chopstrand bumpy when it cures

ChargerMan1

Petty Officer 3rd Class
Joined
Jul 12, 2020
Messages
76
I can't figure out why everytime that I lay chopstrand down and completely wet it down it is bumpy when it cures. Any ideas whats going on?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
49,896
its the nature of csm.

CSM should be used as the first layer then subsequent layers of 1708 over it.

if you want a smooth surface, you will need to sand, then fair
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
18,092
As Scott said, there is nothing smooth about chopped strand mat or many fiberglass fabrics for that matter. The texture of any fabric will show once the resin has cured.

Since chopped strand is not a woven fabric, but a bunch of loose strands of fiberglass lightly held together with a binder, the strands will tend to shift and move around as resin is worked into the fabric. This 'working' of the fabric tends to make it even less smooth, and possibly to the point of being lumpy/bumpy.

Perhaps you could share some details about what you are trying to achieve with the chopped strand mat.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,970
Gee, blot don't rub. saturate the mat with the old up-n-down motion. Then fill the weave with resin, and it will be smooth.

if you tear the mat apart, it will have lumps and clumps....
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,605
While you basically can't "smooth" out CSM, if you use a bubble roller, it does help some to lay flat. But CSM was never made to be a subsurface for a smooth finish. But then neither was 1708 either. The are merely fiberglass mats and weaves to assist in building or rebuilding structure. You have to sand and fair them for a smooth surface if you have plans to use them for smooth surfaces. When boat builders use them, they are applying Gel Coat on their molds first, followed up with either a chopper gun fiber shoot, or hand laid woven mats.That is why those procedures come out flat and shiny. JMHO
 
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