I am doing a conference room at the USAF Arctic Survival School as a DIY project. The color used is Open Prairie. After my 3rd coat of sandwash, I still could not get rid of the streaking, lap marks, and multi tone patches. I had already used way more paint than the directions called for in a room this size. I used good prep; washing and priming the walls. I used a Ralph Lauren paint roller because it was made for this type of paint (don't use it). One thing I noticed was that the paint appeared to be pressure sensitive. If you press the roller harder in one area more than another, you get two different tones. I will tell you how to fix this.
I called the tech support line using the 1-800 number on the can. The support guy was extremely helpful, and I'll pass along what he told me, which worked..The trick is, DO NOT FOLLOW THE DIRECTIONS ON THE CAN.
Here's what you have to do. 1.Do not use a pan for your roller. The sand settles in the pan and you'll get sand clumps coming off onto your wall. Instead, get a 5 gal bucket and pour 1 gallon of sandwash into the bucket. Use an application grid (which is a small metal washboard device that hangs inside the bucket). 2.Add 8 ounces of flowtrol (or any brand) latex paint conditioner to the one gallon (don't skip!). Mix using an electric drill stir. 3.Use a 3/4 nap LAMBSWOOL paint roller. They're about 10 bucks, but this is key to success. 4. Get a sea sponge and quality paint brush ready for use. Have a couple of plastic shopping bags ready to put your wet rollers in in case you need to switch to a sponge. Better yet, work with a second person as a team. Don't attempt this without a good masking tape job, your not going to cut in a pretty bead with your 6" brush. If it's not too hard to do, you'll be better off pulling the baseboards off. You get better results.
Application. First, The name of the game is go thick. You're going to lay this stuff on just short of sagging. Second, and this is important, once you have gone over an area and moved on, don't go back to try and fix it no matter how tempted you are. When you stand back to see what it looks like and you see a spot that has a lap mark, don't be tempted to try and redo it. What will happen is you will get a two-tone job. Just make sure there is complete coverage as you move down the wall.
Before you start, soak the roller in water first and fling the water out of it till it is just damp. Dip the roller in the paint and don't be afraid to get a lot on it. Just don't dunk it or it will drip out of the roller sides. Get a second person to go ahead of you with a brush laying a thick line of paint across the top near the ceiling, and along the bottom if the baseboards are still there. While that is still wet, start rolling 1 column at a time getting more paint if your roller starts drying out (the first couple of columns will until your roller is saturated). Go thick. Ram the roller up against the ceiling (this is where the good masking job comes in) and down into the baseboards. Use a sponge loaded with sandwash only on areas where your roller won't fit.
Corners. Get someone to slap a thick line into the corners before you get there with the roller. Roll the roller into the corner as far as you can UNLESS the next wall is a finished wall. Use masking tape in the corner of a dry finished wall to avoid getting new paint on it... it will become two-toned if you don't.
As it begins to dry, you will still be horrified. You're going to see lap marks, but this will settle down of you followed directions. The finished results are worth the prep. This is not a very forgiving paint and you can't just slap it up like your doing a large apartment complex.
Let me repeat the one thing that will screw up a good sandwash job. DO NOT try to go back and repair a spot you did 5 minutes ago. And do not take your roller and go lightly (gently) over an area just to even the texture. Going gently will put a layer of lighter colored paint on, and you will have a light spot. You cannot just fix a spot, you have to re apply the whole wall. You will be able to tell after about 4-5 hours (in low humidity) if your application will dry even, even though is will not be perfect at that time. That will take several days (because is is on so thick).
Now, before I scare everyone away from using this, I have to say the results are dramatic. I now have museum quality walls, which is what I was shooting for. We're going to put up dozens of framed photos honoring Gen Curtis LeMay, the founder of the USAF Survival Schools. Don't get too picky about the texture difference betweem where you used a brush and a roller along the ceiling. I'm telling you not one person noticed that looked at it...only I could tell.
The tech support guy was also very helpful in getting us a refund on what I thought was fair. I used eleven gallons of paint on a 21x11 room while "learning" to apply this stuff. I'll negotiate what I think is fair next week.
I hope this helps. Hopefully you read this before you started. If you didn't, I hope this helps you fix what you started. You'll be happy you put the work into it.