<p>To fix this, I had results with the following way:</p>
<ul>
<li>Change your extrusion width from being equal to your nozzle size (0.4 mm) to slightly larger (I use 0.45 mm). That way you better combat the shrinking of the filament.</li>
<li>Having the <code>Print thin walls</code> setting activated to force the printer to print intermediary walls if there are areas where less than the prescribed wall thickness for a single wall fills in spaces that are as a result of the wider outer walls left. The result for a 1.2 mm wall, the central part is a 0.3 mm zigzag.</li>
<li>Lower the extrusion temperature a tad as hotter filament shrinks more on cooling! For PLA about 200 °C is my sweet spot.</li>
</ul>
<p>Additionally, there are extra steps that could be taken:</p>
<ul>
<li>Finally, you could play around a little with the extrusion multiplier to try to get rid of the tiny bit of under extrusion you have.</li>
<li><a href="https://3dprinting.stackexchange.com/questions/6483/how-do-i-calibrate-the-extruder-of-my-printer">Calibration</a> could help too.</li>
</ul>

CC BY-SA 4.0
2019-06-19T16:02:58.177Z
Are you sure "Print Thin Walls" (`fill_outline_gaps`) does what you think it does? My understanding is that it has nothing to do with filling a "remainder" between walls. Cura uses low-extrusion zigzag for this in place of an additional low-extrusion wall, and this is controlled by `fill_perimeter_gaps`, "Fill Gaps Between Walls", which is on by default but omitted for really tiny gaps due to `filter_out_tiny_gaps`. AIUI, the behavior of `fill_outline_gaps` is to keep regions of the sliced outline narrower than the nozzle width, extruding w/ low flow.
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2019-06-19T16:05:42.557Z
@R.. I have had the issue before, flicking it on and going 0.45 mm extrusion fixed it.
Trish
CC BY-SA 4.0
2019-06-19T16:07:00.350Z
Is it possible just the 0.45 mm line width fixed it? I've been trying to better understand what the gap options do and think (thought?) I did, so I'm interested in your results here. I actually had very bad results with `fill_outline_gaps` causing blobs and stringing (mysteriously Cura ignored my retraction settings for this layer?!) on top of a horizontally-printed threaded bolt by printing an extra top layer where just a tiny portion of the thread much smaller than 0.4 mm was present.
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2019-06-19T16:15:37.483Z
@R.. reordered, added explanation why it helped for me
Trish
CC BY-SA 4.0
2019-06-19T16:17:25.477Z
Still, are you sure you didn't mean `fill_perimeter_gaps`, "Fill Gaps Between Walls"? That's the option that seems to be documented as doing what you want, and that seems to do it for me.
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2019-06-19T16:19:53.077Z
@R.. I did switch "print thin walls", which might contain flipping the other.
Trish
CC BY-SA 4.0
2019-06-19T10:29:24.183Z
2023-09-04T11:18:59.837Z
2023-09-04T11:18:59.837Z
Trish
<p>Now that print settings are shared we can see that this problem is not related to too fast printing (only 20&nbsp;mm/s) or too low print temperature (210&nbsp;&deg;C should get PLA fluid enough). To explain this, a low temperature and too fast printing cause under-extruded lines.</p>

<p>There are 2 other causes that might be worth investigating:</p>

<ol>
<li>Under-extrusion. From the top layers one can see that there may be insufficient material printed. <a href="/q/6483/">Calibration of the extruder</a> helps in this respect.</li>
<li>Inaccurate positioning. This may for instance be caused by loose belts or a mechanical defect.</li>
</ol>

CC BY-SA 4.0
2019-06-19T06:55:31.330Z
2019-06-19T13:12:36.193Z
2019-06-19T13:12:36.193Z
0scar
<p>I've experienced this too, especially with flex modified PLA filament. For that, fixing underextrusion and increasing temperature made it go away. Sadly Cura has no option to overlap walls slightly (if printed in the right order, this could be done without affecting dimensional accuracy) except possibly the outer one, so you really have to get extrusion rate calibrated right or this will happen.</p>

