Stress cracks in deck areas

[eddystone]

I wondered whether these still appear on newer boats, say less than 10 years old because of better resin technology/lay up techniques? I'm reluctant to bother to fix mine or at least would only consider painting over them, not grinding out and filling as there is a good chance they could reappear.

 

[doug748]

I don't know but haven't seen any. Maybe they will appear in the coming years, difficult to predict and would anyway vary from yard to yard, I guess.
I have a number of these and have generally ignored them, as repairs have to be very good to avoid looking unsightly. I also have a couple of star cracks in the deck, one may even have been mould release damage, I should get the impact one done as it lies on an horizontal surface. If the cracks were in the region on a sandwich deck I would be sorting it soonest.

 

[Tranona]

Stress cracks are more to do with poor design of the layup (and poor moulding technique perhaps) than the materials. As their name suggests it is stress that causes it. Less common on newer boats because of more careful laminate design, better quality control and less reliance on heavily stressed components such as chain plates going through the laminate and taking the loads. what can happen, and is common on certain models of French boats is voids in gel coat in areas such as moulded in non slip and wear plus power washing can open them up.

 

[jwilson]

Well I have a 10 year old French boat with some minor stress cracking in corners of cockpit locker lids, but nothing in any high stress areas such as round chainplates or stanchion bases. Like most boats I also have a few voids in resin-rich areas at corners in the cockpit, areas subject to the odd knock. I usually fill one or two tiny knock-voids each winter. I don't let a pressure washer near the deck - I've seen to many voids opened up on other boats by these.

 

[stuartwineberg]

I had an interesting chat with a professional GRP guy who works building prestige sailboats. I have a 14 year old Hardy mobo which is very heavy lay up and thick gelcoat. He said that this kind of boat is very prone to stress cracking because the thick gel is relatively inflexible and so tends to crack. On modern boats, the more precise specs actually mean thinner if more consistent gel which flexes more and is less prone to cracking but if not careful can be worn through over years of cutting and polishing. My Hardy was a bit of a mess with star cracking when I got her but he ground it all out and regelled and not a single crack 4 years later. The issue of voids on locker corners and curved edges is also something that seems to happen more on hand laid up boats and again I got these cut out and fixed very easily by him.

 

[stuartwineberg]

I wondered whether these still appear on newer boats, say less than 10 years old because of better resin technology/lay up techniques? I'm reluctant to bother to fix mine or at least would only consider painting over them, not grinding out and filling as there is a good chance they could reappear.

If fixed properly very much doubt they would reappear. The question to ask is whether they pose a risk of exposing the underlying fibreglass to moisture ingress - if so fix it. There are the usual "Captain Tolley creeping crack cure" solutions but not keen personally

 

[eddystone]

I had an interesting chat with a professional GRP guy who works building prestige sailboats. I have a 14 year old Hardy mobo which is very heavy lay up and thick gelcoat. He said that this kind of boat is very prone to stress cracking because the thick gel is relatively inflexible and so tends to crack. On modern boats, the more precise specs actually mean thinner if more consistent gel which flexes more and is less prone to cracking but if not careful can be worn through over years of cutting and polishing. My Hardy was a bit of a mess with star cracking when I got her but he ground it all out and regelled and not a single crack 4 years later. The issue of voids on locker corners and curved edges is also something that seems to happen more on hand laid up boats and again I got these cut out and fixed very easily by him.

Interesting - but given my level of gelcoat repair skills if I tried to grind out all the lines around the stanchion bases etc to recommended 3mm deep I think the deck would end up a complete mess which is why I'm investigating protective paints (I was going to say epoxy but that's probably not a good idea as apparently it's more susceptible to UV degradation than polyester.)

 

[stuartwineberg]

Interesting - but given my level of gelcoat repair skills if I tried to grind out all the lines around the stanchion bases etc to recommended 3mm deep I think the deck would end up a complete mess which is why I'm investigating protective paints (I was going to say epoxy but that's probably not a good idea as apparently it's more susceptible to UV degradation than polyester.)

Others can comment on the idea of painting - I don't have the expertise there. You are right about needing decent gel skills to do it well. As much as anything getting the correct shade of white can be a pig apparently. However IMHO the idea of doing a nice paint job that would presumably cover a large part if not all the deck sounds a huge task unless you are considering just spot painting which would probably look worse than a less than perfect gel job. I know there are high grade fillers you can use instead of gel but not sure how good they are.

 

[Avocet]

I had an interesting chat with a professional GRP guy who works building prestige sailboats. I have a 14 year old Hardy mobo which is very heavy lay up and thick gelcoat. He said that this kind of boat is very prone to stress cracking because the thick gel is relatively inflexible and so tends to crack. On modern boats, the more precise specs actually mean thinner if more consistent gel which flexes more and is less prone to cracking but if not careful can be worn through over years of cutting and polishing. My Hardy was a bit of a mess with star cracking when I got her but he ground it all out and regelled and not a single crack 4 years later. The issue of voids on locker corners and curved edges is also something that seems to happen more on hand laid up boats and again I got these cut out and fixed very easily by him.

My background was in fibreglass sports cars and what you have been told is exactly what happens in my experience. Polyester gelcoat is very brittle. Cars need to have a (visually) MUCH better surface finish than boats. It was always a tightrope act between the gelcoat being too thin (so you'd get "print-through" of the fibre stands showing very faintly, or too thick a gelcoat, which was prone to stress cracks and "rippling". The cars were painted, (and obviously not immersed in water) so osmosis wasn't a problem. Boats tend to need thicker gelcoats to form a better barrier for osmosis.

As far as the OP is concerned, I'm not sure there are any paints that will successfully cover stress cracks, they will always show back through. Someone told me that on a very hot day, if you mix some epoxy (which finds its way into surprisingly small cracks) and then paint that over the crack and immediately cover the area so that it is in the shade, it "sucks" the epoxy into the crack as the air in the crack cools and contracts. This then bonds the edges of the crack together. It doesn't make it invisible, but it does prevent the sides of the crack moving relative to each other, which means it is stable enough to put paint on. I haven't tried it myself though!

 

[eddystone]

My background was in fibreglass sports cars and what you have been told is exactly what happens in my experience. Polyester gelcoat is very brittle. Cars need to have a (visually) MUCH better surface finish than boats. It was always a tightrope act between the gelcoat being too thin (so you'd get "print-through" of the fibre stands showing very faintly, or too thick a gelcoat, which was prone to stress cracks and "rippling". The cars were painted, (and obviously not immersed in water) so osmosis wasn't a problem. Boats tend to need thicker gelcoats to form a better barrier for osmosis.

As far as the OP is concerned, I'm not sure there are any paints that will successfully cover stress cracks, they will always show back through. Someone told me that on a very hot day, if you mix some epoxy (which finds its way into surprisingly small cracks) and then paint that over the crack and immediately cover the area so that it is in the shade, it "sucks" the epoxy into the crack as the air in the crack cools and contracts. This then bonds the edges of the crack together. It doesn't make it invisible, but it does prevent the sides of the crack moving relative to each other, which means it is stable enough to put paint on. I haven't tried it myself though!

Ha, very hot day - not an option for this country then! Only thought of painting because I was planning to address an area of tiny yellow spots/depressions in the moulded in non slip with Kiwi Grip or similar.

 

[rogerthebodger]

Could the same technique that is used to repair star cracks in car windscreen be used to repair stress cracks in GRP boats.