PU-Schaum | 12 häufige Probleme und Lösungen von einkomponentigem Polyurethanschaum-Dichtstoff während des Baus

30 / 05 / 2023

PU Foam | 12 Common Problems & Solutions of One-component Polyurethane Foam Sealant During Construction
PU Expandable Foam is a one-component, moisture-curing, multi-purpose polyurethane spray foam elastic gap filling material. Also known as polyurethane foam, Polyurethane (PU) foam caulk or construction foam spray, it is an indispensable auxiliary material in the door, window and curtain wall industry.
The curing of the PU expandable foam has certain requirements on the ambient temperature and humidity, and many situations may occur during use. In this article we will show you 12 common problems and solutions of the construction foam spray during use.
1. Why do some PU foam sealant have less foaming?

There are two main reasons for this problem:
  • -The expanding construction foam itself has few active ingredients, and the main raw materials for the PU expandable foam to be converted into solids are black material and white material, and the amount of foaming is related to the total amount of the two.
  • -The ambient temperature and humidity are low, the expansion of the PU foam is not in place when it is punched out, and the subsequent curing is not sufficient. 
Therefore, it is necessary to choose Pu foam sealant with good quality and good reputation. During construction in the cold autumn and winter seasons, pay attention to preheating the PU foam and spraying water to increase the humidity. In addition, the winter formula itself foams slightly less than the summer formula. (antas PU foam spray 750ml come with 2 versions and design for summer and winter seasons)

2. Why do some PU expandable foam shrink severely?

The main reason is that the formula is unreasonable. In order to reduce the cost, some suppliers add fillers and increase the amount of white materials to their PU foam, resulting in softer texture, thinner cell wall and lower density.
After the temperature changes, PU foam cannot withstand the changes of thermal expansion and contraction, resulting in shrinkage, the shrinkage is more serious can reach 50%, However, construction PU foam spray standard requires that the shrinkage rate is not greater than 5% under standard conditions.

3. The PU foam sealant is a waterproof sealing material. Why do some PU foam sealant leak water?
The reason why the Pu foam sealant is waterproof is that its cells are closed-cell structure, and the closed-cell rate of its internal structure must reach 80% to play a role in waterproofing and heat preservation. However, due to the unreasonable formula of inferior PU foam, not only the amount of foaming is low, but also the shrinkage is severe, so they have to add a cell opener to open the foam, which solves the shrinkage problem, but the foam is inelastic and leaks.

4.Why can't some PU expandable foam come out?
Generally, as long as the PU expandable foam can be shaken, it can be sprayed out and used up. If it can be shaken but cannot be sprayed out or used up, there may be the following reasons:
  • The PU foam sealant gun is not assembled in place and the valve is not opened. Tighten the sealant gun firmly and open the valve.
  • The muzzle, adapter or barrel of the foaming gun is blocked. To clean up immediately, you can use a cleaning agent to check whether it is unobstructed; or directly replace it with a new foaming gun.
  • The polyurethane foam sealant valve has a "sticky valve" phenomenon, which may be caused by long-term upside-down. "Stick valve" appears before the product is used, it is recommended to contact the supplier for a replacement.
  •  colloidal "gel". The proportion of materials in the production of the product is incorrect, or the shelf life is short, and the polyurethane foam sealant condenses

5.The PU foam is spraying like water and can't be molded?
This kind of situation is relatively rare. Generally, one raw material is missing during the production process of PU foam and there is no foaming. If this happens, the PU foam manufacturer will replace the product, or the product has expired.

6.Why does the PU expandable foam sometimes become brittle and powdery?
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Since the temperature is lower than 5°C, the phenomenon of powdering has not yet been fully cured, but at around 0°C, the phenomenon of powdering and brittleness will disappear after 24 hours.

7.Why are there holes or hollows at the bottom of the styrofoam?

Because the weather is dry and the air humidity is lower than 60%, this will happen. At this time, a humidifier or water mist can be used to increase the air humidity. Another reason is that the product quality is poor, or the formula is unreasonable. For example, summer products are prone to holes when used in winter.

8.What should I do if the construction PU foam is easily blown away when encountering strong winds or high-rise window installations?
The PU foam can should be shaken twice as often as usual, and the nozzle should be chased after the nozzle when the glue comes out. Try not to swing the nozzle to fill. It can be constructed in sections. First apply part of the foam sealant against the wall, and then fill it up after the surface is dry. The vertical seam can be filled in the second half first, and then the rest of the window joints.

9.How to solve the problem that the adhesive force is not, and the surface of the wall cannot stick during construction?
First of all, make sure that there is no oily material or Teflon coating on the bonding surface, and then make sure that the dust and sand on bonding surface have been cleaned or spray a small amount of water on the bonding surface.

10.What should I do if the gap is particularly large or small during construction?
When encountering large seams, if it is horizontal, you can first spray a layer of foam on the bottom, then fill the vertical seams, and wait for the PU foam in the original horizontal seams to dry before filling the seams. This can avoid wasting a lot of PU foam due to one-time filling.
When encountering extremely small gaps, it is necessary to reduce the speed of the sealant gun, or wait until the last quarter of each can is filled.

11.What to do if the curing of polyurethane foam caulk is slow?
Spray a small amount of water on the adhesive surface, and use the swing gun nozzle to fill as much as possible, so that the polyurethane foam caulk can fully contact the air when it comes out of the gun, and shorten the curing time. If the construction period is short, you can choose pre-foamed products, which can shorten the curing time. Generally, the surface treatment can be done 40 minutes after the glue is shot out, it is completely cured and shaped, and it will no longer expand or shrink.

12.Is it better to use the extrusion method or the cutting method when the PU expandable foam is trimmed?
In principle, the extrusion method is better, it can retain the complete skin of the foaming agent, and the water resistance is better, but the extrusion method should pay special attention to the extrusion time, and choose the time period when the colloid has just solidified and has not formed elasticity. Extrusion when uncured will destroy the internal cell structure, resulting in a hollow; after curing is sufficient, the colloid is elastic, and may rebound after extrusion.
The construction of the cutting method is relatively simple, just use a blade to cut off the excess colloid, the surface is regular, and it is convenient for subsequent construction operations, but the cutting method is only suitable for high-quality products with a high closed cell rate, and the foaming agent with a closed cell rate of 80% is cut It can also be waterproof after peeling off the skin.


That’s all and hope this article help and if you have more question about PU foam, feel free to contact us and we are happy to offer expert solution for you. We are selling PU spray expandable foam for construction use, welcome to buy form us.