GRP laminate thickness vs cloth weight ?

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Boo2

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Hi,

Can anyone tell me what thickness of finished laminate will be given by each layer of a given weight of cloth ? Eg: I am using 390 gsm cloth, how many layers will I need for 2mm thickness of finished laminate ? Anyone know a site where this is tabulated or what other conditions affect the outcome ?

Many thanks,

Boo2
 
Boo2 said:
Hi,

Can anyone tell me what thickness of finished laminate will be given by each layer of a given weight of cloth ? Eg: I am using 390 gsm cloth, how many layers will I need for 2mm thickness of finished laminate ? Anyone know a site where this is tabulated or what other conditions affect the outcome ?

Many thanks,

Boo2
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I assume you are not referring to an epoxy resin.

For standard resins the mix is 3 to 0ne, that's parts resin to one part chopped strand mat by weight.

I would say two layers of 390 would be very close to 2 mm.

Also consider adding a single layer of rovinings to smooth out the finish, this layer will most likely not need any additional resin.

Good luck and fair winds. :)
 
I have an old book here on boatbuilding, which claims that as a rough rule of thumb, 1 layer of 450g mat with 2.5 : 1 resin by weight, gives 1mm thickness when consolidated with a roller. Intuitively, that seems a tiny bit thin to me - I'd have thought nearer 1.25mm, but that's just a gut feeling. A lot depends on whether you're putting a gelcoat down first? Also, unless you're working on a flat, horizontal sheet and using a roller, the finished thickness could vary (almost certainly a fair bit thicker if you just use a brush and dab it).
 
Thickness of Fibreglass lay up

Most design engineers will be more concerned with the amount of fibreglass in the layup as relating to the final strength. In serious layups like aircraft skin they go to a lot of trouble to have minimum resin consistent with total saturation. This is done with vacuum bagging and bleeder layers that suck up excess resin.
However in boats where weight is not a critical factor and dimension ie thickness can add to stiffness sometimes more resin is OK. I would still suggest that in most cases you start from the question how much glass do I need for strength then squeeze in just enough resin to fully saturate.
If you need thicker perhaps as a packing then add more glass and resin once you have decided it is not thick enough. If you want stiffness then consider stiffening it by adding foam or balsa with more glass over that. Not by just adding more glass.
Sorry not much help in the end olewill
 
Quandary said:
I suspect Oldsaltoz is speaking from experience rather than conjecture?
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No disrespect intended to Oldsaltoz, on the contrary I'm sure he is well experienced. I based my judgment (I did say 'seemed', didn't work it out) on 45 years experience with the stuff!!!

Dangerous to comment on assumptions.
 
Davegriff said:
No disrespect intended to Oldsaltoz, on the contrary I'm sure he is well experienced. I based my judgment (I did say 'seemed', didn't work it out) on 45 years experience with the stuff!!!

Dangerous to comment on assumptions.
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I have laid up a few things in grp starting with making lightweight tanks for motorbikes long before I ever got near a boat, but I have found that any advice I can give is trumped by the Aussie so I tend to defer to him, though I disagree with some of his techniques, so perhaps I might not be in the danger you suppose.
 
Davegriff said:
No disrespect intended to Oldsaltoz, on the contrary I'm sure he is well experienced. I based my judgment (I did say 'seemed', didn't work it out) on 45 years experience with the stuff!!!

Dangerous to comment on assumptions.
Click to expand...

G'day Dave,
I see your comments as helpful and take no disrespect, in fact was estimate is on the light side hence the reference to a layer of rovings.

It is far easier to add than remove a layer of fibreglass after all, and it looks like we have both been working on fibreglass for much the same number of years.

Good luck and fair winds. :)
 
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