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Acrylic gloss medium cracking problem

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Acrylic gloss medium cracking problem
Posted by HarryHotspur on Wednesday, July 30, 2008 7:03 PM

Has anyone else had this problem? I was modeling a stream about 1"-1.25" wide. First I painted the bottom with acrylic paint. After that dried, I brushed on a coat of acrylic gloss medium. It worked fine, except stupidly I brushed lengthwise up and down the stream. Thus, I had "ripples" moving unnaturally in the wrong direction across the stream. So I tried another coat horizonally, but that didn't solve the problem.

So, after it dried for about two weeks, I poured a thin (about 1/16") coat of acrylic gloss medium over it. That produced very good results, but as soon as it started drying it also developed a crack down the middle. The crack is a jagged line almost directly in the center of the stream for the entire length of the pour, about 10 inches. The crack is about 1/16" wide.

I tried filling the crack with more acrylic, which looked promising until it dried. Then the crack was back, same as before.

Has anyone ever had this happen? Any ideas or suggestions. FWIW, in the past I've used Envirotex, which worked fine but was too flat to suit me. Everyone said use acrylic gloss medium, so I did. Must be something wrong on my end.

- Harry 

- Harry

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Posted by corsair7 on Wednesday, July 30, 2008 7:30 PM
 HarryHotspur wrote:

Has anyone else had this problem? I was modeling a stream about 1"-1.25" wide. First I painted the bottom with acrylic paint. After that dried, I brushed on a coat of acrylic gloss medium. It worked fine, except stupidly I brushed lengthwise up and down the stream. Thus, I had "ripples" moving unnaturally in the wrong direction across the stream. So I tried another coat horizonally, but that didn't solve the problem.

So, after it dried for about two weeks, I poured a thin (about 1/16") coat of acrylic gloss medium over it. That produced very good results, but as soon as it started drying it also developed a crack down the middle. The crack is a jagged line almost directly in the center of the stream for the entire length of the pour, about 10 inches. The crack is about 1/16" wide.

I tried filling the crack with more acrylic, which looked promising until it dried. Then the crack was back, same as before.

Has anyone ever had this happen? Any ideas or suggestions. FWIW, in the past I've used Envirotex, which worked fine but was too flat to suit me. Everyone said use acrylic gloss medium, so I did. Must be something wrong on my end.

- Harry 

It sounds like that pour was to thick.

Irv

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Posted by CSXDixieLine on Thursday, July 31, 2008 6:45 AM

I agree with Irv- the coat was most likely too thick. The acrylic mediums should basically be thought of as paints and should be used the same way. They are really just very thin topcoats and should not be used to "build up" a surface, else cracking will probably occur as the medium dries.

Regarding fixing this, is it possible you can do something like a thin plaster pour over the entire creek bed (cracked medium and all) to re-level the surface, then repaint and start over again? Of course your water level would be much higher than before so this may not be a parctical solution.

Jamie

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Posted by wjstix on Thursday, July 31, 2008 8:21 AM
Too thick acrylic will indeed crack!! You could try filling it in with something like Elmer's glue I guess...that should dry clear, put a few (thin!) layers of acrylic over it and it shouldn't be that noticeable. I've sometimes on an early acrylic coat put a tiny touch of blue acrylic paint in the gloss medium before brushing it on just to give a little color to the water so it isn't completely transparent, you might try a coat of that over the repaired area.
Stix
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Posted by HarryHotspur on Thursday, July 31, 2008 1:24 PM

Good ideas. Thanks guys.

 - Harry

- Harry

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Posted by larak on Thursday, July 31, 2008 10:10 PM

Get a scale figure of Moses?  Ok ok,

How about a thin layer of envirotex? It will fill in the crack, hopefully hold things together and you can add a couple of (thin) coats of medium over that.

Just a thought. 

