Hills from Ecothirm Insulation (Rigid Foam Sheet in the USA)

[dunnyrail]

I recently bought a copy of the US Mag Model Railroader and there was a super article about `Carving Realistic Stone from Foam`. I thought that this had possibilities in the Garden so I purchased a sheet of the thickest that I could find which turned out to be 3 inch Ecothirm. At £30 for an 8 x 4 ft Sheet I reasoned that it was not too bad value to get a couple of big lumps of Mountain from.  I also used a bag of Postcrete for the first effort. Though much of that was used in making the Bricks Stable. I should have cemented up the complete thing before I put the Ecothirm in place. Well I have one more to do so will get it right on the next one.

Pic above is the Ecothirm before hacking.  I used a Hacksaw Blade in a Stanley Knife Type of Holder to cut out a basic Hillside as below.

Then I made Brick Based Sides to hold the Ecothirm in place as below. This is the one that I have done so far and it is these Bricks that I should have cemented in place.

Below is the other area where I will use the other half of the Hills.

The results of much hacking, wire brushing and general abuse of the Foam gave me this result (below). My main concern was to ensure that all the Paper and Silver Coating was removed. The Coating is Silver Sheet, Paper and then More Silver Sheet. Without a doubt the Wire Brush worked best, but I did hack at it all with. Dentist Tooth Hacker before I wire Brushed it all, this loosened and weaken the underlying Silver Covering to let the Wire Brush do its job.

The final job is to get the complete thing covered with Postcrete. I did this by laying the sheet on its side, watering with the Watering Can then just flinging Postcrete on the Damp Sheet. Let it dry for around 10 minutes and then you can do the other side. The Ridges were done when I put the sheet in place between the Bricks. The final result is shown below:-




Inevitably you will miss some bits and they will become apparent when you put the thing in its final resting place, no worries just use a Small Spray with Water and a Tadge of Washing up liquid, damp the area and throw Postcrete at it.

WARNING Use Rubber or Latex Gloves for all your use of the Postcrete, it is not good for the hands.

My final thoughts are that I should have made the end closest to the path somewhat wider, I could still do this by using some of the offcuts and may well do. No doubt the method would work very well next to a fence or wall. I have partially filled in the plot with earth and once planted out with Conifers and Rockery Plants the effect will be much changed. More views on this and the next one when I get round to it.

But what do you guys think?
JonD

 

[funandtrains]

It is probably worth pointing out that there are several different types of plastics used for rigid foam insulation boards some of which cope better with damp, frost and ground salts that others. They also tend to come with different surface layers for using in different locations, the type you have used Jon looks like cavity wall PIR board which will be ok but probably costs more that some and has the foil layer glued on. I would suggest that if people want to order insulation board for this purpose they ask for the type intended to be used under ground floor concrete slabs and damp proof membranes as these will not be affected by cement, ground salts and frost, they will probably also be cheaper not having any surface finish.

 

[dunnyrail]

Steve,
Many thanks for your knowledgable input. If I do more will get the other stuff.
JonD

 

[bobg]

I recently bought 2" thick sheets, on-line, at £16 a sheet (foil-ed of course).

 

[funandtrains]

I specify insulation for construction regularly and the thickest sheets readily available are 150mm. There are quite a few makes available so worth shopping around to find a good deal especially as for this use the best thermal performance is not required only long life.

 

[PhilP]

Doesn't the underfloor stuff tend to be expanded polystyrene? - Or am I showing how out of touch I am??

 

[funandtrains]

Phil yes the under-floor insulation can be expanded polystyrene (EPS) or thermally better foamed polystyrene (XPS). Basically any insulation that is in a wet situation (under floor DPM, below DPC on walls or above the felt on an inverted flat roof) has to be a closed cell type of foam board. The best insulation boards are usually open cell which means water can get in which decreases their performance and if they freeze they turn to powder.

 

[funandtrains]

Now that I'm back at work and access to product info I can recommend that the most well known insulation suitable for this purpose would be Dow Styrofoam Floormate-A which is a rigid, water resistant, blue Styrofoam foam board, but there are several other similar products by other manufacturers. The type that Jon has used is not intended for damp locations in the ground or near ground and will not last as long although the render will protect it for a while as it absorbs water and if wet will be broken down by frost.

 

[dunnyrail]

I thank Steve (funandtrains) for his input. If these all start to break up I will certainly think about doubling up on the Thickness by using the Dow stuff if I can get hold of any from a local builders merchant. I could mount it front and rear having carved it to roughly the same profile then spend another bag of postcrete on it all. This would have the effect of making the mountains somewhat Thicker which would be most satisfying. At the moment though they have been severely rained upon and the other morning, after heavy rain a severe frost. Thus far with no effects. I know it is early days as yet, but at least to my eye I have created something of use and wish that I had the knowledge of the Dow that Steve mentions.

Still we all live and learn in this game.
JonD