Backyard Aquaponics
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It was a perfect storm yesterday. I was framing up a Book case jig for the wife and assembling the first case... I covered the case to allow the glue to set and made dinner. After dinner, as I was surfing the forum, I found Tea20's exceptional fiberglass GBs... and then, it hit me. Not only was I building 3' x 8' book cases, but also a plug mold for 3' x 8' x 16" fiberglass growbeds

I quickly extricated the shelves once the glue set and grabbed some spare melamine shelving, tempered hardboard, and body filler. It was on: the race for a GB plug mold.

As I glued, nailed, and filled, all I could think was; "yes, I finally have a use for the bolts of fiberglass matting/cloth/tape I have in the garage."

Suddenly, the realization hit: "I needed a gel cot sprayer! And, oh crap, how do I best seal the mold, what release agent do I use? Should I use a tooling Gel coat, or a standard pigmented one?" So many questions, that only time and patience will resolve.

Needless to say, after the euphoric brain play; reality set in. Filler takes time to cure, and even more time to sand. That is where I am at, sanding and filling, sanding and filling, and yes, more sanding and filling. But, when this plug is done...

Pictures and more details of the build thus far are forth coming.

Hi JB

Well done for having a go at making your own FG growbeds.

I made my fish tank, sump and grow beds (1mx 2m) and also my wicking beds from fibreglass.

Can I suggest some things that I learnt that may help you.

1/ The plug needs draw angles of at least 5 degrees

2/ Install three air nipples under the 3 x 8 foot side so when it comes time to popping the mould

turn on the compressed air. Otherwise the 3 x 8 side will form a vacuum that will make

separation near impossible.

have fun

cheers Lou

Thanks Trout. By draw angle do you mean a slightly trapezoidal plug, or beveling/round-over of all 90 degree joints? I did a 1" (25mm) round-over and am doing a 2" (50mm) fillet at the lip. The air nipple idea is great. I will incorporate it. Did you coat the plug with a gel coat at all? Or, go the poly and paste wax way?

All of my fiberglass experience is laminating surfboards, and doing costume/prop armor. This big stuff is new to me, though the principles are generally the same.

The draw angle is the angle you give the whole plug so that it can slip out.

The books say about 2 degrees , I can barely get them out at 5 degrees.

As a release agent I generally use wax.

I use gelcoat and then 3 layers of 600gsm matting

You could however use flowcoat instead of gelcoat after the job


cheers Lou

Gotcha. I have some left over carpet to tile transition that is 8 degrees and 12 inches wide. Will 4" of vertical surface (or lightly filled) then angled surface be much of an issue? I know things get tighter towards the bottom (top) of the mold and that is what we are trying to avoid.

Only 3 layers? Best buy a lot of resin then, I can pull quite a few with the 150yds of mat and cloth I have.

Did you glass in any support? Or are they more than rigid enough at full cure?

Standard Marine Polyester for laminating yes? Epoxy is so expensive.

I think the 4" vertical will tie the mould. Personally I would cut some of the transition and apply it

with some packing. The ridge produced will also increase the strength (see diagram)









Polyester resin is what I use.

I didn't use any supports but they are easy enough to add.

cheers Lou

Fibreglass hey

ah man.. let me just say, after about 12 months of making male and female fibreglass molds, pulling quite a few tanks and GB's off them, I've given it up for the following reasons:

- it is more expensive and time consuming to produce than say for instance, corrugated iron tanks

- fibreglass tanks need careful postcuring, to get rid of any uncured styrene or osmosis blisters etc, to make the tanks safe for potable water. Failure to do this will result in the tanks leaching styrene (now listed as a potential carcinogen) into the water. You can even taste the styrene in water from uncured tanks. If you don't beleive me, checkout all the horror stories on the boating/yachting websites of blokes who made fibreglass drinking water tanks for their onboard drinking water storage, only to have their water taste horribly chemically and plastically, given the users headaches etc. I eventually swapped to using food grade resins and gelcoats, just to be safe (but more $). Alternatively you could line the finished tanks with a safe non-toxic bituman paint

What quantities are you thinking of making?

If you are serious about it, you should be prepared to invest in a good air compressor, gelcoat gun and good
protective gear (eg particle and activated carbon mask etc)

Trouts advice regarding tapers is good.

Also make all corners rounded too for ease of pulling the parts off the molds.

Timber bracing battens can be added between layers of resin and matting to add strength. For even more extra strength, add a U shaped rim to the part which strengthens the top rim of the GB or fish tank.

Instead of compressed air to help remove the finished part, I put in a few fittings into the mold which allowed me to connect the tap onto, and used water pressure to remove the part. Using water has another advantage - most of the PVA release agents breakdown in water (they're designed to do this on purpose for ease of release) so when water is injected between the mold and the part, the release agent is removed allowing easy pulling of the part

Once I intially waxed the mold, I opted to spraying the blue PVA release agent with a gelcoat gun which was a lot quicker than re-waxing the mold between every part

If you were in my region, I would offer to give you my pre-loved growbed and fish tank molds, now unused, which I want to get rid of (anyone else interested who wants to pick them up?) Here's a photo of the tanks they produced:

Excellent Information Trout and Jono.

