# Glass block grouting in shower



## oxygenrace (Jan 15, 2013)

I am installing a glass block window (16"x48") in an alcove shower. I want the block to be flush with the tile on the wall surrounding the window. Can I use the same grout for the glass block as the tile. Corning recommends using their grout but I am already have the mapei for the walls. Thanks in advance for advice.


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## CarpenterSFO (Dec 12, 2012)

I've done a few glass block showers, and always stuck to white glass block mortar between the block, and silicone or siliconized color-matched (Mapei, for example) caulk at the border with the tile or other finishes.

I suppose that portland cement sanded grout is awfully close to mortar, but one difference is that glass block mortar is very sticky - it must have a lot of lime, way more than any sanded grout that I've seen. I'd be more likely to add some color to the mortar than to replace it with grout.

All that's based on using traditional glass block, where the mortar is important for holding the block in place. It might be different for a different glass block scheme.


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## oxygenrace (Jan 15, 2013)

I am using Pittsburgh Corning pro vantage 2 mortarless install system. It uses spacers between beds and heads and anchors along the jambs. It uses sealant on the raised edges of the blocks. Then you grout with provantage surface grout. I can only buy big tubs of their surface grout and it's only white, my tile has grey grout. They say to seal their grout twice in wet environments. I would seal regular grout too anyways. Can't see a reason why I couldn't use mapei and seal it?


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## MIKE ANTONETTI (Jul 17, 2012)

Remove equation- glass block is non absorbant 
Your setting material is silicone also non absorbant 
Not sure about width of joint with that system, I assume somewhere @ 1/4"
Sanded grout will work, as said it is not sticky due to lime. Precautions would be not to scratch glass due to sanded grout.
Grout locks in to where it's placed, usually needs equal depth as width.
Portland grout is not flexible, therefore any movement usually shows up as hairline crack .
Drying color may be different as other areas remove water due to absorption and glass area slows drying time, I think longer drying time makes for darker color.
Placement may be a little more tricky, so adjustment to thickness of grout may be necessary.
These are principles of grout that can be used for general applications, knowledge of characteristics of material helps make decisions for variety of uses.


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## oxygenrace (Jan 15, 2013)

Good points. I am using unsanded grout for tile because 1/8". Joints in block likely 1/4" so different grout anyways I guess (sanded). I guess I'll run with prescribed grout for system (white) from Pittsburgh Corning. I'll have to plan another glass block project for all this grout!


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## MIKE ANTONETTI (Jul 17, 2012)

Sand or aggregate will allow for wider joints without shrinking, it reduces capability of shrinking . 
Portland coats the sand and fills around the aggregate , same is true for concrete , large rock, medium, small, sand all mixed in proportion for strength and economy.


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## MIKE ANTONETTI (Jul 17, 2012)

The glass block conventional way of setting is using the mortar to set the block and strike the mortar joints when ready, just like block and brick, glass being the most finicky of the three.
I kinda skipped those when I was an apprentice for the union, all of them are their own field,specialty in my opinion.


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