Originally posted by m67gl
What's the difference between fibreglass and vacuum formed?
Fibreglass is the common name for both as it is the "fibre" that is in the resin to give it strength.
The hand laid up panels are really called GRP (glass reinforced plastic) or FRP (fibre reinforced plastic) depending on what country you are in or what book you read.
Appearance, it is smooth on one side & rough in texture on the other.
GRP is laid up in a mould using hand lay up (applying mat & resing by brush & roller) or by chopper gun (a tool that shoots resin & cuts up glass fibre at the same time). GRP, in the automotive sector, is usually a polyester resin, same as what is used in plastic filler (Bondo, bog whatever). Repaired by hand layup polyester resin & glass fibre.
Vacuum formed fibreglass is called SMC (sheet moulded compound) & is formed in a similar way plastic parts are made. That is a fully encased mould, the resin & glass fibres are pulled through by a vacuum process.
Appearance, it is smoooth on both sides.
The resin commonly used here is Vinyl Ester, sometimes Epoxy. Repaired by using vinyl ester resin or epoxy & glass fibre.
This is also now used in aerospace making carbon fibre & Kevlar parts. The Airbus (Scarebus !! I hate em) is a good example of SMC flying.
Talking Ford & Shelby now, if you look at the fibreglass on a 1965-67 Shelby, you will see it is rough in texture on the underside. that is because it is hand laid up (GRP) & was correct for those years. From 1968 Ford used AO Smith to build the Shelby's & they had started using vacuum formed fibreglass (SMC). So from 1968 on you will see the fibreglass is smooth underneath as on top.
