limestone fireplace hearth discolouration

[ed659]

hi, can anyone assist, about 3 weeks ago we fitted the limestone hearth in position ready for us to build the rest of the fireplace onto it, we laid the hearth as instructed on a fairly thick mix of gypsum, settled, tampered it level etc.. pointed off the gap under the hearth and left it set, that all went ok, still level, but, just last week, we now notice we have what appears to be signs of slight light brownish staining in some central areas of the hearth, we don't know what this is, but wonder if it is possibly moisted soaked up from the gypsum ?? (although it was a dry/stiff mix)... any clues on how to clean this or otherwise would be appreciated. we are building the rest of the fire surround next weekend, but didn't want to use gypsum (as recommended) if this was a problem to the limestone. we were told to use either silicon or tile cement to build the top half of the fire surround.
regards eddie in manchester

 

[Moz]

eddie
sounds like it is damp come up ,limestone is a b*gger , as it needs sealing for this reason with spills , go to your local builders merchant not the DIY sheds ,as they wont have a clue , ask them what they think ...I know limestones a pain ... once marked ,
BAL tile adhesive is a cracker to use for the surround ...btw
hope this may help

 

[ed659]

thanks Moz, we've built the fireplace up now, following your advice we have built it and it looks brilliant, the bal wall tile adhesive was brill, did the job well, we used a little bit of silicon adhesive on the top mantle just to grab the top joints, but used bal wall tile adhesive on the back where it met with the wall. Of course, there are some wall level irregularities, we though we might 'grout' the small gaps, what do you think about grouting the gaps, or are we stretching our luck.

Brill advice Moz, thanks a lot.

Eddie