GRP and epoxy question

[damo]

I am making some components out of polyester resin and CSM (cos I have it in stock), and want to attach them to an existing grp structure with epoxy and woven roving

How long would I have to leave the new grp before using the epoxy?

 

[boatbuilder]

Why?, polyester to polyester is far superior.

 

[damo]

Even though it supposedly does not act well as an adhesive on old grp?

 

[boatbuilder]

It does if prepared properly, a good sanding with 40grit helps

 

[damo]

Ta, I'll probably do that then /forums/images/graemlins/smile.gif

But do you happen to know long before the polyester has cured enough that epoxy would bond to it adequately?

 

[boatbuilder]

The epoxy will bond at any time but you will still have to abrade heavily. so why go to the added expence.
We allways bond poly with poly, whypay more.
However if you use epoxy then you will have a problem getting a bond with poly aat a later date.

 

[damo]

Good info, thanks

 

[Grajan]

Sorry guys ,but polyester needs to post cure for a minimum of one month before overcoating with Epoxy.
Polyester to polyester has been used successfully for many years but very careful preperation is required to application area and surrounding laminate however, chemically it is a weaker bond than Epoxy to Polyester this is why some Insurance companies ask for repairs to be carried out with Epoxy resin and mat

 

[damo]

Thanks for that. I haven't been able to find an "official" source of info - do you have any references I can follow up?

 

[ex-Gladys]

To go polyester to existing polyester it needs to be a mechanical "bond" rather than just surface to surface... For example if you are filling a 4" dia hole, you need to chamfer off the hole both inside and outside at a shallow angle going out to probably 8" diameter. to lay up you put an 8" dia piece of mat in first then 7" then 6" then 5" then 4" on each side to build upthe right depth...

The two overlaps inside and ouotside are what give the bond