Repairing gelcoat dinks and scratches

[SAWDOC]

Hi folks
Some people advising covering a new gelcoat repair with clingfilm or similar( mylar), presumably to help the gelcoat set properly (not sure of that?). Is it neccessary and what exactly is the purpose of the covering?
Thanks

 

[prv]

Gelcoat doesn't set properly with air on it, not sure why. In normal layup it will be against the mould with no air on it anyway, but when touching up you need to make other arrangements. Covering with film is one, the alternative is to mix in 2% of "wax in styrene" along with the catalyst. This forms a wax layer on the outside (not of noticeable thickness) and lets it set properly. Otherwise it stays tacky.

Gelcoat with the wax premixed is available, called flowcoat, but usually used as robust paint eg in bilges, rather than for touchup.

Pete

 

[OGITD]

I think it’s all Bollox!

I’ve seen many strange patches left on other people’s boats after being covered with Clingfilm / Sellotape etc.
Plastic Padding (Gel Coat) doesn’t require additional wax, just mix & use ensuring the scratch is carefully prepared and cleaned with acetone then apply styrene a couple of minutes before the Gel-Coat, this giving a mechanical and chemical bond.
Wet & dry (all the req grades) then cut & polish to a professional invisible permanent finish.
Colour compound added if required to match boat.
Or you can buy the Gel-Coat and add the wax & hardener etc yourself.

 

[Iain C]

Part of the idea is to reduce sanding. Use Mylar, and you end up with a mirror smooth repair that you only need to feather the edges of. Obviously this won't work with stuff like cling film!

 

[Quandary]

3M make a superior version of sellotape that is slightly opaque on the surface, you could write on it and it became clear when rubbed down, we used to use it a lot in the drawing office in the days of tracing paper and plastic drawing film.
I discovered that it is much easier to use than ordinary sellotape over scratches when filling with gelcoat as it is easier to position, lies flatter and is stronger but still sufficiently clear to see through to allow you to stroke it smooth and eliminate bubbles. I still have a roll but the box is long gone and the roll itself is not labelled. I never could get a smooth surface with clingfilm it is just not stiff enough and does not adhere well enough.

 

[Clyde_Wanderer]

Whether using Mylar or tape better using proper gel-coat and as Pete says add wax only to the last coat.
Not using wax means the gel stays tacky/gummy and cant be sanded.
If you go to a proper GRP supplies store you will get a small bottle of wax with the gel.
You will have to sand down either way.
Using a hot air gun helps quick cure so you wont have to hang about waiting for cure.
Mixing a hot mix (plenty catylist) will also aid fast cure.
C_W

 

[lw395]

I’ve seen many strange patches left on other people’s boats after being covered with Clingfilm / Sellotape etc.
Plastic Padding (Gel Coat) doesn’t require additional wax,.......

I have always found gelcoat filler to be totally inferior to real gelcoat. It tends to discolour after a while, and is not as tough.
Best results for me have been covering gelcoat with plain polythene. If it's wider thah just a scratch, stretching the polythene over a flat, smooth piece of plastic helps get a flush surface.
If it's a narrow scratch, a piece of sellotape either side of the scratch masks the surrounding area and allows you to fill slightly proud of the surface. Sellotape is thinner than masking tape, so less sanding back. Somehow filling exactly flush never seems to work out for me?

By the way, W+D paper is now available in ever finer grades, I find 2000 Grit is a worthwhile step on the way to polishing.

 

[lw395]

Top tip, get a small syringe and measure the catalyst. Guessing is just a bad idea.

 

[nigelmercier]

I’ve seen many strange patches left on other people’s boats after being covered with Clingfilm / Sellotape etc.
Plastic Padding (Gel Coat) doesn’t require additional wax, just mix & use ...

I've never seen a repair covered by tape, but it's a good idea to mask closely around the area before using Plastic Padding Gelcoat Filler. This raises the fill slightly so you can sand it, and stops the stuff from going everywhere - it's a nightmare to spread evenly.

 

[alandee]

Using tape over Gelcoat repairs

3M make a superior version of sellotape that is slightly opaque on the surface, you could write on it and it became clear when rubbed down, we used to use it a lot in the drawing office in the days of tracing paper and plastic drawing film... ...I still have a roll but the box is long gone and the roll itself is not labelled. I never could get a smooth surface with clingfilm it is just not stiff enough and does not adhere well enough.

