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Nik Kyklo

Simple Lime plaster as ground and treatment.

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Hello. Does anyone used or uses lime as ground and treatment? There are many topics on Casein but I could not locate something on simple lime. As material (lime) absorbs humidity (which is good), protects and hardens at the same time. I don't know how caustic it is when used on wood and if it damages it rather than protect it. I think, since lime was widely used at Mediterranean environment, surely it was a known and useful material to luthiers. 

Thank you

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Lime (calcium hydroxide)  is highly caustic, both out of the package and after combining with water. So there is a handling issue. You should probably avoid such a reactive material as a ground, since it is likely to cause ongoing changes to the wood and the varnish.

A popular mineral ground is slaked Plaster of Paris, also known as gypsum and calcium sulfate. There is a handling issue when in its initial dry state, but after thoroughly slaking it (adding excess water), it is very stable and non-caustic. It is a good wood sealer and filler and leaves a whitish haze on the wood surface after it dries. But after applying an initial layer of typical oil or spirit varnishes, it becomes completely transparent. This is because its refractive index is very close to the refractive index of typical varnishes. The white haze is caused by light dispersion of many tiny, transparent gypsum crystals.

 

 

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I used it years ago, just old slaked putty put on wet, then dusted off and varnish rubbed  in. I seem  to  remember  it worked  well enough, but I'd be careful. Try it with your varnish to be sure it becomes  transparent. 

Now I use plaster of Paris, as a wet slurry only on the spruce, dried and mixed in th the varnish as a paste on the maple. 

Even  very well  washed, lime or pop can form a glaze on the surface as water  evaporates  through  them, and if you cant rub that off  you'll  see it as a haze in the ground.  So get any water staining done before the plaster goes  on. If you try to add stain later you risk drawing  a glaze to the surface of the wood.

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4 hours ago, Conor Russell said:

I used it years ago, just old slaked putty put on wet, then dusted off and varnish rubbed  in. I seem  to  remember  it worked  well enough, but I'd be careful. Try it with your varnish to be sure it becomes  transparent. 

Now I use plaster of Paris, as a wet slurry only on the spruce, dried and mixed in th the varnish as a paste on the maple. 

Even  very well  washed, lime or pop can form a glaze on the surface as water  evaporates  through  them, and if you cant rub that off  you'll  see it as a haze in the ground.  So get any water staining done before the plaster goes  on. If you try to add stain later you risk drawing  a glaze to the surface of the wood.

Can I ask, what you are using for sealing wood? Are you give the sealer before or after Plaster of Paris?

Thank you!

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1 hour ago, Húslař said:

Can I ask, what you are using for sealing wood? Are you give the sealer before or after Plaster of Paris?

Thank you!

I don't  seal with anything  else. The plaster fills any pores to some extent, and  the thick oil varnish, rubbed on, soaks  into the plaster. I add a drop  of  driers to this varnish.  

When I first was shown this sort of ground, 30 years ago, we used Silex powder, mixed into the varnish. 

I like treating the spruce fronts with the wet slurry.  For some reason I think it has acoustic  benefits, although  I dont really  know. 

Roger Hargrave has a very  comprehensive   explanation  on his Bass building  thread. I haven't  ventured  into  the  wood colouring techniques he mentions, but just use UV, and a light treatment  of nitrite. 

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Thank you very much for your responses. I really don't know about limestone. I am using already plaster of paris. What I see (on some pieces of wood) is that lime makes the grains look better. Something that plaster does not. Also, it hardens a lot after time. Gypsum does not have such properties as far as I know. 

I agree that Hargrave has a very good explanation for plaster of paris. If there is color at varnish (first layers) then it goes into pores and it is a problem. It does seal the wood like seedlac. 

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6 hours ago, Conor Russell said:

...I like treating the spruce fronts with the wet slurry.  For some reason I think it has acoustic  benefits, although  I dont really  know. 

I 'think' the water slurry helps carry the POP deeper into the spruce fibres than the oil paste method does. I tried something similar on my last viola (Given that Roger describes both workflows in the bass book I figured there was no reason why one couldn't use both on the same instrument)

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51 minutes ago, Nik Kyklo said:

Thank you very much for your responses. I really don't know about limestone. I am using already plaster of paris. What I see (on some pieces of wood) is that lime makes the grains look better. Something that plaster does not. Also, it hardens a lot after time. Gypsum does not have such properties as far as I know. 

I agree that Hargrave has a very good explanation for plaster of paris. If there is color at varnish (first layers) then it goes into pores and it is a problem. It does seal the wood like seedlac. 

Interesting  you think the lime enhances the  grain - I do think plaster of paris kills the flame a little. I looked up lime and gypsum, and apparently  lime is less water soluble  than plaster of paris. That makes sense to me - you can whitewash  a wall with lime but gypsum  plasterboard  turns  to slime if left out in the rain. 

I'm going  to  try a few test pieces. I have some putty stored for the last 20 years. If it's  still wet it should  do  very  well.  

Thanks for bringing  it up. 

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On 12/12/2019 at 12:16 AM, Conor Russell said:

I'm going  to  try a few test pieces

Thank you for your interest. I tried lime on small pieces with some old marciana varnish I had. Of course it turns to transparent. What I can see is that it becomes much harder than gypsum. Maybe I had to pure more water at lime. That hardness propably is good. Is there anybody that ever measured elasticity and sound speed alterations before and after lime treatment?

 

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20 hours ago, Conor Russell said:

Interesting  you think the lime enhances the  grain - I do think plaster of paris kills the flame a little. I looked up lime and gypsum, and apparently  lime is less water soluble  than plaster of paris. That makes sense to me - you can whitewash  a wall with lime but gypsum  plasterboard  turns  to slime if left out in the rain. 

I'm going  to  try a few test pieces. I have some putty stored for the last 20 years. If it's  still wet it should  do  very  well.  

Thanks for bringing  it up. 

My experiences with slaked plaster brought me to the same observation, that as a filler, even lightly applied, obscures wood figure to a point. Lately I have abandoned the use of any mineral filler and just ground/seal before applying color varnish.

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3 hours ago, JacksonMaberry said:

My experiences with slaked plaster brought me to the same observation, that as a filler, even lightly applied, obscures wood figure to a point. Lately I have abandoned the use of any mineral filler and just ground/seal before applying color varnish.

I've never  sealed  with anything  but  the  silex, lime or plaster, and my varnish  darkens  endgrain without it. Do you use a wash of glue or shellac to prevent  this?

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34 minutes ago, Conor Russell said:

 

 

I've never  sealed  with anything  but  the  silex, lime or plaster, and my varnish  darkens  endgrain without it. Do you use a wash of glue or shellac to prevent  this?

Lately, I have been sealing what I suppose you could call a type of varnish. Into one ounce of pure gum spirits of turpentine, I dissolve seven drops of linseed oil and one gram of water white colophony. I apply this very lightly with a rag after tanning with nitrate/nitrite. I do two coats on maple, three on spruce, with ample time to dry in the lightbox between. 

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