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Plaster of paris vs Patching coumpound

RWayne's picture

I have been reading this forum for a long time but this is my first post. There seems to be a lot of information and knowledge here. I talked to a gentleman a short time ago who happened to have been a woodworker for over 50 years. one of the things he told me was that one of the best things I could do was experiment.   one of the things I want to try is filling pores of some Red Oak that I have. I will use some test pieces first. Plaster of paris can be used and I had a friend give me some patching compound. My question is are they the same. Can Patching compound be used in place of plaster of paris or should I just stick with getting the plaster of paris. Thanks in advance.

Steinmetz's picture

(post #107337, reply #1 of 14)

RW,

Plaster of Paris is dry powdered chalk. Taping compound is similar, but contains glue and retarding chemicals. Also, it is ready mixed
I think for your purpose, the compound won't 'lift'from the surface over time.
Painters use both when they create a 'limed oak' finish to coarse grained wood. Of course a sealing finish must be applied ie, (Shellac/ poly/lacquer etc. Steinmetz

RWayne's picture

(post #107337, reply #2 of 14)

Thanks for the reply I've got some of both that I will try .

Dennis02's picture

(post #107337, reply #3 of 14)

Wayne -

Read the contents of a bag of tapping mud (patching compound, I'm assuming you mean spackle or that sort of thing which are to a degree similar with taping compound).

I don't speak with any authority with regards to the subject but most drywall patching compound or patching material is made from clay around here, anyway. Plaster of paris is a manufactured product made from otherwise natural minerals, none of which to my knowledge is clay. I agree with the advice you were given: experimentation is the best way to learn practically anything. I'm just pointing out the differences in the material.

Plaster of paris is quite hard when it's cured out. Patching compounds are quite a bit softer. At the level we're discussin, grain filling, this may or may not be an issue. Experimenting as you were advised will disclose how and how well either or both take your selected finish. The only caveat I can think of is that I wouldn't use water borne finishes on the patching compound filled wood. These can and do soften when moistned and might bleed out in a brushed on or wipe on type of water borne finish material.

...........
From Beautiful Skagit Co. Wa.
Dennis
........... From Beautiful Skagit Co. Wa. Dennis
JerBear's picture

(post #107337, reply #11 of 14)

Not to veer off the subject, but Plaster of Paris is different than joint compound or 'drywall mud' as you say.  There are many types of plaster but P.O.P is a gypsum rock that has been ground, filtered, and baked (calcined), to have a certain degree of water driven from it.   The chemical structure is changed and when water is then reintroduced and mixed with it, the crystaline structure changes to a hardened state rather quickly (depending on what is in the mix to retard it).  Ever mix up POP with just water and give it quick stirring?  Hard in 5 minutes tops.  It is very hard


Joint compound is nothing more than gypsum that's been bleached and mixed with fine aggregates and mixed with water.  It hardens by drying.  Joint compund (air dry mud) is very soft but sticks well...much better than plaster.


I do plastering from time to time and when I do the white coating, I often mix the two.  The traditional whitecoat mix is lime putty and guaging plaster (POP)  When I have limed wood, I have used the mix. 


Go over to Breaktime,( that's where I usually lurk, I'm just visiting here),  and click on the archives about plaster.  You'll find all you need to know on the subject.  

Elcoholic's picture

(post #107337, reply #4 of 14)

I'm not sure what product you're calling patching compound.  Drywall mud comes in Taping, Topping and All Purpose compounds.  I have no idea what's in it, I always assumed it was mostly gypsum.  Anyway Topping sands the easiest.  You might try "Fixall" it's much harder than drywall mud and shrinks less.  Let us know how your experiments go.  Are you going for a limed or pickled finish or will you be dyeing/staining.

John O'Connell - JKO Handcrafted Woodworking


The more things change ...


We trained hard, but it seemed that every time we were beginning to form up into teams, we would be reorganized.  I was to learn later in life that we tend to meet any new situation by reorganizing; and a wonderful method it can be for creating the illusion of progress while producing confusion, inefficiency, and demoralization.


Petronious Arbiter, 210 BC

John O'Connell - JKO Handcrafted Woodworking

The more things change ...

We trained hard, but it seemed that every time we were beginning to form up into teams, we would be reorganized.  I was to learn later in life that we tend to meet any new situation by reorganizing; and a wonderful method it can be for creating the illusion of progress while producing confusion, inefficiency, and demoralization.

