Scenery Base Application

[SilverSpike]

Well, day one "Home Alone" and I got some time in the train room last night and worked on three projects.

• Installed 2 more SPST switches onto the control panel for the roundhouse tracks.
• Installed 3 stanchions to the upright 2X4 frame members for bracket and backdrop supports for the lumber/steel industry LDE.
• Mixed up a batch of scenery base and applied it to the scenery frame foundation.
• And I ran trains for a bit with the car cleaner too, got to maintain the track ya know!

This is the mixture, and it is Portland cement, patching plaster, vermiculite, and water, and this is the formula that Joe Fugate uses.

 

Initial stages of the scenery base application

Scenery base applied on frame foundation and around roundhouse and roundtable area

As I was applying the mixture I found that it was setting up quite fast so I added more water and this slowed down the drying process enough to continue working it into the foundation. I went and checked on the application this morning before heading into work and it was still setting up and a bit wet, so it is not fully set up. Hopefully it will be dry by this evening.

 

[MisterBeasley]

Will vinegar slow down the setting on this mixture?  I use it with Durhams Water Putty to slow that down, and it works great.

[SilverSpike]

Mister B,

I dunno, never tried it before with the vinegar as a slow setting agent.

[pcarrell]

It's looking good Ryan!  How heavy is the stuff?

[SilverSpike]

Thanks Philip!

Actually the mixture is very light as it contains a large amount of the vermiculite, here is the formula that I got from Joe:

1 part Portland cement
3 parts patching plaster
4 parts vermiculite (fine)

Then add water and mix well to get the consistency of thick cake batter then either paint on or use a metal spatula, which is what I did.

In this batch that I made last night I only had 2 parts of the patching plaster left, so I subbed in 1 part plaster.

[pcarrell]

Do you think it would be tintable with paint or dye maybe?  Also, how hard does it dry?  Do I need a drill to plant trees, or can I just use an awl?  Since it's thin I'm thinking an awl might be fine.

Sorry, I don't mean to hammer you with questions.  It's just that I'll be coming to this stage again soon and I'm thinking of trying something other then my old tried and true plaster soaked towels.

[SilverSpike]

Philip,

Generally the way this scenery base is done the thickness of the completed material is no more than 1/4", and an awl is perfect for making holes to plant trees and it goes really fast too. The other nice feature with this scenery base material is that you don't get all that messy plaster dust that you would  with having to drill.

Typically this scenery base is painted after it has dried, and I use an earth tone flat latex interior base paint. I have not incorporated any tints or dye into the mixture prior to the application, but that might be an interesting thing to experiment with on my next batch.

This is a test section that I did back in March and it has a fresh coat of earth tone paint on it!

[selector]

You can dye it with a shot of acrylic paint, or in my case I used powdered masonary dyes.  It turns out that I didn't use enough, as a general rule...next time.

I mixed four 3/4 cup measures of the vermiculite, three of the plaster, and one of the portland cement.  To that mix I would add about 1 full tsp of a mix of "mesa" and "brown" masonary dyes, and then add water once the whole batch was mixed.  Like Ryan, I found that I needed a bottle of water nearby to add a tablespoon, rarely any more, once it began to lose its shiny look in the bucket...means it was setting.  Add the water, give it a quick whip, and you are good for another minute or so. 

I could slather a batch like that into place in about two minutes or less, depending on the thickness I needed.  A batch that size over window screening would cover about 1 sq ft.

Don't forget to re-wet the previous pour where you want to join batches...the first will suck moisture from the first as they meet and your new batch won't have enough water and setting time to complete the chemistry properly.  So, spray the leading edge of the older batch liberally.

It's looking good, Ryan.

[bogp40]

Vinegar and or using cold water will slow the setting with plaster product also. Veneering plasters for skim coating blue board like Unical, Diamond etc have a much longer setting time. I will use this for base coats when over plaster cloth or wire screening. I also like the use of the powdered masonry dyes. Add the dye to dry plaster first then add the plaster to the water. The dry mix color is a very close to the final cured color.

