Repairing gelcoat dinks and scratches

[lw395]

Blue Gee sell pigment kits for tinting gelcoat.
You can also get colours from the likes of CFSNET who are very helpful.
The plastic padding stuff does seem to change colour badly and does not seem as tough as proper gelcoat. But it is good for a quick repair midseason.

 

[basil421]

I worked for a number of years in the GRP boat building industry. It may be surprising to some people that almost every moulding produced would have a number of gel voids which had to be repaired.
It was common practice with the repair crew to use Sellotape both to hold the gel coat in place (ie if on a corner as most of them were) and to exclude oxygen from the surface. Oxygen inhibits the cure of polyester resin but only on the exposed surface. If no covering film is used the initial few pieces of abrasive paper will block but eventually it will start sanding properly. The Sellotape just saves time as well as holding the gel-coat in place.

It was also common to over-fill the repair area and then, after the repair had gelled, to use a craft blade to shave away excess gel coat from the repair. If done before the gel coat is too hard but not so early that it is pulled away from the base layer the process becomes remarkably quick. The shaving technique also removed any gel coat with oxygen inhibited surface cure. This enabled the Sellotape to be used on the vertical surfaces only and for the top just to be over-filled but uncovered leaving some “meat” to get the craft blade into.

As the gel coat is thixotropic it is often not possible to get all the air bubbles out of it so it is unlikely that the first application of repair gel will be the only one. It will help to stir the gel coat immediately before application as this will, momentarily as in non drip paints, reduce the viscosity and enable the gel to flow into the repair site better and with fewer air bubbles.

It is probably advisable not to use polishing compounds at this stage as they will get into any voids and discolour the final repair. Rather blow the abrasive sanding dust off the repair site and make a further application of gel coat.

We never used wax solution in the gel coat for repairs as it was unnecessary with this technique

However if I were repairing a large area of damage I would be inclined to use it then as the sanding back on such a repair becomes quite tedious. With a large repair on say the topsides of a hull it is advisable to mask around the parent gel-coat which you don't want to sand just to protect it from your overenthusiastic efforts.

If using colour paste to tint gelcoat be careful not to exceed the manufacturer's mixing proportions as the colour paste itself is not a gel coat and will slow the cure if used excessively.

 

[SAWDOC]

Basil Very clear informative post - thank you!

 

[Bosun Higgs]

Top tip, get a small syringe and measure the catalyst. Guessing is just a bad idea.

Second top tip, from Hunter boats originally. When the gelcoat has hardened and you need to level off with the surrounding, use a new Stanley knife blade like you would a furniture scraper.

 

[lw395]

Second top tip, from Hunter boats originally. When the gelcoat has hardened and you need to level off with the surrounding, use a new Stanley knife blade like you would a furniture scraper.

Yes, I do that. I have a holder for the blades, I think its meant for scraping the paint of window panes. It helps to pick the moment when the gel is not quite fully hard. I should be doing this not posting about it!