Magic Mastic

Expansion Joint, Mastic, Buffer, Deck-o-Seal. 

There never enough of talk about this little and overlooked, but very important component of a pool. Do you know what it means when you hear the terms ‘expansion joint’ or ‘mastic’? 

Most people don’t, until they get a quote from a concrete contractor or pool builder telling them there is about to be some major demolition and construction. The expansion joint is a buffer space left between the structure of your pool and the surrounding surfaces (pool deck, concrete, foundation). This space of about half an inch exists to allow for a little movement over time. 

We have all seen how tree roots and erosion can move even the heaviest slabs of concrete. While the results are not usually as dramatic as a couple of feet, most of the time, the change over many years is just a half inch to an inch. This is why builders leave a small gap around the pool’s edge and anything around it. 

The pool is built as a structure in and of itself. Its structure is reinforced with rebar in order to maintain its shape under great pressure from both the earth around it and the water inside it. A deck then is usually built around the pool but is not a part of its frame. This means the two surfaces will behave differently and be affected by various environmental inputs. So we build in a margin for error.

However just having a little space in the concrete is not enough. That little space could actually cause a major problem, if not taken care of correctly. If the space were left empty, exposed to water and wind, the little gap between the pool and the deck could begin to erode and cause the very problem we were trying to prevent. Now most expansion joints were sealed at some point, but if not done properly (or left for too long) cracks and separation in the ‘mastic’ will enable water to migrate underneath the deck leading to further erosion and movement of the decking around the pool. Mastic refers to the material used to fill an expansion joint. The purpose of this is to form a seal and not allow any water or other elements seep into the gap between the coping and deck.  

This is why it is extremely important to have your expansion joint inspected and make sure there are no gaps or cracks anywhere along the perimeter of your pool. If there are weak points it is vital to address them immediately. And when it comes to repair, quality matters. 

For Kohler Pools mastic repair is at minimum a 3 day process. 

Day 1

The job begins by removing all existing material and cleaning the expansion joint. This includes addressing any pre-existing erosion issues underneath the old mastic. We fill this space with a base layer of sand. After it is prepped, the base layer is then allowed to sit for 24 hours and the re-inspected the next day. Any areas that have settled over night will filled with additional material to bring it to level.

Day 2

Once the job area is properly prepped the mastic is laid carefully in the expansion joint. This step has to be done with attention to detail, as any imperfection can cause gaps or tares. It is vital that the expansion joint is completely sealed to prevent any erosion below its surface. In order to improve the quality of look, a light layer of sand is added on top of the fresh mastic and then allowed to sit undisturbed for 24 hours. This allows the finish to more closely match the look of the grout on the pool's coping. 

Day 3

Finally the excess sand that was poured on top of the mastic is swept up and cleaned. Revealing a finished surface and allowing for a thorough inspection and any imperfections to be addressed.

This three step process is the best way to protect your pool and deck from expensive damage. Little problems now, if unaddressed, can turn into much larger problems later. Call us with any of your mastic questions or concerns.