Gelcoat Deck Repairs

[MattA24]

Hello, many thanks again for all the kind advice this board has offered me so far. I'm afraid I have a few more questions though:

The gel-coat decks, coachroof, and cockpit of my boat need lots and lots of little repairs. Things like osmosis blisters, old screw-holes, and a few impact marks.

I'm trying to decide between fixing the holes with gelcoat repair filler, or filling them with thickened epoxy and then painting over the entire deck.

I'd love to keep the gelcoat, but I'm concerned that with so many patches of little repairs to do, the boat will end up looking really spotty.

I'm also concerned that with gelcoat filler being polyester based, it will shrink and crack like every bit of car body filler I've ever seen.

Has anyone suffered from either of these problems? Would you advocate trying to keep the gel, or epoxying and painting over the lot?

Finally, some areas of the gelcoat appear to have little pin-holes in it, similar to paint that has bubbles of air in it while it dries. They look like they have been there since the boat was made (70's). What should I do with them?

Cheers!
Matt

 

[maby]

I would certainly have a go at repairing the gelcoat first - it is much easier to do an almost invisible gelcoat repair than it is to do a really good job of painting old GRP.

A lot will depend on how discoloured the existing gelcoat is - will it come up really white if you give it a good buffing with a cutting compound? Get a tube of Plastic Padding gelcoat repair paste and experiment - even if you do eventually decide to paint it all, you will need to fill out the damage first and the gelcoat paste will be fine for that. I think you may be pleasantly surprised - I repaired a gelcoat ding over the weekend and had great difficulty finding it the following day.

You'll need to grind back the damage to get a good clean base and feather the edges so that you can blend the repair in. I used a Dremel type tool with a small spherical grind stone - don't be afraid to go deep enough and make sure you feather back a couple of mm around the hole. Then mask it up with masking tape all round the area to be filled - this is important if you want to be able to blend it all in. Mask up close to the edge of your feathering. You need to get it really clean before applying the paste - I just dusted it out with a soft brush, but cleaning it with acetone might be a better idea.

Mix the paste according to the instructions, then spread it into the hole using a flexible spatula. I used an artist's pallet knife which is very flexible and has smooth edges which leave a good finish. Spread it out to the masking tape and try to get a good smooth surface using the spatula - the thickness of the masking tape will allow you to achieve a good flat surface with just a thin layer to sand back. Peel off the masking tape before the paste has hardened and resist all temptation to touch it for at least ten minutes!

Give it the recommended period of time to harden, then carefully smooth it back with very fine wet-and-dry used wet. Unless you are doing a very large area, do it by hand - power sanders are far too difficult to control in order to match the profile of the original surface. Once you've matched the repair into the original surface, bring the shine up with a fine cutting compound and apply plenty of polish - provided the original gelcoat is not too discoloured, it should be hard to see the repair. If it is, you've lost nothing - just slap on the paint!

 

[oldsaltoz]

You can apply flow-coat over the old gel-coat and cover the whole area.

Note: Flow-coat and Gel-coat are the same thing, Flow-coat is Gel-coat but with a wax added, this means you do not have to put plastic sheeting over it to get to cure.

So, the first step is to clean the area, and it MUST be clean, this means a good wash with a strong detergent and lots of scrubbing, then a wipe with some Acetone on a white rag.

Next carry out and minor repairs / fills etc, give it another clean down and wipe with acetone then apply the flow-coat with a little less that normal catalyst to allow for the extra solids in the resin and apply with a brush and wipe with a pad, but only very thin and keep a wet edge at all times, the wet edge is important if you want a good result..

When you have completed the thin coat apply the second coat using the same procedure.

Thin coats tend to give a better finish than a single heavy coat. So if you are not too concerned, just apply a single coat.

The finish will last a hole lot longer than any paint.

Good luck and fair winds.

 

[MattA24]

Hi Maby,

I was wary of the plastic padding stuff, because it's made by plastic padding and thus I am suspicious it is just car body filler. I'm glad to hear you've had good results with it, as my boatyard chandler's has in stock, which is convenient.

Hi OldSaltOz,

Flowcoat sounds very interesting indeed. Can I double-check that you are advocating filling holes, etc, with the filler of my choice (eg epoxy, which I've got lots of) then applying Flowcoat over the top to protect and blend the repair?

