Split surface with all geometry on same layer


I have a fairly complex model that keeps generating multiple surfaces out of a single completely co-planar surface. I think it happens when I move parts of the geometry along a single axis. All geometry is on layer0.

I don’t see how to attach a screen shot, but basically a flat surface gets subdivided along a particular line. There is no line object between the surfaces, and everything is completely co-planar. All my objects are designed to be cut out of 1/2" plywood, so they are basically 2d objects 1/2" thick

If I try to repair by control-pushing the other side (which is technically identical) it will end up removing the surface I push (!!) but NOT the others.

It’s happening so consistently I’m getting very tired of the only workaround I have found, deleting all the surfaces on one side, (sometimes there are a dozen or so, along tongue and groove lines) and then ctl-pushing the other side to restore the object.

Sometimes I can reduce to 2D by pushing, and then the lines between surfaces get ‘called into existence’ and I can select and delete them and then repush back to 1/2" thickness, but other times the object just disappears. How does sketchup decide whether to remove geometry when you push an object down to 0 thickness?? It seems completely random.

Thanks for any suggestions.


Seventh icon from the left at the top of the message window is the upload button, or you can drag and drop into the message box.
Sounds like you have some hidden geometry lurking in your model.
Turn on hidden geometry in the view menu and see if something shows up.
Upload the model so we can check it for you.


SU does create hidden geometry on coplanar surfaces as you do some types of edits.

Would you be able to illustrate an obvious example @Box?
(I am trying to recreate an example - it never works when you want SU to create it).

Or, am I only thinking of situations where SU is trying to compensate (by adding hidden geometry) for my modelling error, when my coplanar surface has misaligned edges, so slightly off square?


Yeah SU does throw in geometry as you model and normally removes it if coplannar unless there is some tiny inaccuracy.
You can see here the geometry appears as I rotate the shape, but goes when I stop. There have been cases of this happening and the hidden geometry remaining, but it’s rare.

I was more talking about having stray hidden geometry lying about that interacts with what you are drawing.
As you see the rectangle gets broken by the stray hidden edges.
These can often be saved into a template so you are forever fighting them.



The main reason I get hidden geometry created by SU is usually the intersection of a few lines is off by a fraction, although it would normally then prohibit push pull.

I have had issues where lines are created by SU as well, after a push pull to a flat surface where generally the surface should eliminate itself.


Okay, it’s not rare for me to have these lines created… It happens a lot. Showing hidden geometry was key–the lines between faces are being created and being hidden. But I’m not doing either one.

Still, this is a big help! Since I don’t ever hide lines or surfaces, only groups or components, this didn’t occur to me.

backWoodSurfaceIssue.skp (277.2 KB)

I guarantee I didn’t create this line all the way across the bottom, nor did I hide every individual segment!

I find I am more likely to get these lines created if I limit movement to one axis with a key command, as opposed to just carefully dragging in the correct direction. As mentioned here, they sometimes disappear after the move, but I have to assume they sometimes only get hidden…


Well, it is there and it must have got there somehow, I think we would need to see how you created the shape to spot when the edge came into existence.
There is a hidden edge sticking out from the other face too and that can’t be created in mid air.
Some part of your workflow is making this happen.


Which version of SketchUp are you using Make, Online or Pro?

There are some hidden line geometry in your model and when a push pull is completed, a few lines are left, which is a bit mysterious.


I can’t find the hidden edge you are talking about… never mind. Pushed to 2d, and it showed itself…

Well knowing to look for hidden edges is the main take-away here. I have no idea how they are being created, but at least I can get rid of them now.


I’m still curious though, what makes my model disappear when I push to 0 depth, and other times not.

I may actually want to make these objects 2D at some point, and it’s sure easier to convert them to 2D by pushing, rather than having to select one surface and all the z-axis lines and deleting them…


The Push-Pull tool will generally delete the active geometry if a face of an extrusion is “pushed back” to its opposite face. When the final thickness would be zero, SketchUp deletes the remaining edges and face (rather than leaving them as 2D geometry). I’m not sure I like this behavior, but that’s what I see (FYI, I usually use SketchUp Pro 2016; rarely do I use my copies of 2017 or 2018).


A work around is to copy the face of your geometry and after push pull paste in place the face copy.


I show it here.

If you want one face or want to start again with one face, use triple click, shift double click, delete.


Triple-click, yikes!!

Great method, tho, thanks!

I did also discover that, on this piece at least, if I selected the other face and pushed it instead, the geometry was preserved. So maybe there is a sense of the ‘original’ face and the ‘new face’ created after a push…

Anyway, lots of great techniques here, thanks so much!


If it didn’t, creating holes would be more complicated.
If you use move, the face (and edges) remain.


Thank you. Yes, move rather than push… great!