Using grout that had hardened in the bag

Question

I had stored a bag of grout in a musty basement. When I went to use it, it had sort of hardened into a big block. I could pulverize it but when I rehydrated it and applied it it just stayed as a powder and didn’t harden into a solid. Is there any way I can get it to solidify again?

Answer 1

Grout is a cement product. It cures by bonding with water at the molecular level, which yours had done in the bag by absorbing vapor over time. When you pulverized it you did not reverse this process, but simply broke it into smaller pieces. Since the chemical process had already occurred, it wasn't going to occur again when you installed the grout.

There's no real limit to grout storage duration if you keep it in a sealed container. A paper bag isn't that.

Answer 2

Buy a new fresh bag.

Old grout, mortar, cement if in musty damp conditions is ruined.

Answer 3

To directly answer the question, the grout may be reconstituted by de-hydrating the mix. To do this, you would need to heat the dried pulverized mix to about 150°C to drive off latent moisture. Once the product is completely dried (has a consistent temperature of 150°C), you will then need to cook it to between 1300-1450°C to complete the process of breaking the hydrogen bonds. The drying step is important to prevent BLEVE during the cooking phase. After this is done, you will be left with clinker which can again be pulverized and then used as a new concrete product.

Of course, this will be much more labor intensive and financially expensive than simply buying a new bag of grout, but I figure the question can be answered without resorting to treating concrete products as a magical one time use commodity.

@MLu does bring up a valid point for anyone considering doing this. Many additives to the original mix, (tint, plasticizers, fiber, hardeners, etc.) will likely be destroyed in this process and will need to be accounted for.