OK the plug did not lock up...

[Kez]

I have done up a plug for a fuel cell. I made the plug out of solid 2X4 with the proper taper so the mold can come out. The plug is glued to a parting board.

I have primered and sanded the plug 5 times using spray can primer. I then sprayed on a coat of Krylon. The spraying was done outside and a few gnats landed in the paint. There are a few other dust specks.

Question: If I sand it smooth, I will be exposing some primer. Do I need to recoat with paint before waxing? Or can I sand out the blemish and then wax and PVA?

I am self taught and have successfully moulded a mono hull. But I did not have any exposed primer on my mold. Since this is just a fuel cell and I only need to pull two pieces out of it. I am hoping I can get away with it without having to spend more time on finishing the plug.

By the way, the layup will be epoxy not polyester resin...if it makes any difference.

Thanks.

 

[Mike Hughes]

Just use some 240 wet sand paper. The black stuff. You can knock down the crap and make it look good enough. No need to repaint it for just a fuel cell. Wax it up and PVA and your good.

Mike

 

[P THOMAS]

Yes if you just sand it smooth it will be ok, if youwant it real shiney got to 400-600 wet sanded and then use the wax. maybe you would have problems if a spot of primer shows but if it was a sandable primer it will shine up ok. Use a no siicone wax or the pva will fisheye, if it does just give it a couple coats.

 

[Kez]

Thanks guys. So it is OK that the primer is exposed. Interesting information on the silicone wax causing fisheye. I bought the mold release wax from a fiberglass supply store and I have no idea whether it contains silicone. But when I applied the PVA, it fisheyed like crazy. I have tried both brushing with a foam brush and using a disposible sprayer with the same results. The fortunate thing is that the fisheye did not appear to have transferred to the final part.

For the fuel cell, I just want two pieces out of it and if there is imperfections I am not too concerned.

Final question: Can I use car wax instead of mold release wax? The car wax seems to spread more easily.

Thanks,

kez

 

[Kez]

Update:

I sanded the blemishes with 320 wet and the primer started to show through in a few area. I then noticed some scratch marks from the sanding. In an attempt to remove the scratch marks, I used Turtle wax rubbing compound.

I proceeded to waxing the plug with mold release wax (don't know if it contains silicone or not). After putting the wax on and buffing it off twice, the plug did not feel as slippery as I would like. How many coat of wax is recommended? Do you wait before buffing it off?

Thanks,

kez

 

[P THOMAS]

Part All brand wax does not have silicones, it is used if PVA is applied. I think most mold release waxes do and they are not supposed to be used with PVA. Your part should release ok with the wax you used. You should get a preety shiny finish sanding 600 and waxing. Some enamel like the krylon dont buff out too well .

 

[Terry Keeley]

Part All brand wax does not have silicones, it is used if PVA is applied. I think most mold release waxes do and they are not supposed to be used with PVA. Your part should release ok with the wax you used. You should get a preety shiny finish sanding 600 and waxing. Some enamel like the krylon dont buff out too well .

I know Phil's the expert here but I would never lay up a mold or part without PVA, had a plug stick once, only once...

 

[Bill Gibson]

If you put on several coats of Part All wax and then apply PVA , things will come apart nice and easy, especially if you dunk the piece in water and walk away for a little while.....

 

[Kez]

Thanks all for offering your inputs. The mold release wax I have says "TR High Temp" on the can. It is blue. I have used it successfully to mold a deepvee of my own design. I did use PVA over the waxed plug.

Now my original was whether I can cheat and get away with exposing some area with primer. Since everyone agreed that it is OK for a fuel cell, I started waxing it. It may be because of the paint I use, the plug never some to a high gloss luster. I have let the paint harden for a week.

Will more coat of wax really build up? I can not tell any difference from the first coat to the third. Do I keep building up more coat of wax? I hate to lock up this plug and have to start over. May post a picture if it helps.

