Tim,
I have used a shurflo to throw sealer, as well as a airless. Each has its advantages as well as disadvantages.
SHURFLO- quick and easy to use, but uses a ton of sealer very fast
AIRLESS- distributes sealer fast and even, uses less sealer, but has a lot of overspray. Airless has a roller attachment that works great when day is windy, but uses more sealer and takes more time.
My choice most of the time is a pump up deck sprayer, not a chemical sprayer. Less overspray and sprays pretty fast. I have spent lots of green back trying to figure out the best way to do my sealing, and so far, 75% of the time, i use just a pump up deck sprayer.
Price wise, we go from .75 up to 3.00 a square ft, depending on the size of the deck. 2.25/linear ft for rails, and 6 to 12 bucks for each step, depending on the size. I am definitely no wood expert, but have done more decks this season so far than all of last year, all coming from referrals. Good luck, and let us know how the new invention works your building.
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Craig Knight
Power Wash Unlimited
www.powerwashunlimited.com