Staining on old grout in a tiled pool.

[Sayulita Watrrfalls]

I have a 5 year old venetian tiled pool whose white grout lines are staining. I used a small wire wheel in a drill to remove the surface layer, but the staining had penetrated through the depth of the grout. It could be black algae I suppose, so I thought I would acid wash, rinse, bleach, rinse and then apply a thin layer of new grout. As the tiles are small 2cm x 2cm with thin grout lines I would prefer not to remove the old grout to the skim coat as most of the tiles would release completely.
I have been looking into epoxy grouts vs unsanded cementacious polymer grout. The new grout depth will be 1mm.
What would you recommend? I am in Mexico so water temperature is fairly constant.
Gracias!
Gary

 

[sktn77a]

When grinding out and replacing grout, a lot depends on the width of the grout line (ie the spacing between the tiles). How wide is this in your case?

You realize the amount of work you're letting yourself in for (having replaced grout in tiled floors. myself)? There are grout dyes/paints that might work and be easier.

 

[Sayulita Watrrfalls]

Grout width is 1/16 to 1/8". Which grout dyes/paint would you recommend?

 

[BubbaBasco]

What type of grout was originally used? Seems like you'd want to avoid that given your experience with it.

We are just completing a similar build and have been very happy with Bisazza fillgel epoxy grout. My understanding is that epoxy is definitely the way to go. Don't have any experience with how it holds up yet, but certainly expecting it to last much longer than 5 years.

And if there's any way to get more than 1mm of depth, that would obviously be beneficial. Seems like with that little depth, when wiping up the excess grout during install you'll likely get down to the base frequently. Would definitely test the various products you're considering before committing to a solution.

 

[sktn77a]

At 1/8" you'd need unsanded grout if you decide to go that way. And it'll be a you-know-what to scrape out!

I've used this before on a small shower:

UDT Grout Colorant

Easy to use, professional-grade UDT Grout Colorant penetrates old grout lines, restores & recolors while retaining a natural look. Available in 12 colors.

ultradt.com

It never looks as good as it does in their pictures but it was much better than it was before.