 

[Mark Poole ModVP]

If you use paste wax it has to be done like this......swirl on let dry to a haze, about an hour. Buff off. Wait at least 5 hours before swirling on another coat. If you don't do this you will not get individual coats of wax built up. Wax at least 6 times, more does not hurt. This next step I always do. I swirl on one more coat, a very light coat. Then I let it dry for several hours. This is what I brush the gel coat over and then lay up the mold. This light coat of wax will be so thin that it will not cause deep swirls in the mold. When you pop the mold off, the light swirling will sand out with 1000 grit wet sandpaper. I have never stuck a mold.

I would not have shot it with Krylon. I would have sanded the primer up to about 800 to 1000 grit wet paper, then waxed it as explained above. Basically if you use enough coats of paste wax it will not stick. Each coat will fill up more and more micro imperfections.

 

[Kez]

If you use paste wax it has to be done like this......swirl on let dry to a haze, about an hour. Buff off. Wait at least 5 hours before swirling on another coat. If you don't do this you will not get individual coats of wax built up. Wax at least 6 times, more does not hurt. This next step I always do. I swirl on one more coat, a very light coat. Then I let it dry for several hours. This is what I brush the gel coat over and then lay up the mold. This light coat of wax will be so thin that it will not cause deep swirls in the mold. When you pop the mold off, the light swirling will sand out with 1000 grit wet sandpaper. I have never stuck a mold.

I would not have shot it with Krylon. I would have sanded the primer up to about 800 to 1000 grit wet paper, then waxed it as explained above. Basically if you use enough coats of paste wax it will not stick. Each coat will fill up more and more micro imperfections.

Thanks. That answered my other question. I will try waiting 5 hours before waxing another coat. That explained why I noticed no difference when I waxed on 4 coats within an hour.

 

[Kez]

This is how the plug looks like after 8 coats of wax. As you can see it is not shiny and lacks the luster of a polished finish. I am not sure if it is because of the Krylon paint not being hard enough.

Please check the taper of the plug, do you think it will release OK?

Final question: For a fuel cell I am planning on a 3 Oz cloth followed by a 6 Oz. Will this provide adaquate rigidity?

Thanks,

 

[Mark Poole ModVP]

Can't tell how much taper is in it unless you put a square next to it. Even if this thing has a degree or two of taper it will be very hard to free without an air hole. Also, not sure what the gel coat will do to the Krylon. I learned a long time ago to pull molds off well polished primer.

If this is going to be a fuel cell what kind of resin will it be built with? I kow of a couple of nitro boat hulls that were ruined after the fuel tank split open.

 

[Doug Kirkland]

This is a picture of a console for my flats boat I am building from scratch. I use only Dura tech primer for my plugs when I buff this out I will wax it with mold release 6 or seven times allowing at least ONE hour flash time between coats then a shot of pva and then I'll spray it with

Tooling gel (red) wait about 1 hour then start my lay-up when its ready I'll then tank it in water then if it doesn't release and this shape is similar to your fuel tank and hard to release, I'll drill a small hole MOLD SIDE just thru the mold for air assist (Always works) then you can fill the hole with a touch of clay to build the part and if necessary use the hole for the next release. I hope tis helps just puttin my two cents in...... good luck.

Doug Kirkland

 

[Kez]

Finally laid up the fuel cell using two layers of 3 Oz cloth. I am quite surprised at the strength with just 2 layers of cloth. It took a lot of "persuation" to get the fuel cell to come off the plug. I finally did without damageing the plug.

But when I tried to fit it into the hull, I found out I have not accounted for the thickness of the cloth when I made the plug and it will not fit into the hole I cut into the hull. Please see pic.

I do not have the motivation to make another plug again. Any suggestion? You can see I start to sand the fuel cell. I am reluctant to open the hole any bigger as I do not want to weaken the hull.

Has anyone tried making a fuel cell out of 1/16" ply?

 

[Tom Foley]

JUST BUILD A METAL TANK AND BE DONE WITH ALL THIS FUSS :unsure:IMO

 

[tnrcboatracer]

Is this to be a sealed fuel cell, or a pocket to hold a plastic or metal tank? IF it is a pocket, once you attach it to the hull, the weakness is gone.

I've never had much success with keeping a glass fuel tank sealed due to vibration and 65-70% nitro fuel. Metal tanks are best. And they have built in sump tanks. (Thanks Walt).