spider Cracks?

[H20fwler]

What is the proper way to fix spider cracks in jell coat on a fiberglass boat? These cracks are along the cabin section and not in structural areas. I think they are caused by sitting in the sun but it could be vibrations.

[jimslade]

spider cracks are caused by stress in the glass. the only way to fix them right is to grind out and re-gell.sorry there is no easy fix.

[John ilett]

Are spider cracks not usually just cracks in the gelcoat? As it is more brittle than the laminate, when something stresses the laminate too much such as flexing or something hard hitting the deck it cracks to resemble a web pattern. If the laminate seems ok then just grind the gel away and re do that spot. This is not to say that glass is not damaged but often it's just the gel.

Sometimes these spider cracks are in builders moulds too from accidental damage so the crack is then also moulded into each part made. You can tell if you look close. A moulded spider crack is nothing and could be cut and polished away.

[jimslade]

In my experiance if you don't grind a small amount of the glass away the spider crack will return.

[yipster]

i have some smaller than the spiders cracks but they are way down on the list, pitty there is no easy cure...
beside stres could it have anything to do with vinylester top / gel coat?

[jimslade]

No, vinyester is flexible compared to standard polyester resin. I would clean the gelcoat out with laquer thinner and regell with thinned out gell and hope for the best. You may get lucky.

[Guy G]

John is right! I have see a million in my life time and you have to go into the glass work 7 out of 10 times. Depending on age and area. Also you may want to look at how it was built, is there porosity in the area you ground out. People have a habit of putting cabosil in their gelcoat when they may of had a thin spot in the spray up. If thats the case, you'll be chasing cracks.
Good luck!

[yokebutt]

Fwler,

Frequently, small cracks in the gelcoat is nothing to worry about, but it can be a sign of something being seriously wrong, it all depends on where they are and what they look like. Often, cracks are just a result of gelcoat being applied too thickly in the mold.

That said, a crack IS a local stress-riser and CAN work itself into the underlying laminate over time.

Yoke.

[yokebutt]

Jim,

Vinylester is not necessarily always stretchier than polyester, it depends on what it's formulated for, always read the documentation on materials carefully before using.

Yoke.

[Buckle]

before grinding away, eliminate the stress concentration/sourse before hand. check for bulkheads behind, mechanical fastening etc near by. Often these act as a stress concentrator. Sometimes, Grinding away, laminating and repairing isnt the solution, as the cracks will come back. u need to elimate the problem before. perhpas theres a need to stiffen the backside of the laminate.

Many grp boat builds have numerious warantee issues. 50% of most boat manufactures do. the other 50% also do, but their customers havent noticed that they also have a problem.

[fiberglass jack]

super glue does the trick,take a blade and score along the cracks a couple of mils to make a v then put some superglue into the gap .theres even a superglue called gap filler just for this let dry and sand any high point then paint or gell i do this all the time in the boatshop what better to stick polyester together trust me it works.never had a job come back.some times the cracks are in the mold when they layup the boat from banging with hammers and so on and transfrere to the boat they sand and plosh them out before they sell it but sometimes come back just sand and polsh and see what happen first before you start cuting away on your boat

[Buckle]

I've heard of numerous ways to find quick fixes for gel repairs but that takes the... What do you tell customers about the colour differential over cracked areas? - or do they accept that as the norm? I wouldnt like to place money on that bodge lasting - have you ever considered how the superglue would weather in respect to the gelcoat, provided it last? You are asking for warantee issues Jack? Superglue is relatively brittel. It has no elongation and would therefore fail.

Once the crack is been ground out, you can save time by blading (with a stanley blade etc) gel into the ground area. The blade helps to fair the surface, minimising the repair, which induces porosity at the surface.

[westsail42]

More data...

Structural flexing may not the only cause of spider cracks. My westsail, still in kit form, has spider cracks all over the deck. It has been sitting on the hard in the sun for the past 30 years. So structural flexing could not be the cause. Must have been the sun. We also determined the gelcoat was applied a bit thick at the factory, which did not help things.

Yes, the only sure "repair" is to grind/fair/paint.

Or find a way to cover it up as spider cracks are more of a cosmetic problem in most cases.

[fiberglass jack]

it works trust me after u fill the cracks paint the area use this in non structual area forfot to say that but get 2 pieces of fiberglass and glue them then try to pull them apart the glass will rip apart a better bond then resin loctite sells a glue called gapfiller which is a thick form of everyday superglue.

[fiberglass jack]

u can take a grinder and remove all the area and replace with glass and gell over the area. this is the best way .some shops use a dremel and put a putty into the removed areas then gell

[wdnboatbuilder]

Could it be caused by the fact that polyester's never stop hardening.

[Buckle]

wdnboatbuilder - I think you may be mis-guided somewhat. There are many wife tells in the industry, I think you many have half the story using the expression "polyester's never stop hardening".

When you catalyst a polyester or vinly ester product, be it gel coat, barrier coat, resin etc, the product will reach a state of cure after a given time frame. Lets assume after 24 hours at room temperature, the laminate will cure to have a HDT (heat distortion temperature) of 28. If you were to measure the HDT after a month at room temperature, this would have risen to something typically around 50/55 degrees C.

HDT can be influcenced by many factors, such as cataylst/accelerator quantities, type of resin system, mould technology, laminate design, manufacturing schedule etc, etc.

You would of most probably heard of post curing. Post curing is basically about increasing the HDT of the laminate and gaining the advantages that follow such as stabilization of the laminate (very important for surface finish issues etc), better mechanical properties etc, etc. The aim of post curing is to subject the laminate to a temperature greater than that it would be subjected to operate in. Generally, the hotter the post cure, the higher the HDT.

But what happens if you dont post cure the product? - Well the product typically undergoes its own natural post cure, althought most people aren't aware of it. The environment in which you boat etc is in is constantly undergoing a post cure cycle by means of the sun. Look at the side of any boat. The side which usually faces south has weathered to a great degree than the opposite side.

Going to back to the laminate after a month's worth of room temperature cure, the HDT would rise from 55 to 70 odd when subjected to natural heat.

If the laminate undergoes heating to a degree greater than the Tg (glass transition temperature) of the laminate, the laminate will naturally creep, leading to stress concentrations, which typically lead to gel coat cracking etc.

I think you may of basically being trying to say what I have just said. If you didnt, you learn something each day.

Remember, go forth and increase you HDT today.

Buckle

[wdnboatbuilder]

Fair enough