Will epoxy coat smooth over imperfections?

[pcatterall]

My hull has been slurry blasted. The surface has many minor imperfections around 0.5mm deep and over the whole hull. I understand that I must epoxy before any filling to provide a good key?
Will the epoxy do anything to fill these 'holes' or will I still have effectively the same surface?
If I have to use filler ( as I suspect ) then I am concerned to understand the practicallities of the process. I understand ( thanks to responses on my previous thread) that I can/should put on an epoxy coat then do the filling on tacky epoxy then fair off the filler when the filler and epoxy are still uncured ( this sounds messy).
In terms of effort, mess and timing could I do the whole hull; epoxy and fill then let it all completly cure and fair off the hardened surface. This would provide the key for the next epoxy coat.
In terms of labour and epoxy cure time could 1 (old) guy epoxy and fill both sides of a 33' hull in a session or should he settle for one or (better) look for volunteers ( this is the' big society' after all)
Finally will microballoons mixed with the epoxy be ok or should I go for a 'readymix' product?
Many thanks, guys, for the good information and help to date.

 

[Rigger Mortice]

Epoxy paint won't fill .5mm imperfections. Epoxy filler will.

I can't see how you can fair it when it is uncured and I think you will have to let it cure. You will probably have to do it at least once more to get a good finish.

It's one hell of a job to do in one session and I wouldn't fancy doing one side on my own in one go. Look for volunteers but you may well find that the "Big Society" is no more than meaningless hot air!

I vaguely remember that microballoons were not recommended below the waterline but, whatever you use there is no need to buy a propriety filler. It's easy, cheaper, and probably better to buy the different ingredients and mix it yourself......particularly in the quantities you will be using.

Heat for curing the epoxy may be a problem.

 

[30boat]

You should fill and fair first and then epoxy.If you fair after the epoxying you risk abrading the protective coat off.Microbaloons will make a good sandable filler for this application.

 

[Rigger Mortice]

Well, you learn something new everyday.

As 30boat and I seemed to be contradicting ourselves over microballoons I thought I would check it out and this is what I came up with from the SP website.....


> SP-High Modulus Microballoons
SP-High Modulus Microballoons are hollow phenolic resin spheres which have a distinctive reddish/brown colouration. This makes them particularly useful for cosmetic fillet joints and fillers in wood construction, as well as structural adhesives for less demanding applications on softer timbers such as cedar. Although not as waterproof as glass bubbles, microballoons are often preferred for their excellent sanding characteristics. Microballoons are not normally used with polyester or vinylester resins because they can be subject to styrene attack which may cause the spheres to collapse.

When storing microballoons, it is particularly important to exclude air as they readily absorb atmospheric moisture which will affect the performance of the filled mix.



> SP-High Modulus Glass Bubbles
SP-High Modulus Glass Bubbles are hollow glass spheres with a more variable particle size than microballoons. Being composed chemically of glass, they are physically harder than microballoons and filled resin mixes are noticeably more difficult to sand. However, glass bubbles produce a more waterproof filler mix and are often used on below-waterline applications on boats. Being significantly less expensive than microballoons they are often preferred if easy sanding performance is not of prime importance. They can be mixed with microballoons in any proportion for colour purposes.

(The underlining is mine)

I must admit that I thought that microballoons and glass bubbles were one and the same. The "microballoons" which I have are clearly glass bubbles and it explains why they are not quite as easy to sand as I had expected. The supplier charged me for microballoons!




.

 

[30boat]

Well, you learn something new everyday.

As 30boat and I seemed to be contradicting ourselves over microballoons I thought I would check it out and this is what I came up with from the SP website.....


> SP-High Modulus Microballoons
SP-High Modulus Microballoons are hollow phenolic resin spheres which have a distinctive reddish/brown colouration. This makes them particularly useful for cosmetic fillet joints and fillers in wood construction, as well as structural adhesives for less demanding applications on softer timbers such as cedar. Although not as waterproof as glass bubbles, microballoons are often preferred for their excellent sanding characteristics. Microballoons are not normally used with polyester or vinylester resins because they can be subject to styrene attack which may cause the spheres to collapse.

