I started to put down a 2" ridgid foam layer on top of my plywood last night and want to know the best method to cut it. I tried a large serated bread knife, but that didn’t work very well. Would a hack saw or a coping saw work better? I’m looking for the cleanest cut possible.
Also, what to use to fill in the seams and voids between panels? I’m using Liquid Nails Projects adhesive to secure it. Will that also work as a filler?
Any useful advice would be appreciated.
Jim
Jim, you will probably get the cleanest cut from a sharp, plain, straight bladed knife.
Be careful with Liquid Nails, the original solvent based stuff will eat the foam. They have a special formula product for use with foam.
(Ignore the trolls.)
I use a drywall saw but it’s not the cleanest method. I’d go for the sharpest and largest knife, since you will need some leverage to cut thru the mass.
I recently found that tile adhesive works splendidly for affixing styrofoam to wood base. I lay some weight plates down to ensure a good seal overnight.
good luck w/your project and post some pictures
Thought most used a special hot knife to cut it [which I need to buy].
Many people do use a hot knife, Chief. I don’t have one. I’ll try the great suggestions Elliot and Dave have put forth. Can this foam be scored and cracked cleanly like drywall can? That would be nice.
The Liquid Nails “Project” version I picked up is for adhering things like foam. I made sure of that. And had I not already bought it, I think Dave’s tile adhesive idea is great. Using a trowel, I’ll bet a nice, even coat can be applied across the table top for great coverage.
Thanks, guys.
Jim
Jim, don’t think you can score and break clean. Now if it is the sides of mountains, rough will work as you have never seen a smooth mountain cut.
We are on our 2nd hot wire/knife unit and they work wonderfully. I bit the bullet and purchased the heavy duty transformer and it has worked tirelessly for three years, well worth the money.
Jon
Jim,
Yes you can score and crack the foam. And as the others have said, a very sharp knife is needed.
I made a hot knife cutter for my Weller soldering gun. I used some 12 Ga copper wire, hammered it on an anvil to flatten it a bit and then shaped it into a 3" long loop that I screwed into the soldering gun terminals. This works very well. Make sure you have LOTS of VENTILATION as the fumes are noxious.
The Liquid Nails for Projects (Foam type - important - read the label) also works as a filler. Be aware that it cuts more difficultly then the foam (I have lots of personal experience on this).
BTW - I like Dave’s idea for the tile adhesive also. What I did on my layout is use a tile adhesive serated spreader to spread the Liquid Nails around for a better distribution. Be aware that a lot of weight is needed to ma***he foam into the spread-out Liquid Nails. It is pretty thick stuff. So it will be interesting to hear if the tile adhesive works a bit easier.
Good luck!
Roy
Lots of great information to take with me tonight. I need a smooth, even cut only because the foam is longer than the table. I want the foam to be as square and even as possible at the table’s edge. I’m actually thinking about building my tunnel with chucks of the ridgid foam and topped with spray can expandable foam. That stuff tools pretty easily.
Thanks again!
Jim
Roy’s soldering gun method sounds good.
If you want a fast and dirty method (I used this), try a sawzall. I did this with BB the beagle watching and she turned into a white, beaded ghost.
I’m thinking a table saw might work but you’d have to probably push it thru fast or heat would melt the foam.
Another idea you might try is to get a very large knife, a thick pair of gloves and a propane torch. Heat the knife and go to work until it cools, then reheat.
Sorry for the delay in posting this comment but we all know the reason. I’m surprised that you are going with 2" board over a plywood sublayment. If my assumption that the plywood is at least 1/2" is correct, you could certainly get by with 1" or even 3/4" foam, both of which can be cut fairly easily with a sharp utility knife – much easier job than working through the 2" material. As an option for unevenly scored areas, you can also tape and mud the joints as an alternative to the good suggestions already presented.
Poppyl
I use a hot foam knife, and really like it. I’m also a big fan of 2" Extruded Styrofoam (Polystyrene), although it can be a bit hard to find in some areas of the country. I like the 2" thick stuff because I like to carve depressions (stream beds, etc.) into the foam when I’m constructing scenery, and also find the thicker foam easier to “grow” into tall stacks–topographic map fashion–for creating hills, mountains, tunnels, etc.
My foam gets entirely covered by one or more layers of Sculptamold, so joints and such don’t pose a problem. I mount a fascia (thin Masonite or some similar material, contoured to match the landscape at the layout’s edges) along the visible sides of the pike, so don’t really worry about having the foam cut perfectly vertical along the edges. The Sculptamold comes right up to the fascia.
I ended up using a hack saw blade and it worked like a champ. I use the 2’ foam boards for the same reasons Allan has mentioned. I am going to carve a depression for a river and have a mountain tunnel. The 2" variety gives more hieght quickly and cheaper than thinner stuff.
I like the idea of taping and mudding the joints. I think that’s what I’ll do.
Thanks, all for some great replies!
Jim
yo guys just one thing i’d like to add,because you have covered all the angles. my idea is shapeing by using a wire brush,messy,but relitivelly fast and leaves a great finish. dr dan
You could also make your own hot knife!
I used a old whole house filter wrench(these can be purchased locally) attached two pieces of wood to form a wye ‘Y’. Then string Nichrome wire( available at hobby shop) across the ends. Use a small trans (i.e. 1033) with wire & clips to power it.
Set it at 10 to 14 volts and away you go.
I take it you want to make a long straight cut?
If so use a table saw with the blade in stalled backwards, that is what I used to cut foam for my layout, works well and you end up with a clean cut.
Word of caution do not hesitate when feeding the foam through if you pause the blade will heat the foam from the friction and it will melt that area and mess up the cut.
A hot wire cutter and steel straight edge is the cleanest and straightest way to cut thick foam. I have also used a razor knife with some success.
“Latex liquid nails” is effective glue and has no deterious effect on the foam. Use fiberglas drywall tape and joint compound to fill seams, cracks or gouged areas of the foam surface.
when cutting the foam, I’ve always used a box cutter. Makes nice clean cuts, and then used rasps and other knives for contour cuts and shaping.
Just an idea.
ONE WORD BANDSAW
Cutting foam with a bandsaw is a dream; you can cut blocks,curves any shape really with clean crisp edges paintable edges;
I used mine to cut supports, roadways, etc. even concrete highway barriers that fit around my highway; the barriers are sloped on one side.
try the hotwire foam factory they cutting tools that may help. here is the link
http://www.hotwirefoamfactory.com/products/customer/home.php