Toaster;
Hello , Bob had a lot of excellent information, you asked the difference in chopper laid / hand laid. As the name implies hand laid is just that, fiberglass consists of resin (liquid) set up with a catalyst ( hardener) and any number if binders ie. roving ,cloth and mat , these are usually purchased on a roll or sold by the yard, the resin itself renders no strength and is very brittle but when you combine the two , this magical stuff come out. ie. fiberglass. Hand laid you usually mix up resin apply it to the surface your working on in this case it would be the inside of the mold and then you lay out the matt or cloth and brush or spray out more resin saturating the material and as Bob mentioned it's imparitative you smooth out all of the bubbles, puckers and wrinkles, these cause week spots , you should see no voids , one thig to look for when examining a body , a special roller for fiberglass is the best tool to roll these bubbles out with . When this is done this becomes almost transparent. The other method , the Chopper gun looks similar to a spray gun it sprays out mixed resin in the mold and then on the head of the gun is an attachment that has a rotating sharp blade and it's job is to cut the stranded fiberglass ( your binder) the glass comes in a box like rope and is fed into the chopper part of the gun and then these little chopped up strands are blown into the wet resin and then it's allowed to set-up ( kick/ harden ) When the resin is mixed you add the catalyst (hardner) and this is what makes it harden. it sets up on the chemical reaction it generates when mixed, like body putty, same principal , too much harder and look out, you can actually get it to ignite. As Bob mentioned it's all in the operator of the gun, CONSISTANCY, if not it'll be thin in some areas and thick in others. Hand laying is definately more consistant, but much more time consuming, alot like Heli-arc and Mig welding , Hope this sheds some light on the subject. Oh and one other point It ITCHES LIKE HELL ! ALWAYS take cold showers it opens the pores and the little buggers come out , hot showers drive um deeper. It's really cool stuff to work with once you get the hang of it.