We poured the footings for our garage / workshop today.  It's the first house that I have ever built and the first concrete that I have ever poured.  We used a concrete pump and the first stuff that came out of the pump was really wet.  The pump operator described it as the "grout" that was used to get the pump moving but he obviously regarded this as completely normal.

Is this right?  I'm not too worried about the footings but what is worrying me is that when we come to pour the walls the first stuff that goes down the gap is going to be this wet slop rather than what I would regard as "proper" concrete.

What happens when you guys use a pump?

Thanks very much.

Andrew

In my area we call it the "wash".
If there's a pile of dirt somewhere in reach of the pump tell him to bring the hose right over.
The wash is so liquid that it won't make any difference when the dozer attacks the pile.
Also, the floor will most likely not be poured therefor you could wash inside the building.
Having a rake handy isn't a bad idea in case the wash is followed by concrete.
Don't forget to add a meter of concrete for the pump. This allows for wash and end. Pumps can't empty their hopper completely in order to clean itself.

they do this to prime the pump,but when pouring the wall,it should be primed before you start to pour the walls

aa_uk,
ditto. You should plan to "waste" the washout and not allow it to be placed in the wall or anywhere where it might matter. Regards.

Andrew 

The first material that comes out of the pump is called the "prime" . Short for priming material.

Boom pumps, line pumps etc, have to "pre-lubricate" the pipes in order for the concrete which follows, to pass thru the system without plugging up.

If no priming material is used, typically the concrete will lose all it's paste or mortar to the walls of the pipe
which will then cause a "dry pack" or "plug".......not the way you want your pour to start off :-)

Plugs can also be caused by poor concrete quality and cheap mix designs.
"Chute" mixes are the cheapest available mixes but are a nightmare to pump as they plug continuously.
A concrete pump is actually a quality control device. If it pumps well, it is high quality concrete. 

Priming material can be actual grout, which is cementicious, and usually can be accepted into the formwork. It is so thin that it spreads
out quite readily in the formwork and causes no problems as it is such a small quantity, relative to the pour volume.
Also, real grout is very high strength as the portland component is 33 to 50% of the volume.
Masonry grout works best in line pumping, rubber hose situations , however.

Bentonite is an excellent prime, and is not compatible with concrete.

"Prime" can also be a proprietary "slick" which,depending on the manufacturer, will be compatible with the concrete... or not.
 Slick Pak is mixed with water in the pump hopper and makes a slime comparable to Ghostbusters.

 This provides lubrication to the pipes, similar to what K Y Jelly does for bedroom acrobatics. lol

It is important to consult with your pump operator to determine which variety of "slick" material he is using.
Most experienced operators will waste their prime outside the pour and then swing over to place the actual pour material.
That is the safest and best practice. 

Products manufactured by Fritz Pak, imho, are the best in the industry and can actually be added to the mixer to aid pumpability,
with harsh or rocky mixes, as well as their being a top notch prime.

"Washout" material is the leftover concrete in the pump hopper, pumping cylinders, and boom pipes,
 which is generally washed out on site, at the end of the pour.
 
Some boom pumps have quite large hoppers so there can be up to 1/2 yd of waste at times.
Often, leftover concrete can be pumped back into the mixer , to reduce the pile left on the jobsite.  

Thank you all very much for your very helpful replies.