polyester resin w/o glass

[schmidty]

I am trying to figure out how to waterproof/finish the outside of my tear. I was thinking of just using polyester resin w/o using any fibergalss. I can make the structure of the tear plenty strong with the wood frame and don't think I need any added strength from the glass. So would a normal polyester resin weatherproof my teardrop enough? Would it have UV protection. If it doesn't I may just go with a few layers of spar varnish. The tear will always be covered except for when I am actually using it. What do you all think? Polyester resin, spar varnish or something else? By the way, it will be a wood tear/cricket.

[Chris C]

Polyester has no UV inhibitors. You'll have to apply a finish coat of polyurethan with UV inhibitors for it to last...........and then you'll have to periodically refinish.

[SteveH]

schmidty,

Just my opinion, but If I were going to do that, I'd use epoxy resin instead of polyester. Epoxy will harden slower allowing the resin to soak into the wood better and also give more working time. I know it's a little more expensive, but a better product, again IMHO. Take a look at the West Systems resin at West Marine...it's pretty reasonably priced by the gallon.

[madjack]

...let me add my 2cents worth, MinWax ClearShield...by itself. It is a heavy duty, oudoor, UV protected polyurethane...have had excellent results on out door adirondak type furniture (over 10yrs on 1 set with no noticable deterioration)...thin it about 10% with thinner of choice and spray...sand between coats with a 220 grit paper...put at least 3 coats...the more coats, the deeper the finish will look('cause it is deeper)
madjack

[asianflava]

I was told, or read, or heard, that you should put some spar varnish on top of epoxy also.

[doug hodder]

Most of the epoxy systems make a catalyst made for a top coat, you don't top coat a boat with the same stuff as you did the structural work with...it has UV inhibitors in it, but it still needs to be top coated with either varnish or a clear coat....the real plus to epoxy is that it helps build up the protective coat and really gives you depth to the finish fast...Most everyone building boats have gone to the epoxies rather than the polyester...it's too hot and there is practically no working time to it...it's nastier to clean up too....just my opinion....Doug

[DestinDave]

I've just finished laying up the keel on a 60-foot sailboat. All told we used 22 gallons of epoxy resin, a full roll of glass mat, and a full roll of woven roving mat. We used a new-to-me product by Interlux (the marine paint people) called Epiglas. It is a crystal clear resin and can be used with 3 different hardeners. We started out with the fast hardener but mixed up in 1/2 gallon pails it would kick off in about 5 minutes. We switched to the standard hardener and in 1/2 gallon pails and working in a shop temperature of 68 degrees it allowed us about 1 half hour working time per batch. I really like the clear finish of the product. I made sure we had enough left over for my tear...
I did a search online and it is available at many marine stores and online. Prices are comparable to West System, System 3, Raka, etc...
Anyone else ever use Epiglas ?

[asianflava]

Isn't there a difference in strength when it is mixed hot? For some reason, I was under the impression that the faster the cure, the weaker the bond. I don't know where I got this idea and I don't even know if it is true but, I have always gone by it.

[angib]

We started out with the fast hardener but mixed up in 1/2 gallon pails it would kick off in about 5 minutes.

Whenever you mix epoxy, or indeed any resin, you want to have flat trays ready to take it - for general laminating work, paint roller trays are ideal and any unused resin will snap out, if the tray is twisted after the resin has cured.

It's a simple volume-to-surface-area ratio deal - increase the surface area by putting it in a flat tray and the resin can't build up heat so quickly and so it won't gel as soon. It's tempting to say dump the resin on the job (for a really big surface area) and then come back and tidy it up when it's all laid out - but in reality, it seems you always miss bits if you do this....

Isn't there a difference in strength when it is mixed hot? For some reason, I was under the impression that the faster the cure, the weaker the bond.

Most epoxies have similar, but not identical, strength with all their hardeners, though sometimes the slow or ultra-slow hardeners are slightly less strong.

Most epoxies are proprietary products and most good manufacturers give you proper technical data on line. For Dave's Epiglass, page 48 of the Epiglass Resin Guide shows the performance is similar, though the wood bond is slightly weaker with the slow hardener.

Since you mentioned 'mixing hot', which is a polyester term, I should add the traditional warning - do not deviate from the specified resin/hardener ratio for epoxies - this will not alter the cure speed (as it does in polyesters), it will just prevent a proper cure happening. To alter cure speed, a different hardener must be used. If you want to, it is ususally possible to mix the hardeners together to give you a 'semi-fast' or 'slightly slow' hardener, which is then used at the specified ratio.

Andrew

[critter]

hey guys,
building weee kender on a budget and was going to use fiberglass,poly resign & hardner & then sand smooth and prime and paint w/enamel.will this hold up? i will use it on the bottom and cover w/undercoating.any one see any drawbacks with this?

[Nitetimes]

hey guys,
building weee kender on a budget and was going to use fiberglass,poly resign & hardner & then sand smooth and prime and paint w/enamel.will this hold up? i will use it on the bottom and cover w/undercoating.any one see any drawbacks with this?

That's what's on the top of mine. Some say no, some say so-so, I say if it works go for it. It does have to be covered with something UV resistant and since you are painting that shouldn't be a problem. I thought it was pretty easy to work with and it dried nice and quick, something I needed at the time. People have been using this stuff to patch cars as long as I can remember and it seems to last forever on them or at least until it rusts around the patch. It's also a relatively easy way to get it smoothed out for cheap, a little bondo in the bad spots, sand, prime and your ready to paint.

[angib]

critter,

For an economical job, that sounds just fine. Polyester resin/glass sheathing worked fine on old boats - maybe it only lasts half as long as epoxy, but it also costs half as much!

Andrew

[Arne]

Andrew, perhaps, but twice the work when done the second time....

----

My take on poly resin. I never use it. It usually cures faster than epoxy, so it has less saturation time. I know people who try to get 48 hour epoxy resin so it soaks further into the wood, making a much stronger joint.

The neat thing about cpes is it is thin like water. That property is what allows it to soak deeply into the wood. It is not for this project, but the principle is the same.... extend the set time, and make it thin to soak in.

And I believe poly resin is noticably more brittle (joints may show cracks after a while).

[DestinDave]

Absolutely correct Andrew - if rolled out or brushed out the resin will not build up heat as fast nor as intensely. The only reason we did it like that is we have tons of plastic mixing pails and using 4-inch throw-away brushes we'd just slop it on the sides and apply the glass mat and wet it out. A nasty mess to be sure but it went rather quickly and compared to the cost of trays, rollers, brushes, etc., well, time is money too... I don't suggest this method for finishing a nice teardrop.
I have used epoxy resin mixed with acetone to dilute it to a watery consistency as a primer coat for wood which allows it to soak into the fibers and then a second coat at regular consistency. The wood was then scuff-sanded and followed up with multiple coats of UV quality varnish with light sanding in between coats. Don't know if this is an acceptible practice, just something I tried and it worked prety nicely. Anyone know of any problems with doing this? I'm thinking of doing this on my tear... Dave

[critter]

hey guys,
sounds like thinner is better,is there a way to thin the poly stuff or should i just put it on as planned ,was planning on applying w/squeege relly thin for a couple of coats then sand and paint.
always lookin for a better idea!