grp and west system compatability

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tesswoodnutt

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In the process of a major refit, and used to using West System epoxy, but like the lower cost of traditional resin. Is it possible to bond and fillet with West System then reinforce with grp? Or can you use the fillers (colloidal silica, micro fibres and the like) that come with West System mixed into resin to make a cheaper filleting mixture?
 
G'day Tess and Welcome to the YBW forums with this your very first post.

You can use almost any filler with epoxy or standard resins, balloons are oly good for fairing and filling, not good for load bearing.

Micro-fibres make a very strong filler and glue, just make sure you remove as much excess as possible when its still wet, because its hard work to sand it back.

Standard resins will bond to standard resins, but the bond is only as strong as the mechanical key you provide by sanding or grinding the old material. An epoxy will form a mechanical and chemical bond, so can be stronger.

If wieght is not a problem you can build your gusset from standard resins then bond it with an epoxy for maximum strength.

Epoxy resins and cloth should be miced/made at a ratio of 1 to 1 by wieght using propper epoxy resin cloth, no chopped strand mat.

Standard resins come in closer to 3 of rsin to one of cloth or mat. this is why it is heavier than epoxy condstruction.

The fact that less resin is required when using an epoxy can mean less cost at the end of the day dispite the higher cost per litre of epoxy.

I hope this helps.

Avagoodweekend......
 
A short answer is that epoxy will bond to polyester but not vice versa. In other words you can't apply conventional resin to epoxy (it will stick but the bond is weak).

Polyester will bond well to previously cured polyester but it is essential to abrade the surface first. Polyester exudes a fine layer of wax on its surface as it cures and that must be removed before adding more.
 
if your issue is the price of West epoxy compared to Polyester resin, then I'd look to using a non-brand name epoxy. Epoxy has much better mechanical properties for filleting etc than polyester, as polyester has no "gluing" capability. Here in Autralia, I can buy epoxy for less than 140% of price of polyester, and as you tend to use less, it's overall cheaper.
 
Thanks all for the comments, I think we'll try a filleting mixture with polyester resin, and finish the job (bulkhead to hull join...I said MAJOR refit didn't I?) with glass cloth and epoxy. These forums are fab aren't they?!!! Cheers!
 
If you want to bond the bulkhead to the hull, don't use polyester filler as it will give no strength. The best bond will be achieved by mixing 'microfibres' into epoxy resin until you get a stiff paste and applying it with a round-ended piece of wood. That alone will do the job.if you feel the need you could add a strip of glass tape & epoxy over the top.

The fillet bonding technique is used a lot for plywood boats. The microfibres are cellulose and come as a lightweight powder. You can buy them where you get your epoxy.
 
The only way we found to get the wax, or bloom off epoxy was either a scourer like Vim, or by sanding, but be prepared to go through a load of sandpaper as it clogs big time. We built a Wharram using West system, so are familiar with filleting, glueing etc, but now I'm begining to realise that epoxy and polyester resin are completely different animals!
 
If Polyester resin will not bond to Epoxy does this mean that Gelcoat ( which I believe is a modified polyester resin) should not be used on epoxy ?
 
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