beginning lamination questions - first layer against mold and filler question

Hello! I want to make a fiberglass part in a mold and I need the final thickness to be about 4mm! I don't want the first layer to be gelcoat because the final part will be painted and not used to sits in water but will be used inside. Can I apply a simple layer of polyester resin instead of the gelcoat, let it harden and then start laminating? I have one more question. Can I add a filler in polyester resin to be able to laminate 4-5 layers of 450 gsm csm in one go so as not to heat up too much? Does the particular filler affect the structural durability of the composite? Thanks

 

You can certainly omit a gelcoat,but unless you have a particularly compelling reason to avoid buying some,it may not be the best idea as it is likely to be a better moisture barrier than the main laminate.Why add a filler to the resin? You can easily laminate in two stages,perhaps two plies of mat,followed by the final three soon after the initial cure and it won't have detrimental effects on the structural quality of the piece.

 

Resin doesn't work well as an in-mold coating, and with no in-mold coating you will have many thousands of tiny defects in the surface that will haunt you when it comes time to paint it.

Fillers can be used, but they aren't typically used unless you plan to do high volume production of non structural parts. For low volume, or one off parts, fillers are more trouble than they are worth.

 

Thanks for the answer! The part I want to do must be scratch and impact resistant! Will the gelcoat provide these characteristics?? P.S. I would like to paint with 2k polyurethane paint. What type of gel coat can I use? clear gel coat? Thanks

 

Clear gel is exactly the same as pigmented-but without the pigment.Use whatever is most convenient and once the surface is free from wax or other contamination,2K paint will work very well.If there is no other consideration a pigmented gel of about the same shade as the desired finish will minimise the paint thickness necessary to give good coverage.

 

You can use almost any gel coat you want.

How much of an impact, are you hitting it with a hammer?

 

it will not be hit with a hammer!
It will be used in the sports industry! So it will be subjected to human impact and shear forces it will not be hit with a hammer!

 

Thanks a lot for your help!!

 

What type of a product can I use for cleaning the wax from the surface of the plug and need to sand the surface before painting for better adhesion?

 

You will be washing and sanding the surface, that's all that's needed before painting. And your paint of choice will describe the process for that paint.

 

Thanks a lot!!

 

Yes, you can apply a simple layer of polyester resin instead of gelcoat, let it cure, and then start laminating. If it fully hardens, lightly sand it for better adhesion. To laminate 4-5 layers of 450 gsm CSM in one go, you can add a filler to reduce heat buildup. Milled fibers improve strength, while microspheres reduce weight but weaken the composite. Use fillers sparingly to avoid compromising structural integrity.

 

It is very difficult to apply a uniform layer of resin to a mold surface, you'll get fisheyes, sags, and a very uneven layer. That's why in mold coatings exist.