A combination of porous grout joints, an incomplete thinset adhesive application and acid-based cleaners used on tiles installed in the Falls High School swimming pool is being blamed for causing the tiles to come off the bottom after the pool was renovated earlier this year.

That finding was contained in a preliminary report put together by the engineering firm Encompass, which investigated the pool tile problem, and provided Friday to Falls Superintendent Nordy Nelson.

The entire report has been posted on the school district’s website at: http://www.isd361.k12.mn.us/pooltilefailure_09-07-12.pdf

The FHS swimming pool underwent the renovation project between March and June of this year to deepen the end where the starting blocks are located to 5 feet.

The pool reopened July 9, but then closed a few days later because of the problem with tiles coming off the bottom. The report notes that multiple ridges or “tents” were visible within the tile floor where tiles had buckled upwards.

The pool remained closed with the water drained and tiles removed as the school district awaited test results to find out why the tiles didn’t stay in place.

 

Adhesive failure findings

According to the report’s preliminary conclusions, the adhesive failure only affected the newly-installed floor tiles and is attributed to the following deficiencies:

• The tile grout was over-mixed or re-tempered resulting in a porous grout joint. 

• The thinset mortar was applied so thin that it did not completely cover the underside of the floor tile.  

• Acid-based cleaners (muriatic acid and Top Ultra) used on the tile prior to filling the pool with water were absorbed through the porous grout joints and migrated under the tile through grooves and channels created by the incomplete thinset application. The acids dissolved the cement within the thinset and grout and the peroxide dissolved the polymer additives in the thinset, thus, severely weakening the bond between the tile and thinset. 

• The thinset bond to the tile, weakened by the acid cleaners and by the incomplete thinset application, substantially reduced its ability to resist forces from thermal expansion and moisture absorption of the tile. These forces exceeded the thinset bond strength resulting in the delamination and ridging of the tile. 

The loss of bond strength and cause of the pool floor failure, the report concluded, was the effect of the acids on the thinset.

Reopening the pool

Following “pull tests” conducted Tuesday at the pool on tile samples, Nelson said the process to reopen the pool will be able to proceed by grinding down the existing thinset adhesive to the bare concrete and putting new adhesive in place. 

While he hopes the pool could be reopened in a few weeks, Nelson said a reconstruction schedule should be posted on the school district’s website sometime this afternoon.

 

Pool work responsibility

The pool renovation work had been awarded for a bid of $198,000 and took place to comply with a new rule on pool depth implemented by the National Federation of State High School Associations requiring a minimum of 4 feet to be able to use starting blocks.

Nelson said the project’s general contractor will be responsible for fixing up the pool at no additional cost to the school district.

 

Effect on Bronco girls season

Had the problem with the tiles coming off the pool bottom not occurred, Falls’ girls swimming and diving team was supposed to host seven home varsity meets this season.

Two of those meets have already been held in the opponents’ pools. The possibility of hosting the remaining home meets this season will depend upon when the FHS swimming pool could be reopened.

Absent a full-length swimming pool to practice in, the Bronco girls have used the adjacent diving well for lap swimming and also began this week to start practicing twice a week in Canada at the Memorial Sports Centre pool in Fort Frances.