Talcum powder in resin

[dgadee]

Forgot to get talcum to thicken some gel coat when I was at my supplier. I can't see any reason why I can't use stuff out of the chemist. Can anyone tell me differently?

 

[earlybird]

Your boat will have a beautiful perfume!!

 

[Chrissie]

Isnt talcum made for soaking up water? its the reason, amongst other inappropriate fillers used, that caused so many cases of osmosis in older boats. Get yourself some proper glass bead thickener or woodpulp thickener, better still, the proper combination of each.

 

[nauticalnomad]

Forgot to get talcum to thicken some gel coat when I was at my supplier. I can't see any reason why I can't use stuff out of the chemist. Can anyone tell me differently?

Ive used it in wests epoxy resin and applied it to my van- It works fine for that.
Havent had any osmosis on my transit van as yet......

 

[G12]

Just out of interest, why would you want to further thicken Gelcoat? It's pretty thick already....

 

[dgadee]

I have taken off the wooden top of a galley which someone added, replaced a sink with a different sized one, and am just going to refurbish the original gel coat so that everything matches. Not much danger of osmosis.

I have microballoons but they are reddish. Talcum is, I think, pretty normal for getting a reasonably hard wearing gel coat.

 

[G12]

Don't forget to add the wax additive to the gel if you're just painting it on or it'll be a right sticky mess. It shouldn't need thickening. If it's just chips and ding's that you're repairing then use resin proof tape over the gel to seal it from the atmosphere while it goes off. If you're careful then you can get it almost perfect 1st time...

 

[dgadee]

Yes, using flowcoat. Don Casey is my source for thickening suggestion - in case one coat isn't sufficiently thick. Page 109 of sailboat refinishing. I am adept at grp but this is first attempt at this technique.

No one has suggested everyday talc differs from non perfumed, so will give it a go.

 

[G12]

Yes, using flowcoat. Don Casey is my source for thickening suggestion - in case one coat isn't sufficiently thick. Page 109 of sailboat refinishing. I am adept at grp but this is first attempt at this technique.

No one has suggested everyday talc differs from non perfumed, so will give it a go.

Well one thing I can tell you is that the perfume in talc can attack drysuit seals so it's definitely different to non perfumed talc which doesn't. You can buy non perfumed in boots or similar shops no problem. Boots do their own brand.

Good luck!

 

[pappaecho]

Yes talcum powder and calcium carbonate are used as fillers for polyester resin. I thin that the talcum we used to use, came from Norway and was ground up rock, and probably not as fine as the pharmaceutical grades, with or without perfume. I seem to remember that both products were coated with 1% calcium stearate ( soap to you) to make the powder mix with the resin better

If you want to thicken the resin give it a go!

 

[Chrissie]

Have a look at this article, research has been going on for many years and the causes for Osmosis found many years ago, but the boats were already in exsistence, and boat builders dont like to admit what they have put into their mix. There are still many thousands of people out there who havent heard about all the research and still do things the way they were done when they were a lad.

Article by Steve Smith, Chemist.
.....The net result of adding talc, limestone or other mineral fillers or pigments would be a dramatically enhanced tendency of the hull to show GRP laminate deterioration of the type commonly referred to as osmosis. There are three reasons for this. First, special mixing equipment is required to mix powders with liquids without mixing in fine air bubbles. This is routine for paint manufacturers but not for boat manufacturers, thus many fine bubbles in the resin would be expected. These bubbles are additional voids into which water can diffuse, thus creating osmotic blisters. Second, adding mineral fillers would interfere with the ability of the resin to wet out bundles of glass fibre, allowing voids in which water accumulates, hastening chemical decomposition of the GRP laminate. Third, mixing limestone (calcium carbonate) or other water-soluble minerals will cause osmotic blisters as the limestone dissolves in the water that is drawn to diffuse through the laminate.
Normally, no manufacturer is likely to admit to anyone they are doing this, much less doing it only to save money. There is no good reason for it. ….. …The chemical consequence of mixing powdered limestone, or any water-soluble mineral for that matter, into GRP in a boat hull is to guarantee that there will be osmosis blistering and deterioration, as the water diffusing into the GRP will dissolve the limestone just as underwater seepage dissolves limestone, creating caverns with stalactites and stalagmites.
© copyright 1972 - 2009, The Brain Trust, a California irrevocable trust,
reprinted with permission Steve Smith The Real Story of Osmosis Blistering, Treatment, Cure and Prevention. March 2003

PS, Its probably absolutely fine for you to mix talc in your flow coat for an internal coating,as you are planning, bear in mind there will be no strength in the stuff you are applying, a readymade gelcoat filler as has already been mentioned would do the job without the shrinkage you would get from a polyester flowcoat.

 

[Ardenfour]

Have used plain flour to thicken epoxy for years - no ill effects

 

[nigelmercier]

Have used plain flour to thicken epoxy for years - no ill effects

Thoughts that come to mind:

If you used self-raising flour it would add buoyancy.
Mixes in a piece of cake.
It could increase the roll.
Boat keeps self-steering to Sandwich.

But flour? Really?

 

[alahol2]

Article by Steve Smith, Chemist.
.....The net result of adding talc, limestone or other mineral fillers or pigments would be a dramatically enhanced tendency of the hull to show GRP laminate deterioration of the type commonly referred to as osmosis. There are three reasons for this. First, special mixing equipment is required to mix powders with liquids without mixing in fine air bubbles. This is routine for paint manufacturers but not for boat manufacturers, thus many fine bubbles in the resin would be expected. These bubbles are additional voids into which water can diffuse, thus creating osmotic blisters. Second, adding mineral fillers would interfere with the ability of the resin to wet out bundles of glass fibre, allowing voids in which water accumulates, hastening chemical decomposition of the GRP laminate. Third, mixing limestone (calcium carbonate) or other water-soluble minerals will cause osmotic blisters as the limestone dissolves in the water that is drawn to diffuse through the laminate.
Normally, no manufacturer is likely to admit to anyone they are doing this, much less doing it only to save money. There is no good reason for it. ….. …The chemical consequence of mixing powdered limestone, or any water-soluble mineral for that matter, into GRP in a boat hull is to guarantee that there will be osmosis blistering and deterioration, as the water diffusing into the GRP will dissolve the limestone just as underwater seepage dissolves limestone, creating caverns with stalactites and stalagmites.
© copyright 1972 - 2009, The Brain Trust, a California irrevocable trust,
reprinted with permission Steve Smith The Real Story of Osmosis Blistering, Treatment, Cure and Prevention. March 2003

I don't know the truth of the matter but neither, I think, does this writer. Purely on the basis of this article it is written as speculation/opinion and not as a result of research.