An alternative approach to fir porch floor replacement

Here in the Twin Cities of St. Paul and Minneapolis, we have a lot of historic housing stock with covered fir porches.

We need porches to take advantage of our short and glorious summers. But wood exposed to sun and weather year round takes an extreme beating and it is challenging to keep fir porches looking good.

The combination of sunlight and water is so much more destructive than people realize, but normally it is sunlight that is the real kicker. Porches are designed to deal with water; they are usually slightly canted for good drainage. And if you keep your porch shoveled, you should have minimal damage from snowmelt.

But year-round sun is a wood-killer.

This is why so many porches are painted; paint forms a much more effective barrier against UV damage.

If you can keep up with periodic topcoats of paint, fir porches last up to 60 years without replacement.

Here’s the story of a damaged fir porch.

This is a case study of a “one-season porch” (an unenclosed fir porch with a roof, but only half-walls) that struggled with both sun damage and extreme water and rot issues.

The owner of the c1920 home had completely replaced the porch with new fir in 2000 and painted it. But the water damage was so constant that by 2022, not only was all the paint gone from the most sun-exposed surfaces, the board edges were literally crumbling and exposing the fastening nails.

So, even though this will appear to be overkill, here were his final preparations:

Each individual fir board was measured, pre-cut, and sealed on all sides with a de-waxed shellac to give the best primed surface possible.

Dewaxed shellac is used as a universal tie-coat because it bonds to anything.

This gave the paint its absolute best chance of staying stuck to the fir. Usually you don’t want to coat the tongues and grooves of any wood flooring because the tolerances are so tight that the tongues may no longer fit.

In this case, the fact that shellac soaks into wood easily, especially just a single coat, meant that there were no issues with fit.

Then each individual board was double-coated with a water-based exterior porch paint, also on both sides.
It is rare that individual wood boards are finished prior to installation, especially not on both sides.

Most floors, however perfect the milling of the individual boards, are slightly uneven after they are fastened down. Those highs and lows are called “lippage” and can most easily be sanded to level after installation.

But that means you can only apply finish after the surface has been sanded, when you can only coat the top faces of the boards. In this case, to make it easier to coat all four sides of the boards, the decision was made to pre-plane the boards, but not sand them after installation.

So there was a real risk of floor full of lippage. But as you can see from the finished product, that floor is as even from board to board as if it had been sanded!

To further ensure that the porch was as water resistant as possible, stainless steel staples were used.

These are close to twice the price of regular galvanized staples, but will not rust away as quickly.

As a relatively small part of the overall project expenses, the peace of mind will be worth the additional cost.

Many people ask if painted wood on floors needs additional polyurethane on top of the paint for further protection.

If you were using ordinary interior wall paint on your floor, then the answer would be yes because regular paint isn’t formulated to handles the wear of foot traffic. But if you are using multiple layers of a paint designed for exterior surfaces, it will be plenty tough, and probably better wear-resistant than most floor polyurethanes.

Do you need advice for your specific hardwood floor problem?

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