Petronious Arbiter, 210 BC

Jayst's picture

(post #107337, reply #5 of 14)

There was recently a column in FWW by Jewitt on using either pumice or plaster of paris followed by linseed oil to make a translucent (and colorless) grain filler.  I need advice on how truly colorless the plaster of paris would be for use in walnut. (ie, I don't want the pores to turn white.) I have already had a bad experience using the thick mixture of shellac and pumice suggested on a FWW videotape about French polishing.  All the pores in a mahogany piece turned white after about 9 months when they were initially colorless, and I had to strip it and refinish with just shellac.


The column says you could color the plaster of paris with Japan colr or aniline dye before using it.  Does anyone have any experience with this?  What else would you suggest as a grain filler for Western Walnut, which I was planing to finish with shellac, unstained. (except in a few areas where I was going to match heartwood with sapwood, using transtint dye.  Thanks a lot.


Jay

SgianDubh's picture

(post #107337, reply #6 of 14)

JAYST, here's one old discussion I was involved in on the subject. http://forums.taunton.com/tp-knots/messages?msg=9684.1


Here's another with some images. http://forums.taunton.com/tp-knots/messages?msg=23549.1


Slainte.


Jayst's picture

(post #107337, reply #10 of 14)

Thanks, obviously you have experience with this.  I've been working on one of those Philadelphia secretaries a la Lonnie Bird, except I embellished it with book matched crotch walnut veneer on the desk top  and satinwood crossbanding on the drawers.  


What would you recommend for the Western walnut which is somewhat more variegated than Eastern walnut?  It has streaks of darker brown and purples running through it.  Really quite beautiful.  I was not going to stain it. If the plaster in the pores turn white,  I'll die.  I've used por-o-pac in the past and it was a difficult to tint with Japan color, also leaving the pores prominently visible.  There was once an article describing the use of fine wood dust in slurry with shellac. Any experience with that?  Thanks for the advice.


Jay

SgianDubh's picture

(post #107337, reply #12 of 14)

JAYST, it sounds like you are trying to achieve a blending pore filler colour, and for this one of the proprietary grain fillers will work very well.


One of the interesting things about all walnuts is that although the colours may be quite varied when the wood is newly exposed it very rapidly takes on honeyed brown tones-- a year or less makes a big difference in the colour.


If you went the plaster of paris grain filling route then I don't think you'd have a problem with whiteness showing through in your lifetime. I've seen pieces from the 1800's where the whiteness starts to reveal itself, and this could be due to several factors.


If your plan is to not dye or stain the natural walnut and you do want to fill the grain you can do a nice job in a couple of ways.


The first option might be to seal the wood fibres with a film forming polish-- dewaxed shellac does a good job as it's compatible with all other film finishes. Then fill the grain. The sealing of the wood fibres helps resist the colour changing characteristics of the grain filler which contain dyes, pigments, clay like substances and so on. once you've filled the grain you build up the polish layers to whatever you want, using whatever polish you've chosen.


A second option could be to fill the grain prior to polishing, and here the colour changing characteristics of the filler can alter or darken the wood more than in the first option, which might be desirable.


To adjust the colour of proprietary grain filler to the shade you want I suggest you use UTC's (universal tinting colours) as one option, and start with a filler a shade or two lighter than you're after-- you can even start with a neutral grain filler and adjust the colour from there.


There are ways of bodying up shellac with pumice to help fill the grain, but I've never used wood dust to achieve the same effect, but it seems more than likely that it can be done. Slainte.


Jayst's picture

(post #107337, reply #13 of 14)

I generally do like to seal the wood with a thin coat of shellac before filling the grain.  I've found the "neutral" or "natural" color grain fillers to have a bland yellow-ochre color which is un-natural.  I would like the pores to be dark.  Can you recommend a specific product brand or tell me more about the details of the method of coloring and application of the plaster of Paris. 


I was planning to spray on several coats of shellac to build body, wet sand to 1000 and  French polish with pumice, but not as a pore filler.  A final polishing with automotive compounding liquid and a buffer has worked well for me in the past.  It's the pores that kill me.


Thanks very much.


Jay

SgianDubh's picture

(post #107337, reply #14 of 14)

You'll find a description of the plaster of paris process in the link I supplied earlier in the thread-- about post 6 or 7. The colouring agent  I use is usually water based powder paint. Crayola is one brand of paint I recall from my time living in the US, but any brand should do.


The natural proprietary grain fillers are the colour you describe, but you can adjust the colour with powdered UTC's (universal tinting colours) available from art shops and many polish supply houses. You can also buy filler close to the colour you want and darken it to suit. I think I've already said that though.


Your shellac polishing over the filled grain should go easier.


Here's a description of the plaster of paris technique lifted straight from an article of mine, minus the photographs. Slainte.


1.       The tools and ingredients needed for the job are fairly simple, photo 2 right- fine plaster of paris, water soluble powder paint, a clean rag or two, hessian (US burlap) a fine nylon abrasive pad, a little fine abrasive paper (320 grit) and two buckets, one for water, and the other pail for a dry mix of plaster of paris and powder paint.


