Cause of Bubbles in Polyurethane Sealer
Question:
In the basement of our 1950s house, we stained the concrete floor and then applied a water-based acrylic urethane sealer the next day, after the washing step. The sealer manufacturer recommended using an airless sprayer, but the local Home Depot did not have an appropriate sprayer to rent. As I was talking about the issue, another Home Depot customer overheard me and said he had success applying sealer to decorative concrete using a basic plunger sprayer, similar to what you would use to apply garden chemicals. My wife and I decided to try it out, but the first coat was full of bubbles. My wife quickly rubbed the area with rubber gloves to smooth it out. She then applied a second sealer coat in a similar fashion, but achieved better results. Can you explain what caused the bubbles and recommend the best type of sprayer to use on future projects?
Answer:
Polyurethane sealers require more TLC when applying compared with single-component sealers, such as acrylics. As evidenced by your experience, the method of application is very important, as is surface preparation.
Two factors could have caused the bubbling. First, applying a water-based polyurethane with a garden-type pump-up sprayer is trouble. These sprayers do not reach the level of pressure needed to achieve a thin, even spray pattern. If the sealer is applied too heavily, a surface skinning effect can occur, causing gas and air to be trapped in the sealer.
Second, the concrete surface must be dry at the time of sealer application. If a polyurethane sealer comes in contact with moisture, a chemical reaction takes place, causing bubbles and foam. When I hear basement, I think damp, little air movement, slow drying and trapped moisture. I always recommend doubling the dry time on all below-grade floors that are going to be sealed. To speed the dry time, open up all doors and windows in the room and use a fan to generate good air movement.
As far as sprayers are concerned, the higher the pressure, the better the results. If an airless sprayer is not available, I would recommend applying the sealer with a micro-fiber mop, using a push-and-pull motion to get thin, even, streak-free coverage. This method often provides the best coverage and film thickness for water-based sealers. In a pinch, back rolling after spraying with a pump-up sprayer might have helped vs. using a gloved hand.
In general, I am not a fan of spraying water-based sealers. But if the sealer manufacturer’s application guidelines recommend specific equipment, use it! Specific sealer types (water-based, solvent-based, polyurethane, epoxy, etc.) perform best with a specific method of application. Always refer to the product application guidelines for the best equipment and methods to use.
In the basement of our 1950s house, we stained the concrete floor and then applied a water-based acrylic urethane sealer the next day, after the washing step. The sealer manufacturer recommended using an airless sprayer, but the local Home Depot did not have an appropriate sprayer to rent. As I was talking about the issue, another Home Depot customer overheard me and said he had success applying sealer to decorative concrete using a basic plunger sprayer, similar to what you would use to apply garden chemicals. My wife and I decided to try it out, but the first coat was full of bubbles. My wife quickly rubbed the area with rubber gloves to smooth it out. She then applied a second sealer coat in a similar fashion, but achieved better results. Can you explain what caused the bubbles and recommend the best type of sprayer to use on future projects?
Answer:
Polyurethane sealers require more TLC when applying compared with single-component sealers, such as acrylics. As evidenced by your experience, the method of application is very important, as is surface preparation.
Two factors could have caused the bubbling. First, applying a water-based polyurethane with a garden-type pump-up sprayer is trouble. These sprayers do not reach the level of pressure needed to achieve a thin, even spray pattern. If the sealer is applied too heavily, a surface skinning effect can occur, causing gas and air to be trapped in the sealer.
Second, the concrete surface must be dry at the time of sealer application. If a polyurethane sealer comes in contact with moisture, a chemical reaction takes place, causing bubbles and foam. When I hear basement, I think damp, little air movement, slow drying and trapped moisture. I always recommend doubling the dry time on all below-grade floors that are going to be sealed. To speed the dry time, open up all doors and windows in the room and use a fan to generate good air movement.
As far as sprayers are concerned, the higher the pressure, the better the results. If an airless sprayer is not available, I would recommend applying the sealer with a micro-fiber mop, using a push-and-pull motion to get thin, even, streak-free coverage. This method often provides the best coverage and film thickness for water-based sealers. In a pinch, back rolling after spraying with a pump-up sprayer might have helped vs. using a gloved hand.
In general, I am not a fan of spraying water-based sealers. But if the sealer manufacturer’s application guidelines recommend specific equipment, use it! Specific sealer types (water-based, solvent-based, polyurethane, epoxy, etc.) perform best with a specific method of application. Always refer to the product application guidelines for the best equipment and methods to use.
0 Comments:
Post a Comment
Links to this post:
Create a Link
Home Page