A few newbie questions on epoxy layup step.

[Patricks Dad]

Patrick and I will be starting the fiberglassing step this saturday morning (no sleeping in this weekend!). We've put up a plastic barrier on the ceiling and another layer on the walls to contain dust. The hull has been wiped down multiple times and will be again before we start. I think we're getting close to being in good shape on this step (other than talent) but I have a couple questions for the experts:


1. The Canoecraft book suggests a light sanding after the first coat of epoxy (I think - don't have it here at the office today). Why? If you want to get the 2nd coat on before the first layer cures, wouldn't sanding first result in a gummy mess and cut into the weave of the glass? What am I missing? If it's just to lightly take any tooth off, I guess I understand but I would think it would have to be pretty light.

2. What is your favorite brush? I looked at a couple stores last night for dark /short bristle brushes. I found only light bristle brushes. And the shorter ones looked pretty cheap and likely to shed hairs easily. I'm thinking that a dark bristle that is shed by the brush would be easier to see. What is your view on foam brushes for the first coat?

3. To wipe down the hull before we start and to clean brushes doyou use lacquer thinner or acetone (I stopped by a boat store yesterday and they were advocates of acetone rather than lacquer thinner). The precautions on both sound pretty nasty. Is there a preference or perscription I should follow?

Thanks!

[Glen Smith]

After applying the first coat of epoxy (saturation coat) to the cloth, you will have a series of hills and valleys. Sanding will cut down the top of the hills and produce a more even second coat. You have to wait until the epoxy is no longer tacky and can be lightly sanded without gumming. This depends on the brand of epoxy being used and the shop temperature. With West 105/207 this means about 4 to 6 hours in my shop. Just give it a light hand sanding with 120 grit paper and let the paper do the work, don't apply pressure.

My favourite brush is the el cheapo blonde bristle brush. I first run a steel wire brush through the bristles to dislodge as many loose bristles as possible then shake it a lot to remove the loose ones. These brushes do shed bristles during the job but so far I have always managed to spot and remove them immediately. I do not attempt to clean these brushes after use, just trash them. I would never use a foam brush to apply epoxy, it can't hold enough. I sometimes use one to smooth out the epoxy after application or for "bubble bursting".

To wipe down the hull before glassing I use lacquer thinner. It is widely available, does a good job and is cheaper than acetone. As stated before, I do not clean my brushes.

[Rod Tait]

Absolutely DO NOT sand uncured epoxy. It will gum up and make a mess that you will have a hard time scraping out, especially if it is the first coat. Apply the first coat, scrape off any excess with spreader and then tip off with a dry brush (el cheapo and throw away). After a few hours (4-6 for 207 at room temp), simply apply a second coat without any prep. I like rollers for subsequesnt coats and then tip off again with a dry brush. I apply four thin coats and take extra time on the fourth to get a very smooth surface by tipping off very slowly and several times as the epoxy sets up. With patience, you will amazed at how smooth you can get it. If you can not put all the coats on every four hours or so, then let the last coat harden ( at least 12 hours for 207) and then sand with 80 grit to rough up the surface, clean with laquer thinner, let fully dry and then apply next coats.

For more info, go to my web site and print out the info from the "How To" page.

[Todd Bradshaw]

This is obviously one of those "more than one way to skin a cat" things. By contrast, I never put any kind of solvent on a hull at any stage of fiberglass or filler coat application as I don't believe it does anything except introduce possible chemical contaminates to the equation. I'll vacuum the bare wood hull, maybe even go at it with a tack rag if I feel it's still dusty, but never any solvents. I use Gougeon foam rollers or squeegees for glass and filler coat application and never use brushes. The easiest way to avoid finding stray brush hairs in your finished glassing job is to keep brushes away from the hull altogether in the first place. Filler coats are rolled on and then tipped-out with a "brush" made from a small chunk cut from a foam roller and hot-glued to a stick. I never sand between the glass bonding layers and filler coats or between filler coats. First of all, it isn't needed and doesn't improve the bond, secondly, the glass is still quite green and you run the risk of bruising the peaks of the weave, which can leave marks. If properly applied and rolled out or squeegeed, the glass should be down tight on the wood and be covered with a very uniform cloth texture before you ever start the filler coats. There shouldn't be any bumps there which need to be removed before filling.

Filler coats also seem to be rather controvercial. A lot of people here decide before glassing how many filler coats they will apply - which is totally nuts in my book! The thickness of the filler coats will vary with different resin brands, different application methods, different working temperatures and even how early or how late in a particular batch of resin's pot life you dip the roller or brush to pick up some resin to put on the boat. Wouldn't it make more sense to apply the number of coats that the hull actually needs than to try to pre-determine how many it will take before you ever do the job? My rule of thumb is to apply filler coats until the weave is totally gone, and then add one more for a bit of a sanding cushion. I never sand between coats and I don't sit around all afternoon chasing drips in the filler coats. I roll one on, tip it out and close the door and leave it alone. Drips or runs will happen, but they're small and will be sanded out after all the coats are on and the hull has had time to cure properly. In my opinion, this school of thought that if you can apply your filler coats very smoothly you won't need to sand the finished hull smooth is a load of bull. There is a major difference in the looks of a hull that's been sanded smooth and one that hasn't and anybody who doesn't believe it is kidding themself. You can have horrible drips and runs in your filler coats and after a couple hours of easy work with a random orbit sander end up with a hull that's smooth as a baby's bottom.

