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Building a bait tank mold....need some advice?

Old 03-09-2017, 06:23 PM
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Default Building a bait tank mold....need some advice?

The idea is to affix the finished bait tank to the underside of my stern transom cap.
This is the point I have progressed to.
I built a frame out of foam board and rounded the corners. It is 16wide x 24long x 22 deep at the top. The base tapers down to 14wide. I layered bondo onto the foam frame and have sanded and layered twice. I have a better finishing putty that I will be applying next to improve the finish. Plan to final sand the mold with 320 grit. The outside of the mold will provide the interior finish to the bait tank. The rough fiberglass finish will be hidden with in the transom.

Once the mold is finished, I plan to brush on 2 layers of gel coat, followed by 2 to 3 layers of 1.5 oz csm. Maybe a final layer of 1708.

My question is will a few coats of wax followed with 2 coats of PVA to the mold provide the preparation needed to allow the mold to separate from the tank? Or, do I need to spray paint a glossy paint finish to the mold? Then wax and PVA?

Any other pointers gladly accepted.
Old 03-10-2017, 01:03 PM
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I will be following this thread... but if you take a look on youtube there is a series of videos of a guy that made a mold out of foam for a motorcycle part. you can watch that and get an idea on what to do. Here is the link to video 1 hopefully you can navigate to the rest of the videos good luck
Old 03-10-2017, 06:51 PM
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If your not going to paint (which I would), wax, wax and wax. On new molds I would wax at least 3 times before making the first piece and they were always painted. Rexco or meguiars, never cared much for the PVA spray stuff- I always felt you can't beat a hand rubbed wax. Also, using an air wedge to pop the piece makes things go so much easier- not saying you need a wedge but spraying air inbetween the mold and part is all the difference. You can also use a ton of wedges.. I would take the bondo to 1200 grit if your not going to paint it. Then bondo might be smooth enough to create a nice finish if you wax it enough. Since this is a one time mold, just be prepared to destroy the mold when you separate it from the part.
Let me know how it goes or if you have any other questions.
Here's a link to some of my work: http://www.greenhulk.net/forums/showthread.php?t=171678
Old 03-10-2017, 10:24 PM
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Mako, thanks for the link. In part 3, my mold is analagous to the finished plug of the motorcycle seat. Once faired, he paints it with Awlgrip primer, sands (400 grit), and waxes it.

Looks like I'll be better off painting mine. I'd rather not have to destroy my mold in the separation (it has been alot of work and maybe someone else with a Pro-Line 251 will want a bait tank like this?). I hope I will have enough taper on all sides that the mold pulls out OK.

My tank will be like his mold in that the inside is finished and a flange will be built against a plywood table. This flange allow for the tank to fit up against the underside of the transom cap and will be afixed and sealed with 5200.
Old 03-11-2017, 05:18 AM
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I would agree with Joeu3 I would shoot duratec on the mold wet sand it to 320/400 then wax wax wax wax and wax then 1 good glossy coat of pva dry and shoot gel on it. I would have also used mdf or melamine and bog to build the mold and use the foam for corners and such if it was needed. The foam can contort and twist if it is not supported really well so you could end up with a funky part.
Old 03-11-2017, 05:35 AM
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I have been working on a mold and baitwell for a few weeks. Will post a few photos shortly. It is a lot more work than you think.
First is that poly will melt the pink foam unless it is 100% sealed.
Finish needs to be perfect to get the part off the mold. 300-600 grit and it will destroy the plug during removal. My first try went bad. 1200-1500 and a mirror finish even for a unseen part.
Wax and more wax. I lost one mold with PVA where it caused alligator skin in the gell coat.
I have sprayed 3 coats of auto 2-part uerathane as my final finish, cheapest you can but at the paint store.
I tried air, lots of wedges, and ended up forcing water between the part and mold. Let it sit for a while and float it out.
Keep posting.
You may have better luck but I destroyed both my molds getting the part out. Several 100 hours labor lost.
Old 03-11-2017, 12:33 PM
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Originally Posted by duke460 View Post
I have been working on a mold and baitwell for a few weeks. Will post a few photos shortly. It is a lot more work than you think.
First is that poly will melt the pink foam unless it is 100% sealed.
Finish needs to be perfect to get the part off the mold. 300-600 grit and it will destroy the plug during removal. My first try went bad. 1200-1500 and a mirror finish even for a unseen part.
Wax and more wax. I lost one mold with PVA where it caused alligator skin in the gell coat.
I have sprayed 3 coats of auto 2-part uerathane as my final finish, cheapest you can but at the paint store.
I tried air, lots of wedges, and ended up forcing water between the part and mold. Let it sit for a while and float it out.
Keep posting.
You may have better luck but I destroyed both my molds getting the part out. Several 100 hours labor lost.

