Wall Insulation v. Grodan Rockwool

Rockwool meant for wall insulation is cheaper than Grodan rockwool and other brands meant to be used as a grow medium. Even rockwool chunks are more expensive.

So, 1) can you use construction/wall insulation rockwool as your grow medium; and 2) (Grodan claims to offer different firmnesses for different stages of growth), is wall insulation rockwool too firm or should I be concerned about additives that would either negatively affect plant health or should not be inhaled/smoked?

Apostatize said:

Rockwool meant for wall insulation is cheaper than Grodan rockwool and other brands meant to be used as a grow medium. Even rockwool chunks are more expensive.

So, 1) can you use construction/wall insulation rockwool as your grow medium; and 2) (Grodan claims to offer different firmnesses for different stages of growth), is wall insulation rockwool too firm or should I be concerned about additives that would either negatively affect plant health or should not be inhaled/smoked?

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Mixed opinions online. This recent article suggests you can usw it if you wash it first.

It's the same stuff , different density.

Rockwool rwa45 is dense slabs for heat and sound insulation, but it's not as dense as rockwool cubes for growing.

I'd imagine it could be used , but not sure it would physically support a plant as well as Grodan

coreywebster said:

It's the same stuff , different density.

Rockwool rwa45 is dense slabs for heat and sound insulation, but it's not as dense as rockwool cubes for growing.

I'd imagine it could be used , but not sure it would physically support a plant as well as Grodan

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Thanks! I've tried rockwool blocks (6" and 8"), slabs, 5-gallon grow bags filled with 3/4" cubes (with two 2" starter blocks stacked and buried in the center), and now 1-gallon grow bags filled with 3/4" cubes (with two 2" cubes buried in the center).

So, if I continue to use two 2" starter cubes rooted together as an anchor inside each 1-gallon bag, I might try lowering my overall cost by supplementing my 3/4" cube purchases with wall insulation that I'll clean and cut up before using.

A 1-gallon grow bag, 4" tall cube anchor, and gutter it rests in should support each plant if the bag's filled with cut up wall insulation rockwool (adding 3/4" cubes as needed for additonal support). Plus, I add trellising nets in flower.

Sometimes, I'd tear up a slab to fill in gaps between cubes and slabs are not nearly as firm as cubes. Now that I know rockwool wall insulation can be safe, I can start saving a few more dollars.

Thanks again.