What's the best way to stain a Black Locust Deck to a weathered grey patina look?

Hi,

​I'm building a black locust deck and the customer wants grey patina look on the deck. Area being done is some total shade some total sun.  Customer doesn’t want the huge variation and doesn’t want to wait a season to change. 

The deck is in Chicago area. 

What's the best way to stain this deck? How long will it last? What kind of maintenance should we expect?

---

Hi,

In short, the best way to stain a black locust deck grey is:
1. Lime Clean
2. Sand 35 grit
3. Mountain XT Stain (dilute with Pure Citrus or Corn Solvent on new wood)

There are a few deck stain colors in the grey family: Pebble, Pebble Deep and Cape Cod Grey that we use to insure uniformity on patina look decks. Of these Pebble Deep lasts longest. When Locust is uncoated it patina's to a grey, weathered color that turns black when wet. Some people don't mind the grey but don't like the black. Using a deck stain helps with that but will need to be kept clean. 

The long answer...

First year acclimation:  Coating all 6 sides of the board will greatly assist in a slow moisture release during acclimation the first year. This means that moisture will come out evenly and not cause as much splitting, warping, cupping. The board ends are important in this respect since they will release moisture fastest and splitting tends to be worst at the ends. 

[The Clear 00 System is another option. It's more work but lasts longer and is easy to maintain with a clear coat. Depending on what the customer is looking for this may be something to try a sample board of. I'll come back to this at the end and post some pictures.]

PREP: The prep on locust is important. Locust needs the extractives to be treated in order for stain to accept into the wood fiber otherwise is pushed it off in a fairly short time. We use Lime Clean for that. Typically, when pressure washed and stained with conventional stain, locust will shed the stain in about 6 months while it is acclimating. 
The trick is to lime it, sand it with 35 grit and dilute the first coat with Pure Citrus or Corn Solvent so it penetrates deep in. Using a high solids coating also helps a great deal. 

Doing these things insures that the most was done to protect it but there's not a way to say how long since some people don't want their decks to show any signs of weathering while others like the weathered look but just want to keep it from splitting and rotting. 

How long it will last depends on a few factors. If they are looking for a greyed out look then it may last a very long time, maybe up to 5 years. If they want it looking clean and new, it'll need maintenance in a year after acclimation and then probably just needs a washing with Earth Clean once or twice a year. It depends on what they want. Chicago area is a high mold climate so any dirt on the deck will be food for mold and make the deck look dirty. That needs to be kept clean for a grey tone to stay looking good. Protection wise, once coated, the finish won't come out of the wood. It's a high solids coating, not mineral spirits like conventional stains, so once in the wood it remains and can be bolstered with future coats. This is how we initiate a petrification effect, by bolstering and building up protection rather than stripping and restaining every year. 

For me, If I wanted a greyed out look on my locust deck, I would use Mountain XT Pebble Deep diluted with Corn Solvent and then wash it with Earth Clean a year later and hit it with another diluted coat. Then I'd probably leave it for 5 years or so and just let it weather safely. I think I mentioned this but the board ends are really the most important since that is where locust will split first. Also, if it's close to the ground in Chicago area, the bottom side will hold a lot of moisture causing the board to cup in the afternoon sun. That's not a good way to acclimate. So we will coat all six sides of the board if it's close to the ground. If it's not close to the ground it's not as important but the ends still matter. 

The Clear 00 System is a multi coat system for people who want to keep their locust like a wood floor. It uses lime for prep, dense pine and oils in Rainforest Sealer to condition the wood for the first coat. Then the cashew resin forms a hard, waterproof film. In Chicago, this system allows the snow and mold to be kept on the exterior of the wood. The wood fiber cell is totally saturated and protected from the elements and the stain (or Clear) underneath holds it's color for as long as the deck is maintained.

Maintenance for this system depends on how much sun. The Clear 00 System is practically impervious to water and cold, but the UV/IR will slowly weather it away if it's not maintained. For example; a harsh sun, Hawaii, cliffside ocean deck we bolster the film in 6-12 months and give a yearly clear coat as needed. For moderate sun exposure it's best to give it a bolstering coat after a year and then as needed but many people tend to wait 2-3 years and then give it a clear coat. The main thing with this system is just giving it a clear coat of Mountain XT Clear 00 as needed. 

Hope this helps. 
Best wishes,
Tom