CC BY-SA 4.0
2019-06-16T20:17:22.027Z
2019-06-16T20:17:22.027Z
R.. GitHub STOP HELPING ICE
<p>I had the same problem, through multiple models and different brands of PLA. I fixed it by setting the Material &quot;Wall Flow&quot; parameter (both inner and outer wall) to 102%.</p>
<p>Note: The outside dimension is still accurate.</p>

CC BY-SA 4.0
2023-06-04T17:41:11.703Z
2023-10-04T09:58:56.523Z
2023-10-04T09:58:56.523Z
user1493362
<p>Look for the <strong>horizontal expansion</strong> setting in Cura. By default it should be zero. The description includes this:</p>

<blockquote>
  <p>Positive values can help compensate for too big holes.</p>
</blockquote>

<p>The "holes" here includes these gaps. You can set it to something very small (ie: .01 or .03, probably no more than .05) and that will likely be enough to get it to fill in those gaps.</p>

<p>Unfortunately, I only have a little direct personal experience with this setting, hence the probably/likely weasel words, and I can't give much real guidance on exactly how big or small you can go with this.</p>

CC BY-SA 4.0
2019-06-18T04:44:10.283Z
These gaps are not those kind of holes. The holes in question are negative space in the sliced layer, not space between extrusions.
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2019-06-19T06:42:21.917Z
The setting "horizontal expansion" is not meant for this purpose. Horizontal expansion should be used when print have a systematic deviation from the actual model size. E.g. a 20 mm or 100 mm box print as 20.4 mm and 100.4, you can use a horizontal expansion of -(0.4/2) = -0.2 mm.
0scar
CC BY-SA 4.0
2019-06-19T15:56:50.903Z
What @0scar said. Also, I realize my above comment was somewhat terse and maybe subject to misinterpretation. "Horizontal expansion" is an operation on the cross-sectional outlines produced during the slicing process, before any extrusion paths are laid out. It may have an effect on gaps due to introducing new space for extra wall lines, skin zigzags, or infill that presses on the existing wall lines in new ways, but it's not in any way a predictable mitigation for gaps and will alter the dimensions of your print, usually in a bad way.
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2019-06-17T14:17:03.117Z
2019-06-17T14:17:03.117Z
Joel Coehoorn
<p>I know this is an old post but I had this problem in Cura 5.8 and found it was because I was using the concentric setting for my walls.  It seems to be a bug in this version.  I changed to lines and the problem went away.  Before finding this was the issue I had tried upping my extrusion rates and line width all to no avail.  Did not have this problem in previous versions.  I wasted 4 rolls of filament on two bass guitar bodies before figuring this out.</p>

CC BY-SA 4.0
2024-08-31T01:12:56.483Z
concentric and lines are settings for *top and bottom* or *infill*, never for walls, walls are **always** concentric.
Trish
CC BY-SA 4.0
2024-09-01T04:47:11.070Z
Trish, I see that you are right.  I have got myself a little confused now because I changed too many settings trying to fix this.  I am sure I changed something from concentric to lines.  Note, I have two identical printers and this was only happening on the one with a .6mm nozzle.  I had not had this issue on the one with the .4 nozzle.  Anyway whatever I changed, it now prints fine.  Sorry, I am probably not being much help here.
Bill Hubbell
CC BY-SA 4.0
2024-08-30T14:29:11.640Z
2024-08-30T14:29:11.640Z
Bill Hubbell
<p>The print is very solid except for the 4 walls.</p>

<p>From the top, I can slide a paper down to the bottom. This is ONLY between the walls, the rest of the print is solid. The filament is PLA 1.75&nbsp;mm.</p>

<p>But the bottom is solid, no gaps.</p>

<p>I have checked the usual problems on Ultimaker troubleshooting photo gallery, but I can find anything similar.</p>

<p>Any advice to fix this would be very welcome.</p>

<p><a href="https://i.sstatic.net/FAJNf.jpg" rel="noreferrer"><img src="https://i.sstatic.net/FAJNf.jpg" alt="3d print wall separation"></a></p>