When storing microballoons, it is particularly important to exclude air as they readily absorb atmospheric moisture which will affect the performance of the filled mix.



> SP-High Modulus Glass Bubbles
SP-High Modulus Glass Bubbles are hollow glass spheres with a more variable particle size than microballoons. Being composed chemically of glass, they are physically harder than microballoons and filled resin mixes are noticeably more difficult to sand. However, glass bubbles produce a more waterproof filler mix and are often used on below-waterline applications on boats. Being significantly less expensive than microballoons they are often preferred if easy sanding performance is not of prime importance. They can be mixed with microballoons in any proportion for colour purposes.

(The underlining is mine)

I must admit that I thought that microballoons and glass bubbles were one and the same. The "microballoons" which I have are clearly glass bubbles and it explains why they are not quite as easy to sand as I had expected. The supplier charged me for microballoons!




.

I was thinking of glass bubbles.Good thing you pointed that out.They are still quite sandable.I've used them before and didn't find them particularly hard to work with.

 

[macd]

Hi again Pcatterall.
Presumably after slurry blasting, your gel coat is largely intact but a bit lumpy? (Even assuming that, we're all guessing...there's no substitute for running your hand along the hull.)

If so you still have a major job on your hands, but less than if the gel had been removed completely.

Generally the first epoxy coat will be low viscosity, so it's filling effect will be almost nil.
As others have also suggested, I'd steer you away from proprietory made-up fillers on grounds of cost.

So order is:
1. low viscosity 'key' coat.
2. fairing coats, high viscocity
3. barrier coats


The fairing while "still uncured" sounds like it might a reference to my post on your earlier thread about AMC high-build epoxy. It works up to a point with that, but not with any other epoxy I've tried. They're just too cloggy until almost fully cured. If the hollows are as small as you say, you might get away with AMC high-build epoxy with little or no added fillers: it's very thick stuff.

"Could one guy fill and cure one side of 33' boat in a session"?: not in this universe, mate. And especially not in UK temperatures.

Please feel free to PM me if you want further info

 

[oldsaltoz]

Good advice as usual from 30Boat.

This might help answer a few of the questions above.

http://marinewatchnsw.com/library/fibreglass.html

Also note, Fill and fair first, then apply epoxy is the normal order of things, it also allows for the wet on tacky application so reduces time and effort required.

Tip:
When fairing and you think you have finished, do one or both of the following.

In daylight: wet the hull and check for imperfections in the reflections.

In the dark: shine a torch held close to and along the hull, you will see any and all imperfections.

Note, the above will not show up any pin holes, for this apply the first coat of epoxy primer and let it cure, and pin holes will now look like nail holes.

Good luck and fair winds.

 

[Signed Out]

Good link, OldSaltOz. Handy for me too!

 

[oldsaltoz]

Good link, OldSaltOz. Handy for me too!

Yes, I was thinking about 'Q' cells and thought it might be good to find a web page with some info, first time I have seen that one, proves Google is your friend after all.

Good luck, and keep us posted on progress, you will be able to apply the epoxy in a day provided it's warm enough, don't be tempted to add extra hardener, it's not the same as poly resins.

 

[yacht surveyor]

You may find this link from West Systems interesting and informative.

There are a number of pdf versions of their books in here, including
-002-550 Fiberglass Boat Repair & Maintenance
-002-740 Final Fairing & Finishing

It is useful free background reading to help you through what you are up to. Should give you some of the general principles!

