3 replies to this topic

[Doodling]

Do I need to use Plastic Primer if my fibreglass body kit has been gell coated?

[ibrooks]

Gel coat isn't something that's been put on GRP it's the first layer of resin that goes onto the mould and doesn't have any matting in it (it's also generally tinted to whatever colour you want it to end up). Plastic primer is a generic term and can describe several very different things but what you would normally buy as "plastic primer" is formulated to go onto ABS or similar plastic. It's got different solvents in it that are designed to dissolve the top layer of the plastic and provide a key (sort of like etch primer has acids in it to eat into the surface layer of a metal). Most resins used in GRP are resistant enough to solvents and acids that this type of primer is a waste of the extra money they cost - they'll work if you have a good key but no better than a normal primer would in the same situation. Your best bet is an epoxy primer and a good key to start with.

 

Iain

[tiger99]

I agree with most of that, however I have read that GRP sometimes needs an etch primer, which presumably is quite different to the etch primers that we use on steel. Or, of course, the surface could be mechanically abraded to form a key, again as you would do with steel if you want to use a proper zinc primer. (The zinc is pointless on GRP of course!).

 

Not knowing any better at the time, I just used 400 grit abrasive paper last time I painted over gelcoat, to remove the "shine" (and any remaining film of mould release agent, very important to get rid of that for obvious reasons), washed and dried it with warm air, and used a normal primer. It seemed to be ok. Now we have epoxy primers, which are better, so should form an even better bond.

 

There is an interesting discussion here:

 

http://www.dotheton....p?topic=39130.0

[Wise Old Elf]

http://www.option1sp...uk/bodyshop.htm

 

 

These guys are considered to be one of the best companies in the Lotus world. Their prep process is shown on the webpage above.