This is my part time business, FF by trade.
1st: DO NOT USE THOMPSONS!!!!!!!!
2nd: Clean your deck before staining it, the improvement will amaze you. Also, you do not need nor want to use high pressure to clean your deck. Use proper deck cleaning agents and low (realitively) pressure. Around 1000psi or less. If you're using a powerwasher don't let the wand be sitting still when it's spraying. You'll get a white mark, have the wand moving all time that it's spraying.
3rd: The pump up will probably be best for the rails and pickets but I'd recommend that you roll the actual deck boards. The action of the roller works the sealer in better and gives better protection than when it's just sprayed on. (yes, we spray everything,, it's all about time) If you can't get the sprayer to work you can probably brush the pickets in the time it'll take you to clean up the wagner sprayer.
4th: Any good namebrand will do other than the one mentioned in #1. My choices are either Wolmans (hard to find in some areas) or Olympic. I personally prefer the clear sealers but if you go with a tinted sealer you get more UV protection. Just realize that the tinted stuff needs to be applied more like paint than a clear sealer. Don't let it dry and then come back over with another coat. With the clear that doesn't matter.
Any questions drop me an email, will be happy to offer any help I can to AR15'rs. (or if you're in VA I'd be happy to take a small amount of your $$$ and save you the time and hassle)
Ed
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