Alternative to micro balloons

[oldbloke]

You need to be careful putting foaming stuff in relatively enclosed spaces, they can exert quite a pressure. I have seen a ruptured Laser 2 where someone tried to cure persistent leaks will builder's foam and have heard of other, similar, escapades

 

[thinwater]

PU glue can be mixed with water or other medium to thin and increase its foaming ... or used raw - where it has incredible strength but light weight.

Here's an example of diluted PU giving immense strength .... the nose cone of a Model jet of mine ... The model is supplied with an ultra light thin plastic nose cone - first landing and its split / cracked etc.

Here you see my attempt on left with a foam piece to support ... but on the right dilute PU foamed up and creating a strong nose cone for near zero weight penalty ..

As you say - the amount of foaming is impressive and pressure exerted can be surprising. The other advantage - is it does not care about wet surfaces to bind to ... in fact they advise to wet the surfaces before application ...

Good point about the expansion. If you pump in much, you want to make sure you give it a way out, or it will force the skins apart. On the other hand, if only filling small holes and small areas. plugging the injection holes will force the foam into the surrounding cracks and voids, which is a very good thing. It's about moderation and observation. Since the foaming process only takes ~ 10 minutes, stay there and watch (curing takes longer).

 

[Gixer]

Argh I’ve not got any talc, polyfiller?

 

[Stingo]

You should be able to find talc in the baby section of any supermarket

 

[Gixer]

You should be able to find talc in the baby section of any supermarket

Yes, but that means I got to stop on the way down to the boat.

Not a big deal but I have loads of polyfiller

 

[oldbloke]

Quite a few "baby powders" are actually corn starch ,which would be less appropriate for underwater use.

 

[Mister E]

Go to a boat yard and ask if they will sell you a small quantity of filler.

 

[Lightwave395]

I cleaned out and replaced an area of damp balsa core with epoxy foam from East Coast Fibreglass Supplies, brilliant stuff

 

[Neeves]

Talc has developed a bad name as a result of legal cases of talc causing cancer (or something similar to asbestosis - talc is a fibrous mineral). Hence the use now of corn starch. Corn starch I'd have thought would be something of a disaster as a filler in a marine environment whereas talc is a stable mineral in a wet environment.

Alternatives as a filler would be crushed pumice (it washes up on beaches round Sydney from volcanic eruptions - though difficult to collect a meaning full amount). You can buy it from most chemists, used as an abrasive for hard skin, raid your wife's cosmetic drawer

Another option is dolomite fines (mixed magnesium/calcium carbonate) available from your local garden centre. Limestone fines, NOT Lime, would be similar. Cement and poly filler might not be a good idea, one of the components reacts with water to give the finished product, mortar, strength. Fine sand, simply quarts or mixed with shell would be a devil to sand back. Exfoliated vermiculite might be good - but I have no idea where you would buy it - its used as insulation.


Potters Balotini make the reflective product used in road paints, simply melted glass, they might make something effective. I think the reflective product might be expensive - but they might make other products of which I am unaware

There are actually a lot of products you could use as a filler - the problem is finding a source. Coal fired power stations used to produce a waste product like micro beads - it was a lightweight ash product, inorganic. If found use in foundry formulations - so was a commercial product but I forget the name and source.

Jonathan

 

[Daydream believer]

Coal fired power stations used to produce a waste product like micro beads - it was a lightweight ash product, inorganic. If found use in foundry formulations - so was a commercial product but I forget the name and source.

Jonathan

Leca?

 

[thinwater]

The OP is long gone, but ...

The simplest answer is to buy any of dozzens of pre-thickened products in a pair of syringes at the hardware store. It doesn't need to be marine. In the US JB Weld is popular. I always have some underwater epoxy on the boat in case of leaks. Leave it slight below flush and finish with a gel coat patch. After moving some winch handle pockets, I just finished filling the hole this way. I have cans of epoxy and a drum of silica gel, but the mini-kits are easier for something like this.

 

[Gixer]

The OP is long gone, but ...

I’m still here
Havent done the job as I went down Friday evening to do it but it was raining and blowing a hoolie! JB weld, that’s a genius idea!

 

[DownWest]

I know several people who use flour (as in bread..) makes quite a hard fillet, so sanding not so easy, but for filling holes etc works fine.

One pro yard have it in a container labeled coloidal silica

 

[Neeves]

Leca?

Good Idea

Fine Leca would work (or larger Leca ground down) would be good - and conveniently available in your local gardening store (or your own pot plants?). Again its inert.

I'm a bit twitchy about using organics like flour - hence I've never tried them. I find plenty of inorganics available to use, without resorting to the kitchen.

Jonathan

 

[thinwater]

I had to look up LECA. Vermiculite (Wiki) is more common in the US.

Yup, that will work well and is sometimes used commercially for this.

I use colloidal silica. I got a huge bag (10kg?) years ago for use as an additive in climbing chalk, and I seriously doubt I will ever finish it. Good for bonding and fillets, but seriously hard to sand, so not good for fairing. But for the OP's problem, I'd probably use something in a tube or syringe, and then finish with a gel coat patch tube.

 

[Neeves]

Expanded vermiculite and LECA are very different animals and though both could be used to fill epoxy the resultant cured product would have different characteristics. Vermiculite enjoys expansion of 6-20 times (hence its application as an insulating material) and the 'finished' product is 'soft'. Heating it beyond the optimum for expansion will destroy the insulation properties and the product will become 'more like' LECA. LECA is in effect a tough ceramic. It has porosity but is hard, like glass (it will be difficult to abrade). Its also a bit like pumice but harder. Imagine a common fired house brick (from Redland et al) and that's what LECA is like - they are made from similar raw materials at similar temperatures. Much of LECA is 'in effect' a ceramic glass (with holes).

One use of vermiculite was in an expanding mortar - mix in the raw vermiculite, heat up the mortar to 900/1000 degrees, the mortar expands and forms an impenetrable barrier (to molten metals), so used in iron and steel making, foundries etc. LECA is 'simply' calcined clay made in a rotary kiln at 1,200 deg C (as used to make cement).

For filling holes both will work, though I suspect LECA will produce a tougher product (higher tensile strength) - but for filling holes this will not matter. Vermiculite tends to be a golden colour, not unlike some resins. LECA is red/brown/black and hard (its glass + some very hard acicular minerals).

Both expanded vermiculite and LECA are easily available - but if you can source them you could equally easily source a more accepted filler. I actually don't know how you buy expanded vermiculite, again garden centres?, but Leca (comes under different names) - garden centres.

If push came to shove I'd use expanded vermiculite involving much fairing and LECA for anything structural. But neither are commonly used for filling - there are better products.

Jonathan

 

[thinwater]

Areed. As much work as goes into projects, I would not muck about. I use Cabosil for most things.

 

[arcot]

Custard powder

Cornstarch....

 

[Lightwave395]

Areed. As much work as goes into projects, I would not muck about. I use Cabosil for most things.

Don't know why it makes sense to faff around with weird materials when Cabosil is as cheap as it gets...

Cab-O-Sil (fumed silica)

 

[dankilb]

Don't know why it makes sense to faff around with weird materials when Cabosil is as cheap as it gets...

Cab-O-Sil (fumed silica)

+1 with even affordable (non-West) epoxy resin @ around £100 inc. per gallon, I'm not sure about chucking food into it! Silica all the way!