csm question

[ripvan1]

Today I laid some csm over ply with poly resin, tomorrow I want to lay another layer (ran out of time today) - do I need to abrade and clean today's layer or do I simply cover with poly and add new csm ?

Thanks

 

[fishermantwo]

Today I laid some csm over ply with poly resin, tomorrow I want to lay another layer (ran out of time today) - do I need to abrade and clean today's layer or do I simply cover with poly and add new csm ?

Thanks

Its best to lay up the next lot when its still tacky but its ok with in 24 hours or so. Styrene in the fresh lay up will soften the previous.

 

[Clyde_Wanderer]

If strength of layup is important then you would be better to sand with 40# before applying more layers as a wax forms on the surface during the curing which would prevent a good bond.
C_W

 

[ripvan1]

Thanks both, after putting down the second layer of csm can I get a smooth finish by using woven roving and then gelcoating or do I need to go another route (filling/fairing) ?

Thanks

 

[William_H]

Polyester resin on plywood

It is worth just mentioning here that the fibreglass may not remain attached to the plywood especially if the ply gets wet. Epoxy is much better for this role.
However you can alleviate the problem a little by making the fibreglass layers so thick that the plywood is redundant. ie if the ply rots away the f/g will do the job. By contrast a thin layer of f/g over ply "for prototection" will delaminate on eg the hull of a wooden boat. good luck olewill

 

[ripvan1]

point taken olewill, may add 3rd coat, but still wondering whether to finish off with woven to give smoother base ready for gelcoat

 

[lw395]

Depends what you mean by smooth.
You won't get a flat mirror like finish on the non-mould side.
You can get a shiny-ish wipe clean finish with flow coat. A last layer of fine cloth or surface tissue helps get a smoother finish. I think you want to get the gelcoat/flowcoat on while the layup is tacky ideally.

You can get a smoother finish by vacuum bagging the GRP onto the ply, but that's possible OTT.