Removing PU foam – fresh and cured
Fresh PU foam can be removed in minutes with a foam cleaner, cured foam no longer. Then the foam is cut off flush mechanically and the firmly adhering residual layer is softened with a special remover; the Soudal PU Remover needs 30 minutes to a maximum of 2 hours of exposure time for this. On porous substrates such as plaster, masonry, raw wood or textiles no chemistry helps, there the foam has to be removed by abrasion.
Contents
- The diagnosis in 30 seconds
- Why cured foam is so stubborn
- Route A: fresh foam – act immediately
- Route B: cured foam – mechanical plus gel
- What works on which substrate
- Foam on your hands
- Rescuing the foam gun
- Common mistakes – and how to avoid them
- The best thing: not putting foam in the wrong place in the first place
- Frequently asked questions
What you need
Project template “Apply PU foam”Fresh PU foam is gone in minutes with a foam cleaner – cured foam no longer is. Then only the route in stages remains: cut the foam off flush mechanically and soften the last, firmly adhering layer with a special remover. The Soudal PU Remover needs 30 minutes to a maximum of 2 hours of contact time for this. On porous substrates – plaster, masonry, raw wood, textiles – there is no chemical rescue: there the foam soaks in firmly and has to be removed by abrasion.
The diagnosis in 30 seconds
Everything depends on what state the foam is in. Press against it with your fingernail or a spatula:
Case 1: fresh
The foam is tacky, soft, draws threads and can be pressed in. It has not yet cross-linked through. Now you have the easy problem – a foam cleaner dissolves it without leaving residue.
Case 2: cured
The foam is dry, firm, no longer sticks and can be cut with a knife. No cleaner in the world reverses that – the mechanical route plus remover gel follows.
Why cured foam is so stubborn
PU foam does not cure by drying but by a chemical reaction with the humidity of the air. In the process the molecules cross-link permanently into a thermoset – a process that cannot be reversed. That is precisely why a gun or foam cleaner works only on fresh foam: it dissolves the material that has not yet reacted, not the finished polymer.
With cured foam a remover such as the PU Remover works differently. The beige gel (density approx. 1.54 g/cm³, based on water-soluble solvents) swells the top layer so that it can be pulled off as a soft mass. So it does not dissolve the foam, it makes it pushable. On absorbent substrates that is no help but a second problem: the gel soaks in and leaves stains.
Route A: fresh foam – act immediately
You have a window of a few minutes until the surface is tack-free. Use it.
Pick up the coarse material
Take it off with a strip of cardboard or a spatula – do not smear. Every smearing enlarges the area that you then have to clean.
Follow up with foam cleaner
Put cleaner on a cloth and wipe off, do not spray over a large area. The Soudal Click&Clean is made for this, but the manufacturer expressly points out: plastics as well as paint and varnish coatings can be attacked. Check: test beforehand at a concealed spot.
Clean tools and gun straight away as well
The gun is the most expensive candidate. Screw on the can and spray through until no more foam comes out, repeat if heavily soiled and then let dry completely. Check: The jet that comes out is clear.
Route B: cured foam – mechanical plus gel
Cut off flush instead of tearing off
Cut flat along the substrate with a sharp utility knife. Tearing off pulls the coating away with it on plastic windows and painted surfaces – the damage is then bigger than the foam. Check: Only a thin, firmly adhering film is left.
Check compatibility
Apply a little remover at a concealed spot. Glossy surfaces can turn matt through the gel. The PU Remover is not approved for copper, zinc and brass nor for porous substrates – there is a risk of stains. Check: No visible change after the test contact time.
Apply the gel generously, close the can immediately
Brush it generously onto the foam residue with the brush supplied. Then close the can again without delay: humidity reduces the effectiveness of the product. Check: The residue is completely covered, no dry spots.
Leave for 30 minutes to a maximum of 2 hours
Less achieves nothing, considerably more achieves nothing either and only increases the risk for the surface. Check: The foam residue can be pressed in with the edge of the spatula.
Pull off dry – without water
Pull off with the spatula and wipe over with a dry rag. Water while pulling off is the most frequent mistake: it stops the effect before the residue is off at the bottom. Check: The foam comes off as a soft, coherent mass.
Repeat if necessary
Stubborn residue gets a second pass. Take up the last traces in joints and corners only at the very end with a damp sponge. Check: In raking light the surface is free of foam shadows.