Initially looking at 3 GBs, with the possibility of 5 more once I get the area cleared and filled.

In regards to post curing, I have used a heated tunnel for small parts in the 80-90C range with good results, and UV post curing of surfboards. In these bigger parts, is it more time or temperature or both for a legitimate post cure?

I have left-over insulation and radiant barrier material so making a curing "oven" for lack of a better term would not be difficult.

I have the compressor and Protective equipment. The gel coat gun is on the "to save for" list.

Can I forgo the sprayed gelcoat and use a brushed or rolled thinned topcoat (Flowcoat) on the inside after the initial cure and release from the mold?

Thinking on it a bit, and since I am only doing 3-8 units, going through the whole negative positive mold making from my wooden plug seems extraneous. Barring a tied mold, I think I could pop that number of semi-finished casts off the plug itself. Especially if my first layer is cloth and cloth tape backed by mat. Thoughts?

Its 3" Polyurethane Foam That means I do not need a plug at all. I can simply adjust the jig to resin the foam together and laminate the outside much like the surfboards I am use to. Glass in some timber banding and then pop it out of the Jig and laminate the inside. Then hot coat [same as flow or top coat] the inside and ensure post curing is achieved.

I was puttying carpet transition like in Trout's diagram and was like... this takes a lot of time. But, now I am in my fiberglass comfort zone and I think it will work!

So, major change in method, but still fiberglass. May take a little more resin to make a strong laminate, but the time saved from mold making will make up for it in my opinion.

Some of my super rough plugging.

Both, as far as I understand, but temp would probably be the more critical factor. Fibreglass is primarily a chemical reaction, but also a thermal reaction in a sense (low temps and humidity = bad or extended curing)



Please post pics on your oven when you make it. I never got to that stage but am curious to see how it could be done.



Sweet. My weapon of choice was the ever popular "G100", gravity fed "popcorn gun" (ie http://www.ecfibreglasssupplies.co.uk/p ... y-gun.aspx). Nuplex Industries, my fibreglass wholesaler, had to import this gun from the USA so you shouldn't have problems sourcing it if that's what you decide to go for. Can't recall how much it cost, don't quote me but I think about $200 from memory, plus a bit more for the additional brass nozzles.

It's a fantasic gelcoat gun. You can get a range of nozzles for it from about 0.5mm diameter through to 7mm, so you can use the one gun for spraying PVA release agent, gelcoat/flowcoats, spray paint (with 2mm or 2.5mm nozzle), sticky bitumen paint, heck, even sand blasting with the larger nozzle they claim

The best bit about it in my opinion is there's hardly any cleanup. Just dip the nozzle into a bit of acetone, and clean the trigger area, the resevoir itself is a disposable paper or plastic cup. For gelcoat, I would re-use the same plastic cup for about 6-8 sprays, letting the unused gelcoat cure in the cup between coats, which once cured, was easily released by squeezing the flexible cup a few times and the hard stuff either flaked off or dropped out.

It's one of those tools that once used, you can't go without in your shed/workshop.. I use mine more for spray painting than anything else thesedays.. a quality made item which should last you a lifetime. The only thing that can break on it is the o-rings which are easy to replace from any hardware store

It might be possible (I haven't done it), but gelcoat as a first coat would make the part easier to release from the mold compared to a chopped strand and resin layer (which would be more porous). It depends how big your part is, but rectangular growbed shapes tend to be large right and a lot of surface area to unstick. Fishtanks are even worse being deeper.

You don't need to spray the gelcoat layer onto a male mold, just paint it on by brush and the final surface of the part will still be smooth if you've prepared the mold right.

Remember also that female molds release parts a lot easier than male molds, as the part shrinks somewhat on the mold as it cures. On a male mold, this tends to lock the part in place more, on a female mold it starts to release tension and sometimes the part 'pops' off the mold by itself (premature pre-release I think they called it in the industry!)

All I can comment is from my own experience here - for my tanks I was using male molds, and even with a gelcoat layer as first layer, with generous inclined tapers on the sides of the part, and a pretty smooth mold surface (flowcoat sanded back to 600 grit paper), I had great difficult removing parts off the mold until I added the water injection release system.

You may have better success, if you do, please post your experience so we can all learn tips



What will the final waxed surface of your male mold (plug) be made of?

Regarding the comment on your photo about having difficulties with your filler - what are you using? I've heard a range of fillers being used for mold construction, from paper mashe and chicken wire, to gyprocking plaster..


ps the best fibreglassing tip I ever read was before laying up, to dust the skin of your arms with either corn flour or talc powder which blocks up your skin pores (safely and temporarily, easily washed off) preventing the infamous itching from little glass fibres in your skin. This made my fibreglass work so much more enjoyable