This page on spraying stucco with compressed air started with a question originally submitted by Dennis, from Chatsworth California who wrote...."Regarding spraying stucco with compressed air, I was looking at stucco hoppers to attach to an air compressor to do some re-stuccoing on a house.
The specifications stated on a particular hopper/spray gun kit, stated it's air flow/pressure requirements at seven (7) CFM at twenty five (25) PSI. Since most compressors measure their flow based upon either 40 or 90 PSI, how would I compute CFM at 25 PSI? The sales personnel at Home Depot were unable to help me. Thanks, Dennis"
My response was: Hi Dennis: Regarding your question about spraying stucco, if your compressor air tank is big enough to have enough reserve to keep supplying the stucco gun while the compressor is working to keep up with the compressed air demand, you'll do fine.
Worst case is that you'll have to stop spraying for a while periodically as the air tank gets depleted and the compressor tries to fill it back up to the compressor cut out pressure.
I know that if you're spraying stucco for pay, then time wasted while waiting for the air compressor to recharge is money lost. It also means that the qaulity of stucco spray may vary, as the air pressure in the spray gun lessens due to air use.
That being the case, I feel you will need to get a bigger compressor and tank to ensure that you have enough capacity to do the stucco spraying job properly.
I actually used a 3HP compressor recently to stucco spray the ceiling in a small bedroom at my home.
While the compressor was able to supply the air pressure required of the stucco gun, where it fell down was on the volume to the gun through a too small air hose.
If you are using a small compressor to supply a stucco gun, you need to make sure the air volume to the gun is according to the gun's spec. Get and use a larger I.D. hose.
My cheapee home compressor came with a 3/8" hose. The stucco gun spec called for a minimum 1/2" hose. As a result, I had problems with the viscosity of the stucco plugging up the nozzle orifice from time to time, and the stucco not spraying as smoothly as I would have liked.
Good luck with your stucco job.
PS: If you want to ask a question about compressed air flow, here is the air flow forum page on this site.