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Author Topic: Help wanted: How to make look plaster like old concrete  (Read 48561 times)
marc_reusser
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« Reply #30 on: May 01, 2012, 01:12:01 AM »

Decorative concrete work like that culvert is not uncommon. I run across it frequently. Just means that someone may have actually designed it, or that the guy that built it was a "craftsman" (or at the very least cared about his job/work)...which was more common in those days than in these.

If this was built as a WPA project it would also be common/typical to lokk more designed/decorative.


Marc
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mad gerald
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« Reply #31 on: May 04, 2012, 12:19:35 PM »

G'evening all,

after having successfully completed another attempt ...  Wink ... I have a (different) result too ...



... but I think it is still in need for improvement (that's the part me asking you for feedback  Grin) ...

One thing that really keeps annoying me are the tiny cavities you get while treating the Hydrocal with a wire brush ... you can drench the whole item with thinned colour ... and still there are some cavities shining bright white!  Tongue Not quite shure yet, if it is a question of adherence ... or if the colour simply does not even reach particular cavities ... Huh ... the latter opportunity is hard to believe, because the items did get several layers of colour!

Cheers
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« Reply #32 on: May 06, 2012, 12:02:34 PM »

G'day all,

I did another approach ...



... which turned out to look a little different than the other results ....

I think the main problem with that partly "artificial" look is the usage of common water colour (apart from acrylics) from a box of water colours like this one, because the pigments seem to be to coarse and the colour is to covering, not translucent enough ... even when thinned ...  Tongue ... so further attempts have to wait until suitable acrylic colour arrives ...

BTW: I came across this concrete enclosure of a public parking lot today and determined it to be a fine prototype for concrete 'round here ...




Cheers
« Last Edit: May 06, 2012, 12:05:53 PM by mad gerald » Logged

Malachi Constant
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« Reply #33 on: May 06, 2012, 12:35:45 PM »

Those last pieces look quite fine!  Before you make yourself crazy examining them ... try sitting them against some sort of finished building or into a bit of modeled scenery ... just to see how they look "in context" (surrounded by other things).  -- Dallas
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« Reply #34 on: May 11, 2012, 12:22:04 PM »

Gerald, you said

>>One thing that really keeps annoying me are the tiny cavities you get while treating the Hydrocal with a wire brush ... you can drench the whole item with thinned colour ... and still there are some cavities shining bright white<<
Am I right in assuming the hydrocal is a powder?
if so perhaps you could try a little dilute grey acrylic in the water when mixing
I now dont mix powder fillers without it , unless I WANT white  finish
« Last Edit: May 11, 2012, 12:24:16 PM by granitechops » Logged

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mad gerald
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« Reply #35 on: May 11, 2012, 01:29:44 PM »

Gerald, you said
>>One thing that really keeps annoying me are the tiny cavities you get while treating the Hydrocal with a wire brush ... you can drench the whole item with thinned colour ... and still there are some cavities shining bright white<<
Am I right in assuming the hydrocal is a powder?
... yupp ...

... if so perhaps you could try a little dilute grey acrylic in the water when mixing
... spot on ... I'll do so the next time ... I suspect it's kinda question of "surface tension" with the Hydrocal - common plaster seems to provide a better absorption of the water colour or acrylic colour respectively ...

Cheers
« Last Edit: May 11, 2012, 01:32:52 PM by mad gerald » Logged

chester
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« Reply #36 on: May 11, 2012, 04:35:23 PM »

Some fairly good luck eliminating those pesky white spots by diluting chalk powders in alcohol. One needs to keep the chalk in suspension (stir) but it does seem to seep into every pore (poor pour).
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Malachi Constant
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« Reply #37 on: May 11, 2012, 04:57:52 PM »

Try mixing some acrylic color into water ... then use that colored water to mix your plaster.  It might take a couple of tries to figure out how much color you need in the water, but that would allow you to get it mixed in and have color inside the plaster even when it chips.  -- Dallas
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mad gerald
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« Reply #38 on: July 11, 2013, 02:08:25 PM »

