I am a plasterer by trade and we have an exterior rendering job coming.
The exterior face of the house is red brick and has to be scratched, then dry dashed over it. I have heard some horror stories about the scratch not bonding to the brick and I was just wondering if anyone has any help or advice on what mix, additive, to use?
In the UK, in situations where you might be slightly concerned about the surface being rendered, a coat of equal parts water & UniBond PVA Adhesive & Sealer is applied to the surface prior to the scratch-coat going on.
If the brickwork is quite porous, wetting it down beforehand (just prior to applying the UniBond PVA Adhesive & Sealer) with a hose wouldn't be the worst idea, also wetting down the scratch coat before the top coat is applied isn't a bad idea (especially if the weather is on the warm side).
Adding a plasticizer and waterproofing agent to the scratch coat is worthwhile (normally specified, required).
