Porosity in gelcoat applied with a roll

Hi,

I have read that if gelcoat is applied with a roll it will be porous.

Will the porosity be through the whole thickness or just to the surface?
If it's through the whole thickness what's the point of using a roll.

Is it better to apply it with a brush?

Thank you,

AB

 

You are aiming at 0.5 to 0.8 maybe 1.0mm thick gelcoat. It's hard to get this thickness in one roll of gelcoat, but OK with spray, two or three passes (roller) is more common with rubbing down in between. Depends if the surface is horizontal or vertical or curved too as you don't want runs. Get the most liquid version of gelcoat you can find, sometimes called Flowcoat and work fast. Rolling does work fine, but it's more work than spraying. I tend to use a scraper on small areas.

It is important top catch the gelcoat at the right time to cut, if you want to minimise the work.

FWIW I have encountered gel up to 4mm+ on some boats I've repaired but this is incredibly bad practice. Also down as low as 0.2mm .....

 

Are you applying it to a mould or a boat interior ?

 

On the hull after a repair. I have applied it with a roll and it went fine. Lot of sanding but otherwise it has been ok.