gelcoat bow repair with silica thickener added ?

[tomboy352]

Hi my pontoon lines slacked off under load in a winter gale resulting in damage where the bow tried to cut into the pontoon, before the staff saw the problem,

In the past I have repaired small blemishes using clingfilm and tape to hold the gelcoat. As the damage just reaches the matting and is a larger area I was thinking of thickening the gelcoat with white silica dust as is used to thicken resin. The depth of the scar doesnt warrant a layer of matting or even filler. The gelcoat is thicker on the bow.


I have never tried this with gelcoat before . I wondered if it would leave a good finish or if I would have to paint a thin layer over the nearly finished level and rub down to complete the job. Has anyone experience of this ?

Chris

 

[Neeves]

I'm no expert. I have used thickened epoxy, let it set off, sanded down then used a matching white gel coat as a finish. If you are down to the glass I would ensure there is nothing loose, damaged epoxy or gelcoat, paint with epoxy over the whole damage area, to ensure the next layer is wetted completely to the underling and undamaged glass mat. I would spread on a layer of filled epoxy so that the thickened epoxy stands proud. Use packing tape to ensure no sag of the 2 layers, thin layer of epoxy and thicker layer of thickened epoxy. I'd leave to set off, sand down and then paint with a matching white gelcoat.

You may find you don't get the first batch of filler properly fair and need to fill a bit more, again wet out with 100% epoxy, and then sand again. Similarly you might find you do not get the gelcoat quite right and need a second coat.

I think if you fill white gelcoat you will find you will lose the gloss finish and the repair will be more noticeable. It may also be difficult to add filler to gelcoat and you may find when it cures - it has bubbles in it. Maybe it does not matter but white gel coat is more expensive than filled epoxy (you don't mention volumes needed).

I'd not try to rush the repairs nor save a stg pound or 3.

I'd check on the inside of the hull that the interior has no cracks - damage may be greater, or more easily seen, looking from the interior.

Jonathan

 

[RJJ]

Silica is very strong and very hard....therefore difficult to get a good finish in my experience

I would be tempted to go for silica to fill any significant holes, then one of the easily-sanded fillers on top. West systems website has a good table outlining the various filler powders on offer. I can’t see why you couldn't use it for gelcoat as you suggest.

 

[Hunterlees]

I have had success in the past on vertical surfaces using unthickened gelcoat, but taping Melinex sheet (Mylar) over the area. If enough gelcoat is used, then when the Melinex is taped over it flattens it off slightly proud without it running down and this can then be sanded and polished. Hope that makes sense.

 

[V1701]

Depending on what you're using and where good old fashioned waxed/greaseproof paper can be very useful to get filler into shape. it peels away nice and easily after it's gone off...

 

[Concerto]

Personally if you have a white gel coat, I would use Teroson Gel Coat Filler. It is polyester based and a similar hardness to gel coat, which makes it easy sand smooth. Have a look at this PowerPoint presentation I made to the Westerly Owners Association. Plenty of advice provided.

https://wiki.westerly-owners.co.uk/images/8/86/Gel_coat_renovation_19May2020.pdf

 

[William_H]

My choice would be polyurethane 2 pack paint. Assuming you want white or can get the paint coloured to match. PU is a resin so you could use a filler if the holes are deep or just do several coats to get up to level. Sanding each time. PU has very good adhesion and is UV resistant. ol'will

 

[Ceirwan]

My choice would be polyurethane 2 pack paint. Assuming you want white or can get the paint coloured to match. PU is a resin so you could use a filler if the holes are deep or just do several coats to get up to level. Sanding each time. PU has very good adhesion and is UV resistant. ol'will

Repainting the whole boat just to repair some gelcoat damage is rather extreme.
If you don't repaint the whole boat, then a paint repair will always look like a repair, properly matched and blended gelcoat will be practically invisible.

To the OP.
Yes you can thicken the gelcoat with collidial silica, it works well, although it will have an effect on the colour and gloss.

