Wet and dry theory!

[pcatterall]

Previously I posted about restoring the gell coat on my 30 year plus Neptunian.
This was a pale blue colour but had become very mottled over the years. I thought it would have to be painted but saw the PBO article about restoring Gell coat and tested some bits
My finger ends are now worn away and the results are that:

I have had to start with 240 grit ( despite your best advice!) even 400 grit (again,not advised) was taking ages to cut away the discoloured layer even on just a small patch.

With 240 grit it takes about 5mins of hard rubbing to cover a six inch square removing all the discoloured gell coat.

I have then given that area about 1 min with 400 then 600 then 800 then Tcut then 3 applications of wax.

All in all about an hour per square foot!

It looks good though!

My question concerns the use of the progressively finer grits; I realise that the initial 'coarse' grit is having to remove a fair amount of material and that the subsequent finer grits are just removing sufficient material to remove the 'scratches' from the previous coarser treatment.
I can't see any of these 'scratches' so am just guessing the time/effort ( 1 min for a 6 inch square) used on the finer grit stages. I'm also guessing how often I change the paper as I cant really feel when its effectivness is reduced.

Any good tips ( some new finger tips would help!!) ? Am I on the right lines with my 'time theory'

I have not 'gone through' the gell coat yet!

 

[fireball]

er - a machine polisher might help!

 

[rob2]

I'm more worried about your fingers! Cutting back using the finger tips to apply pressure can leave a very uneven finish. The abrasive paper really needs to be on a backing pad with enough give to accomodate the curvature of the hull, giving even pressure over its entire area. This is why a polishing machine is so effective - apart from letting it do the work!

It could be that your times are being increased due to the paper clogging or wearing out. Wet and dry types are most effective if they are used wet and flushed very frequently to prevent clogging. They can also be used with a wipe of soap over them which further reduces the cut (roughly equivalent to using the next finest grade) and also helps to prevent clogging. It doesn't hurt in the initial stages as it also literally washes away some of the contaminates embedded in the surface.

Beware of going at it too hard, though, if you thin the gelcoat too much the depth of colour will become visibly uneven. This is more of a problem with painted areas like I have and particularly on edges where the coating is thinnest, the undercoat can show through.

Rob.

 

[duncan99210]

The secret is to keep the area being worked on wet. If you don't then the fine grain of the abrasive on the paper quickly becomes clogged with debris and stops working. I use a little spray bottle nicked from SWMBO that she used to use for spraying water on house plant leaves...

I also second the idea of getting mechanical help - a polisher is essential if you are to do more than a very small area of restoration.

 

[Marine Reflections]

Ok some tips... get some surgical gloves if you are working without backing, as I am sure you are aware by now it can become quite painful, with no finger prints.

Stop what you are doing and slow down!

I have tried to warn you regarding the courser grades, it seems to little effect.

You are finishing with 800 when you should be starting with 800!
It is tempting, but trust me, you are only making things harder for yourself, no matter how long it takes. It sounds as if you need a wet sanding DA, it is taking ages because you are doing it by hand.


Your gel coat by the sound of it has been compromised to some depth with really bad oxidation, even if you do work it down to find the original colour you are leaving it in a condition where the oxidation will return prematurely, only now you will be left with half the thickness you started with.

In order to 'see / feel' the condition as you work, you will need a very bright torch to show the true condition, by using this you will see the scratches created and being removed as you work. I use one of these but it won't be cost effective for one job, a decent torch will work, just not as well.

A polisher will help with the last 10% of the process as others have said, but you will need to form a reflection through your grading before even thinking about polishing.

I admire you for having the b4lls to give it a go on oxidation so bad.

 

[Lakesailor]

No finger tips. As said they will just rub the softer spots.
Get a sanding block like this. It has pins inside the rubber flaps to locate the paper.
I've had one for many years (used on car bodywork)

 

[pcatterall]

Very many thanks for all the suggestions.
I will try them all.... except..
Lake sailors pad... I have used them ( having owned 6 classic cars!!) that one I find too hard! my gell coat is not dead flat and the hard backed pads seem to find the high spots only but I will source a pad with some give.

Marine reflections..... I know you must be an expert but I did try the 800 first( for ages and ages!!) then 600 then 400etc!! My own background suggests the following:-
1) I need to remove X microns to get down to a decent surface using a very fine abrasive will get there but at great expense in time and materials using a coarse abrasive will get down there more efficiently but the scratches caused need to be sanded out and there is a risk that too much abrasion will 'go through' the gell coat.
I dont understand how the remaining gell coat will now be prone to more rapid oxidation? Provided that I use progressivly finer sanding and polishing then surely it becomes like the original gell coat but thinner?
I will try the torch trick and also look at a decent machine for the final polishing stage.
I was however advised not to try the sanding stage with a machine as the danger of a 'slip' was to great!
Surgical gloves.. yes!!

