I had porcelain tile installed on my back porch. I wanted dark grout but ended up with white grout (another story). I am going to use polyblend grout renew to darken it. First of all, does any one know if polyblend renew is a penetraing product? Also reading on the internet, I see alot of problems with water causing the color to fade. Overtime there will be snow, mud and water from the dog dish that I might not be able to clean up immediately. Could I use polyurethane over the grout or does the grout need to breathe? Thanks for any advice.
The natural elements of an outside installation are always hard on grout. I wouldn't recommend poly over grout. The worst offender and harshest on your grout will be sunlight. Poly over the grout may actually make this process worse as it would hold in the heat and may magnify the uv rays.
I would find a good penetrating sealer and use that. Grout also needs to be resealed periodically so check the manufacturers recommendations for that.
Don't know if that particular product is penetrating or not.