Gelcoat sanding tips/techniques

[OSM]

Recently had the need to spray a large area with gelcoat as the final step in repair. Applied 'dye' to surface and sanded with 220 then 320 till dye disappeared. Re-dyed the surface again, then sanded with 600 then 800 until dye was removed. Buffed with 3M finishing compound and all looked well until I caught a glimpse at an angle showing sanding marks.

What did I do wrong? What steps do you follow to ensure a finish as smooth as that which comes out of the mold?

There are a few imperfections in the mold which I have been reluctant to sand & buff for fear of same results.

Thanks in advance

[fiberglass jack]

keep sanding I start with 320 sometimes 400 this way you wont get deep scratches like 220 ,u got to work your way up on the grits remove all the 320 scratches with 400, the 400 with 600 and so on go up to 1000 and buff , after buffing u may have to sand again with 1000, use wet paper wet sanding will give a faster result

[Buckle]

After just reviewing our gelcoat repair procedure, its imparitive to match the sanding system to your gelcoat. i.e. a soft gelcoat would choke DA pads quicker than a harder gelcoat.

Starting at 240 sounds good. However before moving up the grade, you should use your dye or guide coat powder so show scratches have been removed.

Once the guide coat has been removed, recoat the surface again and rub with a finer grade until a state where polishingis required.

Depending upon the hardness of gelcoat, you may require a course cutting compound followed by a de-swirler to remove any fine scratched caused by the previous cutting compound.

The point I wish to make is, every gelcoat is different, and therefore a different finishing system may be repaired.

Hope this helps.

Enjoy

[tja]

Clean the surface with water to remove all of the compound. Be sure that all of the compound is off. This is very important. You don't want any compound to get under the 1000 to 1500 grit wetsand paper. Us 3m if you can. After sanding use a more agressive compound. What you used isn't very coarse. I use a product called cutting cream. I can't remember the brand name. If I remember i'll look at work to see what the brand is. Also when you buff don't rush it. Moveing the buffer too fast doesn't let the compound do it's job.