 

The mind is like a parachute. It works better when it's open.  www.stremy.net

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Posted by HarryHotspur on Thursday, July 31, 2008 11:34 PM
I sorta like the Moses idea.  Smile [:)]

- Harry

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Posted by Medina1128 on Friday, August 1, 2008 8:42 AM
I prefer to use ModPodge. You can get it in the crafts section at Walmart. It pours white, but dries clear.
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Posted by doctorwayne on Friday, August 1, 2008 10:50 AM

 

As mentioned, pouring the material was your mistake.  I used patching plaster for the "water", then painted it with interior latex paints, followed by three coats of water-based high gloss urethane.  No cracks, no "creep" up the shoreline, and very durable:

Wayne 

 

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Posted by HarryHotspur on Friday, August 1, 2008 1:15 PM

Doctorwayne -

Your water looks great. Did you create the waves in the plaster or the urethane?  Also, where does one buy water-based high gloss urethane? Does it has a more common name?

 - Harry 

- Harry

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Posted by HarryHotspur on Friday, August 1, 2008 1:21 PM

 Medina1128 wrote:
I prefer to use ModPodge. You can get it in the crafts section at Walmart. It pours white, but dries clear.

I could be wrong, but I think ModPodge is just a brand name for acrylic gloss medium. I've used it before, but not for water. Seems to work fine. 

- Harry

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Posted by doctorwayne on Friday, August 1, 2008 2:12 PM

Thanks for the kind words, Harry.  The ripples and eddies were done with a drywall knife, before the plaster set-up.  I got my high gloss urethane at Home Depot - I bought a quart, which was a lot more than I needed, but it's very tough (I often place my camera in the "water" for picture taking, often atop blocks of wood to get the proper perspective).  The brand is Varathane Diamond Wood Finish, Interior Grade.  I had some doubts about it being water-based, but didn't want the odour associated with regular urethane coatings.  I applied it according to the directions on the can, using a 2" brush.  Maintenance is easy, using a cloth, brush, or brush attachment on a shopvac to remove any dust or scenic debris.

 

Wayne 

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Posted by HarryHotspur on Friday, August 1, 2008 8:43 PM

Thanks for the info and pics, doctorwayne. That really looks great. I presume you dry brushed the "white caps"? 

- Harry 

- Harry

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Posted by doctorwayne on Friday, August 1, 2008 9:24 PM

Sorry, I should have mentioned the painting process.  Once the patching plaster (Durabond 90) was completely dry and hardened, I used interior flat latex paint to colour the water.  I applied the brown and the grey/green while both were still wet, which allowed the colours to be blended together where they meet.  After that paint had fully dried, I used PollyScale Reefer White, applied "wet", using a 1/4" or 1/2" brush.   Again, after that was fully dried, the clear gloss was applied. 

The tough urethane finish, combined with the extremely hard and strong Durabond, makes for a "water" surface that resists chipping, scratching, or other damage, doesn't yellow over time, and doesn't crack, even though it's applied only about an eighth of an inch thick over 3/8" sheathing plywood.  However, the thickness of the plaster doesn't seem to matter, as the lake area in the overhead view is about 1" thick, applied over a much earlier application of the same plaster over screen.

Wayne

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Posted by Been Nothing Since Frisco (BNSF) on Sunday, August 3, 2008 10:23 AM

this may be a littleSign - Off Topic!! [#offtopic], but I still haven't goten a reply on a post i created asking this question but any way,

 If I put down acrilic, or what ever water materiel I would use for water, on a grass mat, after it dried couls I roll the mat back up without damaging and or cracking the water?  

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Posted by kcole4001 on Sunday, August 3, 2008 12:10 PM

I think you'd have to keep a flat spot where the water is poured, otherwise it will almost certainly crack or split and then probably peel off the mat.

If you rolled it up loosely enough, it might just work.

 

Wayne, that's some really nice work! A very interesting technique for water, and probably much cheaper than buying Envirotex, etc..

"The mess and the magic Triumphant and tragic A mechanized world out of hand" Kevin
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Posted by doctorwayne on Sunday, August 3, 2008 12:31 PM
 Been Nothing Since Frisco BNSF wrote:

If I put down acrilic, or what ever water materiel I would use for water, on a grass mat, after it dried couls I roll the mat back up without damaging and or cracking the water?  

"Water" probably wouldn't look very convincing, no matter how well done, if it's not in an area that looks like water would naturally occur:  you need a depressed area for the lake or river bed, otherwise the "water" will be sitting above the level of the ground. 

Edit:  One possible reason that you didn't get a reply to your question is that the brackets in your user name cause the replyers to get a "non-matching quotes" message. Smile,Wink, & Grin [swg]

Wayne 

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