Polyester resin vs CPES

[Lawnjockey]

Going along with my faster, cheaper, better mantra I am thining about the costs of CPES. There is no question that it is a great product but is there a cheaper alternative that is locally available? Inquiring minds want to know.

Here is what I am thinking, give the entire outer wood shell a couple of coats of polyester resin, thinned if possible. Then drill a few small vent holes into the interior to stop possible "balloning" on hot days. Seal all seams and edges with West epoxy going out 6". Seal the edges with a bead of 5200 and put the skin and trim down before the 5200 sets.

As I recall epoxy will stick to polyester but polyester will not stick to epoxy so the order is important. I have hever been able to understand why it is that way but that is what I was taught by people who knew their business and who am I (a lowly lawn monument) to question years of experience.

Since the skin is the ultimate moisture barrier and the edges are the weak links wouldn't the above be a cost effective alternative?

Jocko

[madjack]

Jocko, you may be onto something...while I am not a fan of polyester and keeping in mind it is full of volatiles like CPES, requiring multiple coats to actually waterproof AND the MUCH quicker setup of polyester, what you are suggesting would probably work...with everything sealed with the polyester, the use of West epoxy seems redundant to me...others more knowledgeable than me might have other ideas...I also don't see the hole drilling idea being of a lot of use or effectiveness BUT don't think it has ever been done so...who knows...in keeping with your cost savings thoughts, the 5200, while a super effective sealant may be more than needed...during our research on sealants during our initial build, we experimented with many different sealants from hi-tek to lo and as a result on my present tear, we used a combinatioin of standard RV butyl tape(cheap) and WhiteLightning 3600(even cheaper) an adhesive based siliconized acrylic caulk...my tear has sat out in the sun for the last 3 years without any problems or any indication of any...just a thought.......................
madjack

[Lawnjockey]

I am not a big fan of polyester myself but... The biggest issue I see in this application is its viscocity. I worry a bit about penetration but I think it would be good enough. I have extreme confidence in West epoxy and I just happen to have a couple of gallons taking up space in my pile thus, to make me feel better, a little extra on the edges wouldn't hurt. I think I even have some 5200 laying around too. The 5200 would be more of a dam against wind driven moisture penetration beyond the areas treated with epoxy. Sika flex would work too but I have never found any caulking product with the adhesive qualities of 5200. I don't care for silicone products because of painting problems and butyl never sets and generally causes a mess. The small holes are to prevent blowing out the edge seal in the unlikely event that the 5200 results in an air tight seal. According to Mr. Murphy, such a blow out would happen in the worst place for wind driven moisture, like by the door.

Jocko

[madjack]

...to clarify a couple of my statements...butyl CAULK sux big time...it seals extremely well but will "ooze" for years to come...butyl TAPE is a different animal altogether and is an excellent sealant...the WL3600 I referenced is not a silicone per se, which I have no use for at all but a regular painters caulk with a medium adhesive capability that we have used around the shop for a number of years and have had good luck with...if I had a couple of gallons of West Epoxy and some 5200 just lying around the shop, I would say screw the rest and just them exclusively..........
madjack

[eamarquardt]

5200 is great stuff, however, I once had to remove an aluminun port light on my boat that had been installed with 5200. It was the shape of a pretzle before I got it off (not a problem as it was covered under warranty and the boat builder knew it wouldn't come off intact and provided me with a replacement). The boat's builder also warned me that removing the port might separate the fiberglass as I pulled the port off (but fortunately that wasn't a problem). So, I'd be careful about using 5200 if you ever think you might want to get it apart.

Silicone sealent is cheap and comes apart without too much trouble. You mentioned painting problems with silicone so you must be planning on painting your teardrop. I think cleaning off any residue with acetone or lacquer thinner and and then scrubing it with a scotch brite pad and cleaning the space between your skin and trim with a fine ss wire brush would solve that issue.

Cheers,

Gus

[Pottercounty]

Instead of drilling multiple holes for expansion, couldn't you just crack a window or roof vent? I have a aversion to drilling too many holes...lol...

[Lawnjockey]

The holes were to relieve pressure build up between the skin and the wood.

