Use styrofoam cooler as mold for box seat

[undone]

Rounding of the edges is kind of a non issue, you can shape foam quickly and easily with sand paper and other tools. The inside radius is made with the same putty use for fairing the surface, or a piece of foam shaped and put in the corner.

 

[undone]

To make the surface smooth....

Fill & sand, fill & sand, fill & sand.....give up and say good-enough, then paint.

 

[Woodonglass]

You can use the Blue or Pink Slab foam with Poly resin but...You have to cover it with plastic first. You can use Cheap clear Packing tape. That way the Resin won't Eat the Foam. Use .75 oz and tear it into 3 - 4" "Hairy" pieces and then wet out the Interior of the box and apply the individual pieces and "Dab" them into place kinda like making a piece of Chip Board Plywood. Once it's all covered and tacks up I'd use 6 oz cloth as a next layer cut to fit each side with enuf to lap down onto the floor of the box about 2". Then lay the floor piece on top of the overlaps. Then come back with 1.5 oz CSM and do the same layup. Once that tacks up I'd use cut to size pieces of 24 oz woven roving and do the same lay up. I'd finish off with 3 more layers of 1.5 oz CSM to fill in the 24 oz WR weave. You could then gelcoat the interior and have a nice gelcoated water tight box. On the outside, I'd do a 1.5oz csm lay up, followed by 2 layers of 1708 biax and finish off with 2 layers of 1.5 oz CSM. Sand, Fill, Fair, Gelcoat. Done!!!! Lot's of work!! You could do as suggested and just do this...

You could then sew a padded seat and attach it to the lid. I can even show you how to make a back rest for it if you want one.

 

[metriccrescentwrench]

What about the mat question? "To Mat or Not To Mat"...that is the question.

Nope, don't need the mat if you're using epoxy resin. As stated, it'll add pretty much nothing to strength and will suck up a lot of extra resin.

 

[anamealreadyinuse]

Ungh...its so temping to use a cooler, there is one at Walmart the perfect size. In reality this is a test to see how much I enjoy working with the materials. I'm considering building a small stick-n-glue skiff but figured I'd better see if I like working with the epoxy/fiberglass materials. Thanks everyone, ordering this week so hopefully I'll have something to post soon.

Oh...one more question...does it matter if I drill the drain hole before or after. I'll need to seal it either way but was wondering if there is a reason/method for creating the drain hole before or after?

 

[anamealreadyinuse]

double post...

 

[Woodonglass]

Ungh...its so temping to use a cooler, there is one at Walmart the perfect size. In reality this is a test to see how much I enjoy working with the materials. I'm considering building a small stick-n-glue skiff but figured I'd better see if I like working with the epoxy/fiberglass materials. Thanks everyone, ordering this week so hopefully I'll have something to post soon.

Oh...one more question...does it matter if I drill the drain hole before or after. I'll need to seal it either way but was wondering if there is a reason/method for creating the drain hole before or after?

My previous post was for Poly resin NOT epoxy. Using Packing Tape on the foam works very well. I'd drill the hole after the first layer of CSM was applied. and cured. If you use epoxy You will need to paint the box and that will not be as durable as gelcoat. Epoxy takes a LOT longer to cure, It sags and runs a LOT on vertical surfaces and IMHO is harder to work with for an amateur. It does stink a lot less but I kinda like the smell of poly but everybody KNOWS I'm kinda weird.

 

[anamealreadyinuse]

Okay, thanks for the tips...I'm really in uncharted territory for all of this and reading as much as i can. @woodonglass, so the poly resin sounds like it easier to apply (less runs etc.) than epoxy? Can you not gel coat epoxy? Thanks for help, really appreciated!

 

[Woodonglass]

Nope, Epoxy and Gelcoat don't play well together. If you use epoxy you'll have to use paint as a final finish. Well I guess that's not absolutely true. You can use Gelcoat with epoxy with some really special prep but...I've never done it, don't know anyone that has, never seen it, only heard/read about and and really don't believe in it. but I suppose it does work in some manner but again, I would only believe it when I saw it, and don't expect I ever will!!!!!

 

[kjsAZ]

you can gel-coat Epoxy: http://www.westsystem.com/ss/polyester-over-epoxy/. I had gel-coat over the entire Epoxy build hovercraft I build years ago. Problem is that Polyester and Polyester based based gel-coat adheres pretty poorly to anything but itself (and that only as long as it's not fully cured). The slightest opening in a cover where Polyester can penetrate will still eat a cavity into the foam. To prevent Epoxy from flowing away first of all don't put puddles of it onto the glass and second you should use a high viscosity resin or add some (little!) fumed Silica to it to increase the viscosity. I exclusively use Epoxy as I don't like the brittle Polyester and the almost zero potlife in the AZ summer. It also needs matt to overcome the disadvantages of being brittle which adds a lot of weight for no structural advantage.
Many people used to Polyester have problems with Epoxy at first as the techniques are different. I used Polyester too but am not impressed from it. The reason it is used for a lot for boats is that it's a lot cheaper and you can apply it with a copper gun (resin and glass fibers). Makes for thick and heavy boats at a low price. Real top end boats are build with Epoxy and cloth (glass, carbon, Kevlar) but that's an all manual process.

 

[anamealreadyinuse]

That's good to know as I planned on Gelcoat the inside at least. I'll research the poly resin, I nixed it initially b/c I was told it would eat the foam like you mentioned and wanted to avoid the packing slip step. I'll re-visit that as I really want that smooth gelcoat finish.

 

[anamealreadyinuse]

I do like the epoxy as that is what I'll use for the skiff if I proceed and want to see if i like working with it enough to sink $$ into a boat project. Is there any paint or clear coat type final coat I can use in lieu of the gel coat that will provide as durable finish?

