Gelcoat staining / pitting - what might have caused it?

[MattS]

I have some gelcoat damage on my cabin tops. I can't work out what might have caused it.

It follows a similar pattern on both sides of the cabin top, with the damage following a rough line along the gelcoat where the vinyl decals used to be attached. It also appears to end with a stained line running across the non-slip deck as if a liquid has run across it. The pattern seems too structured to be just random degradation with age?

Does anyone have any ideas as to what might have caused this sort of damage / staining? And if so, whether there's anything I can do to reduce the staining?



Up close, it's a mixture of small 'crazing' in the gelcoat, orange/brown staining, and what seem to be pitting in the gelcoat.

 

[Concerto]

Looking at the photos I can make these comments.

Photos 1 & 2 looks like a run off of acetone used to dissolve the remnants of adhesive.

Photo 3 looks like a reaction between the gel coat and the adhesive or the gel coat has been affected by the acetone and then UV light has discoloured the gel coat.

Photo 4 crazing is something I have seen on boats that are about 40 years old. What causes it, \i have never discovered.

Photo 5 - 9 the small bubbles in the gel coat were due to poor brushing out of the gel coat mix in the mould leaving these bubbles close to the surface of the gel coat.

It would be useful to know what boat we are talking about and when it was moulded. Also you might find my presentation on gel coat renovation worth looking at. https://wiki.westerly-owners.co.uk/images/8/86/Gel_coat_renovation_19May2020.pdf

 

[MattS]

Thanks @Concerto

1986 Moody 28

It makes sense that the run off could be related to using acetone on adhesive, and might explain the pattern of staining roughly around the previous vinyl

Re the bubbles I presume they will have been revealed over the years by polishing in that case? and I guess that they are more obvious around the staining where people have attempted to abrade away the staining in the gelcoat therefore

 

[Graham376]

Our 1988 Moody 376 has a few small areas of light crazing in the gel, in the radius where the sides of the coachroof meet the deck but all other surfaces are good. I had it down to gel getting thin maybe due to overzealous use of abrasive cleaner by previous owners over the years.

 

[MattS]

Our 1988 Moody 376 has a few small areas of light crazing in the gel, in the radius where the sides of the coachroof meet the deck but all other surfaces are good. I had it down to gel getting thin maybe due to overzealous use of abrasive cleaner by previous owners over the years.

I have that too @Graham376 - in the curved areas such as in the curved recesses underneath the teak handrail.

 

[johnlilley]

The crazing is almost certainly u/v damage
Occurs a lot on boats from a few builders, Westerly gel coat particularly so. Not structural but not easy to permanently disguise as painting does not always work as the crazing is inclined to print through unless you cut the gel coat back below the depth of the crazing.
The pitting is almost certainly as has been already noted, air pockets that have been exposed just under the gel coat. Aeration of the gel coat while she was being built. The liquid gel coat was possibly not left to stand for long enough after aggressive machine mixing. Not easy to fix as you cannot fill the little pockets as the air keeps pushing the filler out. Again, a necessity to sand the gel coat to open them more.
The staining.... Not sure but certainly related to the decal or decal removal method. Chemicals can cause gel coat staining, the best way of removing decals is with hot air from heat gun.... If you get the temp exactly right the come off easily including the glue... Too cold they tear and leave glue behind... too hot and they melt and tear. Plastic or wooden spatula won't hurt the gel coat.

 

[FairweatherDave]

Hmmmm. Went round my deck, cockpit and coach roof today looking at the gelcoat and applying some wax. Saw several (plenty) of examples similar to your photos. Westerly...1979.... Applied generous wax on the poor bits, life is too short.....and my DIY skills and motivation a bit on the light side. Interesting nothing like those photos on the hull above the antifoul.....a bit patchy from old repairs but none of the crazing or pitting. Does that gelcoat get an easier life than the deck and cockpit or is it easier to apply wax to the hull?

 

[Ammonite]

Our 1988 Moody 376 has a few small areas of light crazing in the gel, in the radius where the sides of the coachroof meet the deck but all other surfaces are good. I had it down to gel getting thin maybe due to overzealous use of abrasive cleaner by previous owners over the years.

A GRP guy I spoke two said it's because the gelcoat is thinner as what is now an inside radius was an outside radius in the mould and also because it gets more UV exposure due to the reflection off two surfaces.

 

[samfieldhouse]

I ad similar issues on my 1979 Cobra. Thankfully the gelcoat is thick so I attacked it with 800 grit wet and dry. I kept the gel coat wet and applied plenty of car shampoo as I went along to keep everything lubed.
I then moved increasingly through the grits; 800 - 1200 - 1600 - 2000 finishing off with 4000 wet mixed with T cut.
Final polish was with G3 which is great stuff. Worth it... bit only on the really noticeable bits!

 

[FairweatherDave]

I ad similar issues on my 1979 Cobra. Thankfully the gelcoat is thick so I attacked it with 800 grit wet and dry. I kept the gel coat wet and applied plenty of car shampoo as I went along to keep everything lubed.
I then moved increasingly through the grits; 800 - 1200 - 1600 - 2000 finishing off with 4000 wet mixed with T cut.
Final polish was with G3 which is great stuff. Worth it... bit only on the really noticeable bits!

Interesting. Westerly gelcoat is supposedly thick too but at the time when I did quite a lot of work on the deck around the bubbley gelcoat I exposed grey underneath which I took to be the start of the fibreglass so I stopped. I'm launching this week hence my dab of wax short term approach. I do appreciate nice gelcoat but on my deck that would take a serious amount of labour and time.

 

[Ammonite]

Interesting. Westerly gelcoat is supposedly thick too but at the time when I did quite a lot of work on the deck around the bubbley gelcoat I exposed grey underneath which I took to be the start of the fibreglass so I stopped. I'm launching this week hence my dab of wax short term approach. I do appreciate nice gelcoat but on my deck that would take a serious amount of labour and time.

Rather than trying to remove any fine UV crazing entirely and risk going through the gelcoat I use fine wet and dry (1500-2000 grit) with HG Mould Spray (which is basically bleach) as the lubricant. Most of the crazing and staining will dissappear (at least to the naked eye), although you do have to seal it with a good polish/wax having washed off the bleach or it will attract the dirt and reappear.