Cole and Son Hummingbirds: Why Seams Lift on a Chimney Breast and How Bartoline Paste Holds Them

A chimney breast throws three problems at Cole and Son Hummingbirds at once, and the lifted seam is usually the last of them to show. The flue behind that plaster still moves warm air even when the fire is decommissioned, and the surface expands and contracts a fraction more than the flat wall on either side. Hummingbirds prints on a heavier non-woven ground than the older paper stock, which is forgiving in some ways and unforgiving at a seam that sits over a moving substrate. Get the paste wrong and the join opens like a book.

Bartoline heavy-duty flake paste comes into this because it mixes to a higher solids content than the ready-mixed tubs most people grab at B&Q. That matters at the seam, where you want tack that survives a warm surface and a slow drying cycle behind the paper.

Start at the return, not the centre

Most guides tell you to plumb a line down the middle of the chimney breast and work outward. On a breast that carries a bold repeat like Hummingbirds, that leaves you with two mismatched slivers at the outer corners where the eye lands first. Hang the first full drop against the most visible return instead, usually the corner facing the door, and let the pattern break happen on the far side where nobody stands.

The returns themselves are where seams fail earliest. A chimney breast corner is rarely a true 90 degrees. Plasterers round them, and old lath-and-plaster breasts can be out by 4 or 5mm over a two-metre drop. If you wrap a full width around that corner and butt the next seam right on the arris, the paper has nothing solid to grip and the edge lifts within days. Carry the paper around the corner by 20 to 25mm, then start the adjacent drop as a fresh plumbed edge with an overlap. The overlap on a non-woven ground is thin enough to sit almost flat, and it keeps the vulnerable seam off the corner entirely.

Why the paste choice decides the seam

Ready-mixed pastes are convenient and they hold flat wall runs fine. They fail on a warm chimney breast because their solids content sits low and they stay flexible as the surface cycles between warm and cool. Bartoline flake paste mixed at the heavy-duty ratio, roughly one sachet to 4.5 litres of cold water for standard weight and a stronger mix for heavier grounds, gives a firmer film once cured. That firmness is what stops the seam creeping open when the plaster behind it moves.

Brush the paste onto the wall as well as the paper for a non-woven print. Hummingbirds is designed to be hung paste-the-wall, which is faster and keeps the print stable, but the seam benefits from a thin band of paste run onto the back edge of each drop with a 25mm brush. Overlap the wall paste slightly past where the seam will land so there is no dry strip under the join. A dry strip under a seam is the single most common cause of a lift that appears a week later, long after you have cleaned the brushes and put the ladder away.

Give the paste its full soak or wall-open time. Rushing a non-woven onto a wall that is still glossy with wet paste traps moisture at the seam and the edge floats rather than grabs.

Prime a chalky matt wall before anything

A chimney breast painted in a chalky matt finish is a trap. The pigment-heavy, low-binder surface of most chalky matt paints is porous and slightly powdery, and paste keys into the loose surface layer instead of the wall. When it dries, the whole seam can peel away with a fine dust of paint stuck to the back.

Seal it first. A coat of dilute PVA at four parts water to one part PVA, or a proper wallpaper primer, binds that powdery layer and gives the Bartoline paste something solid to hold. Let it dry hard, not just touch-dry.

The corner overlap, worked through

Take a real chimney breast: 92cm across the front face, two returns of 34cm each, and a ceiling height of 2.4m. Hummingbirds has a straight match with a 68.5cm repeat on a 68.5cm wide roll, so the front face needs one full width plus a part-width, and each return takes most of a single drop.

Hang the first drop on the left return, wrapping 25mm around onto the front face. Plumb the second drop on the front face so its left edge covers that 25mm wrap, giving you an overlap seam that sits 25mm in from the corner arris, on flat plaster where it can grip. The pattern match happens on the flat, not on the bend, so any small error in the corner angle disappears into the overlap instead of showing as a gap.

The front face second seam is a straight butt join on flat plaster, the easy one. The right return repeats the left in mirror: wrap the front-face drop 25mm around the right corner, then hang the return drop plumbed to cover it. You end with four seams, only two of which are butt joins, and none sitting on a corner. On a breast that carries warm air behind it, that placement alone removes most of the lifting risk before the paste has even cured.

Roll the overlap seams gently with a seam roller once, not repeatedly. Over-rolling a non-woven overlap squeezes paste out and burnishes the print, leaving a shiny line that catches the light worse than a lift would.

One thing about the fixings above

If you are hanging a mirror or a shelf on the finished breast, drill and plug before you paper, marking the holes on the lining. Fischer SX plugs in a 6 or 8mm hole hold far better in solid plaster than anything driven through paper afterwards.

Trim, eggshell edges, and the skirting line

Where the paper meets a skirting or a mantel painted in Farrow and Ball eggshell, the trim cut wants a fresh blade every two or three cuts. Eggshell is harder than emulsion and a dragging blade tears the wet non-woven at the very edge where a clean line matters most. Run a broad knife along the join, cut against it, and lift the offcut before it dries onto the paint.

The eggshell surface also refuses paste. Any smear that lands on the mantel or architrave wipes off cleanly with a damp cloth while wet, but once Bartoline flake paste dries on eggshell it leaves a matt ghost that needs a proper wipe with warm water to shift. Keep a wrung-out sponge on the go and clear each seam edge as you finish it rather than at the end. The habit costs seconds per drop and saves scrubbing later.

At the top, where the breast meets a ceiling that may itself be uneven, do not trust the ceiling line as a level. Plumb the drops to gravity and let the trimmed top edge follow the ceiling, even if that means the pattern sits a few millimetres higher on one side. A seam that is plumb will stay shut. A seam hung to a wonky ceiling line leans, and a leaning seam on a warm breast opens at the top first, where the flue heat is strongest and the paper is least supported.

That top-of-breast heat is the part no paste fully answers. Bartoline holds the seam shut against normal plaster movement, but a live flue that still carries genuine warmth from a working fire two rooms over will test any join. Whether a decommissioned breast is truly cold, or just quiet, is worth knowing before the first drop goes up.