We began to wonder if the products we used on the tomettes were suitable for limestone. We read the labels carefully and decided that as Sarpasol is an acid, designed to remove the lime bloom from terracotta tiles, it was not appropriate; but there didn't seem to be any reason not to use the hydrofuge / oleofuge protection product. We couldn't find anyone who had used a similar product on a domestic interior, although there seems to be occasional use of water repellant compounds on the exterior of large limestone public buildings.
Sanding clean the limestone fireplace.We asked Monsieur Douady what he thought. He said that if it was his, he would do nothing and let it develop patina, but he obviously knew what type of product we were talking about and agreed that there was no reason we should not use it on the fireplace.
So, one morning I went over any spots and marks on the smoothly cut stone with dry 150 grade wet'n'dry sandpaper, just as I had seen Monsieur Douady after the masons left size 12 bootprints on the hearth stones. The stone is so chalky a light sanding removes all surface spotting, although nothing will safely remove deeply impregnated stains and some marks become permanent because of being 'fired' by the heat of the stove.
Then I wiped off the dust with a slightly damp cloth and gave all the smooth surfaces a coat of Protecteur hydrofuge oléofuge made by Chimybat. Four hours later I gave the hearth a second coat, as it is at the most risk of staining. The product is very easy to apply with a paint brush, which washes out with water. It's invisible once dry and doesn't change the colour of the stone.
PS Rather annoyingly, the stove itself has developed a fault, with one section of its door seal coming adrift. Up until Wednesday evening we were utterly delighted with the stove, as it heats our sitting room and the old kitchen (which is currently our office), as well as our bedroom and the shower room upstairs. It takes logs of up to 15cm diameter and 50cm long, and would burn slowly right through the night. Now, with a piece of door seal missing, it burns faster. I guess we will have to take it back to Bricomarché, where we bought it, or get in touch with the manufacturer, Invicta, and get a new door. I certainly hope this will be covered by some sort of guarantee.