I don't know what was done to it when it was brand new. I have stained it twice, once about 7 years ago and once about 5 years ago. Going by the partial cans in the garage and my own memory, the first time was done with a Behr transparent oil-based stain and the second time with Behr semi-solid urethane-enhanced acrylic stain. I don't recall doing much of any prep before either project.
The stain is actually in pretty decent shape considering I apparently put water based over oil based with no prep. The horizontal top of the fence is pretty much devoid of stain at this point and there is a fair amount of green mildew, but for the most part the vertical boards are looking decent.
This time around I've done more research, but in some ways it is only serving to confuse me. So far the plan is to pressure wash, hand scrub away any remaining mildew with a bleach solution, let dry, then stain. But:
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how long does it take for the wood to be dry enough? This is Oregon, if we prep it one weekend it is likely to get rained on before the next weekend. But I'm guessing that doing it the next day may be too soon.
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do I need to sand off the old finish in order for the new one to take properly? I would really rather not do this, partly due to the effort and partly because the boards are rough-sawn and I don't want to lose the texture. But I don't want it all to peel off right away either.
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I've read conflicting reports of whether a colored stain needs to have a clear coat applied over it or not.
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It seems that every brand of stain out there has it's fans and detractors. How in the world do you pick the best of what seems like a sorry lot?
In case it matters, I plan on using Woodmates stain applicators (pads) this time around, instead of brushing as we did last time. Also, I don't know what kind of wood it is – the posts look pressure treated but as far as I know the rest is not.
Any advice would be most welcome!
Best Answer
Ok let's talk outdoor staining. You are right that the first thing you need to do is clean off any mold, dirt and green slime. As with decks, a good and cheap solution of TSP, bleach and water is a fine cleaner, no need for expensive premixed stuff. Using a one gallon garden sprayer, apply your TSP/bleach solution. Let it sit a bit, but not dry. Scrub with a stiff brush and rinse with a pressure washer or high pressure hose. The drying time is obviously tricky in your area, but usually a couple of days of decent weather does a good job. You can somewhat judge the dryness by it's color as compared to the color when wet.
Since the last stain you used was a urethane based acrylic, you really need to stay with an acrylic product this time. A pure oil based product may not sit well and raise the acrylic and create a mess. Also, since there was spar urethane in the last application, a stain only may not want to stick to the areas where the urethane is still in good condition. The urethane is a hard resin and will repel a simple stain. I would probably look towards using a similar product to what you used last time.
As far as what brand to buy, don't over think it. You are painting a fence, not a church! Avoid any bargain basement crap that is most likely low quality. I love Sekins, but it is very pricey. Most major brands are good. My advise is to try to use the same Behr you used last time. It will be formula compatible and the color will match. Good luck