ASK THE EX­PERT

Dou­glas Kent, tech­ni­cal and re­search di­rec­tor at the So­ci­ety for the Pro­tec­tion of An­cient Build­ings, an­swers your ren­o­va­tion queries

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QSome of the soft red bricks in my 16th-cen­tury in­glenook fire­place are crum­bling. What should I do about it?

The faces of bricks in fire­places can crum­ble (‘spall’) for a num­ber of rea­sons. This may be, for ex­am­ple, be­cause they have been cleaned ag­gres­sively, per­haps by sand­blast­ing, or are suf­fer­ing from a salt prob­lem due to damp­ness after an im­per­me­able floor has been laid nearby in place of an ear­lier breath­able one.

In some cases, the best re­dress can be to ap­ply to the bricks in ques­tion a pro­pri­etary min­eral-based fluid pen­e­trat­ing so­lu­tion de­signed to con­sol­i­date prob­lem­atic sur­faces while re­main­ing vapour open. This com­prises potas­sium sil­i­cate (wa­ter­glass) and should not be con­fused with other colour­less treat­ments on the mar­ket, the use of which would be in­ad­vis­able in this con­text.

Where the bricks are dam­aged to such an ex­tent that their faces have been lost, it may be fea­si­ble to un­der­take some lo­calised re­pairs us­ing a coloured mor­tar to build up the de­cayed ar­eas. Skill is re­quired, though, to achieve a good long-term colour match. In other in­stances, it may be pos­si­ble to re­move the bricks (es­pe­cially if their joints have not been pointed in a mod­ern ce­ment mor­tar) and re­v­erse them to hide the de­te­ri­o­ra­tion. Other ap­proaches are to ap­ply a lime plas­ter over the bricks where this is miss­ing and there is ev­i­dence that it ex­isted his­tor­i­cally, or to in­sert match­ing new bricks.

Only bricks that are se­verely dam­aged should be cut out and re­placed. Ex­act repli­ca­tion is very dif­fi­cult, but there are a num­ber of good sup­pli­ers pro­duc­ing new hand­made bricks at rea­son­able prices. Re­place­ment bricks should match the ex­ist­ing ones as closely as pos­si­ble in size, colour, tex­ture and dura­bil­ity. Q

What can I do to re­pair dam­aged tim­ber stair balus­ters?

You can re­pair a long, di­ag­o­nal split in a balus­ter by work­ing in some PVA and care­fully at­tach­ing a clamp while this sets. A bro­ken balus­ter might need dow­elling and glu­ing back to­gether in a work­shop. If loose, a balus­ter can be rese­cured with glue and a coun­ter­sunk wood­screw fixed di­ag­o­nally through the end into the handrail or string.

If you have a ques­tion for Dou­glas, email it to pe­ri­odliv­[email protected]­turenet.com*

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