Heat helps getting 5200 off. Removing a port hole can be done by carefully heating the metal, not the fiberglass or wood and working it loose. This is done after cutting as much as possible with a razor blade. It is time consuming. I find it strange that a builder would use 5200 for bedding compound when Dolphinite is soo much cheaper and cleaner to work with, not to mention easier to remove the fitting later.

Jocko

[angib]

Epoxy is certainly stronger and more waterproof (well, correctly, water resistant) than polyester but poly is pretty durable stuff - and if UV exposure is involved, more durable than epoxy, even epoxy with UV protection varnish. I would certainly rate polyester ahead of any other coating system, such as paint. Serviceable 50-year-old polyester boats are fairly common.

As a cheaper option, I think your plan is sound. I think if you're going to use epoxy at the likely leak points, just stop the polyester before then - my gut feel is that straight epoxy is better than epoxy-over-polyester. No need to make any clever transition if you're applying aluminium over it - just stop the polyester away from the edge and then apply the epoxy up to the polyester.

Thinning any resin system is bad in my opinion - the thinner evaporates and wherever the thinner used to be will then be a void - and that void reduces the water resistance. I don't believe the idea that 'soaking into the wood' is other than a psychological benefit with resins - I don't think poor protection twice as deep is as good as full protection to a thinner surface layer.

With polyester, the problem is a lack of elasticity - epoxy is brilliant because it stretches so well. So polyester isn't that good at keeping joints watertight, but you are planning to use epoxy at those places, so that's not a worry.

Andrew

[Lawnjockey]

Jack, you got me going on using all epoxy so I started rooting in my piles and this is what I found:




It feels like about 1 1/2 gallons of resin and harden out the wazooo (I think I am allowed to say that). Also a bunch of Microlite, high density filler, micro fibers, etc, all in all a small fortune if I were to buy it retail. I even found a roll of F/G cloth that is 5' wide, from the diameter I would say there is enough to glass the whole thing. Unfortunately I think 1 1/2 gallons of resin is going to be short for even sealing. Perhaps I should do the seams first, then the top and door area until I run out. Then do the rest with polyester.

In the picture I also put some other junk, the 6" porthole is my door window. I have a 12"er somewhere that will be the street side window. Then there are some oil lamps that have accumulated over the years. I have some more around here somewhere including some bulkhead mounted Perko lamps that I am planning to use for lighting. If I can't find them I'll use the trawler lamp in the photo.

The wife will be happy that I am finally using up some of this stuff.

Jocko[/img]

[starleen2]

Ok Jacko - I'll Chime in - the last two builds _ i used polyester resin instead of CPES and epoxy. The first was in 3/8 ply and it did real well. The second build I went to a thinner ply, 5mm luan. I fiberglassed All the joints and sealed the whole thing three thin coats of polyester resin. after about a year - it still looks great. My design is Winter Warrior, so the parts get movement every time I set up or take down - and I've camped in both extremes: hot and cold, with not a mention of bubbling or cracking!
Check out the build link below for more details

[Lawnjockey]

Starleen, that is what I like to hear. By the way, is that the TEXAS you are sitting on? If so, they did a first class restoration on it. I was on it about 10 years ago and it was impressive. I was also on it when Neil Armstrong was walking on the moon. I remember that because it was next to impossible to get a hotel room in Houston due to all the media in town.

Jocko

[Barefoot]

Wow, just in the nick of time:

1)I was about to use spar varnish for top coats, but don't want to re-do year after year. Now, where's that reciept?
2) Are you talking about the two-part material also sold for fiberglass car repair, or something else?
3)If need be, what should be used to reduce it's viscocity --besides summer heat, now six months away.?
4)Will that polyester resin go on top of the polyurethane already on, and stay on? I'd already planned on sanding with 220.
5)If not, what do you think of more polyurethane?

PS)4200 is essentially 5200 that will allow later disassembly and should be available wherever the 5200 is. Neighbors use it especially on outboard motor transom through-bolts, which really do have to come out eventully without tearing up the stern.

[Arne]

quote: Polyester resin will also eat foam if you want to do a lost foam cowl or other shape. For that application epoxy laminating resin is the only way to go.

The strength in the part should come from the density of the fiber and not the type of resin used. Having said that polyester is MORE BRITTLE, so you need to be more attentive to the layup around mounting points.

Both resins are very fuel proof. If you use the polyester be sure to use the unwaxed style resin or you'll have a tough time getting paint to stick to it later on