What works on which substrate
| Substrate | Fresh foam | Cured foam | Caution |
|---|---|---|---|
| Plastic windows, coating, aluminium | Foam cleaner, immediately | Cut off + PU Remover | Gloss can turn matt, test beforehand |
| Copper, zinc, brass | Cleaner, check compatibility | Mechanically only | PU Remover is not approved here |
| Glass, tiles | Foam cleaner | Cut off, remainder flat with a blade | Guide the blade flat, otherwise scratches |
| Raw wood, plaster, masonry, screed | Can only be taken off on the surface | Remove by abrasion, sand, rework | Porous substrates: remover soaks in |
| Skin and hands | Wipe off immediately, then hand-cleaning cream | Hand-cleaning cream and patience | Never acetone or solvents on the skin |
| Clothing, textiles | Dab, do not rub – chances moderate | As a rule lost | Wear work clothing |
| Foam gun | Spray gun cleaner through | Take apart or replace | Clean after every use |
Foam on your hands
The most frequent case, and the one with the most bad advice. Solvents do not belong on the skin. A hand-cleaning cream such as Pevalin Spezial is expressly designed for PU foams too: the abrasives made of maize and walnut shell flour dissolve the dirt mechanically, without blocking drains, and the cream is pH skin-neutral and silicone-free. Application: rub into the soiled hands without water until the dirt loosens, then add a little water, keep washing and rinse off. Do not let it get onto plastics.
Whatever the foam really holds fast on the skin grows out by itself over the next days. Aggressive scrubbing costs skin layer, not foam.
Rescuing the foam gun
A gummed-up gun is mostly a write-off, because cured foam sits in the valve. The Biwa gun cleaner dissolves fresh, not yet cured PU foam without attacking seals or threads, and dries off quickly again. The Soudal Click&Clean additionally cleans the outside: screw the can onto the gun, operate the trigger several times at intervals of 10 to 15 seconds, and work on the outside with the red adapter supplied.
The rule behind it is simple: the can stays on the gun until the next foam can arrives – and the cleaner runs as soon as the foam is off. You will find all guns and cleaners in the category Foam guns & foam cleaners.
Common mistakes – and how to avoid them
- Waiting. "I'll do that later" turns a five-minute problem into an hour of work. Pick up fresh foam immediately.
- Water when pulling off. The PU Remover is pulled off dry. Water stops the effect midway through the process.
- Leaving the can open. Humidity affects the gel – close it after every application.
- Acetone on plastic or varnish. It does dissolve, but often the substrate as well. Always test first at a concealed spot.
- Tearing off foam. Tears coatings and films away with it. Always cut off flush.
- Remover on plaster or raw wood. Porous substrates soak up the gel, the stains stay. Work only mechanically there.
- Putting the gun away uncleaned. The cheapest repair is the one that never becomes necessary.
The best thing: not putting foam in the wrong place in the first place
Masking takes ten minutes, removing takes an hour. How to introduce foam cleanly and dosed is explained in our How to: apply PU foam correctly. If the foam does not cure through, the guide PU foam does not cure helps. And which foam belongs in the window joint at all is explained by Which PU foam for window installation?
Frequently asked questions
Does acetone dissolve cured PU foam?
No. At most acetone softens fresh foam that has not yet reacted. Cured PU foam is a cross-linked thermoset and no longer dissolves chemically. Besides, acetone attacks many plastics and varnishes. Take a gel-based special remover instead and work off the rest mechanically beforehand.
How long do I have until the foam has cured?
Depending on temperature and humidity the surface is tack-free after just a few minutes; the foam is cured completely through, depending on layer thickness and product, only after several hours. For simple cleaning, though, it is the surface that counts: as soon as it no longer sticks, no cleaner helps any more.
Can I use the PU Remover on plastic windows?
Yes, that is what it is intended for – it is designed for non-porous, non-absorbent substrates such as plastic, coatings and aluminium. Do a compatibility test at a concealed spot beforehand, because glossy surfaces can turn matt. It is not suitable for copper, zinc and brass.
How do I get PU foam off plaster or masonry?
Only mechanically. Porous substrates soak the foam into the surface, and a remover would in addition soak in and leave stains. Cut the foam off flush and sand or scrape the rest away – with plaster a rework is usually due anyway.
Does heat help, for example with a hot-air gun?
No. PU foam does not melt cleanly, it decomposes and releases fumes in the process – a health concern and risky for the surface. Stay with cutting plus remover.
How do I clean the foam gun properly?
Directly after the change or at the end of the working day: screw the cleaner can onto the gun and spray through until no more foam comes out. Repeat if heavily soiled and let the gun dry completely. For external cleaning the Click&Clean has an adapter; the trigger is operated several times at intervals of 10 to 15 seconds.
View foam cleaners and removers
Questions about use? Baustoffheld, Lindenstrasse 56, 47623 Kevelaer, telephone +49 (0) 2831 - 916 77 03.
More guides on this topic
All guides on “PU foam, windows and roofs”
Problem solving
Guide: PU foam will not cure – causes and fix
Why PU foam stays tacky or collapses and how to repair the connection
Comparison
Guide: gun foam or hand-held foam – which is better?
Gun foam or hand-held foam: when the foam gun is worthwhile and when not
Buying guide
Guide: which PU foam for window installation?
1K hand-held foam or 2K assembly foam: which PU foam for one or several windows