i have located some free used firebrick. they are 4.5 x 9 x 3 and have d 70 embossed on them. does anybody know what this means? also they have been outside uncovered for 15 years. i live in central canada and can get cold -30 f. to +100 f. does anyone know if they are they worth using?
thanks
bernie
thanks
bernie
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