Gelcoat or Topcoat?

[dod]

Can someone explain why people refer to the outer skin on grp boats as GELCOAT rather than TOPCOAT? (ie Gelcoat + 2% wax solution).
Most reference on repairs to grp seem to quote usage of GELCOAT. Is this just a general term used?
I get similarly confused with the use of the word EPOXY when referring to laminates but that may warrant a separate post. /forums/images/graemlins/confused.gif

 

[macd]

Would you refer to your skin as topcoat? Gelcoat is simply the term for a particular type of resin (which normally contains no wax and will not cure fully in the presence or air) used as a largely cosmetic outer coat for GRP.
Epoxy (resin) is a particular type of resin, quite different in chemical composition from the polyester and vinylester resins normally used in GRP. Apart from being more expensive, epoxy is also an adhesive (hence e.g. Araldite), which the others are not. None of these substances are laminates, but all are often used as the binding agent in laminates. However, epoxy resins (sometimes with other bulking or strengthening agents) are often used on their own (i.e.not as part of a laminate) for repairs or structures; -ester resins are almost never used in this way.

 

[scuby]

Gelcoat is applied directly to the mould before the glass is laid up using resin. It is a thickened and usually pigmented resin intended to give a good hard wearing finish. Topcoat, also known as flowcoat is used to provide a good finish to the inside of the moulding covering the rough glass surface. The point is gelcoat is air inhibited meaning the surface will remain tacky if left open to the air so it can't be used as a paint type coating. Flowcoat has wax added to prevent the surface tackiness, the only problem being the wax will prevent any further layers adhering.
In short we refer to the outer layers which were in contact with the mould as gelcoat because it is.