Thread: How many coats of epoxy?

Three coats is the usual recommendation. This insures it's water tight. Pay special attention to end grain. Every surface should be shinny, no dull spots.

Thanks mate and how long do they need to be left between coats?

i.e. how long til I can turn it over to do the other side and how long til I can recoat?

Originally Posted by hereselmo1

Thanks mate and how long do they need to be left between coats?

i.e. how long til I can turn it over to do the other side and how long til I can recoat?

Mate, do a search using 'wet on wet' - this subject has been comprehensively covered in a number of threads within the last few months, it's one of the more popular 'questions'

Richard

Originally Posted by Daddles

Mate, do a search using 'wet on wet' - this subject has been comprehensively covered in a number of threads within the last few months, it's one of the more popular 'questions'

Richard

There were no matches for 'wet on wet'.

Stupid bloody search engine - actually, wet on wet returns no results but putting the quotes around it 'wet on wet' does

Try searching: epoxy roller wet
or: tipping off

Try this for a start
https://www.woodworkforums.com/f32/id...2/#post1029200

And Mik's FAQ page
FAQ - Boat Building and Repair Methods - Plywood Epoxy Fibreglass Cedar Strip - Michael Storer Wooden Boat Plans

That'll give you a start on the general thoughts. Read a few of the building threads, particularly down in the Storer forum, this does get talked about a lot and different information comes out each time.

Frames are small things - I've got similar in my Little Black Dog - I used a brush with the bristles cut back to 1cm to minimise the amount of epoxy laid on then rolled smooth using a roller but where possible (usually only on large, flat areas), I prefer to use a scraper then a roller.

Wet on wet - three or four layers, put on really thin, each applied while the previous one is still tacky or even 'wet' - just add enough to seal the timber.

Richard

A roller (smallest nap you can get) puts down the most uniform amount of epoxy, next to squeegees. Roll it on and even it out, then brush it lightly to remove bubbles or use a squeegee. A flexible plastic applicator works well on flat surfaces.

Let the goo get good and tacky, before putting more on to prevent sags and stuff. Wait 24 hours in normal weather before you turn something over, to prevent marks and dings. Most epoxies (unless you're using a slower hardener) will be hard enough to turn over in a several hours. I use the fingernail test. If I can dent it with my finger nail easily, then it's probably going to dent if I start handling it (turn it or other wise). If it take a fair bit of effort to dent the goo with a fingernail, then it's probably safe for turning.

Wet on wet means you're applying epoxy over not fully cured epoxy. This is the best bond which we call chemical in nature (it physically links on a molecular level). You don't need to sand between coats with this type of bond, so you can build up film thickness quickly.

The window for a good chemical bond depends on epoxy brand, temperature and hardener combination. Generally, I like the goo to have some tackiness left, before I apply another coat. Technically, I could wait another few hours and still have a chemical bond, but I'm old school and don't trust what I can't feel. The goo makers say if you can dent the epoxy with your finger, you probably will have a chemical bond, but again I don't trust this. So, if I have let the goo cure longer then I think I can get a non-sanding bond, then I scratch the surface with some sand paper, a Scotch Brite pad or something, even if it's still too soft to really sand aggressively (I just scratch it).

If you can't dent it with a fingernail, then you need to sand the surface before the next coat of goo.

Originally Posted by PAR

Wet on wet means you're applying epoxy over not fully cured epoxy. This is the best bond which we call mechanical in nature (it physically links on a molecular level).

You did mean to say chemical bond, and not mechanical, correct?

Yep, good catch . . .

Thanks guys you rock!

I dont quite get how you use roller with epoxy though. Wont it just harden up and ruin the roller straight away meaning I need a new roller every hour or so?

Originally Posted by hereselmo1

Thanks guys you rock!

I dont quite get how you use roller with epoxy though. Wont it just harden up and ruin the roller straight away meaning I need a new roller every hour or so?

I use a roller and toss it. If you shop carefully, they're cheap enough - the last lot I bought were a foot long and I used my mitre saw to cut them down for the small roller cage, simply because that was the cheapest way of doing it. Other times, you'll find the small ones on special. Same with brushes, keep your eyes on the 2 dollar shops for cheapies.

I have tried storing roller covers in a tray with some acetone, all put inside a zip lock bag, but the foam cover comes off so just toss the roller cover and use a new one for each coat. However, you can do the same with a brush and it'll be reusable a few times.

I don't like to use brushes unless I'm forced to because they lay on too much epoxy. For best control over how much epoxy you use, wrap some tape around the bristles and cut them back to about 1cm long, then pull off the tape.

You're better off pouring the epoxy onto the job, spreading it with a scraper as thin as you can, then run the roller over it to smooth it out, then lock with roller with a finger and lightly drag it over the surface to break any bubbles and to smooth out that orange peel surface. Epoxy isn't like paint, it doesn't lie flat, you have to make it so, but also remember that you'll be sanding it so perfection isn't needed (it just reduces the amount of sanding you have to do ).

For scrapers, my favourite is a piece of 2m plastic that's thick enough to be stiff and, being plastic, the set epoxy just pulls off it. But you can use bits of ply and the like, anything that's stiff. I've also used playing cards - buy thicker rather than thinner. They're a bit too flexible to be perfect but as a cheap, single use scraper, they're had to beat.

The trick with coating is thin layers, really, really thin. Be a real miser, you can always do another layer. Done with a scraper, you'll be amazed at how little epoxy you use ... use a brush and you'll be horrified at how expensive it is (a comment that's more appropriate to flat areas, frames don't give you much choice unfortunately).

Richard

Great advice thanks mate.

The ribs are really thin though and I am not sure how a roller will work, even a thin one so I might have to use a brush for this job.

How hard is it to spread the second epoxy coat over a tacky firsty coat. Sounds like it would be a nightmare?

Originally Posted by hereselmo1

How hard is it to spread the second epoxy coat over a tacky firsty coat. Sounds like it would be a nightmare?

Not at all, the new epoxy lays over the top and you're only working the fresh layer, so you don't notice any grip at all.

I've got a lot a frames on the Little Black Dog so I know what you're facing - the cut off brushes do give you a fair level of control, they're just not as good as scrapers which will come into their own once you start coating the plywood sides.

Tip - coat the big flat areas of ply before gluing them to the boat, they're much easier do with lying flat and far far easier to sand. (search term: precoat ... I flamin' hope )

Richard

Thanks Daddles.

Time to get to work then,

I will update my pics as soon as it looks liek we have done something. Seems like a lot of work for no noticable change ATM.

Might even let you come have a look .

Originally Posted by hereselmo1

Might even let you come have a look .

Ahh, we're talking Ashton, Adelaide eh? You're welcome down here any time - often the best way of learning is to see it in the flesh ... er ... wood

Richard