If you ever had a chimney fire i wouldnt rely on the render stopping further damage.
Smoke in attic from chimney.
As soon as the raccoons are gone call a certified chimney sweep to clean your chimney of all nesting debris and install a chimney cap.
Now place another fan in a window on the opposite side of the home.
This is the black smoke you see leaving a chimney when it s in use.
A warm air siphon must be created before a fire can burn properly and draw correctly.
Sometimes it is simply the conditions of the day or the way draughts move around a particular house or the wind being in a particular direction.
Next check the chimney flue from the roof or have a chimney sweep do it to make sure no animals are present.
When you turn on both fans this will pull out the smoky air while you are drawing in new fresh air.
The warm air should rise out of your chimney including the smoke produced.
If your flue system is not warm when lighting the fire then you can alter the ability of the fireplace to draw properly creating potentially harmful smoking problems.
This is more likely to happen where a room has an extractor fan for instance and this creates a down draught in the unused chimney strong enough to draw the smoke into that room.
The smell or smoke coming down the chimney is a result of your house loosing too much air from the unsealed attic hatch.
Rerendering may stop the smoke but my advice would be to fit a twin wall stainless steel liner.
Start a small test fire and this time open a window in the same room as the fireplace with the restored chimney.
The best way to get rid of this smoke is by placing a box fan in the same room as the fireplace.
If you have no smoke coming into your attic or other fireplace you ve confirmed.
There is tremendous heat from chimney fires i have seen stacks split from the heat so for peace of mind get a liner in preferably by a hetas registered installer.
That air has to be replenished because your house is not going to implode and so it is going to reenter the house whichever way it can.
The reason is because when a chimney is being used and smoke is emitted it carries waste particles from the fire.