 

[kjsAZ]

For inside or above the waterline you can use Interlux deck paint. It is not as durable as gel coat but comes pretty close. You can also use LP paints like Awlgrip. They are very good in adhesion and durability. If I would build another hovercraft I'd use Awlgrip instead of gel-coat.

 

[jbcurt00]

If you build your seat w epoxy you CAN'T cover it w gelcoat, it'll have to be painted. Same for the boat. If you do repairs w epoxy, you'll have to paint it. Gelcoat doesn't adhere well over epoxy.

 

[kjsAZ]

If you build your seat w epoxy you CAN'T cover it w gelcoat, it'll have to be painted. Same for the boat. If you do repairs w epoxy, you'll have to paint it. Gelcoat doesn't adhere well over epoxy.

Have you experience with it or do you just repeat what the internet myths tell you? When did you try it? Looks like you didn't read the link I provided. I have covered several Epoxy constructions with gel-coat and it works well. Requires careful prep work but that also applies to Polyester when you want to gel-coat it.

 

[jbcurt00]

The iboats resident experts, both of who have extensive professional experience with both resins have both repeatedly stated its tough to accomplish well, and both recommend paint before gel over epoxy professionally, and more so for DIY. The West link you provided is interesting, but is from a retailer that sells both. So, yes I did read your link. Thanks

 

[Woodonglass]

kjsAZ, I'd be VERY interested in hearing about your epoxy/Gelcoat experience. I'd also be interested in hearing about the CAREFUL prep work involved with Polyester resin when applying the Polyester based Gelcoat to it. What Epoxy did you use and what Gelcoat did you use? Was the application for below or above the waterline? What Special prep did you do for the epoxy/Gelcoat? Details always help us and the members to learn from others experiences. I'm fully aware of some of the MFG's claims to their Epoxies abilities to work with Gelcoat but I've yet to have a PRO from a boatyard or marina here on this forum or any other forum make the claim that epoxy is the preferred resin to use when Gelcoat is the final finish. The Chemical properties of the two just aren't that compatible. We have one of the nations leading epoxy and polyester resin experts here on this forum and he has always stated that it's never a good idea to apply gelcoat over an epoxy base. If you have documented evidence that proves otherwise I for one would be very anxious to learn from it. I'm sure our resident expert, ondarvr, would be also.

Here's an example of a previous iBoats discussion on the subject by some VERY knowledgeable PRO's indcluding ondarvr...
http://forums.iboats.com/forum/boat...9-gelcoat-over-epoxy-can-it-be-done-yes-or-no

 

[kjsAZ]

WOG, I didn't say that Epoxy is the preferred resin to use with Polyester based gel-coat. What I said is that it can be done. It is a lot more work in preparation and even in the Epoxy part. If you make the slightest mixing error in the Epoxy and the hardener isn't exactly the correct amount for the amount of resin and not 100% mixed you already start with a problem. If you did your Epoxy work as it should be done you have to clean/wash off all the blush and other surface contaminations which the Epoxy can and will "sweat out" when cured in open air. Then you have to completely sand off the surface of the Epoxy and make sure that there are zero glossy areas left (or areas not 100% sanded). The surface has to be "perfectly" rough before you spray the gel-coat.
My hovercraft naturally was only a short time in water which doesn't count as a under the waterline application but my last boat (10m WL) in Europe had an Epoxy hull. Due to an impact with a floating object I had to do some serious repair on the hull. Half above and half below the waterline and naturaly all in Epoxy as that was the hull material. Same preparation as above for the gel-coat. I sold the boat 4 years after the repair and you couldn't see any issues with the gel-coat in the entire repaired area when she was hauled out for the pre-sales survey. The boat was moored all the time which means that half of the repaired section was permanently under (salt) water.
It is a lot more work then what you have to do when you apply it to Polyester but it can be done. Is it worth it? For a repair or add-on for sure but as I wrote above I wouldn't do it if I would build another complete hovercraft and most likely not for a boat either.
What I don't know is whether this is applicable for all types of gel-coats and Epoxies or whether there are differences in the materials which make some work and some not. I used the ones recommended by the resin manufacturer in Europe and the hovercraft I build in the US was with West System Epoxy and Minicraft gel-coat (that's why I had the link...).

Edit: forgot to mention that the first 2 coats have to be sprayed wet-in-(almost)-wet to have sufficient thickness. If you sand through the gel-coat it is an area where the bond may be suspicious.

 

[Woodonglass]

No, you did not, and did not mean to imply that you did. This ^^^ is ALL correct! Thank you for your descriptive and informative post! Very nice description of the process. While It's true that it can be done, even West Systems states it's not an optimum methodology and that's what the majority of us here on the forum make the statement that "Gelcoat will not adhere to epoxy" . For the average DIY'r I believe it's a fair statement and will keep them erring on the safe side. I suppose we could be a bit more clear in our advice but overall I still believe the statement is the best one to make. But Hey I AM just an so it's prolly best to do as you see best!!!

 

[kjsAZ]

WOG, correct, it is A LOT of work to gel-coat Epoxy and one should clearly think hard about doing it. The issue is that some boats are build in Epoxy. They first spray gel-coat into the mold, then build up the rest of the hull inside with Epoxy. In this sequence it works very well as Epoxy adheres to Poly just fine. The issue starts if you have to do a repair job and can't operate in the same sequence as you have too build inside out. Then you have to spend the time to get it done right.

I did some stuff with LP paint as mentioned above (I used Awlgrip) and the resulting surface was/is very scratch resistant and durable, almost like gel-coat. That's a very nice alternative if a complete surface area with defined boundaries can be covered. Unfortunately it's not something you can do in a patch job as the transition can't be sanded smooth.