skin coat csm material

I have built a good many frp parts, I was told to use 3/4 oz.csm now building a 23' power boat I have heard of useing 2oz csm for the first skin coat is the 2oz material comon for such a hull?

all using polyester material


Thanks

 

question !!do you understand why such a light glass is used for the first skin ??? on any sizes boat ????
The light glass is not the complete answer to this potentual problem !!.:?:

 

Have you built your parts using csm only?

 

ok yes its possible to build boats useing just chopped strand matt , its what we did 30 or more years ago when fuel was cheap and not to many owners cared how hevy there boats were , The biggest boats i have worked on using just csm were 42 ft long now wovens or stitched matts anywhere in the total construction of this companies boats .

The thin glass in the first layer is for osmosis protection ! it needs to be resin rich and well rolled out so there are no microscopic bubbles any where. !!!
Thats ok but you need to use P matt not E matt !
P matt binder is less likely to absorb moisture !!
Also the first 2 layers should use Vinylester resins which is the third step to osmsosis protection ! this is old knowledge !!

 

Of course tunnels it is possible, I know. If it´s sensible is another question. We all remember the chopper guns (some are still in use).

>>>The thin glass in the first layer is for osmosis protection<<<

and to avoid print through, we should add..

Regards
Richard

 

let me refine my question in the past I have used a light csm skin coat prior to other scheduled laminates, now with this boat, my question is would the 2 oz csm be better by being bulkyer then the 3/4oz csm I also understand the resin should be catylisted a bit hotter then subsequent laminated in order to minimize the resin' styrene attack on the gel coat,

 

3/4 oz is thin for a skin coat, 2 oz would be better for what a skin coat is designed to do.

1. Allow easy air removal.

2. Help prevent print through.

3. Help prevent blistering, by using a more expensive, higher quality resin.

One 3/4 oz won't do any of these very well, the layer will be too thin. On small detailed molds multiple layers of 3/4 may be used if heavier mat won't follow the contours.

Many times you end up with more print through and more of a chance of blisters when using a very thin skin coat, not just because the layer is thin, but because it is frequently under cured. There isn't enough resin to generate much energy for a good exotherm, resulting in poor cross linking.

 

If the gel coat is cured, the styrene won't bother it. If the skin coat is thick and too hot, you might get excessive shrinkage and the skin coat will pull the gel away from the mold in places. Pre-release, it's called and leaves areas that may not be structurally unsound but will be visual defects and possibly 'aero-dynamic' problems.