I am building my MIK building out of 1’ foam and want to cover it with cement, do people that have build with this method paint the foam first to give it some weatherproofing Then start adding the cement coating? Don’t want the cement to just fall off after a few days on the walls. Unfortunatly Doc Watsons article isn’t available any more. Thanks in advance for any answers.
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with concrete - not, that i remember.
i did use acrylic filler on foam.
roughen the foam a little with a wirebrush, apply filler, wait till dry, then smear another coat of filler to close the cracks.
Pete,
I answered some of this in your 2024 Mik thread. We applied the concrete patche, and later QuickCrete, right to the foam. No issues.
Eric
What I first did was to poke a whole bunch of holes in the foam with an awl. This gives the concrete something to grab on to. I’ve never had any problems with flaking even after 15 years.
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I’ve watched several building projects on YouTube’s new construction and seen many with foam being used for forms to hold the concrete in place. Well this could be a little on the large size, but they don’t paint the foam before the concrete goes in. This process will last a 100 years or more, probably longer then most backyard railways built today. I will say here, probably thin concrete covered walls will crack in time and peel off, start with a concrete block for the 100-year structure.
My clean and easy way. In the past Garden Railways had published my artice on this.
Real Cement, The Quick, Easy Way. I guess the pictures didn’t come through, but you can figure it out from the story. At this time I’ve done numerous buildings and structures. I even do faux rocks.
We have a few structures on the Tortoise and Lizards Bash Garden Railroad that are made of “coated” Styrofoam. Styrofoam of itself is quite impervious to the elements and once coated to protect it from UV rays will be here a long time. While latex-based paint can be used as a coating, it adds little weight and provides no virtually protection from dents, marks, etc. to the structure. As such, we like to use a “mortar” on our Styrofoam to encase it in a hard shell. Additionally, using this method, one can easily fill cracks, level uneven areas, and “fix mistakes” in the foam structure.
The first Styrofoam structure we made was a two-story house coated with a “stucco-type” mortar, and while most of the structure still looks fine almost 10 years later, the mortar on the backside that is hit by the sprinklers, turned soft and deteriorated over the years. As to be expected, most products have a limited life in the garden when subject to twice daily watering.
Another problem when working with Styrofoam and the application of mortar is the limited working time. Once mixed to the desired consistency the mortar must be applied in a timely fashion as it continually thickens, often requiring dilution as it is worked.
But the worst problem we’ve encountered when working with mortar is the spreading process, which is akin to putting peanut butter on toast. As you spread the mortar, it likes to “roll” over the surface rather than adhere in a nice smooth, even layer. Furthermore, it’s a mess to do and clean up afterwards.
But what it we could first apply the cement to our structure in a nice even layer, then wet it?
We’ve found hydraulic cement, sold for water-sealing masonry, to be extremely durable and we use it to seal cracks and gaps that develop in our concrete water features. Hydraulic cement comes as a fine powder with a very limited working time once mixed with water. (It can actually be used to seal underwater leaks with the water still in-place.) Once dry, it forms a hard, waterproof surface of real cement that is quite strong. Having no sand or aggregate, it is much finer than the typical sanded mortar mix making it easier to spread onto a surface. However, it is still messy with a very limited working time, even more limited than regular sanded mortar.
We needed a way for the townspeople to get over the retaining wall at the Chameleon Caverns Hot Springs area on the Tortoise and Lizard Bash. Using 3/8” plywood and yellow carpenter’s glue, a stairway with landings and handrails was constructed. After completion of the wood structure, it was painted with outdoor paint. Spray adhesive was then used to coat the surface and a sieve was employed to strain the hydraulic cement powder over the “sticky” structure. A spray bottle of water was then used to moisten the cement and it was allowed to dry. The end result was a nice stairway that appeared to be made of poured concrete.
Over time moisture got into the plywood and delaminated the layers that expanded at different rates. This then cracked the hydraulic cement at the steps, but as shown in Photo 1, the cement facade was actually quite resilient and held together as a solid sheet.