[concretelackey]

Purely my opinion and I have never attempted to test it either. After 18 years in the precast concrete industry I can tell you what we used vinegar for. Cleaning......we use various peices of equipment to test the wet concrete (which uses portland cement as the bonding force) to insure product quality before it actually goes into the forms (molds) and when time allows we would use a small spray bottle and spray a bit of vinegar on the equipment, wait about 15 minutes and wipe off.

The vinegar has a high acid level which actually breaks down the cements ability to form a chemical bond, thereby producing a much weaker product.

My opinion would be to use cold water to slow the cure and hot water to accelerate the curing process. Also, ambient and material temps drastically affect both curing speed and product strength. The quicker you want it to cure the warmer you want the air and materials and the opposite applys for a slower cure. Use the fridge to cool the materials if they can be kept sealed and find a warm place to store the materials to raise their temps.

Again, my opinion only. I have no intent of stepping on toes nor am I saying it will cause your project to crumble when a door slams.

[SilverSpike]

Ken,

Nice to have an expert opinion on cement and concrete, so thanks for the comments.

It has been 4 days now since my initial application and in some areas where I applied the plaster/cement mixure it was a bit thicker than the usual 1/4" and it took a few days for it to dry. I also noticed a few but not many areas that are a bit brittle and crumbly too.

A couple questions: Would too much water in the mixture add to or increase the curing time?

Also, would too much water in the mixture reduce the strength or bonding force of the cured mixture?

Thanks,

Ryan

[concretelackey]

I refuse to call myself an expert but if you want to refer to me as such I ain't gonna stop you.

As for your questions- I can't give a solid answer since I have never messed with plaster or a cement/plaster mix. While both plaster and portland have a base ingredient of gypsum, they are produced with 2 different processes. Plaster is processed at about 300F while portland hits about 2600-2700F, and consideration must be given for the other ingredients used and how they chemically interact with the 2 types in question.

That being said, based solely on a portland cement project I would say the following- additional water (above what is recommended/suggested for the application) will create a need for a longer cure time and WILL decrease the ultimate strength of the mix. The normally accepted process for mixing a portland cement concrete mix is to add only enough water to the mixture to acheive a workable material that can safely be manipulated in the time permitted. Now however, when dealing with construction projects the engineering department will usually specify a range for the water/cement ratio (typically in the area of .3 to .35 [.3 lbs of water per pound of cement]) to acheive both maximum strength and ease of workability. when that ratio is exceeded you now have a diluted product which is weaker. This may explain the brittle results.

Another issue to consider is how quickly the surface drys, NOT CURES. Portland concrete gets hard as it cures, but it is a thirsty animal. Do you best to limit loss of surface moisture from nearby light bulbs and other heat sources as well as moving air from open windows and fans. The easy way to do this is to finish the surface to the texture that you want and gently lay a white garbage bag (preferably not yet used) over it. No need to seal it air tight, just want to protect from direct heat and breezes. Keep it covered for the 1st 12-24 hours so that the material can reach it's initial set (the point of when it is no longer a liquid but a solid) so that any moisture trapped inside stays there. The need for this is twofold-first, cement requires continued moisture to continue the chemical bonding process. Once the cement has absorbed all available moisture it stops getting stronger. Add moisture a year later and the strength will begin increasing again!  The 2nd reason is to maintain an even temperature level, especially when dealing with thin layers that cover a large area. The need prevent a big temperature swing is very crititcal in the first 12 hours or so.

Since we are not answering to any engineer other than ourselves this changes the "job site requirements" a bit in our favor. My suggestion is to mix batches based on your working speed vs. the curing speed. If you have a batch that begins to tighen up (starts to get hard) before you have it applied to your liking just mix the rest of the batches in smaller amounts.

I realize I have exceeded the parameters of this forum  with my "instructional segment on portland" but I feel that if someone understands WHY something does what it does  easier on deciding HOW to do something.

Also, look at what you are applying the mixture to. Is it clean(no dust, no oils or grease) and will it absorb moisture?

Hope this helps.

Ken

[concretelackey]

HOLY CRAP...........DID I TYPE ALL OF THAT?

[SilverSpike]

Thanks Ken, I appreciate the Portland tutorial.

And it does help me in understanding how the product works.

I think smaller batches is the key for my next applications. Thanks again!

Cheers,

Ryan

[concretelackey]