And if so, should I get the filler material level and smooth with the deck, or slightly recessed to account for the depth of the flowcoat?

Also, out of interest, can flowcoat be thickened to any useful end?

Thanks for both of your suggestions.

 

[oldsaltoz]

Hi Maby,

Hi OldSaltOz,

Flowcoat sounds very interesting indeed. Can I double-check that you are advocating filling holes, etc, with the filler of my choice (eg epoxy, which I've got lots of) then applying Flowcoat over the top to protect and blend the repair?

And if so, should I get the filler material level and smooth with the deck, or slightly recessed to account for the depth of the flowcoat?

Also, out of interest, can flowcoat be thickened to any useful end?

Thanks for your suggestions.

The application of any Poly resin is not good over and epoxy, it dose not bond well, unlike epoxy over poly that bonds very well both maniacally and chemically.

Yes, repairs should be smooth prior to applying the flow-coat.

You can thicken flow-coat by adding a filler (talcum powder or other fillers) but, it serves no real purpose and may weaken it and certainly change the colour. The application of successive thin coats produces a very smooth and high gloss finish.

I suspect the old you tube will have some interesting content.

Don't ever forget that a good is finish is 99% due to good preparation thoufg.

Good luck and fair winds.

 

[maby]

Just to add to OldSaltOz's advice - flow-coat is quite fluid and you will not build up any significant thickness quickly - you need to get the surface into decent condition first, then apply flow-coat over it - you are effectively replacing the old gelcoat with a nice new layer. Whether you go down the flow-coat or the gel-coat filler route really depends on the scale of repairs you need to make. If you have a relatively small number of chips and gashes in a gelcoat that is otherwise restorable, then it makes sense to fill them out with a gelcoat repair paste. If there are many repairs to be made or the existing gelcoat is beyond restoration, then fill the holes and apply flow-coat effectively as a paint-on gelcoat.

If you are repairing damage to a relatively new boat, it is probably better to go back to the manufacturer for the specific gelcoat that is used on the production line - there are many different shades of "white". I had a tube of the generic Plastic Padding paste in the draw and decided to give it a try - it is not a perfect match to Beneteau white, but I would defy you to find the repair without guidance from me - it took me quite a long time the following day to find it! They are all variations on epoxy resin and I'm sure that it has a lot in common with Plastic Padding car filler, but it works and you can pick it up in the chandlery rather than having to order it from the boat's manufacturer. On an older boat such as the one you describe, any attempt at obtaining the original gelcoat mixture is unlikely to meet with success so you really have to go with a generic paste, or use flow-coat to cover it all up.

 

[JimC]

Flow-coat is Gel-coat but with a wax added, this means you do not have to put plastic sheeting over it to get to cure.... When you have completed the thin coat apply the second coat using the same procedure.

Won't the wax on the surface of the first coat prevent the second coat bonding to it?

 

[paul-essex]

So What is the trick to painting on "flow coat " with a brush ( on vertical surfaces ) and not get brush marks,
I tend to put it on , rub it down to get rid of brush marks and end up having to put another coat on again and again

 

[Marine Reflections]

So What is the trick to painting on "flow coat " with a brush ( on vertical surfaces ) and not get brush marks,
I tend to put it on , rub it down to get rid of brush marks and end up having to put another coat on again and again

Only the last coat is flow, all others prior are normal gel and use a roller not a brush if possible.

 

[Marine Reflections]

Won't the wax on the surface of the first coat prevent the second coat bonding to it?

Yes.

 

[maby]

So What is the trick to painting on "flow coat " with a brush ( on vertical surfaces ) and not get brush marks,
I tend to put it on , rub it down to get rid of brush marks and end up having to put another coat on again and again

Which is why I suggested trying to fill the damage with paste rather than coating the entire surface - provided you can get a decent colour match, it is easier unless the total number of holes is great.

 

[wiggy]

And how do you get the moulded in deck grip pattern back? I've got some damage in the grip area, could I make a plasticine mould and add after filling and smoothing filled with gel coat fillet?

 

[MattA24]

Hi,

Thanks again everyone here, a huge amount of information and lots to think about.

