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Old 29-11-2009, 22:42   #1
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Deck Crack Repair - Anything Better than MarineTex?

OK, we are prepping our deck for paint. We have some hairline cracks we are repairing. We are grinding them out with a Dremel, and then filling them with Marine Tex. But, Marine Tex is just plain nasty. It's like the pink bathtub ring from The Cat In The Hat. It ends up EVERYWHERE. Then, once it sets, it's NOT quite like sanding "wood", like the literature says.

Anything that anyone would recommend over Marine Tex?

Thanks,
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Old 29-11-2009, 23:19   #2
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Working with epoxy is like a surgical procedure: work clean, work steady, work fast. Avoid the mess instead of cleaning it.

MarineTex is pretty good because it takes UV well. You don't want anything softer (for sanding). I have a tip: use multiple layers of masking tape around the repair. After cure, put your electric sander on it so that the masking tape acts like a depth stop. Now you only have to hand-sand the last bit. Use wet sanding for that.

If the surface isn't smooth (anti-slip) get creative with the dremel to shape the repair like the rest of the deck. You will always see it but others who don't know the repair is there won't notice.

cheers,
Nick.
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Old 30-11-2009, 02:35   #3
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Are these stress cracks concentrated in specific areas, or are they widely spread. It may be that there is need for a bit of strengthening in order to support areas of stress and stop the cracking in the future.
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Old 30-11-2009, 08:39   #4
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As Talbot asked, Why are the cracks there? Are these just fine gelcoat cracks around hardware, or are these long cracks in the deck itself, possibly because of wet coring that swelled and cracked the deck? If the latter, I would open it up, drill some 1/4" holes around the area, and inspect the core. I would also always use epoxy over marinetex. You plan on painting the deck anyway, so no worries about UV problems.
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Old 30-11-2009, 08:51   #5
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These are very fine, short cracks. Just in the gelcoat. When I grind them, they stop at the underlying expoy. They are not concentrated in an area or areas, and there are not many of them. It's just with 47 feet AND fixing all of the nicks and chips along with the cracks, it's... tedious.
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Old 30-11-2009, 09:17   #6
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If you are just grinding out the gelcoat, I don't see why you are messing with marinetex at all. Get a can of gelcoat and add pigment until the color matches freshly sanded and polished existing gelcoat. If you match to oxidized gelcoat the repair will stick out like a sore thumb. It doesn't take much pigment. My boat just needed perhaps a half dozen drops to a quart of gelcoat for a perfect match. Of course there are a few other tricks of the trade to matching but nothing difficult.

Mask off the cracks, as suggested above, fill with gelcoat (plus catalyst), a quick spray with PVA mold release to ensure hardening and you're done. Sort of, after hardening you will need to sand the repair with 320 grit progressing down to about 600 grit wet/dry sandpaper followed with a final buffing.

If the cracks are deeper than gelcoat you can use microfiber epoxy (basically bondo) and if you have to go really deep, I use long fiber epoxy, followed by the bondo, followed by the gelcoat. Repairs like these are not terribly difficult but they are very time consuming to do a good job.

Hope this helps,
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Old 30-11-2009, 11:32   #7
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MarineTex --is-- epoxy. But sure, if the deck is gonna be painted I would go for regular epoxy. Gelcoat is only a sensible option when you don't plan to paint the deck. But it tends to show the crack again after some time. That's why MarineTex is a good option. You can use the same pigments with it for color-matching.

cheers,
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Old 30-11-2009, 12:32   #8
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Marine Tex & JB Weld are in the same boat, primarly metal repair. They both cure to a grey color. Come in 2 tubes resin and hardener. Is this the marine tex you are talking about? Cause I wouldn't use either one over West System for any fiberglass repair. Bondo, I don't think so. Most of these products are only moisture resistant not water proof, will pop and fail, again epoxy. If these are only chips and scratches and not structural,how about West 407 low density filler. I used it on my front deck after removing all the teak. Unlike 410 it can stand the deck heat. It sands easly and if you tape the cracks as suggested it is not messy. After fairing would put a a couple of thin coats (it will bubble if applied to thick) of clear epoxy to make it waterproof. Carefull not to sand through it before appling primer. Front deck still good after 6 yrs. Good Luck
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Old 30-11-2009, 13:23   #9
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Hi Nick,

Just my two cents - if one repairs a crack with gelcoat and it comes back, then the repair wasn't thorough enough. I've had a few repairs that were restricted to gelcoat but the majority went into the underlying fiberglass. Those needed either the microballoon and in some cases the long fiber plus microballoon. The usual spot that needs repair are around corners where the layup was less than sterling. In my own partictular case I am also doing some repairs where the resin from the layup didn't penetrate. I see a crack in the gelcoat and when I grind it out I find dry glass fiber. Bummer. Spots like those will come back if I just gelcoat. For those around corners or at sharp bends, if I repair them properly they should not come back.

For Mark, I call it bondo because it so similar but so long as it is above the waterline even bondo will work according to all the glass specialists I've spoken with.

Gotta run, just looked and its time to turn the ribs on the grill. LOL

Regards to all,
Rich
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Old 30-11-2009, 14:58   #10
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Quote:
Originally Posted by cabo_sailor View Post
Just my two cents - if one repairs a crack with gelcoat and it comes back, then the repair wasn't thorough enough. I've had a few repairs that were restricted to gelcoat but the majority went into the underlying fiberglass. Those needed either the microballoon and in some cases the long fiber plus microballoon. The usual spot that needs repair are around corners where the layup was less than sterling. In my own partictular case I am also doing some repairs where the resin from the layup didn't penetrate. I see a crack in the gelcoat and when I grind it out I find dry glass fiber. Bummer. Spots like those will come back if I just gelcoat. For those around corners or at sharp bends, if I repair them properly they should not come back.
Rich, I agree that the substrate must be good first... but we're talking fiberglass repair now, not gelcoat repair. When you are sailing the whole hull is flexing and that creates a lot of stress in the gelcoat at points that have stress-risers already like around fasteners, sharp corners, hatch openings etc. The gel coat is much harder than the fiberglass, so it can crack while the fiberglass is intact. When you fix that with gelcoat, you are doing secondary bonding with polyester (we're talking about polyester gelcoat, right?). That secondary bond is very weak compared to primary polyester bond (so it is no where near the strength of the original gelcoat... which failed in the first place, so it's guarenteed to come back with the repair!). The bond is also very weak compared to a secondary bond with epoxy. When you use epoxy for the repair and you do it right (beveling the crack, not contaminating it etc.) the repair will be stronger than the original gelcoat.

MarineTex: I know there's a gray version but I am sure the OP is using the white version. I never heard that it was targeted for metal repairs like JB Weld. It comes in jars with the hardener in ampules. I don't know the UV resistance of JB weld but I would not rule that product out too quickly because it is very capable in non-metal scenario's too. The gray color is the problem for using on a deck.

ciao!
Nick.
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