i had some serious issues with this (lava rock) stuff today, clogs for breakfast. is it always that intense?

Tricky Stuff! I like the old throw some of the aggregate in a bucket of water and if it floats it has not been properly soaked. I have only pumped light weight a few times and never had any problems.

I am a 'bucket' guy myself Seed. It won't tell you if you are going to have a good day, but it will usually tell you if you are going to have a bad day.

METHOD:

After you throw a couple of hands full of the mix into the 5 gal bucket open your hand and "palm down" slowly push your hand down into the water until you reach the bottom. If you feel the aggregate before you reach the bottom you are dealing with light weight that has not been properly soaked. Just because it is not floating on top doesn't indicate a good day; feel SLOWLY all the way down. ;~)

The ACPA recommends that the supplier to soak the rock for  at least 3-5 days. I've pumped this mix 4 times now and it has only been a good day on one of those occasions.

try pumping it with a squeezy if you can use one i think you would find you wouldnt have any trouble with a squeezy pumping light weight

Light weight aggregate is a big pain for a ready mix company that doesn't use it all of the time. Some smaller companies put it in a drum with a bunch of water and think that they have done their part. The soaking over time is what works for most companies. Three days is on the short side of all right. More like five days; and turning the piles with a loader is also very important. Many companies will be able to deliver the first several loads with out a problem, but when you get a very big pour "problem" loads will begin to pop up. This is usually a sign that the readymix company is not turning over the stock pile while soaking. Every new load is an adventure. ;~) 

i have pumped light weight mix a couple of times with my schwing 32m. Never had a problem.  well the first time i pumped that mix was with a gate valve. other pumpers couldnt believe a gate valve could do it. it worked out ok. a guy in town thought he could do the same thing and i ended backing him up with my 32 meter 1200 pumpkit on it

Lightweight is indeed a strange substance.I have found that if a tester is there the air/unit weight will shed light.To little moisture shows up this way as well.

There's really no big deal about liteweight! Just remember some rules.Water is good,too much is really bad,as the wettest presoak is still gonna float some! Suck all the grout up and leave a hopper full of floating rock can be a nightmare,then the sands in the grout seperate and settle,well you get the picture! The theory of lightweight is the aggregate is porous,it has air pockets and when you put pressure to it it FORCES water into these pockets,thereby reducing slump.The harder you push it,the more slump you lose! Slump tests need to be taken at POINT OF PLACEMENT(the end of the hose) not POINT OF DISCHARGE(the end of the mixer chute)!Some testing inspectors aren't clear on which is which,so I'm only too happy to set them straight!! Superplacistizer is really not a good substitute for water! When you push the water into the rock the SuperP just seems to go away! I'm not clear why,it's just a professional observation! Around where I work,5" hose is the standard,but where I trained,4" was the norm.I've pushed 300 yards through 250' of 4" many a day and one project it was 3 pumps,300' of 4" each ,900 yds total EVERY other day' 21 5-7 story buildings!We started pumping at 7:00 and were all finished by 1:00! But we operators were allowed to set the slump,and 280 bar was optimum pump pressure! What I'm really trying to say is dont be afraid of lightweight,but pay attention to it. Its easy when you get the hang of it!

Mudslinger has hit on the road to success when dealing with lightweight.

The operator needs to have a greater ammount of control.

A good operator that stays 1/2 step ahead while pumping lightweight can have a good day even with bad mud.

Listen to your pump, it knows more about the mud than anyone on the job; you just need to pay attention to it. ;~)