting wood from sun damage – they are much like wearing a sweatshirt to the beach; they block the sun from reaching the wood.
But paint still can’t block everything, and standing water from snow and rain, the weakening effect of sunlight, plus the erosive action salt and sand underfoot will eventually grind paint away too.
The simple answer is that, no matter what finish you put on your exposed porch, you will have to periodically reapply a top coat of some kind, even if you use porch paint (enclosed, three-season porches are more protected so the finish will last longer there).
There is no magic bullet that will protect your porch forever; the longest you can completely neglect that wood is two years.
Two years?!? Yes. Two years. But the good news is that if you refresh or reapply a top coat to your exposed porch every two years you should be able to avoid resanding it for at least a decade.
But compared to the huge effort of resanding, recoating is child’s play and worth every minute of your time.
What product should you use? Trust these two options offered by Pete’s Hardwood Floors.
Option 1: Rubio Monocoat Hybrid Wood Protector.
The reasons we recommend it:
- It’s a linseed-oil-based, zero-VOC finish – no need for a respirator, and no worries about fumes drifting over to your neighbor’s yard.
- It is a one-coat finish that is water-resistant in 36 hours and ready for traffic after 48 hours – very helpful if you are trying to coat during the thunderstorm season.
- It does not form a film layer of any kind and has a very matte appearance. Flaking or peeling is essentially impossible because there is no build above the wood whatsoever.
- Because it is a penetrating, rather than a film-building finish, you maintain it by just cleaning the surface and reapplying a thin coat of the original product. If you do it annually, there is usually no need to even sand. Just re-wash with the Exterior Wood Cleaner and then coat.
- The oil contains UV blockers to slow down the sun damage and mold inhibitors to keep the algae at bay.
- It comes in twenty colors – and the colors can be mixed with each other to increase your design options.
But there are a few caveats:
This product requires that you prep your wood (new or old) with Rubio’s Exterior Wood Cleaner. We know firsthand that this is true: earlier versions of the product did not require this step and there were multiple adhesion failures and many disappointed customers. So, use the Rubio Exterior Wood cleaner, even on new wood and even when recoating.
Covered porches will need an oil refresh every other year, but fully exposed decks will need touchups annually. Yes, you read that right: annually.
A touchup is much easier and faster than a full resand, and it does involve re-washing the deck with the Exterior Wood Cleaner. But putting a booster coat on an otherwise intact Rubio coat is fast and uses less than half the amount that the project would have intially required.
Rubio Monocoat Hybrid Wood Protector 1 liter $160 (+/- 300sqft per liter)
Exterior Wood Cleaner 1 liter $52 (+/-250sqft per liter) and this is required before applying the Hybrid Oil!
This product is safe to ship to all 50 states, so we sell it right in Pete’s online shop.
Rubio now recommends that you add their Accelerator to the Hybrid Wood Protector in a 1:10 ratio.
This is a relatively new recommendation, but significantly improves performance. However, they do not package the accelerator with the HWP so you must buy it separately.
The darker the color of the Hybrid Wood Protector, the better the protection.
The color known as “Pure” does not contain pigment, which increases the rate at which sunlight can reach and damage the wood. So Rubio discourages the use of Pure on decks and southern-facing porches because they will “grey” more quickly.
Hybrid Wood Protector will bond to green-treated lumber, but performance over time is not as good as it is for untreated woods. Expect a more frequent recoating schedule on these woods.
Rubio Monocoat Accelerator
Option 2: Waterlox Marine Finish. We love it for many reasons:
- This is essentially a “long-oil” varnish, which means it has a higher proportion of oil to resin, which makes it stretchier and better able to handle all the swelling and shrinking your outdoor wood will encounter through the seasons.
- The high proportion of tung oil in this finish also allows superior penetration of the finish into the flooring. This allows most of the Waterlox to cure below the top level of the wood, which makes it less likely to peel or flake, but it still has a lovely sheen.
- The penetrating nature of Waterlox makes it forgiving to touch-up.
- Marine Waterlox has a UV protective component that slows down the destructive effects of sunlight.
- Its fabulous, rich, deep-amber color looks good on every wood type, but is especially attractive on the older fir and pine of many porches.
Some caveats for Waterlox Marine:
Waterlox Marine Finish must be used over two base coats of the Waterlox Orignal Sealer or Waterlox Marine sealer. Don’t use the Waterlox Marine directly on bare wood; it just won’t bond as well.
Most porches require at least two coats of the Marine Finish, and both Waterlox and Pete’s would recommend three coats, allowing at least 24 hours between each coat. Do not apply coats if you are expecting rain within 24 hours.
This product is relatively high in VOCs and the vapors can drift back into your property or affect your immediate neighbors.
This product should be touched up or recoated at least every other year.
Marine Waterlox Gallon $130 (400-500sqft per gallon)
- VOC restrictions affect where we can sell this product and how it can be shipped, so we don’t offer it online. Call us at 651-698-5888 and we’ll figure out a way to get you some!
Marine Waterlox Quart $50
- VOC restrictions affect where we can sell this product and how it can be shipped, so we don’t offer it online. Call us at 651-698-5888 and we’ll figure out a way to get you some!
- Sorry, due to hazardous substance restrictions, we can’t ship this outside of the 7-state area of Minnesota, Wisconsin, Iowa, Illinois, Nebraska, South Dakota and North Dakota.
Pete’s Bonus Tips
Careful, decks are not quite the same thing as porches.
You can use floor sanders to sand decks, but you have to be more cautious for two reasons:
Reason One
Decks are top-screwed or, worse, top-nailed. If the fasteners are not well counter-sunk, they will catch the sandpaper on your sander which will rip it off and waste money. Worse, they can damage the rubber pad of the sander itself, which will cost you even more money.
Check that all your deck fasteners are counter-sunk at least 1/8”.
Reason Two
Some decks are laid with slight gaps between boards or using boards with decidedly champfered edges (the top two edges are cut off at a slight diagonal).
This means that the wheels of drum sanders and edgers can drop down into these channels, which will cause the business end of the sander to drop down as well, which can leave unexpected stop marks or divots.
If the deck isn't too cupped, the U-Sand can be a great solution - no wheels to fall between the cracks.
Buy online, or stop by our cute store in St. Paul, Minnesota.
Pete's sells supplies online across the continental U.S., and rents equipment to Minneapolis/St. Paul DIYers. Our store at 186 Fairview Avenue North in St. Paul, MN is at the corner of Fairview and Selby.
It's just the cutest sander rental shop you'll ever visit. Call us at 651-698-5888.
Store hours:
- Monday - Friday: 8:30-5
- Saturday: 8:30-3
- Sunday: Closed