Your job is only going to be as good as what is underneath.Preperation is a key factor in determining how the coating performs,if you just clean and not strip you are bound to have premature failure in areas where the old sealer was about to fail...I always strip off everything and get the wood looking as nice as I can.You would be surprised how much better it looks if you start off with a nice clean surface.I just saw a painter staining an apartment building steps next door without stripping off the old stain...what a mess,you can see the old stain on the sides and it looks horrible...bottom line for the best job strip,strip,strip.
P.S Don't forget to neutralize with a wood britener(oxalic acid or citric acid) and then rinse,rinse,rinse.Good luck!
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[This message has been edited by JR Wood (edited October 28, 2000).]