After reviewing my options I think I'm going to fill the gaps with the plastic-padding style filler, then possibly flow-coat over the top if it looks patchy afterwards. Does this sound sensible?

A few more questions if I may:
- It has been mentioned on this tread that a second layer of flow-coat wont stick to a first because of the wax. Is this the consensus?
- Does anyone have a recommended substance (easily obtainable in the uk) to dewax the existing gel? How do you know when the wax is gone?
- Out of interest, is there anything that can be done to persuade a polyester coating (eg flow-coat) to adhere to cured epoxy?

Again, my deepest thanks for offering your advice,
Matt

 

[William_H]

I don't think the wax in flow coat is a problem at all in subsequent layers. The wax is initially dissolved in the resin so will easily dissolve in subsequent resin layers. If the next layer is put on not to long after the first it will chemically bond anyway. ie after it has gelled or gone reasonably hard but not really cured as occurs after few days.
There is no way to get polyester to adhere to epoxy except by mechanical bonding which is done by roughing up the surface. Which will probably be adquate anyway.
As mantioned it is area of non skid that causes the biggest problems in deck repairs. There are sort of silicon rubber molds that are available to mold in the non skid into repairs though I have never tried it. In my case I painted the whole deck with polyurethane 2 pack paint which does adhere well and is tough. I added particles to the final coat (Inter grip)
This can easily be either too harsh or too smooth but it does sort of look OK in disgusing the smooth areas where before it was non skid.
Don't do what I did and paint with gloss white. It keeps the boat cool but I can't sail without sun glasses. good luck olewill

 

[maby]

And how do you get the moulded in deck grip pattern back? I've got some damage in the grip area, could I make a plasticine mould and add after filling and smoothing filled with gel coat fillet?

That's what the professionals do - I watched one fix a GRP void on our previous boat. I believe he used modelling latex - which you should be able to get on the web. He put a small ring on the non-slip deck close to the place he was going to repair, poured in some of this latex, waited for it to set, lifted it off, filled out the void and pressed his new mould on to it. It took him a couple of attempts, but it was difficult to see where the repair was afterwards. I guess he may have used some kind of wax or grease as a release agent to stop the gelcoat sticking to the mould - I didn't see that bit.

 

[Jim@sea]

Hi Maby,

I was wary of the plastic padding stuff, because it's made by plastic padding and thus I am suspicious it is just car body filler.
.

I was an expert with car body filler as I had a bodyshop for 25 years. (But an amateur in repairing boats).
It seems to me that Plastic Padding have 3 products and the "Marine Filler" is ordinary car body filler, called Bog or Slonk. They also have a "two tin product" which is better for boats called Marine Epoxy which can be used below the waterline which presumably makes it better for above the waterline. The only problem with this stuff is that there is a lot of "old stock" about which has hardened off in the tins and is difficult to mix. I had some left over from 2006 which I used up and when I bought some last week (2014) it was also difficult to mix and when I compared the batch numbers (on the lid of the tins) they were the same so Plastic Padding must have imported an awful lot pre 2006. So try the International two pot stuff instead.
The stuff which is good is the Plastic Padding "Gelcoat Filler" (White) and it is this I am using to repair any damage on my boat.

 

[Marine Reflections]

That's what the professionals do - I watched one fix a GRP void on our previous boat. I believe he used modelling latex - which you should be able to get on the web. He put a small ring on the non-slip deck close to the place he was going to repair, poured in some of this latex, waited for it to set, lifted it off, filled out the void and pressed his new mould on to it. It took him a couple of attempts, but it was difficult to see where the repair was afterwards. I guess he may have used some kind of wax or grease as a release agent to stop the gelcoat sticking to the mould - I didn't see that bit.

Correct, it's exactly how it's done and yes he would have used a release agent.

You don't apply over the top of flowcoat without first removing the wax. It won't bond for long if at all.

As we know the difference between gel coat and flowcoat is simply the addition of wax.
Gel coat will not cure fully whilst exposed to oxygen, it will set but will still be tacky and sanding will be a joke.
It will need to be sealed off to cure fully with a light misting of PVA or covered with a release film for example. As long as no oxygen gets to the gel it will cure fully.