G'day all,

... shame on me, as I did not dare to make new attempts finishing this exercise ... but Marc's report 1/35 paper structure vignette (from approx. page 10 on) encouraged me to make another attempt ... and here it goes:

I followed Marc's reference, except that I chose a different thickness (3 mm) as I did not have 0.060 styrene for a mold (I used wood strips instead). I only made two slabs measuring 31 x 31 mm, with a thickness of 3 mm. These dimensions in 1/16 scale would match the size of a common prototype concrete slab (500 x 500 mm, thickness 50 mm). I did not pre-colour the plaster und did not test cutting a larger sheet in shape. In the meantime I made a larger piece measuring 62 x 62 mm, which is going to dry over night.

At first I thought my stipple treatment unfortunately happened a little too late, as the surface was not cool/damp enough anymore, but IMHO it worked well enough for a frist try.

When dry,  I dampened the plaster again slightly with a paint brush and used some highly diluted Vallejo acrylic colours (different ones on left and right piece).

Pics do not show all details of structure and colouring, may be with a little luck I'm gonna do some better shots tomorrow ...





Cheers
« Last Edit: July 11, 2013, 02:20:14 PM by mad gerald » Logged

marc_reusser
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« Reply #39 on: July 12, 2013, 02:08:13 AM »

Gerald,

Great to see you experimenting with this.

It looks as if these are plaster only, and that you did not include any fine sifted dirt.?

My critique would be the following items:

1. Try tapping the mold with something while the plaster sets, to remove the air bubbles that are showing.
2. I highly recommend that you add coloring to the plaster, as it makes it far easier to work with the later washes and colors, as you are not fighting the white  of the plaster.
3. Consider using a paint other than Vallejo for the first color coats, Vallejo contains a lot of Latex, and even in washes, can tend to seal areas of the porus plaster causing smooth, dark and "painted" looking areas.

Look forward to your next pieces.



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mad gerald
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« Reply #40 on: July 12, 2013, 02:26:23 AM »

Marc,

thanks for dropping in and your helpful advice ... already started wondering about the unwanted effects you mentioned ... so here are two close-ups - another larger sheet of pre-coloured plaster is in progress ...





Cheers
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« Reply #41 on: July 12, 2013, 02:36:21 AM »

On these last two pieces, the texture is bothering me...the to one has surface swirls/drags, that resemble what is know here as skip-trowel plaster for stucco walls, the bottom one, though I like the texture, it has the odd diaginal grooves...it looks more like some of the old  salvaged Limestone pavers I have seen/used.

I like the gdarker grey under wash on the first ine, nbut the  beige top was was applied to thick and begins to look painted on.


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« Reply #42 on: July 12, 2013, 03:34:54 AM »

Its good to see that I am not the only one with a fetish for small plaster castings of concrete prototypes!

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« Reply #43 on: July 12, 2013, 12:20:20 PM »

Those are truly adequate. HO scale? -- Russ
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mad gerald
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« Reply #44 on: July 13, 2013, 10:42:43 AM »

G'day all,

@Marc
Your words make me feel uncomfortable ...   Roll Eyes ... but you're bl**dy well right ...  Wink

As the larger sheet of plaster turned out to be a POS, I did not even think about colouring it.

As I don't have a large variety of water based colours available, I came to the idea: Why not modelling concrete with real concrete ... um well, or at least with joint mortar/grout (please correct term if not correct) ... ?

So I mixed some gray joint mortar with water, added some plaster and proceeded the same way as last time, creating 2 pieces measuring 31 x 31 mm, using the technique introduced by Marc. A little disadvantage is, that the joint mortar needs approx. 12 hours before it dried completely, but IMHO the result is far more convincing as my attempt using (and colouring) plaster ...







Its good to see that I am not the only one with a fetish for small plaster castings of concrete prototypes!
... these pieces really look tiny ... is this H0 scale ... and what do they represent?

Cheers
« Last Edit: July 13, 2013, 11:15:12 AM by mad gerald » Logged

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