crack gelcoat

[gmerrill]

i own a 07 compac legacy.  it developed some gelcoat cracks around the top right at the
front of the hatch.  i call compac they are sending me some gelcoat even offer to repair if
i brought it down there but i am 12 hours away.  i have made larger the cracks and bevel
them out.  do i put a fiberglass filler in then cover it with gelcoat or do i just put the hardner in
the gelcoat and put in the cracks.  i email compac but no response

greg

[gmerrill]

compac got back to me and told me to use a fiberglass filler then top it with the gelcoat.  said i could use
the gelcoat but would probaly crack again.

greg

[newt]

Greg,
The cracks are do to that area flexing. Is there something you can shore up to keep it from moving? From your discription I have a hard time figuring out what is moving.

[curtisv]

If fiberglass filler is needed, it sounds like there was a void (an air bubble) in the layup just under the gelcoat.

[brackish]

I've owned about a half dozen GRP boats and been around many dozens more.  I've never owned one that did not develop, over time, hairline gel coat cracks around areas that are stressed.  There is no reinforcement in the gel coat, only in the glass reinforced layer below, so any flexing or temperature differential expansion/contraction will cause stress and potentially, hairline cracks. 

If they are true hairline stress cracks they will cause no problem.  They do not allow water into the substrate, that area being solid polyester resin reinforced with various glass cloths, and because that area is not constantly submerged as in osmotic blistering.  They will not necessarily get worse if left alone, if the stress in the area is relieved by the initial cracks.

My view is that you might be doing more harm than good, trying to fix them.  However, since you have already started the process, the gelcoat they sent you is polyester resin that has been colored and probably had UV inhibitors added.  If the cracks are on a horizontal surface, I would just use that.  The filler would normally be a polyester resin material that is altered with fillers to lighten it, change the viscosity, and would normally weaken it a bit.  However, if your repair V's are large, filler may be needed.

You will have to finish it out with ever smaller grit sanding material, paste or paper.  You will eventually get to the point you are using micron paper, not the stuff you can get at the local home center.  It can be ordered or possibly folks in your area who do solid surface counters would have some.  This is the only way to match the gloss level of the surrounding gelcoat.

My 2005 has a few hairline gelcoat stress cracks in places I would normally expect them to appear.  Sail more, worry less.

my $.02 worth, probably worth exactly that.

[gmerrill]

thanks for all of the advice. i thinked i panicked.  the boat maker offered to repair it at no charge.  but i six hundred miles away.
when i research gelcoat cracks.  it is as you guys say a way of life when you own a sailboat.  but i'll try to keep them maintain so
myy boat looks good.   hey thanks again for your support.

greg
compac legacy

[ontarioSuncat]

Clean out the openning with acetone. If the opening is deeper that the original gelcote then it must be filled. Use 3m Premium filler for below and above water line. NOT the high strength version. Follow the instructions and remember the hardner supplied is enough for may more than the small can. Use only a tiny bit. Just before the filler get real hard, wipe the patch with a paper towel wrapped around your finder and wetted with acetone to create a crater in the patch. leave it till tomorrow. Next day with a dremel or a sharpe point of a knife clean out the filler that is around the edge of the patch. You want to create a square sided crater with the filler below the lower level of the original gelcote. Now tape around the patch with masking tape. You do not have to be tight to the patch. Now mix up the gelcote I mix a golfball size and use very little hardner, no more than 10 small drops.  Too much will burn the mix.  Once mixed apply to the gelcote to the patch and fill to the top of the tape. I use a rubber scraper to clean up level with the tape. If the gelcote comes from Factory it will have wax in it. If you bought it at a marine store it will not be waxed. Although you can buy special waxed gelcote. If waxed you do not have to cover it. But you can cover either if you like. I use saran wrap. Apply the wrap to the patch area and tape it down to keep air out. Leave it for a day! Next day remove the wrap and all the tape. You now have a bumpy raised gelcote patch. Use a small sanding block about 1" square. Sand with 80,120,200, 400, 600, 1500, 2000 grits. Dont skip a grit, the 80 grit can get it down to almost the level of the original gelcote. Gelcote is real soft! I have made up several bags of small pieces of each grit. You only need a few passes on each grit. After the 2000 you can polish with rubbing compound. Wax it and your done. Should pass close inspection if the color was close.
If you don't have the exact color. You can mix your own with the store bought color kits. Mix the color and work up adding colors slowly. do this before you add the harder. Place a dorp on the boat to see how close you are. Keep going until you are satisfied. Wipe off tests with acetone. Once you have the color. You can harden the whole batch or just as much as you need for the current repair.

[curtisv]

I had two voids in the layup that resulted in cracks that exposed a place where gelcoat had not bonded to the fiberglass.  One was in a corner at the keel.  The other was a flat surface.  Here is a photo.



After I openned things up to expose the entire void, this is what it looked like.  You can see that the fibers were completely dry in one spot.



That was before I started sanding.  I needed some fillier and gelcoat.  I did this myself and it looked OK but not perfect.  When I had the boat bottom painted a season or two later I had the yard sand again and spray on some gelcoat which came out better than what I could do with the brush on gelcoat.  Not a big deal and at this point you can't tell that a repair was done.

Curtis