Pumice stone

[sergioasolis]

Hi there , Here, I have not found pumice powder not saying FFF grade, however there are pumice stones, could someone help me to know how to grind the stone to a FFF grade?, actually I do not know what is really FFF grade?, just heared, it is what I have to use to fill pore and lever.

Thanks

[KJ401]

Don't worry about crushing or grinding pumice stone - pumice powder does two things in french polishing - fills the grain and cuts the polish as you apply it so the finish doesn't end up ropey (lumpy, uneven). It needs to be very fine and consistent.

But if the timber is open grained, you'd be better to use grain filler before applying polish and pumice.

In the States, pumice can be bought in a couple of grades from Behlens ( at most big hardwares) or try the Old Mill Store.

[sergioasolis]

Thanks, as incredible as it seems, here in Mexico everyone uses sealer instead of a grainfiller, so I have not been able to find a grain fillerl the one I found instead of drying fast, it never dries, so I was thinking on using pumise as I have read, but was worring about the grade, I put little pieces of stone on a plastic bag and then worked with a spoon, I will use it and see the results. If you know of a better way of making a grain filler I will surely appreciate.

Thanks

[Woodwould]

If you live near Popocatépetl, you could hold a frying pan out of the window when it's blowing its top and gather yourself a lifetime's supply of fine grade pumice.

[KJ401]

The problem with using pumice as a grainfiller is that while it will darken somewhat with the shellac when first applied, over time it will show as white flecks in the pores of the timber. The bigger the pores, the more pumice you have put in, the more quickly the pumice will show. Which is why traditional polishing of say mahogany would involve using a grainfiller first, and pumice as part of the application process of the shellac.

You can make your own grainfiller - get say 300ml of raw linseed oil, add whiting to it until it's difficult to stir - like stiffened cream. Then add either dry pigments or artists oil paints to colour the grainfiller - should be the same tone as the darkest tone in the timber you're finishing.

You also need to add something to encourage drying but be careful given your climate - grainfiller that has dried before you remove the excess is not easy to fix. You can use drying agents - say terebine, but this is highly highly flammable (and toxic) and may be difficult to find? You can also use some standard single pack varnish as your drying agent - a little goes a long way. You will need to experiment to find what works best in your climate and workshop.

The grainfiller can also be thinned by adding turps - preferably gum turps but too much will give the grainfiller a white cast and accelerate drying. Apply the grainfiller using burlap, driving it into the grain with a circular motion, take the excess off after about 10-30 minutes (depending on temperature etc) with more clean burlap, again in a circular motion, aiming to drive more into the grain. Final circular wipe-off with cotton cloth to remove the excess from timber surface. Let it dry for a few days; a week ideally. Lightly sand it - if the paper clogs quickly, leave it to dry further. When dry, polish.

Crushing your own pumice - you have to be absolutely certain that it is incredibly fine - almost like talc, otherwise it will leave appalling scratch marks on your work.

[sergioasolis]

Thank you very much, I really appreciate your insights, I will follow your advises to see how well it works here. I will try making my own grain filler, and experiment with pumice in the process of applying shellac.

Do you know what is the real benefits of using grain filler versus sealer? I wish to encourage other people to learn the difference.

I do not live so close to Popocatepetl, but by the way, these days they look really nice, and yes, I learned there are some other volcains close which are a good source of pumice.

Thanks again

Sergio

[kiwigeo]

Do you know what is the real benefits of using grain filler versus sealer? I wish to encourage other people to learn the difference.

A grain filler will fill in pores much faster than a sealer. I have three grain filling methods I use on my guitars. Usually I'm filling in pores on Indian Rosewood which I use for the backs and sides of my instruments.

1. Pumice Method. I apply two spit coats of 1.5lb (blonde) shellac letting each coat dry. I then apply a bit of Behlens 4F grade pumice to a muneca along with a bit of alcohol (methylated spirits) and then work it over the spit coated surface. The pumice grinds up the wood fibres into a paste along with the shellac from the spit coat and it is this paste that fills the pores. The meths bleeds out some of the colour from the rosewood and helps colour up the pumice grains to match that of the wood. The trick with this method is to work in small areas being carefull not to over work the muneca and leave too much residual paste on the wood surface. Also avoid adding shellac to the muneca....theres enough shellac on the wood surface already.

2. Epoxy Method. I used to apply two coats of Zpoxy brand finishing resin as a filler. The first coat would be applied neat using an old credit card to work the resin into the wood pores. Id let that set and then give it a sand till smooth. I then applied a second coat of Zpoxy but this time diluted 50/50 with methylated spirits. Once set Id give it another light sanding to produce a smooth surface. Ive stopped using this method because of issues others have had with skin reactions to epoxy resin.

3. Egg White Method. An old fashioned but effective method of pore filling is to use egg whites. An egg is seperated into whites and yolk. The yolk is given to the dog and the whites are retained. The whites are applied to the wood surface and then a piece of 320 grit sand paper is used to work up the egg white and wood fibres into a paste which then gets worked into the wood pores. This method is safe and I've found it effective. I also apply an egg white wash to the spruce tops of my guitars to stiffen up the grain which allows sanding to nice smooth surface prior to french polishing.

Cheers Martin

[sergioasolis]

Thank you, it is interesting to know about the white of eggs, and the advise of using the pumice shellac on small areas, the epoxy I think will smell much and is more toxic, and expensive isn´t it?

[kiwigeo]

I used to use Zpoxy finishing resin. Its not too expensive and a pack goes a long way. With regard to safety issues with the stuff...like any hazardous substance the trick is to familiarise yourself with the chemicals present and minimize exposure using appropriate personal protection equipment and adequate ventilation.

[edan.123]

I grind my own pumice and use it with fine steel wool t o scuff back between rubbers when french polishing I pick it up off the beach grind it in a flour mill then a mortar and pestle sift it through a very fine tea strainer cheers Ed