Dang, that several hundred hours part is the worst part of losing a mold.

Ive been working on a console for a while now and starting to see some light at the end of the tunnel. I wasted some material and tore apart a few molds myself before i made one correctly. I got some good advise on how to build mine ill gladly pass on if your interested.
Old 03-13-2017, 06:11 AM
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When you build the plug you have to make sure you have a bit of taper or you will essentially be trying to pull a mushroom through a hole where the stem fits but the top will not. Flimsy molds or plugs rarely come out in one piece. A cup gun will spray PVA more perfect than any thing I have ever tried. I regularly wax 320 grit finish plugs with 4 coats of partall and then a tack coat of pva then a flow coat of PVA and pull a part with a good finish. If done right with wax and flow coats of PVA you can pull a half decent finish mold or part off of a 100 grit sand finish. I learned a bunch of shortcuts when I worked building plugs and molds for the concrete architecture industry like columns and arches and fountains tubs ect for stuff with a bunch of detail in it.
Old 03-13-2017, 02:07 PM
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Duratec has a sealer/primer (Styroshield?) that is supposedly safe for foam, even the polystyrene board from HD/Lowes/etc. Never tried it but looks like a great way to make quick, cheap plugs for stuff like this - the foam board is so easy to shape and work with, but having to coat w/epoxy or similar and then resurface before using polyester products on it makes it less appealing. And from experience, if you get a little melted foam coming through it can turn your gel coat into a permanently sticky mess that never cures correctly.

Duratec primer over MDF works wonders but a little more limited on what curves you can easily make. Will probably give the StyroShield a try eventually, depending on cost. May not be worth buying it for small projects.

Another tip that was passed on to me is to drill a small hole in the bottom of the plug/mold where a drain fitting or other hole will eventually get drilled in the part. Cover with packing tape on the inside while laying up glass. Then when ready to pull part, you can stick a blow gun tip in the hole and use compressed air to help pop the part off.
Old 05-18-2017, 06:44 PM
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Default Type of paint for mold?

I had to put this aside for awhile since I was busy with transom work and mounting a bracket. But this is where I am in the project:
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The following are some pictures to show how I got to this point. I started by using 2 inch wall insulation foam to build the box. I stripped the reflective layer off the outside, used drywall screws, tape, and thickened resin to hold the box together. Then, I cut and sanded the foam to round corners. The foam board had a very irregular surface. I used a gallon of Bondo to fill and smooth. Lots of sanding and more filler. For the final coats of filler, I used a better polyester filler I obtained from an auto body supply company. It allows a much thinner and smoother application and sands more easily.
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At every step, I would experiment with the compatibility of the products since I have never done anything like this before. Resin and Bondo working with the foam board, etc. I just did another test which didn't work well. I sprayed appliance epoxy paint on a small section of cured filler. I waxed the paint finish 3 times. I then layed up gel coat followed by a few layers of glass and resin.

When I separated the test piece, it appears the epoxy paint had bonded to the gel coat. I didn't wait too long between the coats of wax so I don't know if that is the issue or a paint/gel coat compatibility issue. I chose the epoxy paint for hardness and for a better finish.

I just started this process over using some West Marine topside polyeurethane paint and will do the layup tomorrow.

