Glassing over gel-coat?

[yamanube]

I have always sanded through the gel-coat/paint before laying fiberglass but have also seen many builds where repairs where made, footholds put in or other work was done and the glass was layed down over the gel-coat. I would think that it would not hold as strong and will always sand down to the glass but wanted somebody to clear this up for me.

:reporter:

 

[Idok]

no good.

ALWAYS grind off the gelcoat.

if you scuff it up, it will adhere....but the BEST way to do it is grind it completely off....

 

[stanton]

no good.

ALWAYS grind off the gelcoat.

if you scuff it up, it will adhere....but the BEST way to do it is grind it completely off....

x2

 

[sjetrider]

why? Gelcoat is polyester based, so if you are using polyester resin why grind through the gel coat? Its a chemical bond, not like epoxy resins.

 

[SUPERJET-113]

I agree.
This has been explained a 199 times on this board.
Gel coat is just pigmented polyester resin. So it will stick the same either to the gel coat or to the cured polyester resin/glass that is already there.
The original gel coat and glass/resin are chemically bonded together, so it doesnt matter.
When a boat is re-gel coated the entire existing gel coat is not removed. Its sanded and more gel coat is applied.

Also when doing a repair or re-gel coating it's not real a chemical bond because the gel coat or glass/resin that your applying on is already cured, so it will be a mechanical bond(after you sand), but it will stick the same to gel coat or fiberglass/polyester resin ...
If your grind all the gel coat off, your just making more work for yourself.

Now primer or paint you would want to grind all off to the glass/resin or SMC and only use epoxy on SMC.

 

[stanton]

gel coat cracks and delaminates pretty easily. if you want a solid lasting bond...

 

[SUPERJET-113]

I always grind the gel coat off where I do a repair or like where the foothold will rest, I grind that off too.

But tell me, when you reinforce a whole tray do you grind off all the gel coat?
If you were to re-gel coat a whole bottom of a ski(not SMC bottom) would you grind all of the gel coat off?
Thats the point I was getting at.

 

[stanton]

I always grind the gel coat off where I do a repair or like where the foothold will rest, I grind that off too.

But tell me, when you reinforce a whole tray do you grind off all the gel coat?

i would. its easy with the right tool.

 

[WFO Speedracer]

The right tool for that costs in excess of $600.00,if I were regelcoating a bottom I would sand with 80 grit and shoot new gelcoat on top of the old,if I were reinforcing a tray I would grind the gelcoat to roughen it and glass over it,if I was doing a foothold I would do the same ,if I was doing a structural repair I would grind all the gelcoat around the area off down to the glass and glass everything back in then gelcoat over it,I hope that clears it up.


http://www.paintshaver.com/marineshaver.html

 

[SUPERJET-113]

The right tool for that costs in excess of $600.00,if I were regelcoating a bottom I would sand with 80 grit and shoot new gelcoat on top of the old,if I were reinforcing a tray I would grind the gelcoat to roughen it and glass over it,if I was doing a foothold I would do the same ,if I was doing a structural repair I would grind all the gelcoat around the area off down to the glass and glass everything back in then gelcoat over it,I hope that clears it up.


http://www.paintshaver.com/marineshaver.html

I agree and Holy , thats a bad ass machine!

 

[Idok]

The right tool for that costs in excess of $600.00,if I were regelcoating a bottom I would sand with 80 grit and shoot new gelcoat on top of the old,if I were reinforcing a tray I would grind the gelcoat to roughen it and glass over it,if I was doing a foothold I would do the same ,if I was doing a structural repair I would grind all the gelcoat around the area off down to the glass and glass everything back in then gelcoat over it,I hope that clears it up.


http://www.paintshaver.com/marineshaver.html

thats how we do ALL glasswork here


the whole tray, the whole engine compartment, the whole etc etc....





takes a few hours to do an entire engine compartment witha 4" grinder......thats the crappy part, other than that its easy! Hell, cracker took the gel off his entire hull and Ill bet it didnt take more than a day or 2