2.       Put about a cupful of plaster of paris into one of the buckets. Add a teaspoonful of the powder paint and stir it all together with a dry stick. This innocuous looking mix will seem like nothing special- just some slightly off white powder, but it’s surprisingly powerful- a test dip into the mix with a damp cloth will show what I mean. You can add a bit more paint if need be after doing a test grain filling on some spare timber, perhaps using the earlier made stain sample.


3.       Fold up a small piece of cotton rag - an old T shirt for example, carefully into something approximating a french polishers rubber minus the cotton wool wadding. Dampen the corner in the water and dip it into the dry plaster/paint mix. Work the slurry on the end of the rag into the oak. The technique is a bit tedious and rather pernickety, but the result is quite dramatic. Working in small squares rub hard with the damp powder loaded rag in long looping elliptical motions across the grain. Plaster and paint are forced into the open grain and pores. Pick up a bit more plaster to fill another area, or dip the rag into the water to make the already applied plaster workable again and so on-photo 3 , above right.


4.       After filling an area about 250 mm (~10”) square, excess filler is removed from the surface of the timber. There is a point at which it is just right to burnish off the excess plaster, and only doing the job will teach you when to stop filling, and when to start burnishing off. Burnishing off is done with hessian (US burlap) or some other coarse cloth. Grab a small square of hessian and burnish across the grain. It’s quite physical work, requiring a lot of downward pressure. You’re burnishing the near dried plaster off the surface of the timber leaving behind only the stuff forced into the open grain. It’s important to burnish perpendicular to the grain- photo 4, right. However, it’s also my practice to rather go against the normally described methodology, where, after I’ve done the burnishing I’ll take a nylon abrasive pad and rub with the grain. Done gently, and carefully I’ve found that this helps to remove cross grain striations and any little bits of plaster still remaining on the top surface. It’s a bit of fine balancing act to get right, and if I’m after a semi-fill, I’ll burnish with the grain with both the hessian and nylon abrasive pads to pull some of the plaster out.


5.       After the panel is complete, and the filler worked around the edges the job should be left to dry thoroughly followed by light hand sanding with 320 grit paper- hold the paper in the fingers, photo 5, right rather than use a sanding block. This process is important to remove any cross grain striations left over from the grain filling and burnishing process, but a light touch is essential. The paper clogs readily and doesn’t last very long before it’s too choked to use. A file card (like a fine wire brush) can be used to remove some of the attached plaster and will extend the life of the paper.


After sanding check how evenly the grain is filled by pouring some naphtha on the surface and spreading this about with a cloth, photo 6 below left, White (US mineral) spirits can be used too, and it’s slower drying. Squinting towards a low angled light source bounced off the surface reveals any missed bits- a torch or flashlight works, photo 7, below right. It’s easy to miss filling a few spots, especially where the small sections you work on overlap one another, and this trick helps find those spots It’s quite normal to go back and repeat filling locally, which I had to do here, but sometimes it’s best to do the whole panel again- better safe than sorry.


PlaneWood's picture

(post #107337, reply #7 of 14)

I use Benjamin Moore Wood Grain Filler, #238 05.  Comes in quart cans.  Made specifically for filling the grain (pores) of open grain wood.  Available at any Benjamin Moore paint store.  Just follow the instructions when using.


I would not use plaster of paris or patching compound. 




PlaneWood by Mike_in_Katy (maker of fine sawdust!)
PlaneWood


PlaneWood by Mike_in_Katy (maker of fine sawdust!)
PlaneWood

SgianDubh's picture

(post #107337, reply #8 of 14)

Mike, why do you dismiss the use of plaster of paris as a grain filler?


It is, after all, a long established and very effective method. I've been using it successfully myself for many years.


It's certainly not the only method-- there are commercially available alternatives ready mixed in a can, but there are effects that can be created by using plaster of paris and colouring agents that are very hard or perhaps impossible to replicate with proprietary formulations.


I simply find your position curious. Slainte.


PlaneWood's picture

(post #107337, reply #9 of 14)

Well, it's just totally Un-American!!!!!  :)


Basically, I wouldn't use it cause I have no experience with using it for such an application.  And, never have heard of it being used for such, which ain't saying much at all!


Nice thing about this place is that you can learn something new every day.  I used to tell my kids and my Boy Scouts that the day you quit learning is the day you die.  And, if you ain't dead, you might as well be!




PlaneWood by Mike_in_Katy (maker of fine sawdust!)
PlaneWood


PlaneWood by Mike_in_Katy (maker of fine sawdust!)
PlaneWood