Any suggestions?
Old 05-18-2017, 08:01 PM
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You can epoxy over the foam. Build up your mold, epoxy and sand. You can then paint or just wax over the epoxy
Old 05-18-2017, 08:31 PM
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here is what you can put over foam if you want to build a mold out of pink panther foam and glass over with poly or vinyl

http://www.fibreglast.com/product/91...9oahoCBTDw_wcB


I have done lots of plug making and any plug made out of foam or mdf is usaully a one off and it gets destroyed. the glass will heat up and break down the mdf or foam and warp it




here is a write up from the one I built in my seacraft

got the plug built for the live well, I used 3/4 MDF and a 8" sonnet tube. I ripped the sonnet tube into 4 even pieces( as even as I could get them.) after I got all my measurements on the MDF and cut . I shaved 3/16" off the edges that the sonnet tube was gonna get stapled to, to make it flush with the MDF. After I got the 4 sides and corners all stapled together I cut the top big and used a flush router bit to run it around the outside to make it a perfect top.

once I got that nailed to the rest, I got a 3/4" round over bit to make the rounded edge. .

after I got it nailed together It was time to do a little tooling on it to smooth it out. I got some evercoat glaze from the autobody place and started with all the staple holes.

I also put a block to extend the rear drain lower


it took about 3 hours or fairing and sanding to smooth out all the inperfections.

after I got it smooth and sanded I put some radius wax around the block and some larger radius wax around between the table and the mold

once that was set I waxed it with 3 coats and sprayed 2 coats of PVA.



I let it dry and it was time to spray it with Gelcoat. I mixed 2 quarts of Gelcoat together with the dark blue tint. I made extra gelcat to store because I would never be able to match it.

I shot the gelcoat with the cup gun.

I layed up another mat and 1 layer of 1708 on it and let it set up over night .

I Popped it off the mold and it was relatively easy

this is where it got tricky I set the circular saw to just under 3/4" and made some rips. I then got in with the flat bar and chiseled away without damaging any gelcoat. once I got a small area of gelcoat opened it went easy, One plastic wedge under and it popped right up


I cleaned it up with the air nozzle then took it outside for a wash and cleaning. I then took my air trimmer and cut all the excess off. I dropped it in the front part of the console and it fits pretty good. I little more trimming and I will be glassing it into place.
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Old 05-19-2017, 05:53 AM
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I would use duratec primer on it. You will still need to test it to make sure it's not going to melt the foam. Spend time with a 18" board sander to make sure the plains are strait, dips and high spots will make it diffecult to remove. Then sand to 1000 grit and buff with a wool buffer and machine glaze. Apply mold release wax.

If you want one that's going to last for more than one part I suggest putting about 1/4" of fiberglass on the mold your making then bondo,duratec,wax and build your part off it.
Old 05-20-2017, 06:10 PM
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Originally Posted by wolfmw View Post
Duratec has a sealer/primer (Styroshield?) that is supposedly safe for foam, even the polystyrene board from HD/Lowes/etc. Never tried it but looks like a great way to make quick, cheap plugs for stuff like this - the foam board is so easy to shape and work with, but having to coat w/epoxy or similar and then resurface before using polyester products on it makes it less appealing. And from experience, if you get a little melted foam coming through it can turn your gel coat into a permanently sticky mess that never cures correctly.

Duratec primer over MDF works wonders but a little more limited on what curves you can easily make. Will probably give the StyroShield a try eventually, depending on cost. May not be worth buying it for small projects.

Another tip that was passed on to me is to drill a small hole in the bottom of the plug/mold where a drain fitting or other hole will eventually get drilled in the part. Cover with packing tape on the inside while laying up glass. Then when ready to pull part, you can stick a blow gun tip in the hole and use compressed air to help pop the part off.
I often use MDF for plugs. Great stuff that doesn't cost an arm and a leg.

Styrosheild sorta works but it ain't all it's cracked up to be. It is a highly filled polyester resin base. It still eats into the foam a bit so it doesn't leave a really accurate surface. If I was using a polystyrene foam, I'd just give it a couple of coats of epoxy to seal it. After that you can stick with epoxy fillers and primers or switch to a polyester primer like Duratec to fair it out/and or act as a tie coat for filler. Easier is to just start with urethane foam if you are planning on using polyester body fillers and primers.

About that tip on using a blow hole - be careful you don't apply too much pressure or you could crack the part in corners. Short blasts will work to release the part.
Old 05-21-2017, 06:42 PM
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Well, my West Marine paint was beyond its self life. It didn't harden properly. So, I tried the spray on appliance paint again on a test piece. I let it dry longer and applied the gel coat and resin with longer cure times between the two. I got the same result as before.

