FIBREGLASS MESH

The render on an insulated wall holds together because of a layer of fibreglass mesh pressed into fresh basecoat over the boards, whether they are EPS or mineral wool. Renders World sells fibreglass mesh in two rolls, Atlas 150 and CT 325 from Ceresit. Choose by the maker of the adhesive and basecoat already on the job, then by roll width. The rest of the beads and mesh for the same wall are in our beads and mesh range.

Where fibreglass mesh does its work

Fibreglass mesh sits inside the reinforcing layer: boards on the wall, a coat of adhesive mortar over them, the mesh bedded into that coat, and the finish on top. Atlas describes its roll for this job over both EPS and mineral wool, and Ceresit sets CT 325 into the reinforcing mortars of its own external wall insulation systems.

• Field of the wall: length by length over the boards, with extra pieces laid diagonally at the corners of windows and doors.
• Arrises: corner beads with mesh wings carry the reinforcement round the corner, while a bead without wings needs a strip of fibreglass mesh from the roll carried round it.

If a wall has already cracked, why render cracks on insulated walls sets out each cause and the repair that stops it coming back.

Why installers match the mesh to the basecoat

• Same brand, one assessed layer: Atlas 150 is a component of Atlas insulation systems covered by European Technical Assessments, and CT 325 is listed in the assessments of named Ceresit systems. Atlas fibreglass in a Ceresit basecoat, or the reverse, is not a build-up either system assessment describes.
• Made for an alkaline bed: the fibreglass in Atlas 150 is alkali-resistant, and Ceresit declares the strength of CT 325 after 28 days in an alkaline solution as well as in its standard condition.
• A grid that holds its shape: CT 325 has a gauze weave that prevents the grid from shifting, with squares of 4 mm, so the openings stay square while the strip is pressed in.

Choose between the two fibreglass mesh rolls

The two rolls divide on which maker's system the wall is built to, and then on width.

Width is what you notice on the wall. The 110 cm roll needs fewer lengths and fewer vertical laps than the 1.0 m roll on the same elevation. The two weights are close, so neither is the stronger choice: decide on the system first, then on width.

How to fit the mesh into a wet basecoat

Fibreglass mesh goes into fresh mortar, never onto a dry coat.

1. Spread the system's adhesive mortar over one width of the mesh with a toothed trowel.
2. Lay the mesh in from the top of the wall down, flat and taut, and smooth it with a trowel while the mortar is wet until no grid shows.
3. Lap the next length onto the last, keeping its edges off the joints between boards.
4. Bed a diagonal patch at the corner of every window and door opening.

For CT 325, Ceresit gives the working figures: a 10-12 mm toothed trowel, laps of about 10 cm, corner patches of about 20 x 30 cm, and on mineral wool boards a priming coat of the mortar first. The full method is in the guides to the basecoat and mesh layer from start to finish, the top-down strip method used by installers and the lap widths between strips and around openings.

How much mesh to buy

• More than the wall area: every lap and every patch at an opening comes out of the fibreglass on the roll.
• The m² in a listing name is fabric: it is the cloth on the roll, not the wall it covers.
• For CT 325: Ceresit gives about 1.1 m of mesh per m² of wall.

The overlap guide works the arithmetic through strip by strip.

Site habits that keep the layer sound

• Store fibreglass mesh rolls upright and dry: Atlas asks for ventilated rooms away from heaters, and Ceresit for a dry place free from pressure, so nothing gets stacked on a CT 325 roll.
• Keep Atlas 150 under cover until it is used: it should never be left in direct sunlight or the weather, which on a scaffold means back indoors at the end of the day.
• Add a layer where the wall takes knocks: on a plinth or a ground-floor facade under higher mechanical loads, Ceresit's guidance is CT 325 in two layers. Plan the second layer before the finish, because it adds to the basecoat build-up.

What to order with the mesh

The mesh needs a bed to go into and boards under it, so these are worth ordering in the same go:

• The bed: the adhesives and basecoats range holds the mortar the mesh is pressed into.
• The boards underneath: EPS boards set the joint pattern the mesh is planned against.

Ordering, collection and returns

• Renders World sends fibreglass mesh out the same day when it is in stock.
• Our team works out the delivery cost after you order, and delivery is to the kerbside.
• You can collect from the Renders World shop in Southampton during opening hours; contact us for details.

You can return items within 14 days in their original condition (see cancellations and returns).

Fibreglass mesh: your questions