Master plan is to just prove the techniques over winter ( lots of foot square patches over the boat !!) The crew will need some liesure activity on our proposed French canal cruise next year so I will leave 'joining up the patches' to them!!

Incidently my 'other boat' ( a Leisure 20) had horribly oxidised dark blue hull gell coat ( much worse than the Neptunian) A really good T cutting then wax protection has made it look great.

I will try and post some pics.

Very many thanks

 

[pcatterall]

Hopefully the photo will appear!!
This is about one hours hard work!!
Hopefully you can see the part which has been done!!
The areas either side look very dirty but the whole area has been washed and its just very deep discolouration you can see. Swimbo says its well worth doing and just regrets that her nails would cost ( me) a fortune to restore if she tried to help!
Cheers

 

[Stu Jackson]

You might want to consider these ideas: http://forums.catalina.sailboatowners.com/showthread.php?t=117266

 

[theoldsalt]

pcatterall,

"I dont understand how the remaining gell coat will now be prone to more rapid oxidation? Provided that I use progressivly finer sanding and polishing then surely it becomes like the original gell coat but thinner?"

Beacause the original gelcoat had a protective layer which needs to be replaced to prevent rapid oxidation. That is why we apply a "polish" or wax to the gelcoat which needs to be "worked" into the surface.

 

[Lakesailor]

Lake sailors pad... I have used them ( having owned 6 classic cars!!) that one I find too hard! my gell coat is not dead flat and the hard backed pads seem to find the high spots only but I will source a pad with some give.

I see your point. It's a matter of getting practised with the flat of you hand and using the paper doubled or tripled. Maybe the power sanders with flexi pads would make it easier as suggested.

 

[Marine Reflections]

You certainly can see where you have done and it looks great, a huge difference

Is it possible that the finer (800) grades you started with were being clogged?
The reason I ask is because either side of the worked section looks as if an acetone wipe or 10 followed by an oxalic solution would have helped help a little more prior to sanding. I can't remember if you did do this prior or just went into the sanding.
There is the possibility that someone has coated the gel with an after market liquid resin type coating, as these discolour and are hard to get through to the real gel.

I dont understand how the remaining gell coat will now be prone to more rapid oxidation? Provided that I use progressivly finer sanding and polishing then surely it becomes like the original gell coat but thinner?

You will notice (when you shine a torch on the area) that leaving the surface with 800 despite polishing will not be as smooth as needed, try following on from there with 1200/1500 then polishing, it will be much smoother and with a sharper reflection.
As I say, it will look ready by the naked eye, but under closer inspection it will still have the 800 marks in there and probably much deeper ones from previous grades, t-cut and wax will not remove /correct these but will gloss over them making you think it's all good.
The differences in the profile despite being hardly visible trap light and expose more surface to UV therefore degrading prematurely. Waxing over these will also only trap oxygen that will continue to oxidise the surface.
It will be much clearer to see once you get a good torch on the subject, else it's like looking for a snow fox in the arctic.

The dangers of using a machine to sand are there, but you are able to use a far higher grade (finer) with much faster results and less scratch depth to recover from, but yes there are dangers if you are not able to gauge the worked depth and the cost of purchase will not be returned for a one off.

There was a thread this year where a forum member was asking if anyone had used my services and that he had been quoted (by me) up to 60 hours to restore a heavily oxidised boat, the reply from most that he was mad to even consider it, that may have been true to a degree as anyone can wield a polisher and make it all look great, but to do this properly takes time and effort as you are finding out. I failed to comment on the thread, but I wished I had now as it ranks fairly high on Google under my company name search.

I am no expert (but thanks) as after 20 years I am still learning how the elements interact with various surfaces, but an ex is a has-been and a spurt is a drip under pressure, hopefully I am neither yet!

Tony

 

[pcatterall]

Thanks guys! pretty well done to death now I guess. I will save your tips along with my many other favourites. Except..... dare I ask if the gell coat dicolouration is really 'oxidisation' from air contact or is it pigment degradation due to uv exposure? I guess that wax could protect against both?
I will be buying 1000, 1200 and 1500 grit as well.
Thanks again

 

[LittleSister]

Resin (?) coating on gelcoat question

There is the possibility that someone has coated the gel with an after market liquid resin type coating, as these discolour and are hard to get through to the real gel.