To make flowcoat, a liquid wax solution is added prior to adding the curing catalyst. This wax will migrate to the surface of the repair forming a wax barrier to oxygen and allowing the gel to cure fully without the need of PVA or having to cover the repair.
You will then be able the sand and shape the repair how you want.

To de-wax use acetone.

For a diy solution to repairs as others have mentioned the plastic padding type is fine, it is simply car body repair filler with white pigment added, it will fill and fair easily. It won't provide an invisible repair but will be doing a good job of keeping water and moisture out of the glass fibres.

 

[Marine Reflections]

Hello, many thanks again for all the kind advice this board has offered me so far. I'm afraid I have a few more questions though:

The gel-coat decks, coachroof, and cockpit of my boat need lots and lots of little repairs. Things like osmosis blisters, old screw-holes, and a few impact marks.

I'm trying to decide between fixing the holes with gelcoat repair filler, or filling them with thickened epoxy and then painting over the entire deck.

I'd love to keep the gelcoat, but I'm concerned that with so many patches of little repairs to do, the boat will end up looking really spotty.

I'm also concerned that with gelcoat filler being polyester based, it will shrink and crack like every bit of car body filler I've ever seen.

Has anyone suffered from either of these problems? Would you advocate trying to keep the gel, or epoxying and painting over the lot?

Finally, some areas of the gelcoat appear to have little pin-holes in it, similar to paint that has bubbles of air in it while it dries. They look like they have been there since the boat was made (70's). What should I do with them?

Cheers!
Matt

Hi Matt,

You are correct in your thinking, the 'temporary' car body type of filler is just that, temporary. It serves a purpose for a quick repair as mentioned above, but will cause further problems down the line. It is for this reason professionals don't use it but use gel coat that has some filing additive added - colloidal silica, talc etc.

The pin holes are just where oxygen has been trapped in the gel, probably too much catalyst when curing or mixing additives before catalyst but not allowing the introduced air to escape before adding catalyst.
The trapped oxygen bubbles are then exposed whilst sanding to contour, or rise to the surface of the mould.

These can be drilled out with a dremel or similar and filled as normal repairs. They cant be just filled as there will be a substantial amount or old wax, dirt etc within each hole.

The trick of all you are asking is to zero in on finding the exact colour match for your gelcoat. You will then have all the filler and coatings you need without fear of it being patchy. Once each repair is done you will not be able to see them at all. Ok might need some practice for the last bit
Colour matching can be quite tricky at first, but is just the same as an artist replicating the colours in a scene.

You will need to find some gel coat that has not discolored over time, a panel in the cockpit for example, or expose some fresh gel by sanding and then polishing back to a reflection.
Buy some various pigments that you suspect are the additional colour from white - Ivory for example and have a play.
Use the existing gel coat as a palette, touch some white gel coat on your finger and then onto the area, add a tiny amount of pigment next to it and rub them together to see if you are getting close with that choice of pigment.
You will soon see if you need to add more or less pigment, or even an additional colour.

As there are many thousands of shades of white it can be frustrating, but highly rewarding when you get it spot on.
Gel coat dries the same colour as it was when wet so you can experiment as long as you need to before adding the catalyst.

Just to mention - any additives in gelcoat should be added before adding catalyst.

 

[MattA24]

Hello everyone,

Again, thanks for the overwhelming quantity of information.

Someone here mentioned that sticking flowcoat (or any polyester) over epoxy will only bond mechanically, which I'm sure is true, but got me thinking: Isn't this true of almost everything I'd apply flow-coat over, and in particular, my original gel coat?

Which then makes me wonder, is there someone that can be done to existent original gel to chemically reactivate it after all these years, and allow the new stuff to chemically bond?

Matt

 

[Marine Reflections]

Yes, Styrene can be used to reactivate the existing gel coat prior to a fresh application.
It makes it more receptive.

You will still need an exposed, clean, rough yet smooth surface to adhere to though as it exposes more surface area and creates a better interlocking bond.

Just to mention, chemicals such as Styrene and gel coat catalyst need to be handled with extreme care and consideration, as does the working area.

Gas / vapour masks, eye protection and gloves are absolutely vital, even in a well ventilated environment.