Mastiff soiled sofa cushion — deep foam odour fix

A large sectional cushion soaked through by a Mastiff is a serious job — those dogs produce a huge volume of urine and it will have saturated the foam core, not just the fabric surface. The only products that permanently eliminate pet odours are enzyme-based cleaners — anything else masks the smell rather than destroying the uric acid crystals, which means your dog will sniff it out and return to the same spot. To point you to exactly the right thing: is the cushion cover removable, how long ago did this happen, and have you already treated it with anything?

Good — you haven't locked anything in with the wrong product, which helps. The foam is your main challenge here. Blotting the surface does almost nothing for deep foam saturation; the urine wicks down and spreads out inside the foam block, so you need an enzyme cleaner that can penetrate and dwell long enough to break down the uric acid throughout the whole affected area. What I'd recommend is Bio One Pet Odour Eliminator — it's a concentrated enzyme formula specifically designed for exactly this kind of deep-soak situation, and it's what professional cleaning companies use. How does your cushion cover attach — zip or pull-off?

That's the best possible news — it means you can treat the foam directly, which will actually work. Here's what to do: remove the cover and wash it on a hot cycle if the label allows. For the foam, mix Bio One at the recommended dilution and apply it generously — you need to saturate the foam to roughly the same depth the urine reached, so don't be timid with it. Press it in with gloved hands, then wrap the foam loosely in a plastic bag and leave it for at least 30 minutes, ideally a couple of hours. This keeps the enzymes active and stops them drying out before they've finished working. Then press out the excess liquid and allow the foam to air dry fully — outdoors if you can, or near an open window. Do not put it back in the cover until it is bone dry, or you risk mould.

Honestly, with a Mastiff and foam this deep, plan for two treatments. Once the foam is dry after the first round, smell it before you reassemble. If there's any trace left, repeat the same process — re-saturate, bag it, dwell time, dry completely. The enzymes need contact time and moisture to work, so the second treatment will catch anything the first didn't reach. Bio One is concentrated enough that even two full applications are cost-effective compared to replacing the cushion. After that, your dog shouldn't be drawn back to the spot because the uric acid that triggers that behaviour will be gone.

Good luck with it — you've caught this at the right time and you're doing it properly by removing the foam rather than treating it in situ. One last tip: once everything is fully dry and reassembled, a light spray of Bio One on the fabric surface as a final pass is worth doing. It closes off any residual scent trail your dog might otherwise still detect. Should clear it completely.