<p><em>Print settings:</em><br>
<a href="https://i.sstatic.net/LvRFW.png" rel="noreferrer"><img src="https://i.sstatic.net/LvRFW.png" alt="cura settings 1"></a>
<a href="https://i.sstatic.net/pYMH2.png" rel="noreferrer"><img src="https://i.sstatic.net/pYMH2.png" alt="cura settings 2"></a>
<a href="https://i.sstatic.net/cnUB0.png" rel="noreferrer"><img src="https://i.sstatic.net/cnUB0.png" alt="cura settings 3"></a></p>

CC BY-SA 4.0
2019-06-16T12:18:31.370Z
Increase the infil overlap.
Perry Webb
CC BY-SA 4.0
2019-06-16T14:08:34.247Z
Where do you put the paper in between: between infill and the walls, or in between the walls? If the first is applicable, the previous comment holds, else I'll write an answer, I've fixed this for my printer. Please add some basic information on temperatures, speeds, filament type, etc.
0scar
<print-quality><ultimaker-cura><3d-design>
How to fix wall separation in 3D prints (gaps in between wall perimeters)?
theMouse
# How to fix wall separation in 3D prints (gaps in between wall perimeters)?

(Asked by: username_0 on 2019-06-16)

The print is very solid except for the 4 walls.

From the top, I can slide a paper down to the bottom. This is ONLY between the walls, the rest of the print is solid. The filament is PLA 1.75 mm.

But the bottom is solid, no gaps.

I have checked the usual problems on Ultimaker troubleshooting photo gallery, but I can find anything similar.

Any advice to fix this would be very welcome.

[![3d print wall separation](https://i.sstatic.net/FAJNf.jpg)](https://i.sstatic.net/FAJNf.jpg)

*Print settings:*  
[![cura settings 1](https://i.sstatic.net/LvRFW.png)](https://i.sstatic.net/LvRFW.png)
[![cura settings 2](https://i.sstatic.net/pYMH2.png)](https://i.sstatic.net/pYMH2.png)
[![cura settings 3](https://i.sstatic.net/cnUB0.png)](https://i.sstatic.net/cnUB0.png)

**Tags:** print-quality, ultimaker-cura, 3d-design

> **Comments:**
> **username_1**: Increase the infil overlap.  
> **username_2**: Where do you put the paper in between: between infill and the walls, or in between the walls? If the first is applicable, the previous comment holds, else I'll write an answer, I've fixed this for my printer. Please add some basic information on temperatures, speeds, filament type, etc.  

---

## 6 answers

### Answer by username_3 on 2019-06-19. Score: 5

To fix this, I had results with the following way:

* Change your extrusion width from being equal to your nozzle size (0.4 mm) to slightly larger (I use 0.45 mm). That way you better combat the shrinking of the filament.
* Having the `Print thin walls` setting activated to force the printer to print intermediary walls if there are areas where less than the prescribed wall thickness for a single wall fills in spaces that are as a result of the wider outer walls left. The result for a 1.2 mm wall, the central part is a 0.3 mm zigzag.
* Lower the extrusion temperature a tad as hotter filament shrinks more on cooling! For PLA about 200 °C is my sweet spot.

Additionally, there are extra steps that could be taken:

* Finally, you could play around a little with the extrusion multiplier to try to get rid of the tiny bit of under extrusion you have.
* [Calibration](https://3dprinting.stackexchange.com/questions/6483/how-do-i-calibrate-the-extruder-of-my-printer) could help too.

> **Comments:**
> **username_4**: Are you sure "Print Thin Walls" (`fill_outline_gaps`) does what you think it does? My understanding is that it has nothing to do with filling a "remainder" between walls. Cura uses low-extrusion zigzag for this in place of an additional low-extrusion wall, and this is controlled by `fill_perimeter_gaps`, "Fill Gaps Between Walls", which is on by default but omitted for really tiny gaps due to `filter_out_tiny_gaps`. AIUI, the behavior of `fill_outline_gaps` is to keep regions of the sliced outline narrower than the nozzle width, extruding w/ low flow.  
> **username_3**: @R.. I have had the issue before, flicking it on and going 0.45 mm extrusion fixed it.  
> **username_4**: Is it possible just the 0.45 mm line width fixed it? I've been trying to better understand what the gap options do and think (thought?) I did, so I'm interested in your results here. I actually had very bad results with `fill_outline_gaps` causing blobs and stringing (mysteriously Cura ignored my retraction settings for this layer?!) on top of a horizontally-printed threaded bolt by printing an extra top layer where just a tiny portion of the thread much smaller than 0.4 mm was present.  
> **username_3**: @R.. reordered, added explanation why it helped for me  
> **username_4**: Still, are you sure you didn't mean `fill_perimeter_gaps`, "Fill Gaps Between Walls"? That's the option that seems to be documented as doing what you want, and that seems to do it for me.  
> **username_3**: @R.. I did switch "print thin walls", which might contain flipping the other.  

