Understanding Polymers in Concrete Repair
Polymers are added to almost every serious concrete repair and bonding product on the market, yet a lack of understanding of how they actually work on site is one of the most common causes of repair failure. Here's what they do, and the do's and don'ts that keep them working as intended.
The history of polymers in construction
Sour milk mixed with zinc powder produced an early version of today's water-soluble polymer paints; the word "latex" comes from the Latin for milk. Modern polymer solutions used for mortar modification or as bonding agents are emulsions of acrylics or poly vinyl acetates (PVA), and still have the milky appearance their name suggests. The technology has moved on a long way since then, and the benefits of polymers in cement-based products are now well understood and used on most construction sites, but a lack of understanding of their practical use on site still leads to avoidable failures.
The do's and don'ts of using polymers in construction
Viewed under a powerful microscope, polymers added to cementitious mortars can be seen producing a clear, film-like "shrink wrap" around each developing crystal as the cement hydrates.
- Don't water cure polymer-modified products. If the mortar is kept wet, this film doesn't form, and the polymer becomes ineffective.
- Protect against evaporative surface set. Polymers act as a slight retarder of the set of cement. In dry, windy conditions a film can form on the outside while the mortar underneath is still plastic, so always protect polymer-modified mortars from this.
- Wet the trowel. Wetting a trowel with a dilute polymer solution helps prevent trowel drag. Applying a dry trowel to a polymer-modified surface will produce dragging cracks in the finish.
- Match the polymer to the job. Different polymer formulations achieve different effects: mild acid resistance and water-proofing can both be induced into floors and cement-based slurries through the right polymer selection.
Getting the right polymer for your site
Selecting the wrong polymer, or applying the right one incorrectly, is a common and entirely avoidable cause of on-site failure. For guidance on the correct polymer-modified primer, bonder or repair mortar for your project, browse our priming & bonding range or request a method statement from our technical team.