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I am sanding the outside of my PC hull, getting ready for painting. I am learning that this is the most distasteful and (I suspect) unhealthy part of boat building. I'm wearing a respirator, but I hate all the epoxy dust. I don't care about the boat's finish; a rough "workboat" texture is fine with me. But I understand that sanding is necessary for adhesion of the paint. So, I'm wondering how much (or how little) sanding I can get away with. Is a light scuffing enough, or do I really need to dig in? I'm using exterior oil based paint--not marine paint (and don't give me any grief over my cheapskate decision .

This question becomes even more important when I start painting the deck because I plan to use a single coat of epoxy over 6-oz cloth in order to create a canvas deck-like appearance. Obviously, I cannot sand too aggressively or I would simply grind down the fabric.

I won't answer your question on how much sanding you need to do since there are others that know far more then I.  I will offer you a couple of suggestions that helped me with the sanding/dust issues.  I got a big fan, one of the 21" window types or even bigger if you have one and directed it to blow bow to stern.  It really helped keep the dust moving in one direction rather then floating around the air above the boat.  My shop has two over head doors so opening both usually results in an air flow in one direction and the fan just added to that.  If possible move the boat outside and sand there.  Still use the fan.  I attached a shop vac hose to the palm sander I used on a lot of the hull and it helped.  I have a shop dust collection system but found the portability of the shop vac appealing.  I also stopped every now and then to vacum up loose dust that was lying on the hull, floor or other surfaces where it collected.

I got so I enjoyed sanding the wooden parts of the boat and oars I built.  I found turning the rough feel of the wood to something smooth very satisfying in a zen like way.  I never got that feeling from sanding epoxy.  I used a 3/4 face mask and goggles while sanding epoxy surfaces.  Good luck with your boat and don't worry about cutting costs or just finishing it enough for your taste.  There have been discussions on whether you should just build something to sail or a work of art.  They boil down to doing it the way you want.  I lean towards over building but have not yet sailed a boat I started 2 years ago.  Just do it your way.

Great advice, Terry. I can't move my boat outside, but I do have a large garage and I plan to drag the boat closer to the double doors before continuing the work. I finished sanding the bottom over the weekend, but I am now trying to figure out a saner way of working on the rest of the hull. The fan is a great idea. I will try that.

I completely agree about sanding wood versus sanding epoxy. I actually pride myself on my woodworking skills and when I'm building a table out of walnut or cherry I can get a bit obsessive with the finish work. But sanding epoxy with a power tool...well, that's just gross. Since I want to keep building boats, I need to develop techniques and skills that limit sanding to a bare minimum.

I suspect that I sanded more than necessary when I worked on the bottom over the weekend. Part of the problem is that I am still learning my glassing skills and I ended up with a bumpy surface that needed a lot of sanding to reach the low spots.  I did a much better job on the hull sides--three thin coast produced a smooth, even surface.  I'm hoping that I can scuff it up with some hand sanding and then slap on the paint. Which brings me back to the original question...

Sanding and fairing are different. Sanding is a process of smoothing a surface, fairing is leveling a surface, big difference and the usual "tell" of a novice build.

You don't need a respirator, but a good dust mask is required.

The box fan is a good idea and I mention it all the time. It's better if you can generate a cross flow, by placing the box fan at one end of the shop and having an "intake" at the other.

If the garage door is the "exhaust" then place the fan there and close the door down to the height of the top of the fan. The open a window or door at the other end of the area. This will create a cross flow and the dust will "go with the flow" out the fan at the garage door. If you attempt the "pressurize" the area by placing the fan at the intake and letting it blow toward the exit, then the dust does eventually find a way out, but it first is stirred up and floats around in "eddies" until it happens on an escape route.

The shop vac trick is helpful too. One trick I've done is to use a box fan and a big corrugated piece of 20" flexible duct. I screwed this to the fan housing and made one big ass shop vac. I placed the duct in the area I would be sanding and all the dust generated would float over and get sucked down the duct. Naturally, the fan was placed in a window or otherwise vented outside. You can tell what I've been working on by the colored stripe on the driveway from this monster.

Most paint just need to be scuffed, epoxy needs to have it's shinny knocked off. Most any grit will do, but I don't go over 220 for paint (unless sprayed, then it 320 or less) and most rough paint jobs don't need any finer than 100 or 120 grit. Primer will easily fill in a 120 grit scratches (assuming two coats). If the paint is really thin, 180 grit will fill in and 220 for those looking for a nice smooth, buffable finish. No need for anything over 280, unless you're doing a show quality paint job.