Best is normally to sand damage out to a nice transition, fair flush with the thickened gelcoat, then sand back the filled area a little, and finally put a few coats over the area again with wax in the final coat this time.
I have had success using gelcoat with wax already added (flowcoat), but you need to do your next coats before the previous one has fully setup, otherwise you'd need to dewax and sand between every coat.
Sand, wet sand, cutting compound & polish.

 

[tomboy352]

Repainting the whole boat just to repair some gelcoat damage is rather extreme.
If you don't repaint the whole boat, then a paint repair will always look like a repair, properly matched and blended gelcoat will be practically invisible.

To the OP.
Yes you can thicken the gelcoat with collidial silica, it works well, although it will have an effect on the colour and gloss.

Best is normally to sand damage out to a nice transition, fair flush with the thickened gelcoat, then sand back the filled area a little, and finally put a few coats over the area again with wax in the final coat this time.
I have had success using gelcoat with wax already added (flowcoat), but you need to do your next coats before the previous one has fully setup, otherwise you'd need to dewax and sand between every coat.
Sand, wet sand, cutting compound & polish.

Thanks, This is my prefered option. I have ordered a gelcoat match from Halbergrassy at £42 for a sample size and Im off to Glasgow , so I will pick up some parafin wax from Allscot Distributors as my last lot has dissappeared in the bottle
Prepare Job
nearly fill with a gelcoat/silica mix
sand down, finish with flow coat with wax added
final wet sand and polish

Double up on my winter spring lines !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Chris

 

[William_H]

Repainting the whole boat just to repair some gelcoat damage is rather extreme.
If you don't repaint the whole boat, then a paint repair will always look like a repair, properly matched and blended gelcoat will be practically invisible.

Now there is a wild statement if ever I heard one. (are you a politician? ) I think in fact any repair will always look like a repair. PU paint can be tinted like polyester resin (gel coat). if OP pays top dollar for gel coat from the boat builder yes he might get close to colour match but will it allow for fading or colur change over time of the rest of the boat. ol'will

 

[Ceirwan]

Now there is a wild statement if ever I heard one. (are you a politician? ) I think in fact any repair will always look like a repair. PU paint can be tinted like polyester resin (gel coat). if OP pays top dollar for gel coat from the boat builder yes he might get close to colour match but will it allow for fading or colur change over time of the rest of the boat. ol'will

Not sure what politicians have to do with it?
I'm just stating the facts, like most things, there's a correct way & there's a bodge, the OP can make his own mind up, but you can't repair gelcoat damage with paint.
You can either fill and paint a patch, that will always look like a patch that sits proud of the surrounding gelcoat. Even if you got the paint the exact same colour, it would still sit proud and have a different gloss level.
You'd be just as well using a generic white gelcoat filler. Which would also be a lot cheaper than a 2 part polyurethane paint.
That said, a boat properly painted with a 2 part poly will look absolutely fantastic. Expensive though.

If the OP doesn't want to have a go at color matching then quite often the local repair guy will be able to mix him a small batch for a fee and do the matching for him, although I see he ordered it already from the manufacturer.

A properly done gelcoat repair will be invisible, I know of boats that have had massive holes repaired and you really can't tell.

Thanks, This is my prefered option. I have ordered a gelcoat match from Halbergrassy at £42 for a sample size and Im off to Glasgow , so I will pick up some parafin wax from Allscot Distributors as my last lot has dissappeared in the bottle
Prepare Job
nearly fill with a gelcoat/silica mix
sand down, finish with flow coat with wax added
final wet sand and polish

Double up on my winter spring lines !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Chris

Sounds good to me, you will probably want 2-3 coats if possible, rolled is best if you can't spray, with brushing you often have to sand most of it off again.
A guide coat really helps you nail the sanding without going too far.

If you want some really good advice on the subject then google for 'Minaret gelcoat repair cruiser forum', he's a professional resin guy who has written tons of fantastic advice on how normal folks like us can get a great professional finish.