milky patches in clear gel coat

I'm posting this for an associate who recently purchased a new Bell Canoe in BlackGold (carbon/Kevlar composite weave) with clear gel coat via a "pro deal" discount. (Since the purchased involved a "pro deal" discount, there was no guarantee that minor imperfections would not be present.)

Bell's BlackGold lay-up under a clear gel coat appears carbon black, without any real hint of Kevlar's gold. Therefore, any imperfection in the gel coat distinctly stands out. This is the case with an area approximately 8" in diameter along the hull that has a milky-white cast.

Bell reportedly offered no explanation on the cause of such blooms, nor did they have any suggestion as to how such a condition might be corrected or minimized. My suspicion is that this is the result of trapped moisture between the gel coat and the composite, but this is just a suspicion. Has anyone else come across this problem before, or have experience as to it's cause? And is there any treatment or method that can be used to minimize or eliminate the bloom short of taking the gel coat down to the composite and applying a new gel coat?

Thanx! ...thom

 

Thom,

It could very well be "frothy" resin, if it's made with epoxy.

Yoke.

 

Yoke...

Thanx for the quick reply!

Just about all commercially built canoes, including boats from Bell Canoe Works, are put up with polyester resin versus epoxy resin.

...thom

 

Hi Buddy,

Firstly you will be pleased to hear your problem can be easily fixed.

Secondly, my suspicion is that it is a polyester gelcoat. Epoxy gelcoats are someone difficult to work with etc. In addition to this, polyester gelcoat is 10 a penny compared to epoxy. Very few people in industry use epoxy gel coats.

On a slightly different note, your canoe will most definately have the full hybrid layup (carbon/kevlar). Many different variations of hybrid fabrics exist. So dont worry that your canoe hasnt got any kevlar. Im sure the kelvar is under-neither the carbon. Look inside. Kelvar is yellow ish. I expect carbon is more aesthetically pleasing to look through a clear gelcoat, as kelvar is very difficult to cut. Actually you cant cut kelvar, it breaks by shearing it. THerefore the edges of the fibres usually go all stingly. Hence why you have a carbon outer skin. It just looks better,

Remember it was heavy discounted due to the surface defects, which may be more expensive to repair compared to manufacturing a complete new moulding. Labour is free of charge for you if you do-it-yourself.

I suspect your milky chalking can be a result of numerious factors.

1. Surface grime/grease in the mould.
2. Chemical attack.
3. Undercure of the polyester gelcoat. Thus by laminating onto an undercured gelcoat, the epoxy laminating system has inhibited the cure. Hence the milky chalk mark.

Either way, grind the affected areas back to the laminate below. Be careful not to damage the matrix below. Then re-gel. Usually most companies double gel. Apply 0.5mm of gel at a time and shear well with the brush. Build up a gelcoat thickness greater than required, and once fully cured, rub lightly. The trick is to use fine wet'n dry paper and not coarse. This helps eliminate porosity. If you dont shear the gelcoat upon application, you will hit porosity sooner when rubbing.

Once rubbed to something like 1200 grit, polish to a good shine. It would be worth while polishing the entire canoe. The whole job would only take a few hours.

Let me know if you have any problems. Hope this helps.

Buckle

p.s. I think you have an excellent bargin on your hands.