Cheers,

Martin

 

[pcatterall]

Thanks guys for some good info, I will need time to absorb this but need to comment on one point where I seem to have conflicting opinion.
My understanding was to always apply an epoxy coat before filling as the filler would not bond. Some advice on this thread supports this and some is in conflict.
In terms of planning the work I guess that fill and fair first would be best as I can then 'just' roll on the epoxy coats 'wet on tacky' as advised
In terms of timing I had thought that ( after preparation and mixing) I could roll on an epoxy coat ( one side 25sq yds) in a couple of hours. In terms of fairing ( just the filling bit) I had thought as little as 5mins per m sq a (couple of hours again) The filling I refer to will just be a scrape with a flexible blade as the hull shape is true and just the small pock marks need filling.
Filler required assuming that the whole surface ( rather than the holes) gets 0.5mm should be in the order of 400cc per sq yd; around 10lt per side.
Thanks again for the words of wisdom.

 

[yoda]

When I grit blasted my hull to remove the pox I was left with a very pot marked hull. I used hemple epoxy filler which while expensive (but not as bad as you may think in a big tin) was very easy to apply with a plastic applicator (cheap from car body repair suppliers) and also easy to sand. Having worked with fillers of various epoxy/bubbles/micro ballon combinations I think the proprietry filler was still the best way to go. I also epoxy coated afterwards and took advice from Hemple about the process (very helpful) as I wanted to use their 3 coat system rather than the international which was probably going to need 6/7 coats.

Yoda

 

[macd]

Filler required assuming that the whole surface ( rather than the holes) gets 0.5mm should be in the order of 400cc per sq yd; around 10lt per side.

Think you might find it simpler if you ditch the hybrid imperial/metric. I litre over 1 square metre is 1mm thick.

 

[Elessar]

Think you might find it simpler if you ditch the hybrid imperial/metric. I litre over 1 square metre is 1mm thick.

Yes this is right for the wet film thickness. Remember only solvent free epoxy has the same dry film thickness.

For solvented epoxy it typically shrinks to 40-50% of the wet film thickness.

To the OP, fill first, then sand then epoxy.

 

[the far canal]

I would not bother with the first "key coat" as this is only really needed for wood which will absorbe epoxy from the filler mix and make a weak bond, grp will not. I always use west system low density filler for cosmetic jobs, sands really easy. west system have lots of good advice on there web site, well worth alook.

 

[TQA]

The fairing process traditionally invoves the use of long flexible sanding boards almost universally known as "torture boards".

Getting the thickness of the board and length is critical to making it do the job. I have been around a couple fairing their 40 footer after a peel and it took them over 3 months working most days.

Mind you the end result looked like it had been Awlgripped by pros.

If it is just the underwater part of the hull why bother. Just get the required thickness of epoxy on and go sailing.

 

[William_H]

If it is just the underwater part of the hull why bother. Just get the required thickness of epoxy on and go sailing.

I wonder why you don't try to smooth out the gel coat (or what is left of it ) before epoxy.
However by the time you put on 3 coats of epoxy. a primer and antifoul the small imperfections may be covered up. And finally covered by muddy water! olewill

 

[fastjedi]

How come the hull has so many imperfections after slurry blasting? My hull was dry grit blasted in September. A couple of days with a random orbital sander + a tube of epoxy filler for a few pin holes and an imperfection in the keel casting and we are as good as new?

 

[pcatterall]

I wonder why you don't try to smooth out the gel coat (or what is left of it ) before epoxy.
However by the time you put on 3 coats of epoxy. a primer and antifoul the small imperfections may be covered up. And finally covered by muddy water! olewill

I agree! It would be nice to have ( for the first time) a smooth shiny bottom ( but,
thinking back about 68 years......!?)

The fairing is nothing like as drastic as I may have suggested, the hull contours are fine so its just a question of scraping a bit of filler over the hull so it fills the imperfections. Not a long board and trowel job.
There is a suggestion that, rather than fill, I should sand down to get it smooth but sanding down to to remove a lot of small holes seems more work than filling the holes.

Thanks again for all the advice

 

[Bobobolinsky]

You can fair with a standard plasterers float and hoick. A good plasterer can fair a hull in a couple of days.