With 105/207 you may need to break the filling up into a two-day project. If so, or any other time you wait much beyond the initial cure stage between coats, go over the hull with water and a Scotchbrite pad to remove the amine blush befor starting the next coat. You don't need any solvents, sandpaper. etc. - just water and a Scotchbrite pad. Then wipe it dry with clean lint-free towels.

[Glen Smith]

Absolutely DO NOT sand uncured epoxy.

I must disagree with you here, Rod. The method I posted above is the one prescribed by Ted Moores and I have used it with success on my projects.

Of course, it has to be timed correctly. Sanding epoxy too soon will produce quite a mess as you stated.

[Todd Bradshaw]

I'll go with Rod on this one. I can't think of a better way to screw up a perfectly good glassing job than to sand green, unfilled fiberglass and I don't care what Ted does. There shouldn't be any hills or valleys there that need sanding and even if there were, they should be small enough that the filler coats bury them.

[Glen Smith]

To Patrick and Dad: if you are using West 105/207 epoxy and Ted Moores' book "Canoecraft" to guide you, I can vouch for Ted's methods. They have never failed me and I am sure many others could say the same.

[Juneaudave]

This really is one of thoses areas where everyone has a different recipe for success. For a first time builder, you can't go wrong with the Canoecraft instructions...but I would go ahead and read the fiberglassing sections on John Michne's site, Rod's site and the myriad of others out there.

For me, I use the blond short haired brushes (because they are available and cheap) for the first coat and rollers to fill. Glen's advice to go at them with a wire brush helps. For rollers, I buy the mini foam rollers (or use 1/2 of a West System roller or similar). Don't try to cut in half a full sized epoxy roller that has the short nap (sometimes they are pink in color). These will fray on the cut edge and leave a mess.

I don't sand unless I wait too long....One nice thing (or bad thing) about the MAS slow is that it can remain open overnight and still be ok to apply another coat. I think West loses it chemical bonding capacity at 6-8 hours (which means you have to keep at it to avoid sanding)

I have precoated and not precoated. I don't see the advantage in doing so...

I do wipe down the hull with laquer thinner, but give it time to evaporate or whatever it does. In my mind, if you can vacumm really good, this step is not necessary if you have been carefull to not contaminate your hull after final sanding. Amongst the sites that I have looked at, most recommend that you do not use either thinner or a tack cloth for wipe down. However, I usually do it and can't see as it has been a problem for me though.

[Patricks Dad]

Thanks for all the responses on my questions. I can see that there are lots of perspectives and people use what works for them. This makes complete sense. I have read many sources of input and we will figure out what works for us.

We're using West 105/207. We'll try to avoid sanding if at all possible and keep the layers smooth as possible. I doubt we'll wipe the hull down with lacquer thinner first (we've vacuumed and wiped with dry rags til its very clean). We'll try to get it all done in 1 go (maybe through the night if needed). We'll put on as many coats as needed until we have a smooth and covered surface. We'll avoid foam brushes (but will likely use brushes and throw them away to avoid the clean up).

All your advice has been very helpful. We'll let you know how it works out. I'm sure it will be fine.

thanks a bunch!

[reinbilt]

Randy,

I always use a 4 inch foam brush to tip off all of the fill coats. I pretty much do exactly what Rod suggests for everything else. The only epoxy I've ever used is West. Good luck this weekend.

[Rod Tait]

It is difficult to determine when epoxy is cured enough to sand since it is a question of which brand of epoxy? what is the temp during application? and during curing? time in the pot, amount being applied and so on?

I refrain from suggesting to a first timer ( which is what most of my customers are) that they can sand after a determined amount of time because it leaves them open to the possibility of gumming up the epoxy with sandpaper. The only way to find out if it can be sanded is to try it, and that may be too soon (or too late). Best to get those coats on without sanding and as smooth as possible so that you have less dry sanding later. In our shop, under supervision, we have customers who are able to hand sand the final boat with 220 wet/dry sandpaper because they took the time to get it right initially.

As a note, the info on my web site relates to glassing while using West 105/207 which is the only resin we use on our boats. Other resins which are thinner or take longer to cure requires a completely different knowledge base.

[Glen Smith]

That is very true, Rod. That is why I feel everyone should make a test panel before trying a new (to them) product or technique. It can save a few surprises further down the road.

[Patricks Dad]

Patrick and I got up early this morning (an accomplishment all by itself). We started the first coat before 8AM. Here's a picture:


We just finished the 2nd coat awhile ago and are waiting to put on the 3rd. The 2nd coat seemed to cover the weave pretty well (In several places, the first coat seemed to cover it too - hope it wasn't floating but we squege'd pretty well). We'll see later if we need to add a 4th coat.

Regarding the 2nd coat, we put it on with a brush and sqeegee'd it but it seemed to me that it was just removing good epoxy (and leaving streaks that needed to be brushed out again). I couldn't see any reason to not just brush it on and leave it alone (but given we started with the squeegee, we kept it up for the whole coat for a consistent finish...

I'll post another picture after the final coat tmorrow.

[mtpocket]

It's a beauty, I knew you guys could do it. Thanks for sharing the pics with us. Pat yourselves on the back!

[Juneaudave]

Kind of fun, isn't it!!! That looks great!!! Glad to see that all of our advice didn't mess you up...Juneaudave