Frequently Asked Questions - Installation

  What type of mortar should be used with glass block?

For exterior applications the building codes allow for the use of types N or S mortar. Regardless of the type used, Pittsburgh Corning recommends the use of Portland cement (as opposed to the use of Masonry Cement), hydrated lime and sand that conforms to ASTM C-144 standard. Hydrocide powder, an integral type water repellent available from Sonenborn Building Products, may also be used. The use of accelerators and/or acid washing is not recommended.

What size mortar joint should be used with glass block?

Typically in straight flat walls both horizontal and vertical joints vary in width between ¼ inch and ½ inch. Reinforced joints should not be less than ¼ inch, otherwise, the cross wires of the reinforcing could point load the glass block and cause breakage. In curved walls the inside vertical mortar joints should not be less than 1/8 inch wide and the outside vertical mortar joint should not be more than 5/8 inch wide.

What is the rough opening required when installing glass block with mortar?

Assuming the use of spacers or a ¼ inch wide mortar joint, multiply the number of glass blocks by the nominal size then add to that sum an extra ½ inch. Apply this formula to determine both the width and heighth of the opening. A nominal size opening of 4 feet by 6 feet would require a rough opening size of 4 feet, ½ inch by 6 feet, ½ inch.

Can glass block be cut?

This is NOT recommended. Because of the partial vacuum in the block any drilling or sawing could cause the block to implode. Also an installed cut glass block will eventually form condensation, mold or mildew on the inside. Projects should be planned so that only whole glass block units are used.

How is a shower door attached to the end of a glass block wall?

Sling type shower doors usually come equipped with a perimeter frame that is anchored to the floor and at the same time supports the weight of the door. The glass block mortar joints may be used as a means of attaching the door frame only, without providing the main support. Ideally the mortar joints should be 3/8 inch to ½ inch thick. Drill into the mortar joints a little off center to make sure that the drill bit does not nick the perimeter seal or any part of the glass block. Insert plastic type plugs into the drilled hole. Apply a couple of beads of sealant to the back of the door frame, just before you screw the frame up against the end of the glass block wall.

Are there specific details for installing fire rated glass block window assemblies?

The framing, anchoring and installation details are the same as installing any non-fire rated glass block panel and as shown in our published literature. The one distinct difference is that the sealant used at the jamb and head locations must be a fire retardant type sealant. Also all 90 minute rated glass back window assemblies may only be installed within masonry or concrete walls, may only by framed and anchored with ¼ inch thick steel channels or angles that form channels and the expansion material within the channels must be doubled or ¾ inches thick.

Finally our very true plastic spacers are listed by Underwriters Laboratories under classification number R18572 and can be used to construct fire rated glass block window assemblies.