Uh... guys gals etc...for your own sanity please read !!!!
3m is a product added to plaster as an additive. it's a bag of granular material, it's doesn't get or cause stains. you did not purchase 3m plaster, you purchased plaster with 3m added. almost all of the griping i just read could have been avoided or explained by your pool guy or plaster company had they known or chosen to, additionally, unfortunately, most of you would not have listened anyway from the rants i saw. Brush marks are from not brushing properly or long enough (the powder reattached permanently). blotchy could be from a number of causes (irregular wear probably from chemical imbalances), stains (tan (salt added improperly or chlorine burn or muratic acid added improperly), brown/rust (specs are usually granular fertiliser from your yard or neighboring yard (birds) or recent wrought iron fence grinding/welding that should have been kept out of pool or done before plaster) biological (plant droppings etc...), gray is often metal (magnesium or zinc i believe), but sometimes is the plaster curing, curing often takes a year) that are topical are not from any plaster defect. Stains that are inside (bearing in mixer going bad=rust stains in the plaster, not on)(dark or light swirls of dye improperly mixed altho some is expected)the plaster are !
the great news is that you purchased a 3m additive !!! almost all of you need to drain your pool and acid wash it lightly. this will remove a small amount of plaster material revealing more 3m and even out the blotchyness and darken the overall look. light acid wash is the key.... heavy washes produce a dark beautiful finish that is abrasive (sandpaper). some of you with biological stains tan/brown simply need to heavily shock and brush your pool / citric acid will cure many as well(crushed up vitamin c tabs will tell ) .
don't bother cursing me or asking additional questions, i got here by accident and thought some of you may genuinly want help. there are tons of web pages you can visit that would have answered all of these issues, taking less time than the bitching.