---

### Answer by username_2 on 2019-06-19. Score: 4

Now that print settings are shared we can see that this problem is not related to too fast printing (only 20 mm/s) or too low print temperature (210 °C should get PLA fluid enough). To explain this, a low temperature and too fast printing cause under-extruded lines.

There are 2 other causes that might be worth investigating:

1. Under-extrusion. From the top layers one can see that there may be insufficient material printed. [Calibration of the extruder](/q/6483/) helps in this respect.
2. Inaccurate positioning. This may for instance be caused by loose belts or a mechanical defect.


---

### Answer by username_4 on 2019-06-16. Score: 3

I've experienced this too, especially with flex modified PLA filament. For that, fixing underextrusion and increasing temperature made it go away. Sadly Cura has no option to overlap walls slightly (if printed in the right order, this could be done without affecting dimensional accuracy) except possibly the outer one, so you really have to get extrusion rate calibrated right or this will happen.


---

### Answer by username_5 on 2023-06-04. Score: 0

I had the same problem, through multiple models and different brands of PLA. I fixed it by setting the Material "Wall Flow" parameter (both inner and outer wall) to 102%.

Note: The outside dimension is still accurate.


---

### Answer by username_6 on 2019-06-17. Score: 0

Look for the **horizontal expansion** setting in Cura. By default it should be zero. The description includes this:

> Positive values can help compensate for too big holes.

The "holes" here includes these gaps. You can set it to something very small (ie: .01 or .03, probably no more than .05) and that will likely be enough to get it to fill in those gaps.

Unfortunately, I only have a little direct personal experience with this setting, hence the probably/likely weasel words, and I can't give much real guidance on exactly how big or small you can go with this.

> **Comments:**
> **username_4**: These gaps are not those kind of holes. The holes in question are negative space in the sliced layer, not space between extrusions.  
> **username_2**: The setting "horizontal expansion" is not meant for this purpose. Horizontal expansion should be used when print have a systematic deviation from the actual model size. E.g. a 20 mm or 100 mm box print as 20.4 mm and 100.4, you can use a horizontal expansion of -(0.4/2) = -0.2 mm.  
> **username_4**: What @username_2 said. Also, I realize my above comment was somewhat terse and maybe subject to misinterpretation. "Horizontal expansion" is an operation on the cross-sectional outlines produced during the slicing process, before any extrusion paths are laid out. It may have an effect on gaps due to introducing new space for extra wall lines, skin zigzags, or infill that presses on the existing wall lines in new ways, but it's not in any way a predictable mitigation for gaps and will alter the dimensions of your print, usually in a bad way.  

---

### Answer by username_7 on 2024-08-30. Score: -1

I know this is an old post but I had this problem in Cura 5.8 and found it was because I was using the concentric setting for my walls. It seems to be a bug in this version. I changed to lines and the problem went away. Before finding this was the issue I had tried upping my extrusion rates and line width all to no avail. Did not have this problem in previous versions. I wasted 4 rolls of filament on two bass guitar bodies before figuring this out.

> **Comments:**
> **username_3**: concentric and lines are settings for *top and bottom* or *infill*, never for walls, walls are **always** concentric.  
> **username_7**: username_3, I see that you are right.  I have got myself a little confused now because I changed too many settings trying to fix this.  I am sure I changed something from concentric to lines.  Note, I have two identical printers and this was only happening on the one with a .6mm nozzle.  I had not had this issue on the one with the .4 nozzle.  Anyway whatever I changed, it now prints fine.  Sorry, I am probably not being much help here.  

---