I think that may be what we have on our hull, and I'd be grateful for any tips. It looks like a thin varnish on top of the dark blue (now 30 years old) gelcoat, and this 'varnish' is completely gone in a few areas, with a obvious, slightly ragged, edge to the remaining stuff. I'm not sure whether we should just leave the 'varnish' to gradually fall off of its own accord, meanwhile its perhaps protecting (?) the greater amount of gelcoat it does, or whether it's a good idea to try to get off the remains, and if so how? Will using fine wet and dry as discussed just cut through it, or will it tend to contaminate the gelcoat underneath in some adverse way while it's being done? Can we feather the edge of it a bit, or will that just really mess up and highlight its patchiness?

The gelcoat surface isn't in great visual condition, and while we polish it up a bit from time to time, the surface finish is never fantasticgreat, and doesn't last very long, soon picking up dirt and what looks like limescale. We're not greatly worried about it (we're more interested in sailing than polishing!), but it'd be good to have a more serious go and smartening it up sometime.

 

[Marine Reflections]

I think that may be what we have on our hull, and I'd be grateful for any tips. It looks like a thin varnish on top of the dark blue (now 30 years old) gelcoat, and this 'varnish' is completely gone in a few areas, with a obvious, slightly ragged, edge to the remaining stuff. I'm not sure whether we should just leave the 'varnish' to gradually fall off of its own accord, meanwhile its perhaps protecting (?) the greater amount of gelcoat it does, or whether it's a good idea to try to get off the remains, and if so how? Will using fine wet and dry as discussed just cut through it, or will it tend to contaminate the gelcoat underneath in some adverse way while it's being done? Can we feather the edge of it a bit, or will that just really mess up and highlight its patchiness?

The gelcoat surface isn't in great visual condition, and while we polish it up a bit from time to time, the surface finish is never fantasticgreat, and doesn't last very long, soon picking up dirt and what looks like limescale. We're not greatly worried about it (we're more interested in sailing than polishing!), but it'd be good to have a more serious go and smartening it up sometime.

Hi
It won't cause any harm to the gel coat to leave it on there, but as you have found, it will be harder to maintain or get it to look it's best.

The coatings are used in an attempt to restore faded or swirl marked gel coats without the hassle /effort of correction.

Quite right to focus on the sailing, but as you say, it would be nice to return it to a better condition, certainly if or when you ever sell, it certainly will look better and be much easier to maintain.

It would be nice to see some photos, as it's a bit like giving you a haircut in the post, but a few tips for you..

You could remove by:

Scraping off with a polished / rounded blade, like a window scraping razor blade but smooth/sharp with no corners on to prevent digging in to the gel coat. I make my own, but I'm sure they are available to buy.

Chemical stripping that won't harm the gel coat, similar to the mild anti-fouling removal strippers used on gel coated hulls.

Sanding / correcting as above posts.

The question you have to ask is why the coating was applied in the first place.
It was more than likely applied due to the gel coat fading.

You would then have to correct the faded gel that the coating is hiding.


I would go with a combination of all three methods as some areas will be bonded better, then correct the surface underneath depending on what condition was found.

I have seen this more than a few times and the correction that would have been needed at the time of coating would have been far more simple, but we get sold stuff don't we!

30 year old gel coat should be thick and solid mind, not like today's thin soft gel coats, so very easy to work on.

For now enjoy the sailing, it's doing no harm being on there.

Tony

 

[LittleSister]

Hi
It would be nice to see some photos, as it's a bit like giving you a haircut in the post, but a few tips for you..

Thanks for the advice and info - very much appreciated. I'll have a rummage around for some photos, but probably not tonight.

The colour of the gelcoat isn't bad, I think, considering,certainly compared to some of a similar age I've seen. The boat seems pretty stoutly laid up, so it's likely the hull gelcoat is a decent depth (it is on the deck moulding as we can see from chips and holes drilled, etc.)

I'm very impressed by some of the pics on your website. You must have very strong arms, and lots of patience!

 

[Jim@sea]

The chances are that you will end up painting the hull. Perhaps around the year your Neptunian was new I was experimenting with new ways of sanding both vehicle bodies and boat hulls. For a particular job I ended up with an "Air Fed" Orbital Sander, I could put 800's on it, wet the area to be sanded with water which included a bit of Fairy Liquid, and started, after a short time I could then "Dunk" the orbital sander into a bucket and carry on. With the sander being fed by a compressor there were no electrics so there ws no risk. And NO Dust.
Certainly If I had a blue hull I would experiment below the waterline as it wont show once the antifouling is applied. Sand an area with an orbital sander 1ft x 1 ft, so its flat and you have removed the oxidation, give it a wipe with a tack rag, then paint it with a 2 pack varnish or a 2 pack Blue. The finish will be good, and you have re-applied a protection. I recently did this to a 1986 boat below the waterline.