how long to leave pol resin for adding the next layer?

[slowlearner]

after 12 months I finally fixed my front fender at 2:30 this arvo with some polyester resin. The underside is fully hardened from what I can see. It's now 6:30pm here. Is it ok to put resin on the top side now (against the resin I put in this arvo) or do I have to wait longer?

I have a fibreglass handbook, but do you think I can find a simple answer in that?!

[Dirkvhp]

From what I remember from a fibreglass course that I did and checking my fibreglass book ("The Fibreglass Manual" - by Keith Noakes) you don't have to wait to lay up multiple layers of glass as long as you lay up the next layer while the first is still wet, no need to wait for them to "part cure".

There is a proviso here, you shouldn't lay up more than about total 4mm thickness (consisting of a number of layers) as the heat generated by the resin going off can damage your mold, your project or the bit you are fixing!

Obviously, from your post your project has cured a bit since your message. From my fibreglass course and the book, it can take quite a while for polyester resin to reach full cure (from weeks to months!) and you probably don't want to wait that long.

From my experience (one course and a few small projects at home and for the car, so don't take my advice as gospel! ) you should wait until the resin has cured enough that you are able to sand it. You will need to sand it to ensure a good bond with the next layer. I would use a medium-coarse grit sandpaper to do this (but not too coarse).

As previously mentioned, if you can work quickly enough to place multiple layers you can avoid the sanding... I try to do this where I can by setting up for the layup as well as I can:

• cut/tear multiple layers of fibreglass to shape (as many as you need)
• prepare a cup of uncatalysed resin (1 for each layer)
• Add the catalyst to each cup as it is needed
• apply resin, lay mat and roll out the bubbles.... repeat

This way I avoid any intermediate sanding.

Hope this has helped you along...

Regards
Dirkvhp

[Dirkvhp]

Oh,

And another thing....

You probably already know that most body fillers are polyester resin based...the rules that apply to them apply pretty much equally to fibreglassing.

You can sand many of these within 1/2 an hour of them going off... and you can apply additional layers too, check a can of body filler and see what it recommends (I don't have one handy!)

Regards
Dirkvhp

[slowlearner]

thanx