Flooring and Carpeting/tile grout
I just recently replace aprox 10 floor tiles and applied grout between the joints. After 12-36 hours a few of the grout joints have started to crumble and when I lightly scratch at it with my scraper it turns back to powder.
I haven't put any sealant down yet. The grout is from an old bag thats probably 5-10 years old. The floor was walked on aprox 12-18 hours after application.
What could the problem be? And do you have any advice on properly laying grout?
The grout is notoriously old...it has lost the polymer to bind it together. It is doomed. Remove it ...vacuum out and get a new bag/ box. Apply the new and see the perfect results.
Sorry for your inconvenience.
Mix the new grout in small batches ...10 tiles wont take much so you will end up throwing some out obviously.
Add a cup or 2 water to a small bucket add enough powder to the water to make a pudding/cake batter type consistency. If it is too wet add more powder..too dry add a dash of water. Sometimes a bit stiffer is the way to go ...dries quicker too. Mix smooth let set for 5-10 minutes in the bucket to temper...mix smooth again and proceed.
Apply the grout with a cheap throw away GROUT FLOAT. Use a diagonal direction to the joint...not 90 degree. Force the grout in to expell air and hidden voids. (Forcing means rolling the edge of the float to press the grout down and in) Then smooth it over with the diagonal stroke.
Use the grout float like a squeegee and remove excess grout. Allow to dry until a haze forms on the tile + 15 minutes at the joint. Wipe off the haze with a clean sponge typically sold for 1.97 , made for tile jobs. The big yellow sponge. Clean water in a clean bucket.
Wipe on the diagonal as much as possible..avoid a 90 degree stroke. If the grout in the joint is too wet it will be removed ...fill and wait another 15-20 minutes. Do not allow to dry more than 2 hrs. It becomes very difficult to clean. After the sponge makes a pass flip it over and make another pass with the clean side. RINSE each time after 2 passes. Wring the sponge out as dry as possible each time. As you do this you can shape the grout joint ...not to high ...not to low.
Minor haze after you have achieved a satisfactory result can be buffed off with a dry cotton T shirt some hours later, just to make sure that you don't disrupt the grout joint and it is completely dry.