Buildertrackworld: Plaster blowing above wood burner.

Just after some advice really.

I have a 8kW wood burner installed and it appears to have blown the plaster above the fireplace twice now 🙁

The fireplace is stone which has been dubbed out with ~ 100mm+ thick (fireplace was very uneven) of sand + cement + lime + sbr and then a finishing coat of vitas heat proof plaster which I thought would do it; however stupidly I tapped on the plaster and it appears to have blown it again at some point over the winter.

Anyone got any tips on how to stop this happening? Or should I just live with it.

Only thing which I wonder may be contributing is the opening (~ 1000mm x 1000mm) doesn’t have a fireplace/mantle which may help to deflect the heat as the lintel gets very very hot sound plausible?

Stainless sheet fixed with stand off spacers, mounted above the burner, so you have a reflector with an air space behind.

Have you been patching it or doing the whole chimney breast as one unit.

Two things to consider – heat deflection – lintel , stainless sheet etc

Eco fan or similar to move the heat away .

My parents had this issue with their inset – they just aimed a fan at it to draw the heat away from the wall and it hasnt blown again.

I do have an eco fan but its pointed towards the room, do you mean point it up?

Stainless sheet seems like a safe bet so might give that ago, as I know where I can get one cut and bent to fit. Would it be worth spacing it off a little and then fitting the void with fire retardant expanding foam to give a bit of insulation?

You want to angle the sheet from low at the back to higher towards the room. Steeper the angle the better.

Small (>25mm) return, pointing down, bent on to each edge. Front edge projects slightly into room and has an upturn edge, again similar size as before.

Fixings should be all metal, ideally small anchor studs, positioned so the sheet just rests on, or hang with over sized holes in sheet and washers to allow for expansion, just finger tight.

No foam, the sheet reflects heat into the room and the void isolates a large part of heat from the masonry.

Obviously works better on burners with rear exit than top exit flue.

Most likely to be differential movement between the base of render dubbing out and the finishing plaster. This is usually caused by the base not drying out sufficiently before applying the finishing coat and especially if its thick. Then add the heat from the burner and very quick drying out and hey presto, separation of finish and base. I just looked on the Vitcas website and they do a base coat so maybe better to use this. Give them a call for some advice.

The base coat was given weeks to dry out before the top coat so it should have been ok.

I will try the metal sheet idea.