For anyone who is interested it is called 'Scotch Magic Tape' made by 3M. Available in drawing office supply shops.

 

[ripvan1]

Part of the idea is to reduce sanding. Use Mylar, and you end up with a mirror smooth repair that you only need to feather the edges of. Obviously this won't work with stuff like cling film!

Does anyone have link to suppliers of Mylar sheeting please ?

Thanks

 

[OGITD]

Does anyone have link to suppliers of Mylar sheeting please ?
Thanks

Have a look here.

 

[Deleted member 36384]

Transtext - If Larger Areas Are Required

3M make a superior version of sellotape that is slightly opaque on the surface, ...... in the drawing office in the days of tracing paper and plastic drawing film. ......

Transtext is a clear film that is sticky on one side and is typically A4 in size. Available from drawing office supplies. I have used that to cover a repair on the surface that was a bit wider.

Transtext - the bane of office managers as it would clog up photocopiers but great when updating old drawings. Prevented redrawing huge sections when old paper drawings were copied to film. It is a good medium to print a design on and then stick to a hull where you need to transfer an image.

Transtext

 

[SAWDOC]

Colour compound added if required to match boat.
QUOTE]

From first efforts with Plastic padding, I seem to have a colour difference between repair and original gelcoat. Is adding colour compound practical for a small repair area and secondly any how to guide?

Thanks

 

[Quandary]

Your boat is white and believe it or not this is the easiest colour to repair small scratches etc. The new stuff is certain to be whiter than the original which has been exposed to light heat etc. for years, even if you use the original gel it will look whiter at first. When you begin to rub down with ever finer grades of wet and dry (600 to 1200) then polish the rubbing will blur the edges and the whole area will look a bit whiter at first. I have never been good at tinting to match white gel coat and have given up on it but still think I can do an unnoticeable (but not invisible) repair. If you do want to try tinting, rub down the gel coat first to expose the true shade and mix your tint right there on the surface. Since you will be keeping this boat for a few years my expectation is that the shades will blend with time. I find this is helped by cleaning with a cleaning/polishing wax like 3M every year as it seems to help but this might be just because I get less sensitive to the touch up bits as time passes and I may have become reconciled to a finish a few degrees lower than perfection.
This all applies to small dents or scratches, a big area is a job for a professional who has access to stuff you wont have.
I helped a neighbour in the boatyard last spring painting two pack on a Dutch high quality steel hull (fine roller, laid off vertically with a pad, a min. two man job) the colour was a very dark blue and even in Scotland in March we had trouble with the heat but the evenness of the gloss we got was very satisfying. A much smaller boat beside us was painted with one pack gloss by the owner working on his own and he just could not keep up with the wet edge to get any thing like the finish.

 

[OGITD]

I was there today!

Colour compound added if required to match boat.
QUOTE]
From first efforts with Plastic padding, I seem to have a colour difference between repair and original gelcoat. Is adding colour compound practical for a small repair area and secondly any how to guide?
Thanks

Allscot on my way back from E-Borough.

And was informed it's 10% of their colour pigment added to the clear Gel-Coat for a match in relation to their colour chart.

 

[SAWDOC]

Thanks Quandary
Are colour or tinting products widely available? - I haven't come across them.

 

[Clyde_Wanderer]

Thanks Quandary
Are colour or tinting products widely available? - I haven't come across them.

One way to get the colour close is to use the gel dust from the sanding, adding it to the new gel helps blend the job better.
When mixing pigments into clear gel, add some pigment aprox 5% by volume stir in well then hold stirrer up to the light and look at the gel as it runs off the stirrer if you see any light through the gel add more pigment until the mixture is completly opaque.
Dont use plastic padding gel filler its c**p and will never finnish perfectly.
C_W

 

[SAWDOC]

One way to get the colour close is to use the gel dust from the sanding, adding it to the new gel helps blend the job better.
When mixing pigments into clear gel, add some pigment aprox 5% by volume stir in well then hold stirrer up to the light and look at the gel as it runs off the stirrer if you see any light through the gel add more pigment until the mixture is completly opaque.
Dont use plastic padding gel filler its c**p and will never finnish perfectly.
C_W

What alternative would you recommend for gel coat filler?

 

[OGITD]

It's not & it does!

Dont use plastic padding gel filler its c**p and will never finnish perfectly.
C_W

It just takes all the grades, a few cups of Tea & some time.

I suppose I’ll just have to take photos next time & post for all to see…. but then some will say that there was never any damage in the first place.