Wet the sanded surface with water. This will give you a fair idea as to how well the varnish will cover the blotchies. Last summer I refinshed my 5 year old strip canoe. I long board sanded through 5 layers of varnish and a layer or two of epoxy. Talk about blotchy looking! Anyway the end result was the best finish yet on this canoe and NO blotchies. Jerry Siegel