MEXICO CITY, March 23 (Reuters) - Mexico's Fortaleza Materiales and Elementia Materiales have launched a public offering worth more than $200 million to buy back around 17% of shares in both construction companies, the two companies said in separate statements on Wednesday.

The move is part of the companies' plan to exit Mexico's main stock exchange, joining the likes of dairy corporation Grupo Lala, telecommunications firm Maxcom and paper producer Bio Pappel, which in recent months have delisted or announced plans to do so.

The two, largely controlled by the families of Mexican magnates Carlos Slim and Antonio del Valle, announced in November that shareholders had approved the delisting months after spinning Fortaleza off from Elementia earlier in the year.

Through the acquisition offer, which is scheduled to end April 21, both Fortaleza and Elementia plan to buy back more than 103 million shares in each company at 19.60 pesos apiece, they said in statements to the stock market.

Both companies will spend around 2 billion pesos, or $100 million, each as part of the deal.

All told, 145 companies are listed on the main exchange, the Bolsa Mexicana de Valores. Of those, six, including Fortaleza and Elementia, are in the process of delisting, and a company last went public on the exchange in 2017. (Reporting by Kylie Madry; editing by Diane Craft)