Thechnical issue regarding plaster.

Jeff thanks for the tiles idea, we have considered it and it may come about if the heatproof plaster doesn’t come to fruition.

Dave W

Old houses used a lot of sand mixed, I think, with lime to make the plaster and then covered with a smoother plaster. Perhaps it is the high sand content that eliminates the cracking. Colin

I have in the past encountered this cracking of the breast above the fire.The cause in these cases was that there was a void above the fire instead of a throating into the flue.Is it possible that this might be the case around your SS liner which will transmit concentrated heat at the lower level .Also I have had to deal with flue problems of the fire surrounds cracking caused by lack of enough air,with fitted plastic windows and doors to elliminate draughts we have reduced the availiable air to cause the flue to draw efficiantly and when instructing clients that an air bick is required they invariably say no to the draught this will cause and the fire requires the amount of air to enter that occupies the flue area.I have had to chop out the breast and form a new flur reducing the void and lime morter is the correct material to use as it can expand unlike cement which cracks in close proximity to heat.Open a window whilst the fire is running to check if the breast cools down this is the first check I would do before doing futher work.

Frank

Bricky, many thanks for your input, yes there is a void above the inset fire casing as the throat was previously removed, the liner fitted from the fire up through the chimney is correct in being double layer stainless steel, it is possible that the liner is overheating at its lower end and the damage is from radiated heat transmitting through the brickwork. In respect of ventilation I was very conscious of this issue as we have all upvc double glazing which does hermetically seal a room, we do have a loose fitting cat flap in a door at the rear of this room which leads outside, I did check with our installer whether we had sufficient ventilation and his reply was more than was required for a 5 kw appliance with plenty of available airflow from the cat flap. Once again thanks for your input.

Dave W

I've reported here before on the experience with my shed woodburner... official installer (so insurance wouldn't be an issue) and a vent in the wall by the side of the stove. Early on i had the fire roaring one night and wondered why the CO alarm started screaming...until i stood up to deal with it and realised how dizzy i was. Nowadays i keep one window cracked open when the fire's lit.

pgk

Serious point pgk, have taken note and will experiment, many thanks.

Dave W

To determine whether the problem is just simply one of rising hot air may i suggest that you get a thermometer & with the fire on full. Leave it to get fully heated. Then you take a range of say 20 readings up the wall ( make some marks to record the positions) above the fire & say 1 inch from the wall & tight against the wall.

Then temporarily place a sheet of ply at an angle of 45 degrees tight to the wall to form an airtight seal & the next day repeat the process & then measure the temperatures at the same points on the wall & just an inch away from it

It will give you an idea of what you are up against temperature wise & if it is rising air that is carrying the heat up the wall

Edited By Sam Longley 1 on 23/03/2018 21:58:43

Can you get hold of some AFP? (acrylic flexible plaster), not cheap, but as it's a small area it shouldn't cost the earth.

Sam and John many thanks for your inputs, have taken onboard all suggestions and will deliberate and hopefully arrive at an action plan, aim is to carry out whatever works are necessary when the weather improves and the fire has been shutdown for a prolonged time in order to thoroughly cool down.

Dave W

I would like to update this subject that I raised earlier in the year, firstly many thanks for all the input that was made; the route taken was suggested by my grandsons friend, who is a plasterer, his recommendation was to strip back all the plaster on the chimney breast, back to bare brick which was found to be sound, then it was rendered with a lime render mix and subsequently finished with standard gypsum plaster. We have started having log fires again and so far there is no signs of the plaster cracking, after previous replasters it started cracking as soon as any heat was generated, so it is looking good so far. The reason given for using the lime render as undercoat was that it is resistant to thermal cracking and was always used traditionally around chimneys and fireplaces and historically all brickwork used to use lime mortar and old properties are testament to its ability to survive long term. I think part of the original problem was that the bond between the brickwork and plaster was breaking down and allowing small movements which caused the plaster to crack, going back to bare brick was the sensible course of action, now its finished I am no longer under pressure from the “complaints” department so hoping for a quieter life, although there is always something else waiting to go wrong.

Dave W

As James Alford says, lime render/plaster is what was recommended for us. Supposedly it doesn't crack...

I had cracking like this behind a old night storage radiator. Brand new 1975 house heater spaced from the wall by the feet like it should have been.