I used to hand baste all my quilts until I discovered spray basting! I am just wondering how much to use? Do you spray it heavily or lightly? I am always afraid it will come apart and think I might be using too much!

I do exactly what Tartan described.

Lightly, and spray from at least 10" from fabric surface, NEVER near your machine (the glue is a vapor that could slip into the interior of your sewing machine and gum up the works), in a ventilated area. Through trial and error, you will discover exactly what lightly means, since as you correctly pointed out, we tend to think we haven't sprayed enough and the spray won't make the batting and fabrics stick together.

It is not good to have over -spray wind up on your floors, as it can be difficult to clean up. For that reason, I spray out doors on my patio on a sunny, windless day.

When the quilt is completed, I wash it to get the basting glue out of the quilt.

Have fun!

A light spray is usually sufficient. Some sprays don't feel tacky right away and its easy to use too much. As the other's have said do pin the perimeter as the layers can lift or separate while manipulating.

I also spray outside following the instructions on the can for distance. I also wash when quilt is completed. I don't quilt immediately after spraying, it needs time to "cure". IMO

I spray very lightly. Everything seems to hold together just fine---no shifting layers.

I used to buy the expensive spray baste, until I discovered you can use cheap hairspray too.
Was sceptic at first, but it works for me. Many of my fellow quilters use it too now.
Give it a try and see for yourself.

Elmer's washable glue works great too. I use it straight but I've read where some mix it with water and mist it on with a spray bottle. Allow to dry or hurry it along with a dry iron. It doesn't gum up my needles or my machine.

I tried it once and didn't like it. If I feel the need again I'll just use hairspray-easier to clean up.

I'm doing QAYG so ironing and pins were sufficient to my needs.

It does keep everything in place though. I just hate getting glue all over the place and don't like the outdoors unless the weather is nice or I'm gardening.

If I go full size again I might do it though. Nail a new tarp into the lawn, tape the backing on and go...