Paul,

Do you use an epoxy wash before painting?  Like Interlux 202 or something?  It is suppose to eliminate blush problems?  I used the slow hardeners that are suppose to eliminate blush but still used the wash on the hull before painting.  Is that overkill?  On the hull it wasn't to bad to work with but I am painting the last parts of the boat and they are more confined.

The warnings on the wash say a mask with organic and vapor filters are required as well as good ventilation.  When I did the hull I wore my mask with the filters and thought it was blown out of proportion.  Then I took off the mask and by the time I walked to the door was getting very light headed.  I guess the mask did it's thing because with it on there was not hint of vapors and without it the room was toxic.

Unless you are in climate controlled conditions or using vacuum bag or infusion methods, you should always assume you have some level of blush on freshly cured epoxy coatings. It's the chemistry to make epoxy and non-blush formulations really aren't, but do tend to decrease the non-reacted amine groups at the surface of a cured batch. Advertising that suggests you will not have these amines is just rubbish.

I can give you a bunch of reasons why this is so and a long drawn out explanation about the chemistry, but this isn't necessary, if you just accept the fact that blush occurs, even on non-blush epoxy and washing and sanding are the nature of the beast.

This said, under certain conditions and at certain temperatures you can have relatively amine free cures, but you're playing a big excrement with your project if you don't wash and sand a cured coating.

My point is, you're going to have to sand the surface anyway right? Why chance rubbing un-reacted amines into the surface, because you didn't wash it first? I've never seen a back yard builder's shop that could guarantee there would be no blush, with any level of confidence. I can, but I have an A/C'd, climate controlled work space and I epoxy under plastic sheeting or Mylar (curing epoxy doesn't touch the air).

I don't use 202, but make up my own washes and solvent needs. I also don't use the special thinners some manufacture ask for. In most cases it's quite easy to figure out what they are and you can make them up yourself.

For example, if you want a good epoxy cleaning solvent, you can buy "special mixtures" from some manufactures. Or, you could mix up 50% acetone with 20% rubbing alcohol and 30% xylene. Naturally you don't use this on your skin, but it will remove uncured goo from tools. If you want a good buzz, hang out with the xylene for a while.

It's generally wise to work safely around most of these chemicals. You can use a respirator or a fume hood or cross ventilation, but it's best to limit exposure if you're of breeding age, unless you don't mind raising three headed babies. Epoxy itself is inert when cured. Epoxy dust is a very aggressive particulate, so you don't want to breath the sanding dust. Un-cured goo isn't especially toxic, but the usual rules apply, such as eating it, wearing it, rubbing it into eyes and on skin. You don't need a respirator with uncured goo unless you're particularly sensitive to alkaline materials.

So, to answer your question Terry, yep, you're pretty anal, but this is a good thing.

Scuff it up and paint it.  If you try to make it perfect you'll be posting for five years.  I finally had to stop sanding and paint the dang boat and even if it ain't perfect it's good enough for me. 

Paul sand it until you are happy with the looks if it.  I normally put on a seal coat of clear epoxy after sanding and clean it with Dawn and water, lots of water roughing it up with a greenie.  Then I paint using my hi tech semigloss house paint. It lasted on the hull for about 8 years with touch ups.  Nice thing about water based semi gloss is the touch ups don't show for 3 or 4 years.  (Don't leave her more than w aweek or so in the water at any one time)  This is a personnel preference issue so the advice is worth its cost...  8) 8) 8)

    I thought I had sanded enough, I got everything smooth to the touch. After the 1st coat of blue paint you could see every dent, ding, scratch, missed scrape ect ect..  Looks great from 10' away but get closeand you can see all the imperfections.  I hope the topside turns out better..  My problem was the sides,  not sanding runs enough, but hay, the bottom of the boat is perfectly smooth at least...

You might try some automotive glazing compound to fair out the dings and top coat again.  It will stick to your paint and smooth small imperfections, nothing over 1/16"" should be filled with it and then give it 3 days or so to cure before sanding if that deep.  Surface scratched etc are good to go in about 4 hurs or so.  Go by the label not my memory....  Then again there are going to be more dings so what the hell.  As long as it floats  8) 8) 8)