Winter is the time to do new projects and maintenance and this year’s included replacement of the stairway. It is easier to cut a straight line than a zigzag and management determined that a simple ramp would suffice for replacement. A new structure was constructed of scrap Styrofoam pieces glued together with yellow glue. A stationary belt sander is used for shaping the foam and new handrails were bent out of vinyl-covered wire. The handrails were placed into the foam to mark their positions (Photo 2) and removed. Cut-off pieces of the wire were reinserted in these positions to leave the stanchion holes in the cement.
We find it best to work in a plastic concrete trough (Photo 3). A piece of newspaper is laid in the bottom of the trough, and in the same manner that the wooden stairway was treated; the outer facade of the ramp was coated with spray adhesive. (The newspaper is easily changed out and keeps the trough from getting “gummy” from the spray adhesive.) A reaction between the foam and the adhesive was noted and the use of the spray adhesive on the foam was discontinued. (If one intends to use spray adhesive on foam, try a scrap piece first.) It was determined that the adhesive is not necessary so long as the working piece is kept within ~30 degrees of horizontal.
The newspaper was removed and the structure placed directly in the trough. Hydraulic cement was poured into a sieve and sifted evenly over the structure leaving a nice, smooth, thick coating (Photo 4). Sometimes it may be necessary to prop the piece in place to sift the cement into a layer, but once complete, the various layers/ areas are easily blended.
If the structure has small holes, cracks, glue gaps, etc. in the foam, a finger, putty knife, straight edge, etc. can be used to push the dry cement into these areas and build them up near flush. The area is then wiped fairly smooth brushing off the excess powder, fingerprints, etc. A smooth layer is then sifted atop this.
The piece is then transferred to a second plastic trough and a spray bottle filled with water is used to mist the cement until it becomes wet (Photo 5). We like to do this until the powder is thoroughly saturated. Excess water on the surface is then absorbed by sifting a little more concrete over the wet spots. Furthermore, at this time more material can be sifted over any remaining low spots to build them up and level them out. One can actually alternate spraying and sifting to build the cement up to any desired thickness/strength.
Once the material dries, a file and sand paper can be used for any necessary shaping (e.g., leveling a road that “crowned” during the sifting/buildup process). Once everything is leveled to satisfaction, a light sifting/misting can be used to blend the surfaces and remove any tooling marks.
The townspeople are now able to get over the wall without tripping on the broken steps making their stay at Chameleon Caverns just that much more enjoyable (Photo 6). The ramp will lighten with age over the next few days and will better resemble poured concrete.
Great description of the process even without photos; a mini MasterClass!
Todd I had read your post from several years ago, and was going to do a test piece to see how well the patching cement works compared to hydraulic cement.Az you can see no pictures came thru , if you can add them it helps but if not I’m pretty sure I get the general idea
Not really sure about any of what I am about to say and for the MIK it may be utterly pointless. But What about instead of concrete or some other such substance; what about bondo or some other epoxy putty. I know when it comes to making counter tops with wood and epoxy resin they use bondo (as a generic term and not a brand) to make faux rock edges like a piece of rough/live edge stone.
Thinking aloud here, would bondo make a chemical bond with styrene foam? Would it not chemically bond at all and only make a mechanical bond? Would it melt the foam into a puddle of goo. This migh take some experimenting.
Another thought is a product called Polygen clay. The show “Tanked” used it a lot in aquarium decoration construction. When coated with a clear coat it was 100% waterproof and was able to be sculpted and molded. And while not bullet proof seemed pretty durable.
The pics are not stored on a server, and I don’t see an icon to drag them from my files as on other websites.
Article was done in 2010.
No icon needed. Just drag and drop into an edit window and it will automatically upload here.
in the top row of the edit space more or less in the middle is a horizontal bar with an upwards arrow.
Ok …now what ?
Ow I have a Rooster autograph! Awesome!
Pete,
It’s the best I could do currently.