How to use construction adhesive so the fix holds

There is a certain kind of job around the house where a screw is the wrong answer, either because you would split whatever you are screwing into, or because you would be looking at the head of it forever afterwards, and that is where construction adhesive earns its place on the shelf.

What construction adhesive is, and how it differs from glue

Ordinary glue soaks into a surface and dries hard. Construction adhesive is a gap filling, high grab product that cures into something closer to a tough rubber, so it holds two things together while still allowing for the small amount of movement that timber and steel do as the temperature swings through the day. That flexibility is the reason it survives outdoors, where a rigid bond would eventually crack along the join and let go.

Soudal is the adhesive and sealant brand we lead with in the shop, and the T-Rex range is what most people end up carrying to the counter, because the SMX polymer it is built on will grab a damp surface and it keeps working through the cold and the heat, which covers most of what a South Australian summer and a frosty Strathalbyn morning will throw at it.

Picking the right one

• Fast grab is what you want when you cannot clamp or prop the thing you are sticking, because it holds position almost straight away rather than sliding while you find something to hold it.
• Crystal clear matters when the join is going to be visible, on glass or on a pale surface where a white bead would stand out more than the thing you fixed.
• The colour of the bead matters more than people expect on external work, because it is either the last thing you paint or the only thing you do not paint, so steel grey or jet black on dark work saves you a fiddly touch up afterwards.

Read the back of the cartridge before you buy, because the surfaces it is rated for are listed there and they are not all the same. Something that grabs beautifully onto timber and masonry is not necessarily the one for a plastic gutter.

How to actually apply it

1. Get both surfaces clean and dry, with no dust sitting on them. Adhesive sticks to whatever is on the surface, so if that happens to be dust, then dust is what it sticks to.
2. Cut the nozzle at an angle and start smaller than you think you need, because you can always trim more off and you cannot put it back on.
3. Run a zigzag or a continuous bead rather than dots, so the load spreads across the whole joint instead of sitting on a few spots.
4. Press the pieces together firmly, then pull them apart and put them back. That transfers adhesive onto both faces and it roughly doubles the contact area you end up with.
5. Prop or clamp anything vertical for the first hour even with a fast grab product, because gravity gets a full uninterrupted hour to work on it and you do not.

Full cure takes days rather than hours on a thick bead, because these products cure from the outside in as they pull moisture out of the air. Leave a heavy job alone over the weekend rather than testing it that night.

Clean up while it is still wet

Wet adhesive comes off with a rag, and a bit of acetone on a cloth will lift the smear off a hard surface. Cured adhesive comes off with a blade and a great deal of patience, so keep the rag in your hand while you are working instead of going to fetch one afterwards.

Jobs it suits

• Skirting boards and architraves that keep working loose, where you would rather not put another nail hole in to fill later.
• A loose tile or a lifted step tread, where drilling would crack the thing you are trying to save.
• Bonding a gutter join or a flashing lap, where you need the seal and the stick at the same time.
• Outdoor timber work such as planter boxes and bench seats, where a screw hole gives water somewhere to sit and start rotting from.

On anything structural, adhesive and fixings work better together than either one does alone. The adhesive does the bond and carries the load across the whole joint, and the screws hold everything still while it cures, and you end up with a join that neither of them would have given you on its own.

Shop related products

• T-Rex Power Fast Grab White Sealant Adhesive 290ml. The general purpose one, and the right pick when you cannot clamp the job.
• Soudal T-Rex Crystal Clear Sealant and Adhesive. For a join you are going to be looking at.
• Soudal T-Rex Power Fast Grab Steel Grey. Blends in on Colorbond, flashings and anything galvanised.
• Soudal All Purpose Silicone Grey 300ml. For the jobs that need sealing rather than sticking.

Did you know we also stock caulking guns, Soudal water resistant PVA glue and the Soudal two part adhesive kit in store. They are not all on the website, so give us a ring on (08) 8536 4333 to check what is on the shelf.

If you need the screws and bolts to go with it, they are in our fasteners and fixings range.

More from the shed

• What tools do you actually need in a home shed or workshop
• How to patch and sand timber before you stain it
• How to hang bikes and sports gear on garage walls

I am self taught on most of this, so if you are standing in front of the shelf and you are not sure which one you want, come in and ask, and if I do not know I will ask Elroy, who I call Guru for good reason.

Candeece