Walls and Ceilings - How to do Knock Down on your own?

What is the best way to do knock down on walls on your own. ?

Is it very expensive?

We are buying an apartment where the walls would need to be plastered and then knock down and then primed before painting.

Please advise.

You can achieve knock down texture with a variety of brushes, everything from a utility brush up to a push broom. You will need a pan large enough to accommodate the size brush you use. You load the brush and bump it around in a random patter on the wall or ceiling (thin slightly if needed). Then knock mud down with hand trowel. Manual application of mud produces a nice stucco finish. This will give you a Spanish or Mediterranean stucco look.

Another option is to by Knock Down in a can sold at Home Depot in the paint section. I recently did a 7' x 4' bathroom using roughly 3 cans. Comes in an aeresol can like spray paint. I would just recommend that you prep very well because once you start spraying it gets everywhere. Let it set up a little then use a drywall knife or trough to push it down. Worked very well for me and I was real pleased with the outcome.
I think it costed somewhere around $10.00 a can. Not very expensive for the achieved look.

MCMBIC

Rent a spray rig. Mix up some mud pretty thin. Practice a little bit, then go for it. Spray cans will take forever. A spray rig is the only way to get knockdown right.

Any of the methods posted will work, however if you're doing an entire apartment bldg, I would suggest that you check with a local tool rental yard about renting a compressor and hopper gun to apply the texture. They usually run about $40-$60 per day for rental units. Use light joint compound, it is partially premixed and comes either in 4.5 gal bucket or in a box about a ft sq, it will need to be thinned down with water to about the consistency of a thick batter. This is done with a high speed drill & a large mixer paddle.

Another option, which might be cheaper than you think, is calling in a pro to do the texture for you. We recently did a fairly large two story house which was being converted into a duplex, total price including materials for the knock-down work was about $400, which the owner did think was a bit steep at first, considering it was done in less than a day, but they were extremely pleased with the results & the short turn around time. House was ready for primer & paint the next day. Try that with a broom, brush, or spray can! :D