Glass blocks make an interesting alternative to more traditional building materials and you can choose from a vast array of sizes, colours and designs. They're especially good in kitchens and bathrooms, as they stand up well to grease and humidity. They're a stylish way to divide a room and make good use of the light.
To work out the dimensions of your frame, lay a single row of blocks on the floor with plastic spacers between them (make sure you include one at each end). Measure the total length, then do the same for the vertical dimension and cut the frame to fit.
Next, fit the frame into place, packing it with small off-cuts of wood to ensure it's level and square if necessary. After that, fix it to the walls, ceiling and floor. Drill holes in the frame, mark the wall - and don't forget to check for any hidden pipes or cables. Then drill the fixing holes and insert 50mm wall plugs and screws into masonry, 38mm screws into wood (ceiling joists or the studs of a stud wall), or hollow wall fixings into plasterboard.
Top tip - Spacers
The cross-shaped plastic spacers sold with glass blocks are three spacers in one, as you can snap them off to make T-shaped and L-shaped versions that fit around the frame. Twist the tabs off when the mortar has set. To work out how many you need, allow 1.5 spacers per block, plus 10%
Top tip - Reinforcing the wall
If the span of your wall is greater than 1.4m, you should lay steel reinforcing bars between each row of blocks. Lay the mortar on top of the blocks and press the reinforcing bar into it. If you need more than one bar for the length of the wall, overlap them by 150mm.
A wall of glass blocks is heavy, so it's important to check that the floor below can take the weight - especially if you're building on a suspended wooden floor. If you're in any doubt, get some professional advice before you start your project.
Nail an expansion strip to the sides of the frame at intervals, stop just short of the bottom of the frame so you can fit a spacer in. Then mix the mortar until it's smooth and lay a bed of it on the bottom of the frame (the sill). Use enough mortar to give you a 10mm joint when your blocks are in place.
Starting at one corner, place an L-shaped spacer against the frame and a T-shaped spacer to support the other end of the block (use one of the blocks to mark out the right position).
Lay the first block in the corner and bed it down firmly onto the spacers.
Put the next T-shaped spacer in place, and add enough mortar to the side of the second block to fill the cavity between the blocks. Then sit the second block on the spacers and push it against the first block, making sure it fits snugly on the spacers.
Carry on until the first row is complete - checking from time to time with a spirit level to make sure it's straight. Put mortar on top of the first row and bed in full spacers between the blocks. You're now ready to lay the second row!
Use a craft knife to cut the expansion strip level with the second row of blocks.
Lift the expansion strip and screw a panel anchor to the side of the frame at either end of the row. Then drop the strip back over the vertical arm of the anchor. Its horizontal arm should fit over the block and the spacers - cover it with mortar and continue laying the blocks.
Clean the face of the blocks with a damp sponge from time to time as you work.
When you've laid all your blocks, remember to leave the mortar to set for about an hour and then smooth out all the joints. Use panel grout (if your mortar is a dirty colour, or the wall is for a shower) and finish it off with silicone sealant where the bricks meet the frame.
When the mortar has set, twist off the tabs on the spacers and smooth the joints with a striking tool. This compacts the mortar and creates a moisture-resistant seal. After striking, all the joints should be full of mortar.
If you're building the wall for a shower, rake some of the mortar out of the joints with a small trowel to leave a depth of 10mm. Then leave it for 24 hours. (You can also do this if your mortar isn't white, and you want a white finish.)
The next day, fill the joints with white panel grout, and mould and compact them with a striking tool. Leave for another 1-2 hours, then wipe the surface with a clean, soft cloth.
Add a silicone sealant in continuous beads where the blocks join the frame at the top, sides and bottom on both sides of the wall.