I have the Duratec primer on order. Looks like I'll be learning to spray this primer and the gel coat. Can anyone recommend a Harbor Freight Tools HVLP spray gun to use?
Old 05-22-2017, 05:09 AM
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Yep. The "purple" one. Can be had for $10 with coupon. Only thing the "pro" version gets you is stainless internals as far as I can tell. Doesn't spray thick stuff too well (1.4 mm tip) but I have sprayed thinned duratec and gel with it successfully.

Also, if you're looking for cheap paint options for something small, I've used rustoleum topside paint. Can be sprayed or roll/tipped effectively, not as durable as big $ paints but dries pretty hard (very slowly though)

Last edited by wolfmw; 05-22-2017 at 05:13 AM. Reason: Add info
Old 05-22-2017, 05:55 PM
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Originally Posted by wolfmw View Post
Yep. The "purple" one. Can be had for $10 with coupon. Only thing the "pro" version gets you is stainless internals as far as I can tell. Doesn't spray thick stuff too well (1.4 mm tip) but I have sprayed thinned duratec and gel with it successfully.

Also, if you're looking for cheap paint options for something small, I've used rustoleum topside paint. Can be sprayed or roll/tipped effectively, not as durable as big $ paints but dries pretty hard (very slowly though)
Did you thin the Duratec with styrene or use the duratec thinner? The duratec thinner is not available from the supplier i used
Old 05-23-2017, 04:39 AM
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Been a little while, but I know I didn't buy any special thinner. Duratec specifies Methyl Ethyl Ketone (MEK - NOT MEKP) as a thinner option and pretty sure that what I used, thinned about 15%. Check the label on the can, it should have thinning directions. Another thing to consider is adding the Durate Hi-Gloss additive to your final coat - extra stuff to buy but saves some sanding. I only got a very small amount of orange peel with just thinned duratec though.
Old 06-08-2017, 12:39 PM
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Bait tank success!

Duratec primer arrived. Bought the Harbor Freight spray gun (never used one before!) Set up a spray booth in the side yard. Went to work....

Shot the Duratec with the spray gun using a Sears 1Hp/3Gal compressor. Set at 40psi. The compressor kicked on and ran constantly, but seemed to keep up. I think I had too much fan in the spray pattern (maybe the Duratec was too thick?). Coverage was thin and had to overlap and get close to the mold to get coverage. Picture after some wet sanding (200 to 400).
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A melamine cutout to form a smooth flange and avoid rough areas at the edge of the mold. Sealed the joint with clay. Used a washer to cut a uniform fillet.
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I applied 4 coats of Partall wax and shot PVA along the flange and about 3 inches up the mold. I had read where PVA caused some wrinkling in the applied gel coat. I wanted to avoid this, but was willing to accept this result in areas that will go unnoticed in my installation. As it turned out, shooting the PVA didn't adversely impact the gel coat finish.

I thinned the gel coat with styrene and added tint. I adjusted the gun to shoot a more round pattern. The coverage was better than with the Duratec. I had another 300 ml to shoot when it gelled up in the cup. I think having the lid on the cup really allowed the gel coat to heat up and go off much faster than usual. Lesson learned: use less MEKP.
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Layed up .75 oz mat over the drain, followed by 1.5 oz mat over the bottom and flange. Wrapped 1.5 mat around the sides with some overlap at the flange and bottom pieces. Finished up for the day as I ran out of resin. This tank measures 22H x 24W x 14D (I figure once it is plumbed it will hold about 25 gallons) and used about 2.5 qts of resin.
Lesson learned: Don't try to do too much at once. I had numerous voids which allowed the gel coat to crack as I removed the tank from the mold. To do over, I would use lighter mat and do the flange, rounded corners, drain separately to give myself more time to roll out the fillets and edges.
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With more resin, added 1808 to the flange. Used coremat to stiffen the corners and middle sections; more 1.5 mat on sides and bottom.
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I ground down the flange edges then popped the tank off the melamine.
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Breaking away the mold.
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I had some flaws. Mostly around the flange fillet and drain. I had to grind these away using a sanding attachment on a rotary tool. Then added paste resin and topped with more gel coat. While not factory quality, I am very pleased with the outcome!
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Old 06-08-2017, 01:48 PM
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Nice! what did you use to tint the gelcoat?

be careful... you're on a slippery slope that can lead to poor decisions like buying a project boat!

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